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Production traits and postmortem factors affecting meat from young bulls

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Production traits and postmortem factors affecting meat from young bulls
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Solomon, Morse Bartt, 1953-
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English
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xi, 135 leaves : ill. ; 28 cm.

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Subjects / Keywords:
Animal loins ( jstor )
Beef ( jstor )
Carcass characteristics ( jstor )
Cattle ( jstor )
Meats ( jstor )
Muscle fibers ( jstor )
Muscles ( jstor )
Slaughter ( jstor )
Slaughter weight ( jstor )
Steak ( jstor )
Animal Science thesis Ph. D
Beef ( fast )
Beef cattle -- Carcasses ( fast )
Bulls ( fast )
Dissertations, Academic -- Animal Science -- UF
Meat -- Quality ( fast )
City of Gainesville ( local )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1983.
Bibliography:
Includes bibliographical references (leaves 122-133).
Additional Physical Form:
Also available online.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Morse B. Solomon.

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PRODUCTION TRAITS AND POSTMORTEM
FACTORS AFFECTING MEAT FROM YOUNG BULLS





By

MORSE B. SOLOMON


















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA

1983























To my parents, Muriel and Louis Solomon, who with great love,

understanding and support allowed me to pursue my dreams; and to my

wife, Betsy, and my son, Neil, who with extreme patience and love,

helped to make my dreams a reality. To them this dissertation is

dedicated.














ACKNOWLEDGEMENTS

The author would like to express his appreciation to Dr. Roger L.

West, Chairman of the supervisory committee, and to Dr. James F.

Hentges, Jr., Coordinator of the Purebred Beef Unit where the research

animals originated. Drs. West and Hentges were most encouraging,

patient and helpful in their guidance of this endeavor from its

inception to culmination. The suggestions and instructions provided by

the other members of the supervisory committee, Drs. Arno Z. Palmer,

Michael J. Fields and Wendell N. Stainsby, were most gratefully

appreciated.

The author wishes to thank Leroy Washington, Keith Blue, Alayne

Gardner, Gary Hansen, Jerry Wasdin, Caren Prichard, Julie Stokes,

Connie Williams and fellow graduate students for all their help,

technical assistance and comradeship.

I would like to extend a special word of thanks to Ms. Janet

Eastridge for her technical and practical assistance and friendship

which she has bestowed upon me.

The author wishes to express his appreciation to Ms. Cynthia

Zimmerman for accepting the task of assiduously typing this manuscript

at the last minute.

Deepest appreciation is extended to the author's parents, Louis

and Muriel; to his sisters, Betsy-Ellen and Chele and brother-in-law,

Herb; and to his wife's parents, Melvin and Sylvia for their support

rendered both morally and financially throughout the author's graduate

program.

iii -









Finally, I would like to express my love and thanks to my wife,

Betsy, and my son, Neil, who were a constant source of support and

encouragement during my graduate program. My wife has made many

sacrifices during the completion of my program and despite having to

withstand a moody husband and many lonely nights, she has provided me

with a never-ending love and understanding that enabled me to complete

this degree.









































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TABLES OF CONTENTS

PAGE

ACKNOWLEDGEMENTS .............................................. iii

LIST OF TABLES ................................................ vii

LIST OF FIGURES ............................................... ix

ABSTRACT ....................................................... x

INTRODUCTION .................................................. 1

REVIEW OF LITERATURE ........................................... 5

Production and Carcass Traits ................... 5
Palatability Traits ............................. 13
Carcass Electrical Stimulation .................. 17
Muscle Fiber Types .............................. 19
Muscle Nucleic Acids ............................ 23

STUDY 1 PRODUCTION TRAITS AND CARCASS COMPOSITIONAL
CHARACTERISTICS OF YOUNG PUREBRED ANGUS AND
BRAHMAN BULLS SLAUGHTERED AT SIMILAR PERCENTAGES
OF MATURE WEIGHT .................................... 28

Introduction .................................... 28
Materials and Methods ........................... 29
Results and Discussion .......................... 33
Summary ........................................ 55

STUDY 2 EFFECTS OF BREED, SLAUGHTER WEIGHT, YEAR AND
CARCASS ELECTRICAL STIMULATION ON THE QUALITY AND
PALATABILITY OF BEEF FROM YOUNG PUREBRED BULLS ....... 58

Introduction .................................... 58
Materials and Methods ........................... 59
Results and Discussion .......................... 64
Summary ........................................ 88

STUDY 3 GROWTH TRAITS, CARCASS TRAITS AND MUSCLE DEVELOPMENT
CHARACTERISTICS OF PUREBRED ANGUS AND BRAHMAN BULLS .. 90

Introduction .................................... 90
Materials and Methods ........................... 92
Results and Discussion .......................... 96
Summary ......................................... 116



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SUMMARY AND CONCLUSIONS ....................................... 118

LITERATURE CITED .............................................. 122

BIOGRAPHICAL SKETCH ........................................... 134



















































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LIST OF TABLES

PAGE

1 ALLOTMENT OF EXPERIMENTAL ANIMALS ........................ 30

2 DIET COMPOSITION ........................................... 32

3 LEAST-SQUARES MEANS FOR LIVE ANIMAL TRAITS AND DRESSING
PERCENTAGES BY BREED, WEIGHT GROUP AND YEAR ............... 34

4 BREED BY WEIGHT GROUP INTERACTIONSa FOR VARIOUS LIVE
ANIMAL, CARCASS AND LONGISSIMUS MUSCLE CHARACTERISTICS .... 36

5 WEIGHT GROUP BY YEAR INTERACTIONSa FOR LIVE WEIGHT,
AVERAGE DAILY GAIN AND LEAN TEXTURE ....................... 37

6 BREED BY YEAR INTERACTIONSa FOR AVERAGE DAILY GAIN,
DRESSING PERCENTAGE, QUALITY GRADE AND HEAT-RING SCORES ... 39

7 LEAST-SQUARES MEANS FOR YIELD GRADE FACTORS BY BREED,
WEIGHT GROUP AND YEAR ........................... .... 44

8 LEAST-SQUARES MEANS FOR QUALITY FACTORS BY BREED, WEIGHT
GROUP AND YEAR ........................................... 48

9 LEAST-SQUARES MEANS FOR PREDICTED CARCASS AND
LONGISSIMUS MUSCLE COMPOSITION BY BREED, WEIGHT GROUP
AND YEAR .......... ................. ................... ... 52

10 EXPERIMENTAL DESIGNa ................................. ..... 60

11 ANALYSIS OF VARIANCE FOR CARCASS QUALITY FACTORSa ......... 65

12 LEAST-SQUARES MEANS FOR CARCASS QUALITY FACTORS BY
BREED, WEIGHT GROUP, YEAR AND STIMULATION TREATMENT ....... 66

13 BREED BY WEIGHT GROUP INTERACTIONSa FOR QUALITY FACTORS ... 67

14 ANALYSIS OF VARIANCE FOR SENSORY, SHEAR FORCE AND
HISTOLOGICAL CHARACTERISTICS ........................... 76

15 LEAST-SQUARES MEANS FOR SENSORY, SHEAR FORCE AND
HISTOLOGICAL CHARACTERISTICS OF LOIN STEAKS AND SHEAR
FORCE FOR BOTTOM ROUND STEAKS BY BREED, WEIGHT GROUP,
YEAR AND STIMULATION TREATMENT .......................... 77





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16 EXPERIMENTAL DESIGN ..................................... 93

17 LEAST-SQUARES MEANS FOR PRODUCTION AND CARCASS TRAITS
BY BREED AND WEIGHT GROUP ................................ 97

18 BREED BY WEIGHT GROUP INTERACTIONSa FOR AGE, AVERAGE
DAILY GAIN, CARCASS MATURITY AND RIBEYE AREA ............. 99

19 LEAST-SQUARES MEANS FOR MUSCLE MEASUREMENTS OF THE
LONGISSIMUS, SEMITENDIUOSUS AND PSOAS MUSCLES BY
BREED AND WEIGHT GROUP ................................ 104

20 LEAST-SQUARES MEANS FOR CHEMICAL AND NUCLEIC ACID
PROPERTIES OF THE LONGISSIMUS MUSCLE BY BREED AND
WEIGHT GROUP ............................................. 107

21 LEAST-SQUAES MEANS KOR LONGISSIMUS MUSCLE FIBER
POPULATION AND AREA BY BREED AND WEIGHT GROUP ........... 112




































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LIST OF FIGURES

PAGE

1 Effects of breed, weight group and year on ribeye area .... 46

2 Effect of weight group on ribeye area and intramuscular
fat (%) ......................................... ........ 54

3 Location of samples from the short loin for various
analyses ........................................... .. 62

4 Effects of breed and stimulation treatment on lean
color and heat-ring scores .............................. 73

5 Effect of weight group and year on tenderness and
connective tissue scores of short loin steaks ............. 78

6 Effect of weight group and stimulation treatment on
tenderness and connective tissue scores of short loin
steaks ............. ................................... 81

7 Effects of breed and weight group on shear force values
of short loin steaks ..................................... 83

8 Effect of weight group and year on shear force values of
short loin steaks ........................................ 85

9 Effect of weight group and stimulation treatment on
shear force values of short loin steaks ................... 86

10 Growth of the longissimus muscle in relation to breed
(Angus *-- ; Brahman *---*) and weight group (WG)
percentages ............................................... 101

11 Effect of weight group on the percentage of aR and "W
fiber types in the longissimus muscle ..................... 114













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Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

PRODUCTION TRAITS AND POSTMORTEM
FACTORS AFFECTING MEAT FROM YOUNG BULLS

By

Morse B. Solomon

August, 1983

Chairman: Dr. R.L. West
Major Department: Animal Science

Seventy-eight Angus and Brahman purebred bulls that were 10 to 18

months of age were slaughtered at four weight groups: 60, 80, 90 and 100%

of the average mature cow weight for the respective breed. Bulls were

slaughtered over a two year period to determine the effects of breed,

weight, year and postmortem electrical stimulation (500 volts, 20-2 sec

impulses on right side) on production traits and carcass and meat

characteristics. After a forage or restricted feeding period, bulls were

placed in the feedlot and fed a shelled corn-protein supplement diet.

Slaughter weights for Angus bulls were 293, 381, 412, and 463 kg and for

Brahman bulls were 316, 420, 463, and 516 kg.

Carcasses from Angus bulls received higher quality grades (St vs

St-) and lower yield grades (1.8 vs 2.1) than carcasses from Brahman

bulls. Marbling score generally increased in Angus bulls as weight

increased, but this was not apparent in Brahman bulls. No major differ-

ences due to breed were detected for predicted carcass composition. Meat

from Angus bulls was usually more tender than that from Brahman bulls.




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Increasing carcass weight was generally associated with an increase in meat

tenderness.

Heat-ring formation, meat tenderness and lean color problems normally

associated with young bull carcasses were either eliminated or reduced by

electrical stimulation. Data suggest that the bulls used in this study

when fed to selected slaughter weights produced lean, acceptable weight

carcasses. Meat was generally tough and unacceptable from the bulls

slaughtered at the lighter weights, but was improved when bulls were fed to

heavier weights or when carcasses were electrically stimulated.

Second year bulls (n = 38) were used to ascertain the effects of breed

and slaughter weight on selected histological, biochemical and compositional

growth characteristics of the longissimus (LD) muscle. The LD muscle from

Brahman bulls contained more DNA and protein, and generally less lipid when

expressed on a total muscle basis. Neither RNA content, protein:DNA,

protein:RNA and RNA:DNA ratios nor percentages and areas for muscle fiber

types were affected by breed. As weight increased, muscle weights, protein,

lipid, RNA, RNA:DNA, protein:DNA and muscle fiber areas increased. DNA

content increased only up to the 90% weight group and then leveled off

while protein:RNA ratio decreased as weight increased. Furthermore, the

percentage of aR fibers decreased while the percentage of aW fibers in-

creased with increasing slaughter weight.














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INTRODUCTION

The ultimate test of the value of meat is its acceptability by

consumers. The extent to which satisfaction is derived from meat

depends on psychological and sensorial responses that are unique to

each individual. The desire for the selection of meat animals with a

greater potential for muscle development and lesser propensity to

fatten than present meat animals has promoted the need to understand

mechanisms of growth whereby lean and acceptable beef can be produced

economically.

The history of castration is probably as old as the history of

domestication of animals by man wherein he sought to fulfill his

requirements for meat, animal products and draft power (Turton, 1969).

The original reason for castrating was probably to render the male more

easily manageable and to enable males to be grazed along with mature

females without indiscriminate breeding (Crighton, 1980). Thus, its

use was one of the first actions taken to regulate genetic changes in

populations of farm animals. This practice was probably reinforced by

the observation that the castrate male had a larger deposition of fat

than its intact counterpart. This was particularly important at a time

when a large amount of fat was a highly desirable feature of the

carcass. However, because of the current market demand for leaner beef

and the necessity for intensification, perhaps the traditional practice

of castrating male meat producing animals should be impeded.

The current economic conditions have caused beef producers to

become more acutely aware of the importance of maximizing production

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efficiency, with their ultimate goal being to produce quality lean

tissue (muscle) at the least possible cost. As a result, much interest

has been generated regarding the use of young intact males in modern

beef production systems. Such interest stems from the fact that bulls

gain weight more rapidly, utilize feed more efficiently and produce

higher yielding carcasses with less fat and more red meat than steers

and heifers (Field, 1971; Seideman et al., 1982). In fact, if only

half of the cattle finished in U.S. feedlots were finished as bulls

rather than as steers a savings of millions of dollars in feed costs

would result, since approximately 13% less feed would be required per

unit gain by bulls.

Nevertheless, increased production efficiency obtained through the

use of intact males has often been offset by management problems,

particularly with animal behavior (Seideman et al., 1982). Further-

more, meat production from intact males has often encountered strong

resistance from packers, since bulls have been shown to produce car-

casses which are less tender and have lower quality grades, darker lean

color and coarser-textured lean. All of these factors result in lower

consumer acceptance of this product at the retail level than steers and

heifers (Field, 1971). Although several problems associated with

producing meat from young bulls exist, perhaps some, if not all, of

these problems can be corrected and thus, the utilization of young

bulls might become more widespread in beef production systems.

Many producers use breed differences as a means of altering

production characteristics of beef cattle. In Florida, producers

utilize the characteristics of British (e.g., Angus) and Zebu (e.g.,

Brahman) breeds, in addition to continental breeds, in their cattle





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operations in order to capitilize on the hybrid vigor resulting from

crossing of these diverse breeds. A number of studies (Luckett et al.,

1975; Peacock et al., 1980, 1982; Solomon et al., 1981b; Adams et

al., 1982) described substantial differences in production and growth

traits, carcass and meat characteristics, and compositional factors

between Angus and Brahman cattle (steers and heifers). Few studies

have been conducted to characterize the performance, growth, carcass,

and compositional factors, as well as meat palatability characteristics

of purebred bulls representing these diverse breed types.

Recent advances in meat technology may enhance bull beef quality

and acceptability. Reviews by Cross (1979) and West (1982) indicated

that electrical stimulation of prerigor carcasses usually will improve

tenderness, enhance lean color and marbling, in addition to reducing

heat-ring formation of beef.

As a result of these considerations, these studies were undertaken

to

1) compare the qualitative and quantitative characteristics of

carcasses from purebred Angus and Brahman bulls slaughtered

at different live weights;

2) evaluate palatability, histological, compositional and

biochemical characteristics of the longissimus muscle from

carcasses representing these diverse breed types;

3) determine the effect of carcass electrical stimulation on the

carcass quality-indicating factors and meat palatability;

4) evaluate the use of slaughtering at similar percentages of

the mature cow weight as a technique for comparing bulls, of

such diverse origins, on an equal compositional basis;





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5) ascertain the plausibility of histologically and (or)

biochemically classifying animals relative to their optimum

slaughter potential by the use of skeletal muscle fiber

characteristics and (or) associated properties of muscle

nucleic acids.













REVIEW OF LITERATURE

Production and Carcass Traits

Sex Effect

A number of studies which have been reviewed by Field (1971) and

Seideman et al. (1982) have identified the bovine intact male for its

superiority over its castrate counterpart in average daily gain (17%

greater), in feed consumed per kilogram of gain (13% less) and in the

production of leaner, higher yielding carcass with 35% less body fat.

Arthaud et al. (1977) reported that at all ages studied (12, 15, 18 and

24 mo at slaughter), bulls gained weight more rapidly, were more

efficient in converting feed to live weight and produced carcasses with

lower fat percentages than steers.

One of the most prominent characteristics of the intact male is

redistribution of body fat and increased body musculature (Seideman et

al., 1982). Galbraith et al. (1978) and Crighton (1980) indicated that

the increased musculature and superior growth performance of bulls were

associated with a positive nitrogen balance which was ascribed to the

protein anabolic effects of testicular hormones.

These differences in growth and lean deposition alone appear to

favor the production of meat from intact males since a lower priced,

leaner product could be realized. Nevertheless, even with these

advantages, the use of intact males has often been offset by management

problems, particularly with animal behavior or by strong resistance

from packers, retailers and consumers.



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Part of the industry resistance to young bulls is caused by

difficulty of removing the hide. Bull hides are generally thicker,

heavier and more difficult to remove than hides from heifer and steer

carcasses (Seideman et al., 1982). This problem increases the

processing costs significantly and reduces the acceptability and the

value of the product (Cross and Allen, 1982) to the packer.

Furthermore, discrimination has resulted because of several other

reasons, including negative connotations associated with the terms

"Bull or Bullock," and price differences between carcasses from bulls

and steers. The price difference is a result of lower USDA quality

grades of bulls and the belief that beef from intact males has lower

consumer acceptance at the retail level because of differences in lean

color, texture, fat distribution, size of cuts and palatability.

Field (1971), citing 13 research studies performed during the

1960's, reported that the average dressing percentage and fat thickness

for bulls vs steers were 59.7% and 9.3 mm vs 59.6% and 14.3 mm,

respectively. Seideman et al. (1982) concluded that bulls had .2%

lower dressing percentages than steers, based on their review of

literature. Champagne et al. (1969) and Landon et al. (1978) found

that dressing percentages were similar between bulls and steers;

however, this was dependent on the age at castration of the steers.

Field (1971), Arthaud et al. (1977), Jacobs et al. (1977), Landon

et al. (1978) and Crouse et al. (1983) reported that bulls had less

subcutaneous fat, larger ribeye muscles, less kidney fat and, thus,

lower USDA yield grades than steers. These authors also reported that

bulls had less marbling and, thus, lower USDA quality grades than

steers when fed for comparable periods on the same diet. Cross and





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Allen (1982) presented data from 16 research studies. Their report

showed that bulls had a mean marbling score of "slight-typical" and a

mean USDA quality grade of "Average-Good" while steers had

"modest-minus" marbling and "Low-Choice" quality grade. Smith and

Merkel (1982) reported mean marbling scores of "slight-typical" for

bulls and "small-plus" for steers in their review of 21 research

studies. These authors indicated that bulls and steers fed for

comparable periods on the same diet will differ in marbling by

approximately 1 to 1 2/3 scores and in USDA quality grade by about 2/3

to 1 full grade. Seideman et al. (1982) concluded that when compared

to steers bulls would, on the average, produce carcasses with lower

quality grades, darker lean color and coarser-textured lean with less

marbling, less quantities of subcutaneous fat and a higher incidence of

dark cutting lean.

Cross and Allen (1982) identified 9 previous studies which

indicated that lean color of bull beef was darker and less desirable

than that of steer beef. Glimp et al. (1971) found carcasses from

bulls to be more mature physiologically on the basis of bone

ossification and lean color than carcasses from steers of the same

chronological age. Crouse et al. (1983) reported similar findings;

however, bulls in their study were 1 month older chronologically than

steers. Sex by chronological age interactions were observed by Arthaud

et al. (1977) for secondary sex characteristics and physiological

maturity. At 12 mo of age, differences between bulls and steers in

maturity scores and lean color were negligible, but at older ages, bull

carcasses consistently exhibited more advanced maturity and darker lean

color.





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Field (1971) suggested that because of their temperament, bulls

may be more easily stressed than steers and, therefore, are more likely

to become dark cutters. Kousgaard (1981) reported that 18-23% of the

young bulls that they studied had 24 h postmortem muscle pH values

greater than 6.0, indicative of dark cutting beef, and as a result had

significantly darker colored lean than steers. Price and Tennessen

(1981) investigated dark cutting in young bulls and reported that 73%

of the bulls that were mixed with unfamiliar animals prior to shipment

were dark cutters while only 2% of the bulls that were not mixed with

unfamiliar animals prior to shipment were dark cutters. Kousgaard

(1981) found that holding bulls for two nights prior to slaughter

increased the incidence of dark cutters by 5% as compared to holding

them for only one night (23% vs 18%).

Boccard et al. (1979) reported that the pigment content of muscle

from bulls was not always higher than that of steers, but rather that

differences were breed dependent. Arthaud et al. (1977) found that

muscle from Angus bulls had higher myoglobin concentrations than that

from Angus steers of the same chronological age. Field (1971) reported

no difference in myoglobin concentrations in muscles of bull and steer

carcasses.

A comparison (Field, 1971) of percentage of retail yield and

percentage of separable lean and bone in bull and steer carcasses

revealed that bulls had an average advantage over steers of 2.6% in

estimated chuck, rib, loin and round. Champagne et al. (1969) found a

difference of 4.8% between yield values of bull and steer carcasses

when actual carcass cutout was used. They concluded that the USDA

yield grade formula underestimates true yield of bull carcasses by





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approximately 2%. Berg and Butterfield (1976) reported that although

differences in percentage of bone are small, bull carcasses possess

higher muscle to bone ratios than steer carcasses.

Jacobs et al. (1977) reported that on a boneless basis, bull

carcasses contained 58% less crude fat and 23% more crude protein than

steer carcasses. Bull carcasses yielded 5.5% more boxed beef than

steers, and trimmed waste fat was 17% less than in steers. Bull

carcasses were worth 32% more to the retailer than were steer carcasses

due to reduced in-store trimming losses and higher retail yields.

Landon et al. (1978) also reported that percentages of total retail

cuts were greater for bulls than for steers. Cross (1982) reported

that the boxed beef and retail segments of the meat industry place

price constraints on young bulls with too little fat (less than 5.1 nm)

and on those that produce carcasses that are too large (over 363 kg).

Seideman et al. (1982) considered the inadequate fat cover and

excessively heavy carcasses characteristic of bulls to be serious

disadvantages of their production.

Breed Effect

A comparison by Peacock et al. (1980) of purebred Angus and

Brahman steers fed a concentrate diet for an average of 176 d revealed

no difference in average daily gain (ADG) due to breed type. However,

in a follow up study (Peacock et al., 1982), where they compared

feedlot gain and carcass traits of purebred Angus and Brahman steers

fed a concentrate diet for an average of 174 d and slaughtered at a

constant weight (411 kg) and age (439 d), Brahman steers gained less

weight per day than Angus steers. Bailey et al. (1982) reported no

difference in ADG due to breed type when bulls from widely divergent





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breed types, which included Bos taurus and Bos indicus x Bos taurus

crosses, were fed to a constant age (400 d).

In a recent study by Adams et al. (1982) where they compared

performance and carcass characteristics of purebred Angus and Brahman

steers fed a high energy diet for 157 and 179 d, respectively, Angus

steers gained weight much more quickly, and consequently were on feed

22 fewer days than Brahman steers. Angus steers were also heavier than

the Brahman steers at the beginning and also at the end of the

experiment. Similar results were reported by Cole et al. (1964) when

Angus and Brahman steers were full fed to a constant live weight (408.2

kg) or age (20 mo), whichever came first.

A number of studies have reported differences in dressing

percentage (DP) between Angus and Brahman cattle. Peacock et al.

(1980) reported that Brahman steers dressed slightly higher than Angus

steers. Solomon et al. (1981b) reported similar findings when

comparing Angus and Brahman heifers. Butler et al. (1956) in a study

comparing yearling Hereford and Brahman x Hereford steers fed either

high or low concentrate diets for 140 d found that steers with Brahman

breeding had higher DP than those without Brahman breeding. They

suggested that the difference in DP between Bos indicus and Bos taurus

cattle probably was due to difference in the capacity and amount of

intestinal tract content (fill) at the time of slaughter. This has

since been substantiated by Tucker (1981).

Adams et al. (1982) found Angus steers to have higher DP than

Brahman steers; however, they pointed out that the Angus steers were

much fatter at slaughter than the Brahman steers. On the contrary,

Cole et al. (1964) observed no difference in DP between Angus and





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Brahman steers fed to a constant live weight (408.2 kg) or age (20 mo),

whichever came first.

Beef is graded on a composite evaluation of both quality and yield

factors and is merchandized according to the final quality and yield

grade. Quality grades (USDA, 1975) attempt to categorize carcasses

into similar palatability groups whereas yield grades are used for the

prediction of the percentage of boneless, closely trimmed retail cuts

from the round, loin, rib and chuck (USDA, 1965). Carcass quality

strongly influences the net income of packers, the price of meat and

possibly consumer demand. Bone, lean and overall maturity scores

combined with marbling scores determine the USDA quality grade.

The amount of fat thickness over the ribeye muscle at the 12th rib

measured at a point three-fourths the distance from the chine bone,

ribeye area at the 12th rib, estimated percentage of kidney, pelvic and

heart fat (KPH) and hot carcass weight determine the USDA yield grade.

Carcass quality characteristics of Angus and Brahman heifers were

compared by Solomon et al. (1981b). Darker, more mature colored lean

was observed for carcasses from Angus heifers than for those from

Brahman heifers. These authors did point out that the Angus heifers

were chronologically 1 mo older at slaughter than the Brahman heifers.

No difference due to breed type was detected for bone maturity scores.

Bone maturity, which is the degree of ossification within the bone

structure, is used to determine stages of physiological maturity (i.e.,

degree of the animal's maturation).

Research conducted by Luckett et al. (1975), Peacock et al. (1980,

1982), Solomon et al. (1981b) and Adams et al. (1982) revealed that





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carcasses from Angus cattle received higher quality grades because of

superior marbling scores when compared to carcasses from Brahman

cattle. This probably results from selection practices wherein the

breeders of British cattle (e.g., Angus) have succeeded in developing

animals that will store a large amount of fat in their muscle at a

young age.

Although distinct breed differences exist between Angus and

Charolais steers (Guenther, 1977) when compared at similar slaughter

weights, age or days on feed, Le Van et al. (1979) indicated that

differences in marbling scores, quality grades and percentage of

carcass cutability between Angus and Charolais steers were relatively

minor when the cattle were slaughtered and compared at similar

percentages of the corresponding breed average mature weight. Bailey

et al. (1982) reported no difference in marbling scores and quality

grades due to breed type when bulls representing different genotypes

were slaughtered at a constant age (400 d). The breed groups included

Bos taurus and Bos indicus x Bos taurus crosses.

In the study by Solomon et al. (1981b), carcasses from Angus

heifers were slightly heavier and had larger ribeyes than those from

Brahman heifers. However, no difference in fat thickness or KPH was

observed. Thus, carcasses from Brahman heifers received higher

numerical yield grades than those from Angus heifers. Adams et al.

(1982) found that carcasses from Angus steers, which were heavier, had

more subcutaneous fat, more KPH and larger ribeye areas and,

consequently, received higher yield grades than carcasses from Brahman

steers. However, in that same study, when carcass traits were adjusted

to a constant carcass weight (279.4 kg), ribeye area was no longer





13 -



significantly different between the two breeds, but fat thickness was

still greater for carcasses from Angus steers.

Luckett et al. (1975), working with purebred steers of Angus and

Brahman breeding fed a high concentrate diet for 100 to 114 d, found

that carcasses from Brahman steers had considerably less subcutaneous

fat and smaller ribeyes than those from Angus steers. Results from a

study conducted by Le Van et al. (1979) comparing Angus and Charolais

steers revealed that differences in growth rate and yield grade factors

were relatively minor when cattle were slaughtered and compared at

similar percentages of the corresponding breed average mature weight.

Several studies (Cole et al., 1964; Solomon et al., 1981b;

Adams et al., 1982) have confirmed that distinct differences in carcass

compositional components (i.e., percentage of lean, fat and bone)

between Angus and Brahman cattle exist. Carcasses from Angus cattle

were usually considerably fatter and had less lean and bone on a

percentage basis than those from Brahman cattle. However, data used in

these particular studies were collected from steers and heifers which

were slaughtered at some constant endpoint (e.g., live weight, age, or

days on feed). Le Van et al. (1979) reported that breed had no marked

effect on relative distribution of retail lean, fat or bone throughout

the animal's body when Angus and Charolais steers were compared at

similar percentages of the corresponding breed average mature weight.

Palatability Traits

Sex Effect

As far as meat quality is concerned, Palmer (1963) reported that

sex or sex condition generally has little effect on tenderness, but

when it does the difference is only marginal and may not be detectable





14 -


by the average consumer. This may be true for young animals, but the

generalization may not apply to mature males. This is reflected in the

work of Hedrick et al. (1969), Hunsley et al. (1971), Prost et al.

(1975) and Arthaud et al. (1977), indicating that chronological age had

a more adverse effect on tenderness in bull beef than in steer beef.

Hedrick et al. (1969) reported that Warner-Bratzler shear force

values and sensory panel scores indicated that steaks from bulls less

than 16 mo of age were comparable in tenderness to steaks from steers

and heifers of similar age. However, steaks from more mature bulls

were less tender. Flavor and juiciness scores were not significantly

affected by sex or sex condition. Arthaud et al. (1977) reported

similar results for bulls and steers on a low energy diet. However,

they found that when the animals were on a high energy diet bulls were

always less tender than steers, regardless of age.

It has been proposed (Boccard et al., 1979; Cross et al., 1982)

that decreases in meat tenderness associated with advancing

chronological age in bulls may be linked to concomitant increases in

collagen (a type of connective tissue) content and subsequent

cross-linking. Prost et al. (1975) observed that bovine intact males

had consistently more intramuscular connective tissue (collagen) than

females.

Boccard et al. (1979) and Cross et al. (1982) investigated the

influence of sex on the amount of total, soluble and insoluble collagen

in bovine muscles. They found that the collagen content of muscle was

higher in bulls than in steers, regardless of age or breed type.

Boccard et al. (1979), working with Afrikaner and Friesland bulls and

steers, reported that collagen solubility decreased markedly between 12





15 -


and 16 mo of age, only in the case of bulls. Cross et al. (1982), on

the other hand, observed that collagen solubility decreased

considerably between 9 and 15 mo of age for bulls and between 9 and 12

mo for steers. Animals used by Cross et al. (1982) represented four

breed types (Charolais, Simmental, Hereford and Angus).

Goll et al. (1962) suggested that differences in bovine collagen

solubility between sexes might arise from the fact that a lipid coating

over the collagen molecules, in addition to the frequency of

cross-linkages within and among the collagen molecules, was more

prevalent in males than in females. Boccard et al. (1979) and Cross et

al. (1982) proposed that the connective tissue toughness in bulls,

which inadvertently would affect meat palatability, may be linked to

sexual development and may be subject to some endocrine function(s) in

the animal. Furthermore, these authors found that differences in

muscle collagen were biologically related to age as well as breed type

and closely linked to the onset of puberty.

The bulk of scientific evidence reviewed by Field (1971) and

Seideman et al. (1982) indicated that meat from intact males was usually

less tender and more variable than meat from steers or heifers;

however, it generally was not less desirable in flavor or juiciness.

The report by Reagan et al. (1971) suggested that much of the observed

variability in palatability among steaks from bullock carcasses was the

result of variations in tenderness properties. These differences in

tenderness perhaps could be caused by myofibriliar shortening (cold

shortening) or connective tissue as previously discussed. Furthermore,

it is becoming increasingly apparent that subcutaneous fat thickness is

related to beef tenderness through its effect as an insulator to reduce





16 -


the rate of chilling and the related muscle fiber cold shortening

phenomenon (Smith et al., 1976; Dolezal et al., 1982). If some

minimum subcutaneous fat thickness could assure that beef from young

bulls would have "acceptable" palatability, then utilization of young

bulls in modern beef production systems might become more widespread.

Breed Effect

The possibility that breeding influenced meat tenderness was first

suggested by Carpenter et al. (1955) when they recognized that as the

percentage of Brahman breeding increased, tenderness of steaks and

roasts of steers decreased. Since this first observation, convincing

evidence of a relationship between breeding and tenderness has been

provided (Burns et al., 1958; Cole et al., 1958; Huffman et al.,

1962; Luckett et al., 1975; Peacock et al., 1980, 1982; Leak, 1981;

Solomon et al., 1981b; Adams et al., 1982).

In all of these studies cited above, carcasses from Angus cattle

produced meat which was more tender than carcasses from Brahman cattle.

Palmer (1963) reported that meat from carcasses with Brahman breeding

was generally less tender than that from carcasses with European

ancestry. However, he did note that certain individual Brahman sires

produced progeny above average in tenderness and that, by the same

token, certain individual sires of the European breeds produced progeny

lacking in tenderness. King et al. (1958) found that the variability

in tenderness of steaks from steer carcasses was closely related to

particular sires and, thus, these findings indicate the possibilities

for producing tender meat through judicious selection and breeding.

Palmer (1963) reported that breed of sire had a pronounced effect on





17 -


meat tenderness with Angus, Hereford and Shorthorn progeny being more

tender than progeny of Brahman and Brahman x Shorthorn sires.

Alsmeyer (1960) reported that cattle with high percentages of

Brahman breeding were less tender than cattle of predominantly European

origin. Furthermore, he noted that the percentage of Brahman breeding

accounted for more variability in panel tenderness ratings than did

cattle of European ancestry.

Carcass Electrical Stimulation

It is obvious from the literature that meat from young bulls is

usually tougher and more variable in tenderness, and darker in color

than that from steers. As previously discussed, differences in

tenderness perhaps could be caused by myofibrillar shortening (cold

shortening) due to inadequate subcutaneous fat cover often encountered

with young bulls or by connective tissue. Perhaps some of these

problems associated with using young bulls for block beef could be

corrected with the aid of postmortem handling techniques.

One such postmortem technique might include carcass electrical

stimulation (ES). For the most part, ES has been demonstrated to

increase the palatability of beef (Grusby et al., 1976; Savell et al.,

1978b; Bouton et al., 1980; Stiffler et al., 1982) and improve lean

color and lean maturity as well as reduce heat-ring formation (Savell

et al., 1978b, 1979; McKeith et al., 1981; Knight, 1982).

Riley et al. (1982) investigated the effects of ES and subcuta-

neous fat thickness on the tenderness of the longissimus muscle of

bulls and steers. They found that ES produced the greatest improvement

in tenderness of steaks from young bulls with less than 7.6 mm fat

cover, but even with this improvement meat tenderness from bulls did





18 -



not equal that of steers. These authors suggested that differences in

tenderness was probably caused by cold shortening. On the other hand,

they reported that ES had essentially no effect on the tenderness of

bulls and steers when the fat thickness exceeded 7.6 mm. Crouse et al.

(1983) found no effect of ES on the tenderness of meat from bulls.

Furthermore, they found that loin steaks from bulls were more than one

sensory panel score inferior when compared to those from steers.

Crouse et al. (1983) suggested that the variation in tenderness

associated with sex condition was related to the connective tissue

component rather than cold shortening, since the average fat thickness

was 8.1 mm for bulls and 12.1 mm for steers. Thus, the role of

temperature decline was likely not rapid enough in bulls to induce

cold shortening.

The literature strongly indicates that ES alleviates the

cold shortening type of tenderness problem in meat (Chrystall and

Hagyard, 1976; Davey et al., 1976; Bouton et al., 1980; Hagyard et

al., 1980; Eikelenboom et al., 1981). Other researchers believe that

benefits of ES are not solely related to the prevention of cold

shortening. Postulated mechanisms include structural alterations

of muscle fibers (Savell et al., 1978a; George et al., 1980; Will

et al., 1980; Voyle, 1981; Sorinmade et al., 1982), increased

lysosomal enzyme activity (Sorinmade et al., 1978; Dutson et al.,

1980) and decreases in the number or strength of the collagen cross-

linkages (Judge et al., 1980).

Stiffler et al. (1982) recognized that the percentage of change in

tenderness values caused by ES was quite variable, when the type of

beef being investigated was considered. They concluded that this





19 -



source of variation was associated with the initial, or inherent,

tenderness of the nonstinulated meat, especially from animals (steers

and heifers) less than 42 mo of age (i.e., the greater the initial

toughness, the greater the effect of stimulation).

Muscle Fiber Types

The development of highly specific enzyme stains has permitted the

identification and subsequent evaluation of individual fiber types

within a muscle (Moody and Cassens, 1968; Ashmore and Doerr, 1971;

Cassens and Cooper, 1971). The muscle fiber is the basic unit of

skeletal muscle and comprises 75 to 90% of the total muscle mass

(Hegarty, 1971). Early anatomical studies (Ranvier, 1873; Needham,

1926) have classified muscle fibers as red, white, or intermediate

based on their gross color. Physiologically, muscles are recognized as

slow or fast, depending on the speed of contraction (Guth and Samaha,

1969), while histochemical studies have led to recognition of three

types of muscle fibers, i.e., types A, B and C (Stein and Padykula,

1962) or types I, II and intermediate (Dubowitz and Pearse, 1960).

Despite the differences in fiber classifications, white fibers can be

equated with type A or II or fast; the red fibers are equivalent to

type B or I or slow, while type C fibers are intermediate.

Ashmore and Doerr (1971) and Ashmore et al. (1972) have shown that

all fibers are red at birth having high succinic dehydrogenase and

nicotinamide adenosine dinucleotide-diaphorase (NADH) activities, but

some show high and others show low ATPase activity. On this basis,

they classified them into a-red (aR) and B-red (aR) fibers,

respectively, with the BR fibers being true red fibers. On the other

hand, the aR fibers have the capacity to transform from an aerobic





20 -



state of metabolism to an anaerobic state, thus becoming a-white (aW)

fibers having high ATPase activity. Not all aR fibers become aW

fibers; some remain as aR fibers, which are intermediate in

physiological and metabolic parameters. The BR fibers remain red

throughout their lifespan.

The number of muscle fibers comprising a muscle is believed to be

genetically determined and firmly established at birth or shortly

thereafter in cattle (Hegarty, 1971). Subsequent increases in muscle

size during pre- and postweaning development are due to the enlarging

or growth of individual muscle fibers and the transformation of the aR

to the aW fiber type (Ashmore et al., 1972).

Transformation is primarily concerned with changes in

energy-producing enzymes, and is accompanied by a rapid increase in

fiber size (Ashmore et al., 1972). Furthermore, these authors

postulated that selection of heavily muscled animals for breeding stock

and progressive elimination of sustained muscle activity could lead to

selection of animals with a high proportion of aW fibers. Several

studies (Mahyuddin, 1976; Suzuki et al., 1976; Dreyer et al., 1977;

White et al., 1978; Spindler et al., 1980; Solomon et al., 1981a)

have presented evidence which indicates that during muscle growth the

percentage of aR fibers decreases while the percentage of aW fibers

increases.

The histochemical (Dubowitz, 1970; Brooke, 1970), ultrastructural

(Gauthier, 1970), biochemical (Beatty and Bocek, 1970) and ontogenetic

differences (Cosmos, 1970) in the three types of muscle fibers have

been reviewed in great detail. Cassens and Cooper (1971) also reviewed

and described the morphological and biochemical characteristics of





21 -



these fibers at length. In summary, acW or "white" fibers are generally

characterized as being large in diameter, have a well developed

sarcoplasmic reticulum, and are high in glycogen, creatine phosphate,

ATP and contraction speed, but are low in myoglobin, mitochondrial

numbers, lipid content, blood supply, oxidative metabolic activity, RNA

and protein turnover (Gauthier, 1970; Ashmore and Addis, 1972;

Cassens and Cooper, 1971). The aR or "red" fibers are just the

opposite while the BR or "intermediate" fibers are intermediate in

these characteristics.

Each fiber type differs in its growth potential, growth impetus,

function and metabolic capabilities (Ashmore and Addis, 1972). Hammond

(1932) noted that the sizes of muscle fibers in sheep increased with

age, exercise, and nutrition. He also noted that fibers were largest

in male animals, intermediate in castrated males and smallest in

females. Other workers (West, 1974; Dreyer et al., 1977; Guenther,

1977; Moody et al., 1980; Solomon et al., 1981a) reported that size

of muscle fibers was affected by animal age, weight, breed type, sex,

genetic conditions or nutrition. Stein and Padykula (1962), Ashmore et

al. (1972) and Johnston et al. (1975) reported that the aW muscle

fibers were generally the largest in diameter, the BR fibers smallest,

and the aR fibers intermediate in size.

Cassens et al. (1969) and Ashmore and Addis (1972) reported that

since the number of fibers in a muscle is relatively fixed at birth,

muscle size is directly proportional to the degree to which aR fibers

transform into aW fibers. The aW fibers may conceivably reach their

full growth potential later in life or at heavier body weights than

either BR or aR fibers and thereby delay the onset of the "fattening

phase" of growth.





22 -



Along this line, Solomon et al. (1981a) observed that small-

framed, early maturing Finnish Landrace crossbred lambs had more aW

fibers and fewer aR fibers in the LD muscle when compared at similar

slaughter weights (32 and 41 kg) than large-framed, late maturing

Suffolk crossbred lambs. They suggested that breed, or more speci-

fically the stage of physiological maturity, may have contributed to a

shift from aR to aW fibers during growth. Furthermore, they observed

that the small-framed lambs had larger LD fiber diameters than the

large-framed lambs at both slaughter weights.

Dreyer et al. (1977) evaluated the semimembranosus and

semitendinosus (dark and light sections) from earlier maturing

Friesland and later maturing Afrikaner bulls fed ad libitum and

slaughtered at similar ages from birth to 24 mo inclusive. For the

muscles studied by these authors, Friesland bulls had more aW fibers

and fewer aR fibers than the Afrikaner bulls when compared at similar

chronological ages, which also would suggest that breed, or

physiological maturity, may contribute to the conversion of aR to aW

fibers during growth and maturation. Furthermore, they found that the

earlier maturing Friesland bulls had larger fiber diameters than the

later maturing Afrikaner bulls in the muscles investigated.

Johnston et al. (1981) presented evidence which also suggested

that feeding system may affect the degree to which aR fibers transform

into aW fibers. Bartlett et al. (1979) compared Angus with Charolais

calves at 25 d of age and found that the Angus calves had a higher

percentage of aW and aR fibers, while the Charolais calves had a higher

percentage of BR fibers.





23 -



In a previous study by Johnston et al. (1975), no significant

effect due to breed type (Angus vs Charolais steers) was detected for

the percentages of LD muscle fiber types when steers were fed for the

same length of time. Although these authors did not state exactly what

age the steers were before going on feed or after the removal from

feed, the steers were described as being similar in age and weight and

derived from similar nutritional regimens. These authors did observe

larger fiber diameters and fiber areas for all three fiber types

associated with the Charolais steers than for the Angus steers.

Guenther (1977) reported that the variation in total amount of

muscle in cattle of different maturation rates and body size (Angus vs

Charolais) was due to differences in the total number of muscle fibers

rather than the size or diameter of muscle fibers. Similar conjectures

were made by Ashmore and Robinson (1969) and Burleigh (1980). Guenther

(1977) noted that the Angus steers used in his study had larger fiber

diameters than the Charolais steers when compared at similar ages from

1 mo to 15 mo inclusive. Hegarty et al. (1973) noted that two

different types of pigs (early vs late maturing) had the same muscle

weights, but developmentally, the muscles were at different stages

of maturity.

Muscle Nucleic Acids

Some animals have the ability to grow faster than others and

produce much greater amounts of muscle in a shorter period of time.

The cellular effect of genetic selection for growth rate has been

studied in different meat animal models. Some investigations compared

different breeds of cattle (Ashmore and Robinson, 1969; La Flamme et

a!., 1973; Lipsey et al., 1978; Trenkle et al., 1978; Eversole et





24 -



al., 1981), pigs (Powell and Aberle 1975; Harbison et al., 1976) and

chickens (Moss, 1968). Growth of animals is characterized by an

orderly increase in the mass of tissues and organs as well as changes

in form and body composition. Enesco and Leblond (1962) indicated that

normal growth occurs in successive stages characterized by an increase

in cell number, increases in both cell number and cell size and

finally, an increase in cell size alone. In meat animals, growth of

the major tissues (bone, muscle and lipid) is most important with

skeletal muscle having the greatest economic value.

Postnatal skeletal muscle growth is characterized by an increase

in muscle cell size rather than an increase in the number of cells

(MacCallum, 1898; Ashmore and Addis, 1972; Ashmore et al., 1972).

Total cell numbers appear to be fixed since muscle cells do not divide

beyond a certain stage of embryonic development (Stockdale and Holtzer,

1961; Ashmore and Addis, 1972). Since the amount of deoxyribonucleic

acid (DNA) per mammalian diploid nucleus is constant (6.2 pg), DNA can

be used successfully as an index of cell (nuclei) number in tissues

composed of mononucleated cells (Vendrely, 1955). Deoxyribonucleic

acid is the component found almost exclusively in the nucleus of the

cell that is the basis of genetic information and controls synthesis of

proteins. The ratio of protein to DNA (i.e., cytoplasm to nucleus) has

been shown (Winick and Noble, 1965; Robinson, 1969) to provide an

index of cell size. Enesco and Leblond (1962) presented evidence which

indicated that increases in both of these constituents contributed to

the growth of young rats. Thus, a distinction between growth caused by

hyperplasia and that contributed by hypertrophy could be obtained.





25 -



In tissues composed of multinucleated cells, such as skeletal

muscle, one cannot calculate cell number and size directly from DNA and

protein. However, Cheek et al. (1971) suggested that in skeletal

muscle the amount of DNA is indicative of the number of nuclei in

muscle and the protein:DNA rate measures the average amount of

cytoplasm associated with one nucleus within the muscle fiber. This

ratio of nuclei to cytoplasm may be of significance in growth of muscle

fibers. At least 70% of muscle DNA is due to nuclei within the

myofibers; thus, cell number can be estimated from the quantity of DNA

in a sample of muscle, adjusted to total muscle mass (Cheek et al.,

1971).

In addition to DNA, ribonucleic acid (RNA) is a part of the

genetic mechanism of the cell and represents a critical part of the

mechanism for cell differentiation and growth. Ribonucleic acid

reflects the activity per ribosome (Burleigh, 1980) and may serve as an

index for the extent to which protein synthesis occurs. A high ratio

of RNA to DNA has been interpreted as a greater capacity for synthesis

of protein (Winick and Noble, 1965; Millward et al., 1973) and may be

indicative of growth potential (Sarkar et al., 1977).

Despite the absence of cell division, total DNA increases in

muscle during growth and development (Moss, 1968). The source of this

replicating DNA appears to be proliferative satellite cells (MacConnachie

et al., 1964; Moss and Leblond, 1971). Swatland (1971) concluded that

hypertrophy in muscle fibers is accompanied by an increase in the

number of nuclei which are derived from fusion with proliferative

satellite cells. A certain amount of DNA is needed to control the

process of protein synthesis and deposition in the muscle (Cheek et





26 -



al., 1971). In actively growing muscles, muscle cells contain many

nuclei (DNA units), each controlling the extent and rate of synthesis

over its domain by providing synthesis machinery, i.e., RNA and ribo-

somes (Thompson and Heywood, 1974). Hormones, nutrition and exercise

can, within limits, modulate the extent of the activity of the muscle

nuclei in providing the apparatus associated with protein synthesis

(Trenkle, 1974; Cheek and Graystone, 1978; Goldberg et al., 1980).

Several investigators (Ashmore and Robinson, 1969; Powell and

Aberle, 1975; Harbison et al., 1976; Lipsey et al., 1978; Trenkle et

al., 1978; Eversole et al., 1981) presented evidence which indicates

that larger (heavier) muscles have more total DNA and total RNA than

smaller (lighter) ones. Therefore, the differences in total nucleic

acids encountered by these authors when comparing different breed types

were usually attributed to differences in muscle weights between the

breeds since nucleic acid concentrations per gram of muscle tissue were

generally not significantly different. Trenkle et al. (1978) also

recognized that full fed steers, which were accumulating protein in

their muscle at a faster rate than limited fed steers, also had higher

RNA:DNA ratios suggesting a greater capacity for synthesis of protein

by these steers.

Muscle protein deposition is not just simply a process of

synthesis. Millward et al. (1976) and Laurent and Millward (1980)

presented evidence which indicated that a sizeable portion of the

protein synthesized is degraded. Laurent and Millward (1980) esta-

blished that this rate of degradation is higher in the faster growing

muscle cells. The net protein accretion between synthetic and

degradative processes represents the actual protein acquisition in





27 -



muscles (Millward et al., 1976; Goldberg et al., 1980; Laurent and

Millward, 1980). As an animal reaches physiological maturity, the

rates of synthesis and degradation become equal and there is no further

net protein deposition in muscle (Millward et al., 1976; Laurent and

Millward, 1980; Lindsay, 1982). At this point, the ratio of protein

to DNA is at its highest level (Robinson, 1969, Burleigh, 1980) and the

absolute rates of synthesis and degradation, although still

appreciable, have declined to a rate much lower than that occurring

during rapid muscle growth (Millward et al., 1976; Goldberg et al.,

1980; Laurent and Millward, 1980).














STUDY 1
PRODUCTION TRAITS AND CARCASS COMPOSITIONAL CHARACTERISTICS
OF YOUNG PUREBRED ANGUS AND BRAHMAN BULLS SLAUGHTERED
AT SIMILAR PERCENTAGES OF MATURE WEIGHT

Introduction

A considerable amount of interest has been stimulated regarding

the use of young bulls in modern beef production systems. Such

interest stems from the fact that bulls gain more rapidly, utilize feed

more efficiently and produce a higher yielding carcass (more retail

product) with less fat and more red meat than steers (Field, 1971;

Seideman et al., 1982). However, as Seideman et al. (1982) explained

in their review, increased production efficiency obtained through the

use of intact males has often been offset by management problems,

particularly with animal behavior.

Furthermore, meat production from intact males has encountered

strong resistance from packers, since bulls, on the average, have been

shown to produce carcasses with lower quality grades, darker lean color

and coarser-textured lean resulting in lower consumer acceptance at the

retail level than steers (Field, 1971). Therefore, when young bull

carcasses are officially graded by USDA graders, the standards require

the grade designation to also include the word "Bullock." Although

several problems associated with producing meat from young bulls exist,

perhaps some or all of these problems can be reduced or alleviated and,

thus, meat from young bulls could help satisfy the demand for lean

beef.




28 -





29 -


A number of studies (Cole et al., 1964; Luckett et al., 1975;

Peacock et al., 1980, 1982; Solomon et al., 1981b; Adams et al.,

1982) described substantial differences in production traits, carcass

characteristics and compositional factors between Angus and Brahman

cattle (steers and heifers). Except for research on size and condition

(Long et al., 1979) and on selected slaughter and carcass traits

(Jenkins et al., 1981) of serially slaughtered bulls representing a

five-breed diallel which included Angus and Brahman, few studies have

been done to characterize performance and carcass compositional

characteristics of purebred bulls representing these diverse breed

types.

Therefore, this study was conducted

(1) to compare production, compositional and carcass characteris-

tics of purebred Angus and Brahman bulls, and

(2) to evaluate the use of slaughtering at similar percentages of

the mature cow weight as a technique for comparing bulls, of

such diverse origins, on an equal compositional basis.

Materials and Methods

Seventy-eight purebred bulls (10 to 18 mo at slaughter) were

used over a two year period (table 1) to ascertain the effects of breed

(Angus or Brahman) and slaughter weight (60, 80, 90, 100% of the

average mature cow weight for the respective breed) on production

traits and carcass compositional characteristics. All the bulls came

from the University of Florida registered Angus and Brahman herds in

which all female replacements during a 30 year period were generated

within the herd with new genetic material obtained from outcross herd

sires and frozen semen. The dam's nature weights for the respective

breeds were 456.3 kg for Angus and 515.3 kg for Brahmans.





30 -







TABLE 1. ALLOTMENT OF EXPERIMENTAL ANIMALS




a % Mature weightb
Breed 60 80 90 100


Year I
Angus 5 5 5 5

Brahman 5 5 5 5


Year II
Angus 5 1 5 6

Brahman 5 6 8 2


b Age ranged from 10 to 18 mo at slaughter.
Percentages of the average mature cow weight for the
respective breed.





31 -



Each year, the fall-calved Angus bulls grazed summer annual forage

(Tifleaf-1 Millet) after which bulls representing the 60% group were

slaughtered. The remaining Angus bull calves were then placed in the

feedlot and fed a shelled corn-protein supplement diet (table 2) until

they reached their appropriate slaughter weight. Winter-calved Brahman

bulls were fed the concentrate diet (table 2) after being weaned to

simulate gains the Angus bulls achieved on forage. After slaughtering

the Brahman bull calves representing the 60% group, the remaining bulls

were fed the same diet (table 2) to their designated slaughter weight.

Bulls were slaughtered when they reached or came close to their

designated target weight. Actual live weights at slaughter for Angus

bulls were 293, 381, 412, and 463 kg and for Brahman bulls were 316,

420, 463, and 516 kg. After slaughter, carcasses were weighed and then

chilled at 0-2 C. Live weights and hot carcass weights were used to

calculate dressing percentage.

At 24 h postmortem, the left side of each carcass was ribbed

between the 12th and 13th rib and quality and yield characteristics

were evaluated by University of Florida personnel. Skeletal, lean and

overall maturity were combined with marbling score to determine quality

grade (USDA, 1975). Other quality traits evaluated were lean color (7

= very dark red, 1 = dark pink), texture of lean (7 = extremely coarse,

1 = very fine), lean firmness (7 = extremely soft, 1 = very firm) and

presence of heat-ring (4 = extreme, 1 = none). Fat thickness over the

ribeye at a point three-fourths the distance from the chine bone,

ribeye area, estimated percent kidney, pelvic and heart fat, and hot

carcass weight were used to determine the yield grade.





32 -












TABLE 2. DIET COMPOSITION



Ingredient Year 1, % Year 2, %


Corn, whole, shelled (IFN 4-02-931) 80 92

Sugarcane pulp, dehy, pelleted (IFN 1-04-686) 4

Cottonseed hulls (IFN 1-01-599) 4 8

Commercial supplement 12a +b

a Imperial Beef Concentrate 52% changed to Purina Custom Mix 38%
(crude protein equivalent approximately 54%) three months into
b study.
Moor Man's Beef Finisher with monensin (crude protein equivalent
approximately 80%) fed at rate of 227 g per day, modified midway
through study by changing crude protein equivalent to approximately
54%.





33 -



The 9-10-11 rib section from the right side of each carcass was

removed at 24 h postmortem, by the procedure outlined by Hankins and

Howe (1946), vacuum packaged and stored at -18 C for subsequent physical

separation and chemical analysis. The 9-10-11 rib cuts were physically

separated into lean, fat and bone, after being thawed at 2 C. The soft

tissue components (lean plus fat) were then thoroughly mixed and ground

together and stored frozen (-18 C) until analyzed by AOAC (1980) proce-

dures for chemical composition. The chemical determinations made on the

soft tissue components were used to predict carcass composition using

the equations developed by Field (1971). Crude protein was determined

as nitrogen (Semiautomated method; AOAC, 1980) x 6.25.

In addition, a sample (2.54 cm in thickness) from the anterior end

of the longissimus muscle at the 13th rib end from the left side of

each carcass was removed, closely trimmed of external fat and

connective tissue, then finely ground and thoroughly mixed. Chemical

determinations for moisture, ether extractable lipid and protein were

also performed on these muscle samples.

Data were analyzed by the regression procedure of the Statistical

Analysis System (SAS, 1979). A 2 x 4 x 2 factorial model involving

breed, weight group and year was used to analyze all response

variables. F-tests were used to determine the effects of breed, weight

group and year on the parameters investigated. The Duncan's multiple

range test (SAS, 1979) was used to"test differences among slaughter

weights.

Results and Discussion

Live animal traits and dressing percentages are presented in table

3. Angus bulls were (P<.05) younger and lighter at slaughter than





34 -



TABLE 3. LEAST-SQUARES MEANS FOR LIVE ANIMAL TRAITS AND DRESSING
PERCENTAGES BY BREED, WEIGHT GROUP AND YEAR



Age Live wt., ADG,a Dressing
Item N d kg kg/d %


Main Effects
Breed (B)

Angus 37 416.2b 387.2b 1.08 56.6b

Brahman 41 442.5c 428.9c 1.03 59.2c

Weight group (W), %

60 20 334.7b 304.7b .76b 54.5b

80 17 442.6c 400.3c 1.10c 58.4C

90 23 457.9d 437.7d 1.15c 58.8c

100 18 482.1e 489.6e 1.20c 59.9C

Year (Y)

1 40 418.0b 405.0b 1.11c 58.1

2 38 440.7c 411.2c 1.00b 57.7

Interactions

BxW *

BxY NS NS *

WxY NS NS

BxWxY NS NS NS


a Average daily gain.
b,c,d,e Means within a main effect group in the same column bearing
f different superscripts are different (P<.05).
= P<.05; NS = nonsignificant (P>.05).





35 -



Brahman bulls, as expected based on the nature of the experimental

design which took into account differences in maturation rates due to

breed types. Interactions (P<.05) between breed and weight group (BxW)

for age and live weight (table 4) indicated that Angus bulls from the

80, 90 and 100% weight groups were approximately 1 mo younger (14.8 vs

15.9 mo) and 48 kg lighter at slaughter than Brahman bulls from the

respective weight groups (table 4). However, Angus bulls representing

the 60% group were only 1 d younger, on the average (334 vs 335 d), and

23 kg lighter at slaughter than Brahman bulls from the 60% group.

These data suggest that the Brahman bulls required longer times to

reach the 80, 90 and 100% weight groups than did the Angus bulls.

As slaughter weight increased, age and live weight increased

(P<.05) as anticipated. Year also had an effect (P<.05) on age and

weight at slaughter. Bulls comprising the second year group were older

(22 d) and heavier (6 kg) at slaughter than those used the first year.

A weight group by year (WxY) interaction was noted for live weight

(table 5). Bulls used for the first year study were slightly heavier

at the 60% weight but lighter at the 80 and 100% weights than those for

the second year. Weights for the 90% group were similar from one year

to the next. Part of these differences in live weight for the

different years may be associated with the difference in number of

bulls between breeds in the 80 and 90% groups (table 1).

Average daily gain was not affected (P<.05) by breed type but was

influenced by weight group and year (table 3). Average daily gain for

the 60% group was calculated by subtracting the weight at weaning from

their weight before going into the feedlot and dividing the total

number of days that transpired during this time. Average daily gain







TABLE 4. BREED BY WEIGHT GROUP INTERACTIONSa FOR VARIOUS LIVE ANIMAL, CARCASS AND LONGISSIMUS MUSCLE
CHARACTERISTICS


b d
Weight Age, Live ADG Maturity d Quality Heate Longissimus
Breed group,% d wt., kg kg/d DPc Lean Overall Marbling grade ring lipid,%

21 12 45
Angus 60 334.3 293.3 .70 52.7 A21 A12 Tr45 11.6 2.0 1.34
Brahman 60 335.1 316.0 .82 56.4 A A Pd 10.7 3.1 .80
47 42 07
Angus 80 421.1 380.5 1.17 56.5 A47 A42 S 12.6 2.1 1.80
Brahman 80 464.1 420.1 1.02 60.2 A A Pd7 10.8 2.7 1.44
54 49 03
Angus 90 444.4 412.2 1.17 58.3 A4 A4 S 13.1 2.4 1.74
Brahman 90 471.4 463.3 1.13 59.3 A4 A3 Pd9 10.7 2.5 1.41
56 A54 17 c1
Angus 100 465.0 462.9 1.26 59.0 A S1 13.3 2.0 3.12
Brahman 100 499.3 516.3 1.14 60.7 A47 A4 Pd87 10.7 2.8 1.33

b Significant at the P<.05 level.
SAverage daily gain.
d Dressing percentage.
Refer to table 8 for codes.





37 -



TABLE 5. WEIGHT GROUP BY YEAR INTERACTIONSa FOR LIVE WEIGHT, AVERAGE
DAILY GAIN AND LEAN TEXTURE



Weight Live wt., ADG Lean
group % Year kg kg/d texture


60 1 308.9 .84 1.8
60 2 300.4 .68 2.3

80 1 388.7 1.21 3.1
80 2 411.8 .99 2.5

90 1 437.9 1.21 3.5
90 2 437.6 1.09 2.5

100 1 484.5 1.18 3.3
100 2 494.7 1.13 2.6


a Significant at the P<.05 level.
SAverage daily gain.
cRefer to table 8 for codes.





38 -


for the remaining weight groups was calculated by subtracting the

weight before going into the feedlot from their final slaughter weight

and dividing by the total number of days that passed.

Increasing slaughter weight was associated with an increase in

ADG, which was significant, however, only from the 60 to the 80% group.

Arthaud et al. (1977), studying production and carcass traits of Angus

bulls and steers fed different energy levels and killed at four ages

(12, 15, 18, or 24 mo) found that bulls, regardless of diet (high or

low energy) had increasing ADG from 12 to 15 mo of age, but then

ADG decreased from 15 through 24 mo. The bulls representing the 60

and 80% groups in the present study were 11 and 15 mo of age at

slaughter, respectively. After 15 mo (80% group), the ADG did not

decrease for the bulls in the present study as did the bulls and steers

used by Arthaud et al. (1977).

Average daily gains for bulls in the different weight groups were

affected by breed (table 4). Brahman bulls (60% group) which were fed

a concentrate diet to simulate gains achieved by Angus bulls on forage

actually gained 17% more weight per day than the Angus bulls (table 4).

However, for bulls representing the 80, 90, and 100% groups, Angus

bulls gained weight faster than Brahman bulls.

Bulls from the second year, for the most part, gained (P<.05) less

weight per day than those used the first year (table 3). However, this

difference due to year was not consistent for all weight groups (table

5) and both breeds (table 6). Bulls used the first year were substan-

tially superior in ADG (table 5) than those used for the second year

study for all the weight groups except the 100% group, where ADG were

similar. Angus bulls from the first year study tended to gain weight





39 -







TABLE 6. BREED BY YEAR INTERACTIONSa FOR AVERAGE DAILY GAIN,
DRESSING PERCENTAGE, QUALITY GRADE AND HEAT-RING SCORES



ADGb, Dressing Quality Heat-
Breed Year kg/d % gradec ring


Angus 1 1.19 57.3 12.1 2.3
Brahman 1 1.03 58.8 10.8 2.5

Angus 2 .96 55.9 13.2 2.1
Brahman 2 1.03 59.5 10.7 3.0


a Significant at the P<.05 level.
SAverage daily gain.
cRefer to table 8 for codes.





40 -



more rapidly than Brahman bulls from year one (table 6). On the

contrary, Brahman bulls from the second year gained slightly more

weight per day than Angus bulls used the second year. The differential

response of breed, weight group and year on ADG resulted in a three-way

interaction (P<.05) of these main effects (table 3).

Perhaps these differences in ADG and, thus, live weight may be

attributed to the changes in diet composition from the first year to

the second (table 2). These changes were an increase in the percentage

of shelled corn (from 80 to 92%) and cottonseed hulls (from 4 to 8%)

with sugarcane bagasse pellets being removed from the diet. In

addition, the commercial protein supplement was changed from an

intermediate crude protein equivalent of approximately 54% used the

first year to one containing a high crude protein equivalent of

approximately 80% the second year. The supplement used the second year

in turn had to be switched back to one containing an intermediate crude

protein equivalent of approximately 54% midway through the study.

The reason for making this switch during the course of the

experiment was because the bulls were not utilizing the high levels of

nonprotein nitrogen in the supplement sufficiently for growth. In

fact, the Angus bulls, which went into the feedlot 3 mo earlier

than the Brahman bulls, because of their earlier calving and, thus,

earlier weaning dates only had one mo to benefit from this diet

modification. The Angus bulls were slaughtered 28 d after making the

switch in crude protein. However, the Brahmans were only in the

feedlot for 56 d prior to the supplement switch.

The breed by year (BxY) (table 6) interaction (P<.05) noted for

ADG indicated that the Angus bulls gained less weight per day the





41 -



second year than the first, suggesting a breed effect on diet utili-

zation for growth. This difference appears to be related to the diet

supplement modification during the second year.

Peacock et al. (1980), in a study comparing feedlot performance and

carcass traits of purebred Angus and Brahman steers fed a concentrate

diet for an average of 176 d, found no difference in ADG due to breed

type. Bailey et al. (1982) reported no difference in ADG due to breed

type when comparing bulls from widely divergent breed types, including

Bos taurus and Bos indicus x Bos taurus crosses fed a concentrate diet

and slaughtered at a constant age (400 d). However, in a study by

Peacock et al. (1982), where they compared feedlot gain and carcass

traits of purebred Angus and Brahman steers fed a concentrate diet for

an average of 174 d and slaughtered at a constant weight (411 kg) and

age (439 d), Brahman steers gained less weight per day than Angus

steers.

A recent study by Adams et al. (1982) substantiated these

findings. These authors compared performance and carcass characteris-

tics of purebred Angus and Brahman steers fed a high energy diet for

157 and 179 d, respectively. Their intent was to slaughter individual

steers as they attained a U.S. Choice finish (visually appraised).

Brahman steers were lighter than the Angus steers at the beginning and

also at the end of the experiment. Angus steers gained weight much

more rapidly, and consequently they were on feed 22 fewer days than the

Brahman steers. Similar results were also reported by Cole et al.

(1964), who compared Angus and Brahman steers full-fed to a constant

live weight (408.2 kg) or age (20 mo), whichever came first.





42 -



In the present study where young Angus and Brahman bulls were fed

to a percentage of the mature cow weight for each respective breed, the

type of diet appeared to interact with breed relative to growth

characteristics. This may be true for only bulls, but could have

possibly affected the results other workers have found for steers.

Angus bulls had lower (P<.05) DP than Brahman bulls (table 3).

This was true at each designated slaughter weight; however, the

difference in DP between the two breeds decreased (table 4) with

increasing weight. Furthermore, a greater difference in DP between

breeds was observed the second year than the first (table 6). Perhaps

these differences reflect the diet compositional differences from one

year to the next and modifications made during the individual study.

Solomon et al. (1981b) found that Brahman heifers dressed slightly

higher than Angus heifers fed different levels of nutrition for 217 d.

Butler et al. (1956), in a study comparing yearling Hereford and Brahman

x Hereford steers fed high or low concentrate diets for 140 d, found

that steers with Brahman breeding had higher DP than those without

Brahman breeding. They suggested that the difference in DP between Bos

indicus and Bos taurus cattle was probably due to differences in the

capacity and amount of intestinal tract content (fill) at the time of

slaughter.

Adams et al. (1982) in their study found Angus steers to have

higher DP than Brahman steers, but the Angus steers were much fatter at

slaughter than the Brahman steers. On the contrary, Cole et al. (1964)

observed no difference in DP between Angus and Brahman steers fed to a

constant live weight (408.2 kg) or age (20 mo), whichever came

first.





43 -



For the most part, increasing slaughter weight resulted in higher

DP, however, the only significant difference found for DP was between

the 60 and 80% group. This agrees with the study by Arthaud et al.

(1977), who evaluated production and carcass traits of Angus bulls and

steers fed either high or low energy diets and slaughtered at four ages

(12, 15, 18, or 24 mo).

Means for yield grade factors by breed, weight group and year are

presented in table 7. Except for hot carcass weight and numerical

yield grade, neither fat thickness, ribeye area nor percentage of

KPH were affected by breed (table 7). Brahman carcasses were heavier

(P<.05) than Angus carcasses as expected from the experimental design.

However, equal fatness and ribeye measurements at the heavier weights

resulted in higher yield grades being assigned to Brahman carcasses.

In the study by Peacock et al. (1982), Brahman carcasses ended up

slightly heavier (9 kg), with less subcutaneous fat and smaller ribeyes

than Angus carcasses. Adams et al. (1982) found that carcasses from

Angus steers had more subcutaneous fat, more KPH and larger ribeyes,

thus higher yield grades, than Brahman steers. However, in that same

study when carcass traits were adjusted to a constant carcass weight

(279.4 kg), ribeye area was no longer different between the two breeds,

but fat thickness was still greater for carcasses from Angus steers.

Luckett et al. (1975), working with straightbred steers of Angus and

Brahman ancestry fed a high concentrate diet for 100 to 114 d, found

that carcasses from Brahman steers had considerably less subcutaneous

fat and smaller ribeyes than those from Angus steers.






TABLE 7. LEAST-SQUARES MEANS FOR YIELD GRADE FACTORS BY BREED, WEIGHT GROUP AND YEAR



Main Effects
Breed (B) Weight group (W), % Year (Y) Interactionsf
Item Angus Brahman 60 80 90 100 1 BxWxY

Hot carc. wt., kg 220.7a 255.0b 166.3a 234.0b 257.7c 293.3d 236.6 239.0 NS

Fat thickness, mm 4.9 4.4 2.2a 4.1b 5.5c 6.8d 4.4 4.9 NS

Ribeye area, cm2 67.1 66.1 55.2a 67.8b 69.1b 74.2c 65.9 67.2 *

KPHe, % 1.6 1.5 1.4a 1.4a 1.5a 1.8b 1.6 1.4 NS

Yield grade 1.8a 2.1b 1.6a 1.8a 2.1b 2.3c 2.0 1.9 NS

a,b,c,d Means within a main effect group on the same line bearing different superscripts are different
(P<.05).
e Kidney, pelvic and heart fat.
= P<.05; NS = nonsignificant (P>.05). None of the two-way interactions were significant at the (P<.05)
level.





45 -


Solomon et al. (1981b), comparing purebred Angus and Brahman

heifers when fed different planes of nutrition for 217 d, found that

carcasses from Angus heifers were slightly heavier and possessed larger

ribeyes than those from Brahman heifers. However, no difference in fat

thickness or KPH was observed, thus carcasses from Brahman heifers

received higher numerical yield grades than those from Angus heifers.

Results from a study conducted by Le Van et al. (1979), comparing Angus

to Charolais steers revealed that differences in growth rate and yield

grade factors were relatively minor when cattle were slaughtered and

compared at similar percentages of the corresponding breed average

mature weight. This is in agreement with the results from the present

study.

As carcass weight increased, fat thickness, KPH and final yield

grade increased (table 7), indicating that heavier carcasses were

probably fatter than lighter carcasses. This is in agreement with the

work reported by Arthaud et al. (1977), Jones et al. (1978) and Solomon

et al. (1981b). Ribeye area, as a measure of muscling, increased at

each successive weight interval only for the Brahman bulls from the

second year group (figure 1). On the contrary, for both years of Angus

bulls and the first year Brahman bulls, ribeye area increased rapidly

from the 60 to the 80% group, changed little or decreased between 80

and 90% and then increased from the 90 to the 100% group.

Other than this three-way interaction (BxWxY) for ribeye area,

year had no significant effect on yield grade factors. Conceivably,

the increased growth rate for the second year Brahman bulls may be

related to the continued increase in ribeye area detected only for this

group of bulls. Furthermore, perhaps this difference may reflect the

protein supplement modifications made during the individual study.





46 -








0 Angus Year 1

Angus Year 2

o Brahman Year 1
80-
Brahman Year 2



E
70
70 -

1-

.0
60 -





50 -




60 80 90 100
Weight group, %



Figure 1. Effects of breed, weight group and year on ribeye area.





47 -


Quality characteristics of the longissimus muscle at the 13th rib

when ribbed at 24 h postmortem, and bone maturity scores are presented

in table 8. Lean maturity scores were lower for Angus carcasses at the

60 and 80% weights than for Brahman carcasses at these same weight

percentages (table 4), indicating more youthful color. However, at the

90 and 100% weights, lean maturity scores were higher for Angus

carcasses than for Brahman carcasses at these heavier weights

suggesting more mature (physiologically) lean. Nevertheless, lean

maturity scores for all the bulls averaged A48, which indicates that

physiologically the bulls were still fairly young. In fact, the actual

average age of all the bulls was 14.3 mo (table 3). Solomon et al.

(1981b) found that the lean from Angus heifers was more mature in color

than that from Brahman heifers. These authors did point out that the

Angus heifers were chronologically 1 mo older at slaughter than the

Brahman heifers.

Increasing slaughter weight was associated with an increase in

lean maturity scores for Angus bulls (table 4). Lean maturities for

carcasses from Brahman bulls appeared to decrease or change very

little as weight increased. Based on these results, it appears that

Brahman bulls changed very little physiologically in lean maturity.

Overall carcass maturity scores tended to follow patterns characterized

for lean maturities from the respective breeds. Adams et al. (1982)

reported no difference in overall maturity scores when comparing

carcasses from Angus and Brahman steers fed for 157 and 179 d, respec-

tively. Year had no effect (P>.05) on lean or overall maturity scores

(table 8).





TABLE 8. LEAST-SQUARES MEANS FOR QUALITY FACTORS BY BREED, WEIGHT GROUP AND YEAR


Main Effects
Breed (B) Weight group (W), % Year (Y) Interactionsk
Item Angus Brahman 60 80 90 100 1 2 BxW BxY WxY BxWxY


Lean maturityd A45 A51 A37 A51b3 51 A52 A49 A46 NS NS NS

Bone maturityd A34b A29a A14a A33 A35b A44c A 34b A29a NS NS NS NS
Overall maturityd A39 A40 A25a A43b A43b A48c A41 A38 NS NS NS

Marblinge Tr93 Pd83 Tr07a Tr47 Tr46 Tr52 Tr23a Tr53 NS NS NS
Quality grade 12.7b 10.7a 11.2 11.7ab 11.9b 12.0b 11.5 11.9 NS NS NS

Lean color 3.7 3.9 3.7 4.0 3.8 3.6 4.1 3.5a NS NS NS NS
Lean textureh 2.4a 3.0b 2.1a 2.8b 3.0b 2.9b 2.9b 2.5a NS NS *

Lean firmnessi 2.5 2.4 3.2b 2.3a 2.2a 2.1a 2.6 2.3 NS NS NS NS
Heat-ringj 2.2a 2.8b 2.6 2.4 2.5 2.4 2.4 2.5 NS NS

abc Means within a main effect group on the same line bearing different superscripts are different (P<.05).
SEvaluated on a 100 point scale within a maturity score.
e Pd = "practically devoid", Tr = "traces" and Sl = "slight"; evaluated on a 100 point scale within each
f marbling score.
21 point scale wherein 10 = Standard; 11 = Standard and 12 = Standard.
g 7 point scale wherein 3 = light cherry red and 4 = cherry red.
h 7 point scale wherein 2 = fine and 3 = moderately fine.
S7 point scale wherein 2 = firm and 3 = moderately firm.
k 4 point scale wherein 1 = none, 2 = slight and 3 = moderate.
= P<.05; NS = nonsignificant (P>.05).





49 -


Bone maturity, which is the degree of ossification within the bone

structure used to determine stages of physiological maturity (degree

of the animal's maturation), was influenced by breed, weight and

year. Brahman bulls had lower (P<.05) carcass bone maturity scores

(table 8) than those from Angus bulls, indicating that Brahman bulls

were more youthful physiologically. These results are probably

associated with the understanding that Brahman are a later maturing

breed type in comparison to Angus which are earlier maturing based on

growth rates.

As carcass weight increased, concomitantly scores for bone

maturity increased. Arthaud et al. (1977) found that except at 12

mo, where maturity scores were lower, bulls evinced similar

skeletal, lean and overall maturity with advancing chronological age as

steers. Solomon et al. (1981b) observed that with increasing live

weight at slaughter due to level of nutrition, bone, lean and overall

maturity scores all increased, indicating advancing physiological

maturity associated with higher levels of nutrition. Furthermore,

these authors pointed out that even though the heifers receiving the

highest level of nutrition also received higher maturity scores,

chronologically the heifers from this group were 2 weeks younger than

those heifers from the intermediate (level of nutrition) group and only

3 d older than those heifers representing the lowest (level of

nutrition) group. These authors indicated that plane of nutrition,

rather than chronological age appeared to influence the physiological

age of the animals.

Bulls from the second year possessed slightly lower (P<.05) bone

maturity scores than those used the first year. Although there were




50 -


differences in maturity indices, all carcasses were within the "A"

maturity score and would qualify for the "Bullock" grade. In addition,

advancing maturity within the "A" score has no effect on final quality

grade.

Significant BxW interactions were detected for marbling scores and

quality grades. Marbling scores and quality grades improved (P<.05)

with advancing slaughter weight (table 4) for only the Angus bulls

(Tr45 to S117 and Sto to G-, respectively). No change (P>.05)

due to weight was encountered for either marbling or quality grades for

the Brahman bulls (Pd68 to Pd87 and St- to St-, respectively).

Most carcasses were in the USDA "Standard" grade. Only Angus carcasses

from the 90 and 100% groups reached the "Good" grade (table 4).

Previous research comparing Angus and Brahman cattle conducted by

Luckett et al. (1975), Peacock et al. (1980, 1982), Solomon et al.

(1981b) and Adams et al. (1982) revealed that Angus carcasses received

higher quality grades because of superior marbling scores when compared

to carcasses from Brahman cattle. Results from the study conducted by

Le Van et al. (1979) revealed that differences in marbling scores

between Angus and Charolais steers were relatively minor when cattle

were slaughtered and compared at similar percentages of the

corresponding breed average mature weight.

Bailey et al. (1982) found no difference in marbling and quality

grade due to breed type when comparing bulls from distinctly different

breed origins, including Bos taurus and Bos indicus x Bos taurus

crosses. Perhaps hybrid vigor due to crossbreeding Bos indicus with

Bos taurus may also eliminate substantial differences (e.g., in

marbling and quality grades) otherwise encountered when comparing the

purebreds from these genetically different animals.





51 -



However, in the present study, when purebred bulls were compared

at similar percentages of mature weights, the Brahman bulls produced

carcasses with less marbling than did the Angus bulls; a situation

probably resulting from selection practices. It appears that the

breeders of British cattle (e.g., Angus) have succeeded in developing

animals that will store a large amount of fat in their muscle at a

young age. Quality grades were higher the second year than the first

for only the Angus bulls (table 6).

No major difference (P>.05) due to breed type, weight group or

year was observed for lean color or firmness. The majority of

carcasses had firm, light cherry-red colored lean in the ribeye. The

lean from Angus carcasses, however, was finer-textured (P<.05) with

less evidence of heat-ring formation (P<.05) than lean from Brahman

carcasses, especially for the second year (tables 4, 6 and 8) and

probably accounts for the lean maturity differences previously

discussed. Heat-ring is the appearance of dark lean color at the

periphery of the ribeye muscle resulting from different chill rates

within the muscle. It appears from this study that heat-ring formation

may be a function of size of the carcass as well as fatness.

Lean from the second year group of bulls was slightly finer in

texture than lean from first year bulls, except in the case of the 60%

group (table 5) where it was just the reverse. Furthermore, bulls from

the first year 60% weight group possessed the finest-textured lean for

the entire two year study.

Predicted carcass components based on the 9-10-11 rib cut and

longissimus muscle chemical composition are listed in table 9. There

were no major differences (P>.05) in predicted carcass composition





TABLE 9. LEAST-SQUARES MEANS FOR PREDICTED CARCASS AND LONGISSIMUS MUSCLE COMPOSITION BY BREED, WEIGHT GROUP
AND YEAR



Main Effects

Breed (B) Weight group (W), % Year (Y) Interactions9
Item Angus Brahman 60 80 90 100 1 2 BxW

Predicted carcass componentsd

Fat-free lean, % 65.22 65.33 67.03c 65.60b 64.58ab 63.91 65.38 65.17 NS
Fat, % 18.52 17.93 15.77a 17.84b 19.15c 20.15c 17.91 18.54 NS
Bone, % 16.28 16.74 17.21c 16.56c 16.32ab 15.95a 16.70 16.32 NS
ef
Longissimus muscle, '
Moisture, % 74.97b 74.43a 75.25c 74.86b 74.77b 73.93a 75.24b 74.16 NS
Ether extractable lipid, % 2.00b 1.24a 1.07a 1.62b 1.57b 2.23c 1.29a 1.95 *
Protein, % 22.98 24.29 23.36 23.45 23.63 23.79 23.41 23.85 NS

a,b,c Means within a main effect group and on the same line bearing different superscripts are different
d (P<.05).
Predicted using equations developed by Field (1971).
e Longissimus at the 13th rib end of the short loin section with the subcutaneous fat removed.
Wet tissue basis.
g = P<.05; NS = nonsignificant (P>.05). None of the other interactions were significant at the (P<.05)
level.





53 -


(percentages of fat-free lean, fat and bone) due to breed type. These

data suggest that based on overall carcass composition the bulls were

slaughtered at similar points in their respective growth curves and,

therefore, were compared on an equivalent basis. Cole et al. (1964),

Solomon et al. (1981b) and Adams et al. (1982) reported significant

differences in percentages of carcass lean, fat and bone between Angus

and Brahman cattle. Carcasses from Angus cattle were fatter and had

less lean and bone on a percentage basis than those from Brahman

cattle; however, data used in these studies were collected from steers

and heifers which were slaughtered at some constant (similar) endpoint

(e.g., live weight, age or days on feed).

As carcasses became heavier, they contained lower percentages of

fat-free lean and bone, and more fat (table 9), which agrees with

findings reported by Hedrick (1968) and Berg and Butterfield (1976).

According to the results from the present study, these bulls produced

lean, acceptable weight carcasses. Year had no significant effect on

predicted carcass components. One might have expected some differences

due to year since it was involved in various interactions for

production and carcass traits (tables 3, 7 and 8).

Longissimus muscles from Angus bulls contained more (P<.05) lipid

(%) and less (P<.05) protein (%) than those from Brahman bulls (table

9). The percentage of intramuscular fat increased from the 60 to the

80% group, decreased slightly between 80 and 90%, and once again

increased from the 90 to the 100% group. Perhaps the changes associ-

ated with increasing slaughter weight for ribeye area can in part be

attributed to similar changes recognized for the percentage of intra-

muscular fat (figure 2). The changes in percentage of intramuscular










80 -- 2.5
Y Ribeye area

Intramuscular fat (%)

U 70 2.0 4
S.3




60 -1.5 .





50 -- 1.0


60 80 90 100
Weight group, %

Figure 2. Effect of weight group on ribeye area and intramuscular fat (%).





55 -


fat parallel those for ribeye area and marbling score. This suggests

that part of the increase in size of ribeye may result from fat

accretion and not actual muscle growth.

Longissimus muscle from bulls representing the first year group

possessed less extractable lipid (%) than those from the second year

group (table 9). Several studies have found percentages of

intramuscular fat to be highly correlated with marbling scores. This

trend was more evident for the carcasses from Angus bulls than for

carcasses from Brahman bulls (table 4).

In general, the results from the present study suggest that

slaughtering purebred bulls from different genetic backgrounds (e.g.,

Angus and Brahman) at similar stages in their respective growth curves

appears to offset many of the compositional and carcass trait

differences otherwise encountered if slaughtered at some constant

(similar) endpoint (i.e., age, live weight, or days on feed).

Furthermore, carcasses from these bulls fed to the selected slaughter

weight produced lean, acceptable weight carcasses. Breed appeared to

be related to indices of quality, i.e., some were more deficient in

quality than others.

Summary

Seventy-eight purebred bulls (10 to 18 mo at slaughter) were

used over a two year period to ascertain the effects of breed (Angus or

Brahman) and slaughter weight (60, 80, 90 or 100% of the average mature

cow weight for the respective breed) on production traits, carcass

characteristics and composition. Angus bulls grazed summer annual

forage (millet) for three mo after weaning while Brahman bulls were

fed to simulate gains the Angus achieved on forage. The 60% group of





56 -



bulls from both breeds was slaughtered after this postweaning feeding

period. The remaining bulls were then placed in a confinement feedlot

and fed a shelled corn-protein supplement diet until they reached their

appropriate slaughter weight. Slaughter weights for Angus bulls were

293, 381, 412 and 463 kg and for Brahman bulls were 316, 420, 463 and

516 kg. The 9-10-11 rib section was used to estimate composition.

Carcasses from Angus bulls received higher quality grades (St+

vs St-) based on differences in marbling scores (Tr+ vs Pd-), and

lower yield grades (1.8 vs 2.1) than carcasses from Brahman bulls. All

the carcasses qualified for the USDA "Bullock" grade. There were no

significant differences in predicted carcass composition due to breed

type.

The percentage of intramuscular fat increased between the 60 and

80% group, decreased slightly between 80 and 90% and once again

increased from the 90 to 100% group. Ribeye area, as a measure of

muscling, for both years of Angus bulls and the first year Brahman

bulls, increased rapidly from 60 to 80%, changed little or decreased

between 80 and 90%, and then increased between 90 and 100%, except for

the Brahman bulls from the second year where the increase in ribeye

area was continuous.

The influence of year on production and carcass traits appeared to

be associated with the change in diet composition from the first to the

second year. Data suggest that carcasses from these bulls fed to

selected slaughter weights produced lean, acceptable weight carcasses.

However, the carcasses from the Brahman bulls were more deficient in

marbling than those from Angus bulls. Furthermore, slaughtering

purebred bulls representing different genetic backgrounds at similar





57 -


stages in their respective growth cycles appears to offset many of the

compositional and carcass trait differences otherwise encountered if

they are slaughtered at some constant (similar) endpoint (i.e, age,

live weight or days on feed).













STUDY 2
EFFECTS OF BREED, SLAUGHTER WEIGHT, YEAR AND CARCASS
ELECTRICAL STIMULATION ON THE QUALITY AND PALATABILITY
OF BEEF FROM YOUNG PUREBRED BULLS

Introduction

Renewed interest in producing "lean beef" has promoted the use of

young bulls in beef production systems. Such interest stems from the

fact that bulls gain more rapidly, utilize feed more efficiently and

produce a higher yielding carcass (more retail product) with less fat

than steers (Field, 1971; Seideman et al., 1982). Nevertheless, real

or anticipated problems associated with tenderness, dark lean color,

low quality grades and the traditional reluctance of retailers to

market "Bull" beef have delayed the use of young bull carcasses as a

source of market beef.

The possibility that breeding influenced tenderness was first

suggested by Carpenter et al. (1955) who detected that as the

percentage of Brahman breeding increased, tenderness of steaks and

roasts decreased. Since this first observation, several studies (Burns

et al., 1958; Cole et al., 1958; Huffman et al., 1962; Luckett et

al., 1975; Peacock et al., 1980, 1982; Solomon et al., 1981b; Adams

et al., 1982) have found that meat from Angus cattle (steers and

heifers) was more tender than meat from Brahman cattle. However,

little work, if any, has been done to characterize the palatability of

meat from intact males representing these diverse breed types.

Electrical stimulation, for the most part, has been demonstrated

to increase the palatability of beef (Stiffler et al., 1982) and



58 -





59 -


improve lean color and lean maturity as well as reduce heat-ring

formation (McKeith et al., 1981). Perhaps, with the aid of postmortem

handling techniques, such as ES, some of the problems associated with

using young bulls (especially of Brahman origin) for block beef may be

reduced or completely alleviated. Therefore, this study was undertaken

to characterize the palatability of meat from carcasses of young

purebred Angus and Brahman bulls slaughtered at different live weights

and to determine the effect of ES on the carcass quality-indicating

factors and meat palatability.

Materials and Methods

Seventy-eight Angus and Brahman purebred bulls that were 10 to 18

mo of age were slaughtered at four weight groups: 60, 80, 90 and

100% of the average mature cow weight for the respective breed. Bulls

were slaughtered over a two year period to determine the effects of

breed, weight, year and postmortem electrical stimulation on carcass

and meat characteristics of young bulls (table 10).

Angus bulls grazed summer annual forage (millet) for three mo after

weaning while Brahman bulls were fed, after being weaned, a concentrate

diet to simulate gains achieved on forage by the Angus bulls. The 60%

group of bulls from both breeds was slaughtered after this postweaning

feeding period. The remaining bulls were then placed in a confinement

feedlot and fed a shelled corn-protein supplement diet until they reached

their designated slaughter weight. Slaughter weights were 293, 381, 412

and 463 kg for Angus and 316, 420, 463 and 516 kg for Brahman. Details

about the diets, origin of bulls, production and carcass traits have

been reported by Solomon et al. (1983).

The right side of each carcass was stimulated with 500 volts (AC)

for 20-2 sec impulses within 1 h after bleeding. The left side of





60 -







TABLE 10. EXPERIMENTAL DESIGNa




b % Mature weightc
Breed 60 80 90 100


Year I
Angus 5 5 5 5

Brahman 5 5 5 5


Year II
Angus 5 1 5 6

Brahman 5 6 8 2

a All right sides from each animal were electrically stim-
b ulated (500 volts for 20-2 sec impulses).
b Age ranged from 10 to 18 mo at slaughter.
Percentage of the average mature cow weight for the re-
spective breed.





61 -


each carcass was not stimulated and served as the control. Electrical

stimulation was performed by attaching cables to the stunning probes of

a Boss Hog Stunner (Model 1004A). Metal probes on the ends of the

cables were inserted into the round near the Achilles tendon and into

the neck at the first thoracic vertebrae and adjacent to the ligamentum

nuchae.

All sides were chilled at 0-2 C for 24 h postmortem and then both

sides from each carcass were ribbed. Quality grade factors, (USDA,

1975), in addition to lean color (7 = very dark red; 1 = dark pink),

lean texture (7 = extremely coarse; 1 = very fine), lean firmness (7 =

extremely soft; 1 = very firm) and presence of heat-ring (4 = extreme;

1 = none) were evaluated by University of Florida personnel.

A 15.24 cm section of the short loin, starting at the 13th rib and

extending approximately to the third lumbar vertebrae, was removed from

both sides of all carcasses at two days postmortem. A 10.16 cm medial

section of the bottom round muscle was also removed from both sides of

all carcasses at two days postmortem. These boneless samples were

wrapped with an inner coat of saran wrap and an outer coat of poly-

ethylene freezer paper. They were held in a 0-2 C cooler until five

days postmortem, and then placed in a -15 C freezer until being cut

into sections for selected evaluations. The sections cut were 2.54 cm

thick steaks from the short loin (figure 3) and 1.91 cm thick steaks

from the bottom round.

Two loin steaks/side were designated for sensory panel evaluation.

One loin and one bottom round steak/side were allocated for Warner-

Bratzler shear force determinations. All the steaks were handled and

cooked according to the procedure outlined by the AMSA (1978) guidelines.





62 -








Posterior end




Longissimus muscle





Extra sample /



Sarcomere length and fragmentation,
index -


Sensory panel evaluation ,



Sensory panel evaluation
I,- -




Warner-Bratzler shear

~~-- - --
13th rib
13th rib roximate analysis

12th rib

Anterior end



Figure 3. Location of samples from the short loin for various
analyses.





63 -



Loin steaks were broiled using a Farberware Open-Hearth broiler.

Steaks were turned at 40 C internal temperature and removed from the

broiler at 70 C. Internal temperature was monitored using copper-

constantan thermocouples attached to a recording potentiometer.

Samples (1x1x2.5 cm) were removed from steaks allocated for sensory

panel and evaluated by an 8 member trained sensory panel for flavor (8

= extremely intense; 1 = extremely bland), juiciness (8 = extremely

juicy; 1 = extremely dry), tenderness (8 = extremely tender; 1 =

extremely tough) and amount of panel-detectable connective tissue (8 =

none; 1 = abundant).

Bottom round steaks were braised in an oven preheated to 177 C.

They were removed from the oven once they reached an internal tempera-

ture of 85 C. Temperatures were monitored in the same manner as for

the loin steaks. The loin and bottom round steaks designated for shear

force measurements were allowed to cool to room temperature (25 C)

before coring. A minimum of 6 cores (1.27 cm diameter) were removed

from these steaks parallel to the muscle fiber orientation for shear

force determinations using a Warner-Bratzler shear device.

A 2.54 cm thick section from the short loin (figure 3) was used to

determine fragmentation index and sarcomere length. Fragmentation

index was evaluated using the procedure described by Davis et al.

(1980). Sacromere length was determined by the laser technique

outlined by Cross et al. (1981).

A split-plot model was used to analyze all the response variables

which may have been affected by ES. The model included fixed whole-

plot effects for breed, weight group, year and their corresponding

interactions. Subplot fixed effects for ES and the interactions





64 -


associated with ES and the whole-plot effects were also included. Data

were analysed by the regression procedure of the Statistical Analysis

System (SAS, 1979). F-tests were used to determine the effect of

treatments on the parameters under investigation. The Duncan's multi-

ple range test (SAS, 1979) was used to test differences among slaughter

weights.

Results and Discussion

Carcass Traits and Composition

Details about carcass characteristics and composition of the bulls

as influenced by breed, slaughter weight and year have been reported by

Solomon et al. (1983). Generally carcasses from both breed groups were

equivalent in composition even though Angus bulls were slaughtered at

lighter weights.

Quality Factors

Results of the analysis of variance and subsequent F-tests for

carcass and lean quality factors are summarized in table 11. Means for

lean carcass quality factors by main effects of breed, weight group,

year and stimulation treatment are presented in table 12. Lean maturity

of the LD muscle were within the "A" maturity score for all carcasses.

However, scores increased from the 60 to the 80% group and then remained

constant (table 12).

An interaction (P<.05) of breed and weight group suggested that

the change in lean maturity over time was not the same in the breed

groups (tables 11 and 13). Lean maturity scores for carcasses of Angus

bulls representing the 60 and 80% groups were lower than those car-

casses of Brahman bulls from these same weight groups, indicating more

youthful color (table 13). However, at the 90 and 100% weights this





TABLE 11. ANALYSIS OF VARIANCE FOR CARCASS QUALITY FACTORSa


Sources of Variation
Main effects Interactions
Breed Weight Year Stimulation
Item (B) group (W) (Y) (T) BxW BxY WxY BxT WxT

Lean maturity NS NS NS NS NS NS

Bone maturity NS NS NS NS NS NS

Overall maturity NS NS NS NS NS NS

Marbling NS NS NS NS NS

Quality grade NS NS NS NS NS

Lean colorb NS NS NS NS NS NS

Lean texturec NS NS NS NS

Lean firmnessd NS NS NS NS NS NS *

Heat-ringe *NS NS NS NS

a = P<.05; NS = nonsignificant (P>.05).
The BxWxT interaction was significant.
c The BxWxY interaction was significant.
d The BxWxT, WxYxT and BxWxYxT interactions were significant.
e The BxWxT and WxYxT interactions were significant.




TABLE 12. LEAST-SQUARES MEANS FOR CARCASS QUALITY FACTORS BY BREED, WEIGHT GROUP, YEAR AND STIMULATION
TREATMENT


Main Effects

Breed (B) Weight group (W), % Year (Y) Stimulation
Item Angus Brahman 60 80 90 100 1 2 Control ES

No. 37 41 20 17 23 18 40 38 78 78

Lean maturityd A45 A51 A37a A51b A51b A52b A49 A46 A48b A28a
Bone maturityd A34 A29a A14a A33b A35b A44c A34 b A29a A31 A31

Overall maturityd A39 A40 A25a A42b A43b A48c A41 A38 A39b A29a
9 a b a b b b b3a b
Marblinge Tr93b Pd83a Tr07a Tr47b Tr46b Tr52b Tr23a Tr53b Tr31 Tr36

Quality gradef 12.7b 10.7a 11.2a 11.7ab 11.9b 12.0b 11.5 11.9 11.6 11.7
Lean color9 3.7 3.9 3.7 4.0 3.8 3.6 4.1b 3.5a 3.8b 2.9a

Lean texture 2.4 3.0b 2.a 2.8b 3.0b 2.9b 2.9b 2.5a 2.7 2.4a

Lean firmnessi 2.5 2.4 3.2b 2.3a 2.2a 2.1a 2.6 2.3 2.5a 2.9b

Heat-ring 2.2a 2.8b 2.6 2.4 2.5 2.4 2.4 2.5 2.5b 1.0a

a,b,c Means within a main effect group on the same line bearing different superscripts are different (P<.05).
dEvaluated on a 100 point scale within a maturity score.
SPd = "practically devoid", Tr = "traces" and S1 = "slight"; evaluated on a 100 point scale within each
f marbling score.
21 point scale wherein 10 = Standard ; 11 = Standard and 12 = Standard.
h 7 point scale wherein 3 = light cherry red and 4 = cherry red.
i 7 point scale wherein 2 = fine and 3 = moderately fine.
S7 point scale wherein 2 = firm and 3 = moderately firm.
S4 point scale wherein 1 = none, 2 = slight and 3 = moderate.





67 -


TABLE 13. BREED BY WEIGHT GROUP INTERACTIONSa FOR QUALITY FACTORS



Weight Lean b Overall Quality Heat5
Breed group, % maturity maturity Marblingb grade ring


Angus 60 A21 A12 Tr45 11.6 2.0
Brahman 60 A5 A3 Pd68 10.7 3.1

Angus 80 A47 A42 S107 12.6 2.1
Brahman 80 A55 A42 Pd87 10.8 2.7

Angus 90 A54 A49 S103 13.1 2.4
Brahman 90 A48 A Pd89 10.7 2.5

Angus 100 A5 A54 S117 13.3 2.0
Brahman 100 A A41 Pd87 10.7 2.8

a Significant at the P<.05 level.
SRefer to table 12 for codes.




68 -



was reversed. Lean maturity was higher for Angus carcasses than for

Brahman carcasses at these heavier weights, suggesting more mature lean

color.

Bone maturity scores (amount of bone ossification) were lower

(P<.05) for Brahman carcasses than for Angus carcasses (table 12).

These scores increased from the 60 to the 80% group, remained constant

from the 80 to 90% group and then increased from the 90 to the 100%

group. Bone maturity scores were lower (P<.05) for the carcasses from

the second year (A29) when compared to those from the first year

(A34). When bone and lean maturity scores were combined to get the

overall maturity, the effect of breed and weight group were the same as

those detected for lean maturity scores (tables 11, 12, and 13).

Solomon et al. (1981b) found that the lean from Angus heifers was

more mature in color than that from Brahman heifers. However, no

difference due to breed was observed for bone maturity. These authors

did point out that the Angus heifers were chronologically 1 mo older

at slaughter than the Brahman heifers. The heifers used in their study

were fed three different planes of nutrition for 217 days. Furthermore,

Solomon et al. (1981b) observed that with increasing live weight at

slaughter due to level of nutrition, bone, lean and overall maturity

scores all increased.

Marbling scores were higher (P<.05) for the carcasses of the Angus

bulls than for those from the Brahman bulls (table 12). Marbling

scores also increased from the 60% group to the 80% group and then

leveled off. However, an interaction (P<.05) of breed and weight group

was found for this characteristic. As shown in table 13, marbling

score increased for the carcasses of Angus bulls as weight group





69 -



increased but did not increase for the carcasses from Brahman bulls.

Since carcass fatness was equal among the breeds in the different

groups (Solomon et al., 1983), this lack of marbling increase in the

carcasses from Brahman bulls suggests that these bulls did not have the

same genetic ability to deposit intramuscular fat as the Angus bulls.

Marbling score was found to be higher (P<.05) in carcasses the second

year than the first (table 12). However, for both years the means for

marbling score were within the "Traces" score.

Carcasses from Angus bulls received higher (P<.05) quality grades

than did those from Brahman bulls (table 12). A significant breed by

year interaction (not presented in tabular form) for quality grade

indicated that Angus carcasses from the second year received higher

quality grades than those from the first year, whereas no difference in

quality grades due to year was detected for carcasses from the Brahman

bulls.

The quality grades for the carcasses in the 90 and 100% groups

were higher (P<.05) than those for the 60% group. Quality grade

increased as weight group increased for the Angus bulls, but stayed

constant for Brahman bulls. This would be expected since marbling

score increased as weight increased, particularly for the Angus bulls.

The mean values indicate that most of the carcasses were within the

"Standard" grade. However, some of the carcasses from the Angus bulls

had sufficient marbling to grade U.S. "Good."

Previous research comparing Angus and Brahman cattle conducted by

Luckett et al. (1975), Peacock et al. (1980, 1982), Solomon et al.

(1981b) and Adams et al. (1982) indicated that Angus carcasses received

higher quality grades because of superior marbling scores when compared

to carcasses from Brahman cattle.





70 -



No major difference (P>.05) due to breed type was observed for

lean color or lean firmness. Lean firmness increased (decreasing

score) from the 60 to the 80% group. This may be due to increased

fatness firming up the muscle as weight increased. The majority of

carcasses had firm, light cherry-red colored lean in the ribeye. Lean

texture was affected by breed, weight group and year (tables 11 and

12). The lean from Angus carcasses was finer-textured than that from

Brahman carcasses. Texture was finer for the 60% group than for the

other groups. However, all were acceptable, i.e., not coarse.

A significant weight by year interaction (not presented in tabular

form) for lean texture was detected. Lean from the second year group

of bulls was slightly finer in texture than lean from the first year

group in all the weight groups except in the case of the 60% group

where it was just the reverse. Furthermore, bulls from the first year

60% weight group possessed the finest-textured lean for the entire two

year study.

The carcasses from Brahman bulls had more heat-ring (higher

scores) than those from Angus bulls (table 12). As shown by the BxW

interaction (tables 11 and 13), the greatest difference in heat-ring

between breeds occurred in the 60% group. The magnitude of the

heat-ring scores indicated that most carcasses showed evidence of

heat-ring as expected from the lack of outside fat to retard surface

chilling rate (Savell et al., 1978b).

The general trend was for lean, bone and overall maturity scores,

in addition to marbling scores and quality grades, especially for Angus

carcasses, to increase with increasing carcass weight. No prevailing

trends were observed for lean color, texture, firmness or heat-ring





71 -



with advancing weight, except that lean from carcasses representing the

60% group was less firm (P<.05) than the lean from heavier weight

carcasses. Differences in lean characteristics could be attributed to

animal age differences. It appears from these data that only some of

the problems normally associated with meat from young bulls were

encountered, i.e., lower USDA quality grades and heat-ring formation.

Other problems were absent: dark cutting muscle; coarse muscle

texture with a dark appearance; and, exceedingly heavy carcass

weights.

Postmortem electrical stimulation improved (P<.05) lean maturity

and, thus, overall maturity scores (table 12). This resulted in more

youthful maturity scores being assigned at 24 h postmortem to sides

which had been stimulated. Furthermore, stimulated sides had brighter

lean color (P<.05) with a finer lean texture (P.05) than nonstimulated

sides. These findings are in agreement with other ES studies (Riley et

al., 1982; Savell et al., 1982) where carcasses from young bulls were

evaluated within 24 h postmortem. Savell et al. (1978b) concluded that

the accelerated glycolytic rate caused by ES enhanced the

quality-indicating factors of the lean when evaluated at 18 to 24 h

postmortem.

Calkins et al. (1980) recognized that although ES had a signifi-

cant effect on lean maturity and color at 24 h postmortem, beyond this

time little difference, if any, was observed between stimulated and

nonstimulated sides. Probably, this is why several scientists did not

find any improvement in lean maturity and color associated with ES when

lean characteristics were evaluated at 48 h postmortem (Grusby et al.,

1976; Strickland et al., 1979; Calkins et al., 1980; Nichols and





72 -


Cross, 1980). However, in a recent study by Crouse et al. (1983),

where they evaluated the effects of ES on carcass characteristics of

young bulls at 48 h postmortem, these authors found that ES sides were

lighter in color and exhibited more youthful lean maturity scores than

control sides.

A breed by stimulation treatment interaction (P<.05) was noted in

the present study for lean color (figure 4 and table 11). Nonstimu-

lated sides from Brahman carcasses had darker lean color than non-

stimulated sides from Angus carcasses. Although ES improved lean color

for both breeds, more of an improvement was detected for Brahman

carcasses than for Angus carcasses. This suggested that muscle for the

Brahman bulls was more reactive to ES than that from Angus bulls or

that much of the darkness in lean color for Brahman carcasses was

caused by rapid chilling and this effect was eliminated by electrical

stimulation.

Longissimus muscle from nonstimulated carcasses tended to be

firmer than those from stimulated carcasses. This was not true for all

weight groups, as shown by the interaction (P<.05) of weight groups and

stimulation treatment (table 11). This interaction (not in tabular

form) indicated that no difference in lean firmness between stimulated

and control sides was observed for carcass representing the 60% group

(both exhibiting moderately firm lean). However, as carcasses became

heavier, lean became firmer only for the nonstimulated sides while

remaining moderately firm for ES sides. Savell et al. (1978b) and Salm

et al. (1981) reported that ES significantly enhanced the lean firmness

and texture of beef. The present study as well as the study by Knight











4 4





3 B- 3
o B
u L
SB l
S.-
o


/-



^- ~A-- Angus, lean color
1AB'6 B--- Brahman, lean color
A--- Angus, heat-ring

B--- Brahman, heat-ring


ES Control
Stimulation treatment


Figure 4. Effects of breed and stimulation treatment on lean color and heat-ring scores.





74 -


(1982) found that, in general, stimulation caused the meat to be finer

in texture, but less firm than that from the controls.

Even with the changes in lean characteristics induced by ES, no

improvement (P>.05) in marbling scores or quality grades was detected

(table 12). All the carcasses qualified for the USDA "Bullock" grade

since maturities did not exceed A100. Stiffler et al. (1982), in

summarizing data from research at Texas A & M University, reported that

ES of beef carcasses increased marbling scores by 11% and, thus,

increased quality grades. The effects of ES on marbling scores and

quality grades are inconsistent. Some studies have shown an increase

with stimulation; others show no change.

Heat-ring formation was alleviated (P<.05) in the ribeye muscle of

sides that had been stimulated (table 12). This decrease in heat-ring

by stimulation was greater in carcasses from Brahman bulls than for

those from Angus bulls (figure 4). Heat-ring is the appearance of

coarse textured, dark colored lean on the outside of the exposed

surface of the ribeye muscle which frequently has a sunken appearance

near the outermost edge of its surface. This undesirable condition is

seen most often in carcasses which have little subcutaneous fat cover

(Savell et al., 1978b). Thus, a differential chilling rate between the

outer and inner portion of the ribeye muscle results in the appearance

of dark regions on the muscle surface. The outer portion chills faster

and thus undergoes a slower glycolytic rate, pH decline and rigor onset

than the inner portion of the muscle which is better protected

(insulated) from cold temperatures.

These dark areas are regarded as a disqualifying feature in the

present carcass grading system, since if the USDA grader detects signs




75 -



of incomplete chilling, such as heat-ring, the carcass cannot be

graded. Electrical stimulation essentially eliminated this problem in

the carcasses of the young bulls used in the present study. Due to the

accelerated postmortem reactions associated with the use of ES, a more

rapid color development and reduced heat-ring formation was observed

which is in agreement with the studies reviewed by Smith et al. (1980)

and Stiffler et al. (1982).

Sensory

Results of the analysis of variance and subsequent F-tests for

sensory, shear force and histological characteristics are summarized in

table 14. Means for sensory, shear force and histological characteris-

tics of loin steaks and shear force values for bottom round steaks main

effects are presented in table 15. Neither panel flavor nor juiciness

scores for short loin steaks were influenced (P>.05) by breed, slaughter

weight, year or stimulation treatment. Flavor and juiciness ratings

for all treatment groups were scored as "slightly intense" and "slightly

juicy," respectively, which is considered acceptable for these attri-

butes.

Loin steaks from carcasses of Angus bulls were rated more tender

and contained less detectable connective tissue than those steaks from

Brahman carcasses (table 15). Increasing slaughter weight from the 60

to 80% group was associated with an increase in steak tenderness and a

decrease in detectable connective tissue for short loin steaks. The

only exception was in the case of short loin steaks from carcasses

representing the 80 to 100% weight groups used the first year (figure

5). In this instance, tenderness and connective tissue scores remained

virtually unchanged between the 80 and 90% group, whereas tenderness






TABLE 14. ANALYSIS OF VARIANCE FOR SENSORY, SHEAR FORCE AND HISTOLOGICAL
CHARACTERISTICS


Sources of Variation

Main effects Interactions
Breed Weight Year Stimulation
Item (B) group (W) (Y) (T) BxW WxY WxT

Loin steaks
Flavor NS NS NS NS NS NS NS
Juiciness NS NS NS NS NS NS NS
Tenderness NS NS *
Connective btissue NS NS *
Shear force *
Sarcomere length NS NS NS NS NS
Fragmentation index NS NS NS

Bottom round steaks
Shear force NS NS NS

a = P<.05; NS = nonsignificant (P>.05).
bThe BxWxT and WxYxT interactions were significant.








TABLE 15. LEAST-SQUARES MEANS FOR SENSORY, SHEAR FORCE AND HISTOLOGICAL
CHARACTERISTICS OF LOIN STEAKS AND SHEAR FORCE FOR BOTTOM ROUND
STEAKS BY BREED, WEIGHT GROUP, YEAR AND STIMULATION TREATMENT




Hain Effects
Breed (B) Weight group (W), % Year (Y) Stimulation
Item Angus Brahman 60 80 90 100 I 2 Control ES

Loin steaksd
Flavore 5.3 5.3 5.3 5.3 5.4 5.3 5.4 5.2 5.4 5.3
Juiciness 5 5 5.6 5.5 5.7 5.7 5.4b 5.5 5.6 5.6a 5.
Tendernessg 5.1 4.4a 3.9a 4.8 5.2 5.I 4.8 4.7 4.8a 6.0
Connective itissueh 5.2b 46a 4.4a 4.9 53b 5. 4.9 4.9 4.9b 549a
Shear force 6.28 7.54 8.66c 6.75 6.32 5.91a 6.02 7 80 6.84 4.31
Sdrcomiere lengthj 1.74 1.71 1.68a 1.72 1.74bc 1.76c 1.75 170 1.72b 1.74
Fragmentation indexk 657.4 a 673.1 b 677.9 b 668. a 656.5 a 657.8 a 657.5 a 673 0 b 664.1 641.0
8ottorm round steaks
Shear force1 4.96a 5.58b 5.88b 5.06a 5.15a 4.99a 4.92a 5.62b 5.27b 4.84a
a,b,c Means within a main effect and on the same line bearing different superscripts are different (P<.05).
dLoin steaks were broiled.
e 8 extremely intense; 1 = extremely bland.
8 z extremely juicy; 1 = extremely dry.
9 8 = extremely tender; 1 = extremely tough.
8 = none; 1 = abundant.
kg/1.27 cm core.
m.
k Determined by the procedure of Davis et al. (1980) wherein 100 very tender; 600 very tough.
Bottom round steaks were braised.




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Year 1, tenderness

o Year 2, tenderness

Year 1, connective tissue
7 -
o Year 2, connective tissue

6 -







0
o 5


4


C 3


2-


1 -


S 60 80 90 100
Weight group, %




Figure 5. Effect of weight group and year on tenderness and connective
tissue scores of short loin steaks.





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decreased and detectable connective tissue increased as carcass weight

increased from the 90 to the 100% group. Perhaps this decrease in

tenderness and concomitant increase in detectable connective tissue was

associated with the increase in sexual development in these young bulls

which is concurrent with an increase in collagen (a type of connective

tissue) content and subsequent cross-linkage described by Cross et al.

(1982).

Arthaud et al. (1977) found steak tenderness to increase with

increasing age (12 to 18 mo) and weight (314 to 453 kg) at slaughter;

however, after this point meat tenderness decreased with advancing age

and weight at slaughter. It has been proposed that connective tissue

toughness in bulls, which inadvertently would affect meat palatability,

may be linked to sexual development and may be subject to some hormonal

function(s) in the animal (Boccard et al., 1979; Cross et al., 1982).

Carcass maturity scores indicated that bulls from the first year were

physiologically more mature than those from the second year (table 12).

Electrical stimulation had a significant effect on panel tender-

ness and detectable connective tissue scores (tables 14 and 15). With

the use of ES, tenderness scores increased from "slightly tough" to
"moderately tender" ratings. Connective tissue scores were improved

from a "moderate" to a "traces" detectable amount. On the contrary,

Riley et al. (1982), Savell et al. (1982) and Crouse et al. (1983)

reported that ES had essentially no effect on the palatability of

steaks from USDA "Good" quality grade bulls with at least 7.6 mm

subcutaneous fat cover or more. However, Riley et al. (1982) did find

that ES significantly improved the tenderness of steaks from USDA





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"Standard" and USDA "Good" grade bulls that had less than 7.6 mm fat

thickness. The bulls used in the present study had an average quality

grade of USDA "Standard" with 4.7 mm subcutaneous fat cover.

The most dramatic and consistent effect of stimulation on panel

tenderness and connective tissue scores was for steaks from the 60%

group (figure 6). This group had the least amount of subcutaneous fat

cover (2.2 mm) and, therefore, the longissimus muscle (short loin) may

have undergone cold-induced shortening, resulting in meat toughening.

In fact, in the present study, muscle fiber sarcomere length was

considerably shorter (P<.05) from nonstimulated muscle representing the

60% group than from all the other groups (table 15). However, ES had

no major influence (P>.05) on overall sarcomere lengths, although

muscle from stimulated carcasses generally had slightly longer

sarcomeres.

The literature strongly indicates that ES alleviates the cold

shortening type of tenderness problem in meat (Chrystall and Hagyard,

1976; Davey et al., 1976; Bouton et al., 1980; Hagyard et al., 1980;

Eikelenboom et al., 1981). Other research workers believe that benefits

of ES are not solely related to the prevention of cold shortening.

Postulated mechanisms include structural alterations of muscle fibers

(Savell et al., 1978a; George et al., 1980; Will et al., 1980;

Voyle, 1981; Sorinmade et al., 1982), increased lysosomal enzyme

activity (Sorinmade et al., 1978; Dutson et al., 1980) and decreases in

the number or strength of the collagen cross-linkages (Judge et al.,

1980).

Stiffler et al. (1982) recognized that the percentage of change in

tenderness values caused by ES was quite variable, when the type of




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8




^------------ ^ --C
S6 -- -----





S4
o
()

n 3
----ES, tenderness

2 Control, tenderness
.(----ES, connective tissue

1 *---Control, connective tissue


/ 60 80 90 100

Weight group, %




Figure 6. Effect of weight group and stimulation treatment on
tenderness and connective tissue scores of short loin
steaks.





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beef being investigated was considered. They concluded that this

source of variation was associated with the initial, or inherent,

tenderness of the nonstimulated meat, especially from animals (steers

and heifers) less than 42 mo of age (i.e., the greater the initial

toughness, the greater the effect of stimulation). This may explain

why ES had more of an effect on tenderness of steaks from the 60%

group. Judge et al. (1980) claimed that ES lowered the shrinkage

temperature of collagen by 0.6 C and that thermal stability of bovine

intramuscular collagen may result from a diminution of collagen cross-

linkages by ES. This may partially account for the lower (P<.05)

amounts of connective tissue detected by the sensory panel in steaks

from stimulated carcasses.

Shear Force

Short loin and bottom round steaks from Angus carcasses had lower

shear values (P<.05) than those steaks from Brahman carcasses, except

at the 80% slaughter point where this was reversed for loin steaks

(figure 7). Loin steaks from carcasses of Brahman bulls showed a large

decrease in shear force between the 60 and 80% weight groups, sugges-

ting that this weight gain was associated with increased steak tender-

ness.

Several studies (Luckett et al., 1975; Peacock et al., 1980,

1982; Solomon et al., 1981b; Adams et al., 1982) have substantiated

that meat from Angus cattle had lower shear values, implying more

tender meat, than meat from Brahman cattle. However, Winer et al.

(1982) reported that beef derived from young bulls of widely divergent

breed types, including Bos indicus x Bos taurus crosses, were not

significantly different in tenderness.





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Angus

o Brahman
10 --4












S 6-
S-
O
t4-









I I I I
60 80 90 100
Weight group, %






Figure 7. Effects of breed and weight group on shear force values
of short loin steaks.




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The usual trend was for shear values to decrease as carcasses

became heavier and fatter. However, shear values for short loin steaks

from the first year had lower shear force values at the 60 and 80%

weight groups than those from the second year (figure 8). After this,

shear values increased from 80 and 90% and then remained the same from

the 90 to 100% group, somewhat resembling trends for sensory scores

discussed earlier. Nevertheless, meat from the first year group of

bulls was generally more tender as indicated by lower shear values than

meat form the second year group. This is in agreement with the

findings detected by the sensory panel.

Loin steaks from stimulated sides had lower (P<.05) shear values

than those from control sides (4.31 vs 6.84 kg/1.27 cm, respectively),

indicating a 37% increase in tenderness with the use of ES (figure 9

and table 15). These data pretty much agree with the findings detected

by the sensory panel and also with previous research (Eikelenboom et

al., 1981; Riley et al., 1982) demonstrating a tenderizing effect of

ES on meat from young, noncorpulent bulls. Meat from stimulated beef

carcasses is, on the average, 15-46% more tender than that from

nonstimulated carcasses depending on age, grade, and the nutritional

status of the animal (Stiffler et al., 1982). Again, the most dramatic

and consistent effect of ES was for the shear values of steaks from the

60% group (figure 9).

Since shear values exceeding 5.2 kg/1.27 cm core can be considered

unacceptable in tenderness, short loin steaks for both Angus and

Brahman bulls would be regarded as unacceptable or in some instances

borderline in tenderness. The sensory panel results also confirm these

findings. However, with the aid of ES, these tenderness problems were

alleviated.





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Year 1

12 0 Year 2





3 10
*
cr)



o 8





6






60 80 90 100
Weight group, %






Figure 8. Effect of weight group and year on shear force values of
short loin steaks.





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Control

o ES
10





S8





t-
6





4
a







,I I

60 80 90 100
Weight group, %







Figure 9. Effect of weight group and stimulation treatment on shear
force values of short loin steaks.




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Histological

Longissimus muscles from Angus carcasses tended to have slightly

longer sarcomeres (table 15) than those from Brahman carcasses, although

this difference was not significant. As carcasses became heavier, and

subsequently fatter, sarcomere lengths increased. These differences in

sarcomere lengths, although in some cases not significantly different,

appear to be related to the amount of subcutaneous fat present, which

may have protected the longissimus muscle from shortening due to cold

temperatures during chilling as previously discussed.

Longissimus muscles from the first year group had longer (P<.05)

sarcomeres than those from the second year and thus may explain differ-

ence detected in shear values between these groups. Sarcomere lengths

from stimulated sides appeared slightly longer than those from nonstimu-

lated sides, however, this difference was not significant (P>.05). The

effects of ES on sarcomere length are inconsistent. Some studies have

shown an increase in sarcomere length with stimulation; others show no

change.

All four treatment groups (breed, weight groups, year and carcass

electrical stimulation) had an effect (P<.05) on fragmentation index

score. Steaks from Angus bulls, year one bulls and stimulated car-

casses had lower fragmentation indices than steaks from Brahman bulls,

year two bulls and nonstimulated carcasses, respectively. As slaughter

weight increased, fragmentation index scores decreased. According to

the coding system developed by Davis et al. (1980), steaks with scores

in these ranges (650 680) would be considered very tough. This was

not apparent in the present study.





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The data from the present study suggest that meat from young bulls

is generally tough and unacceptable but is improved if fed to heavier

weights or if carcasses are electrically stimulated. Since shear

values exceeding 5.2 kg/1.27 cm core are considered acceptable in

tenderness, short loin steaks from both Angus and Brahman bulls would

be regarded as unacceptable or in some cases borderline in tenderness.

The sensory panel results also suggest borderline acceptability in

tenderness for all groups.

These data also suggests that the use of ES on carcasses from

young bulls, especially for the types used in this study (averaging 414

kg live weight, 14.3 mo of age and 4.7 mm subcutaneous fat) eliminates

several of the problems (e.g., tenderness, heat-ring formation, and

coarse, dark colored lean) associated with these types of carcasses.

Therefore, perhaps young bulls can be used successfully in the beef

production system if, and only if, some kind of postmortem handling

technique, such as electrical stimulation is used. However, while

problems in the market place continue to exist because of the negative

connotations associated with selling "Bull" beef, other alternatives

will have to be utilized.

Summary

Seventy-eight purebred bulls (10 to 18 mo at slaughter) were

used over a two year period to determine the effects of breed (Angus or

Brahman), slaughter weight (60, 80, 90 or 100% of the average mature

cow weight for the respective breed) and carcass electrical stimulation

(500 volts, 20-2 sec impulses on the right side) on carcass and meat

characteristics. Angus bulls grazed summer forage (millet) after

weaning while Brahman bulls were fed to simulate gains achieved on





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forage by Angus bulls. Bulls were than placed in the feedlot for

finishing to their designated slaughter weight (293, 381, 412, and 463

kg for Angus and 316, 420, 463, and 516 kg for Brahman).

Carcasses from Angus bulls received higher quality grades (St

vs St-) than those from Brahman bulls. Heat-ring formation and lean

color problems normally associated with bullock carcasses were either

eliminated or reduced by stimulation. Meat from Angus bulls was more

tender than that from Brahman bulls as indicated by higher sensory

panel scores for broiled loin steaks and lower shear values for braised

bottom round steaks (4.96 vs 5.58 kg).

However, a breed by weight group interaction (P<.05) was observed

for loin steak shear values. At the 80% weight group, steaks from

Brahman bulls had lower shear values than those from Angus bulls (6.31

vs 7.19 kg). For the other weight groups, shear force values for loin

steaks from Angus bulls were lower than those from the Brahman bulls.

Increasing slaughter weight from 60 to 90% was associated with an

increase in panel tenderness scores for loin steaks. However, from 90

to 100% no change was detected. Stimulation increased the tenderness

of loin steaks as determined by both panel scores and shear values

(6.84 vs 4.31 kg) and of bottom round steaks (5.27 vs 4.84 kg shear

force).




Full Text

PAGE 1

PRODUCTION TRAITS AND POSTMORTEM FACTORS AFFECTING MEAT FROM YOUNG BULLS By MORSE B. SOLOMON A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1983

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To my parents, Muriel and Louis Solomon, who with great love understanding and support allowed me to pursue my dreams; and to wife, Betsy, and my son, Neil, who with extreme patience and love helped to make my dreams a reality. To them this dissertation is dedicated.

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ACKNOWLEDGEMENTS The author would like to express his appreciation to Dr. Roger L. West, Chairman of the supervisory committee, and to Dr. James F. Hentges, Jr., Coordinator of the Purebred Beef Unit where the research animals originated. Drs. West and Hentges were most encouraging, patient and helpful in their guidance of this endeavor from its inception to culmination. The suggestions and instructions provided by the other members of the supervisory committee, Drs. Arno Z. Palmer, Michael J. Fields and Wendell N. Stainsby, were most gratefully appreciated. The author wishes to thank Leroy Washington, Keith Blue, Alayne Gardner, Gary Hansen, Jerry Wasdin, Caren Prichard, Julie Stokes, Connie Williams and fellow graduate students for all their help, technical assistance and comradeship. I would like to extend a special word of thanks to Ms. Janet Eastridge for her technical and practical assistance and friendship which she has bestowed upon me. The author wishes to express his appreciation to Ms. Cynthia Zimmerman for accepting the task of assiduously typing this manuscript at the last minute. Deepest appreciation is extended to the author's parents, Louis and Muriel; to his sisters, Betsy-Ellen and Chele and brother-in-law. Herb; and to his wife's parents, Melvin and Sylvia for their support rendered both morally and financially throughout the author's graduate program. iii

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Finally, I would like to express my love and thanks to my wife, Betsy, and my son, Neil, who were a constant source of support and encouragement during my graduate program. My wife has made many sacrifices during the completion of my program and despite having to withstand a moody husband and many lonely nights, she has provided me with a never-ending love and understanding that enabled me to complete this degree.

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TABLES OF CONTENTS PAGE ACKNOWLEDGEMENTS iii LIST OF TABLES vii LIST OF FIGURES ix ABSTRACT x INTRODUCTION 1 REVIEW OF LITERATURE 5 Production and Carcass Traits 5 Palatability Traits 13 Carcass Electrical Stimulation 17 Muscle Fiber Types 19 Muscle Nucleic Acids 23 STUDY 1 PRODUCTION TRAITS AND CARCASS COMPOSITIONAL CHARACTERISTICS OF YOUNG PUREBRED ANGUS AND BRAHMAN BULLS SLAUGHTERED AT SIMILAR PERCENTAGES OF MATURE WEIGHT 28 Introduction 28 Materials and Methods 29 Results and Discussion 33 Summary 55 STUDY 2 EFFECTS OF BREED, SLAUGHTER WEIGHT, YEAR AND CARCASS ELECTRICAL STIMULATION ON THE QUALITY AND PALATABILITY OF BEEF FROM YOUNG PUREBRED BULLS 58 Introduction 58 Materials and Methods 59 Results and Discussion 64 Summary 88 STUDY 3 GROWTH TRAITS, CARCASS TRAITS AND MUSCLE DEVELOPMENT CHARACTERISTICS OF PUREBRED ANGUS AND BRAHMAN BULLS .. 90 Introduction 90 Materials and Methods 92 Results and Discussion 96 Summary 116 V

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SUMMARY AND CONCLUSIONS 118 LITERATURE CITED 122 BIOGRAPHICAL SKETCH 134 vi

PAGE 7

LIST OF TABLES PAGE 1 ALLOTMENT OF EXPERIMENTAL ANIMALS 30 2 DIET COMPOSITION 32 3 LEAST-SQUARES MEANS FOR LIVE ANIMAL TRAITS AND DRESSING PERCENTAGES BY BREED, WEIGHT GROUP AND YEAR 34 4 BREED BY WEIGHT GROUP INTERACTIONS^ FOR VARIOUS LIVE ANIMAL, CARCASS AND LONGISSIMUS MUSCLE CHARACTERISTICS 36 5 WEIGHT GROUP BY YEAR INTERACTIONS^ FOR LIVE WEIGHT, AVERAGE DAILY GAIN AND LEAN TEXTURE 37 6 BREED BY YEAR INTERACTIONS^ FOR AVERAGE DAILY GAIN, DRESSING PERCENTAGE, QUALITY GRADE AND HEAT-RING SCORES ... 39 7 LEAST-SQUARES MEANS FOR YIELD GRADE FACTORS BY BREED, WEIGHT GROUP AND YEAR 44 8 LEAST-SQUARES MEANS FOR QUALITY FACTORS BY BREED, WEIGHT GROUP AND YEAR 48 9 LEAST-SQUARES MEANS FOR PREDICTED CARCASS AND LONGISSIMUS MUSCLE COMPOSITION BY BREED, WEIGHT GROUP AND YEAR 52 10 EXPERIMENTAL DESIGN^ 60 11 ANALYSIS OF VARIANCE FOR CARCASS QUALITY FACTORS^ 65 12 LEAST-SQUARES MEANS FOR CARCASS QUALITY FACTORS BY BREED, WEIGHT GROUP, YEAR AND STIMULATION TREATMENT 66 13 BREED BY WEIGHT GROUP INTERACTIONS^ FOR QUALITY FACTORS ... 67 14 ANALYSIS OF VARIANCE FOR SENSORY, SHEAR FORCE AND HISTOLOGICAL CHARACTERISTICS^ 76 15 LEAST-SQUARES MEANS FOR SENSORY, SHEAR FORCE AND HISTOLOGICAL CHARACTERISTICS OF LOIN STEAKS AND SHEAR FORCE FOR BOTTOM ROUND STEAKS BY BREED, WEIGHT GROUP, YEAR AND STIMULATION TREATMENT 77 vii

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16 EXPERIMENTAL DESIGN 93 17 LEAST-SQUARES MEANS FOR PRODUCTION AND CARCASS TRAITS BY BREED AND WEIGHT GROUP 97 18 BREED BY WEIGHT GROUP INTERACTIONS^ FOR AGE, AVERAGE DAILY GAIN, CARCASS MATURITY AND RIBEYE AREA 99 19 LEAST-SQUARES MEANS FOR MUSCLE MEASUREMENTS OF THE LONGISSIMUS, SEMITENDINOSUS AND PSOAS MUSCLES BY BREED AND WEIGHT GROUP^ 104 20 LEAST-SQUARES MEANS FOR CHEMICAL AND NUCLEIC ACID PROPERTIES OF THE LONGISSIMUS MUSCLE BY BREED AND WEIGHT GROUP 107 21 LEAST-SQUARES MEANS FOR LONGISSIMUS MUSCLE FIBER POPULATION^ AND AREA^ BY BREED AND WEIGHT GROUP 112 viii

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LIST OF FIGURES PAGE 1 Effects of breed, weight group and year on ribeye area 46 2 Effect of weight group on ribeye area and intramuscular fat (%) 54 3 Location of samples from the short loin for various analyses 62 4 Effects of breed and stimulation treatment on lean color and heat-ring scores 73 5 Effect of weight group and year on tenderness and connective tissue scores of short loin steaks 78 6 Effect of weight group and stimulation treatment on tenderness and connective tissue scores of short loin steaks 81 7 Effects of breed and weight group on shear force values of short loin steaks 83 8 Effect of weight group and year on shear force values of short loin steaks 85 9 Effect of weight group and stimulation treatment on shear force values of short loin steaks 86 10 Growth of the longissimus muscle in relation to breed (Angus • • ; Brahman — *) and weight group (WG) percentages 101 11 Effect of weight group on the percentage of R and ctw fiber types in the longissimus muscle 114 ix

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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PRODUCTION TRAITS AND POSTMORTEM FACTORS AFFECTING MEAT FROM YOUNG BULLS By Morse B. Solomon August, 1983 Chairman: Dr. R.L. West Major Department: Animal Science Seventy-eight Angus and Brahman purebred bulls that were 10 to 18 months of age were slaughtered at four weight groups: 60, 80, 90 and 100% of the average mature cow weight for the respective breed. Bulls were slaughtered over a two year period to determine the effects of breed, weight, year and postmortem electrical stimulation (500 volts, 20-2 sec impulses on right side) on production traits and carcass and meat characteristics. After a forage or restricted feeding period, bulls were placed in the feedlot and fed a shelled corn-protein supplement diet. Slaughter weights for Angus bulls were 293, 381, 412, and 463 kg and for Brahman bulls were 316, 420, 463, and 516 kg. Carcasses from Angus bulls received higher quality grades (St^ vs St") and lower yield grades (1.8 vs 2.1) than carcasses from Brahman bulls. Marbling score generally increased in Angus bulls as weight increased, but this was not apparent in Brahman bulls. No major differences due to breed were detected for predicted carcass composition. Meat from Angus bulls was usually more tender than that from Brahman bulls. X

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Increasing carcass weight was generally associated with an increase in neat tenderness. Heat-ring formation, meat tenderness and lean color problems normally associated with young bull carcasses were either eliminated or reduced by electrical stimulation. Data suggest that the bulls used in this study when fed to selected slaughter weights produced lean, acceptable weight carcasses. Meat was generally tough and unacceptable from the bulls slaughtered at the lighter weights, but was improved when bulls were fed to heavier weights or when carcasses were electrically stimulated. Second year bulls (n = 38) were used to ascertain the effects of breed and slaughter weight on selected histological, biochemical and compositional growth characteristics of the longissimus (LD) muscle. The LD muscle from Brahman bulls contained more DNA and protein, and generally less lipid when expressed on a total muscle basis. Neither RNA content, protein:DNA, protein:RNA and RNA:DNA ratios nor percentages and areas for muscle fiber types were affected by breed. As weight increased, muscle weights, protein, lipid, RNA, RNA:DNA, protein:DNA and muscle fiber areas increased. DNA content increased only up to the 90% weight group and then leveled off while proteinrRNA ratio decreased as weight increased. Furthermore, the percentage of aR fibers decreased while the percentage of cxW fibers increased with increasing slaughter weight.

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INTRODUCTION The ultimate test of the value of meat is its acceptability by consumers. The extent to which satisfaction is derived from meat depends on psychological and sensorial responses that are unique to each individual. The desire for the selection of meat animals with a greater potential for muscle development and lesser propensity to fatten than present meat animals has promoted the need to understand mechanisms of growth whereby lean and acceptable beef can be produced economically. The history of castration is probably as old as the history of domestication of animals by man wherein he sought to fulfill his requirements for meat, animal products and draft power (Turton, 1969). The original reason for castrating was probably to render the male more easily manageable and to enable males to be grazed along with mature females without indiscriminate breeding (Crighton, 1980). Thus, its use was one of the first actions taken to regulate genetic changes in populations of farm animals. This practice was probably reinforced by the observation that the castrate male had a larger deposition of fat than its intact counterpart. This was particularly important at a time when a large amount of fat was a highly desirable feature of the carcass. However, because of the current market demand for leaner beef and the necessity for intensification, perhaps the traditional practice of castrating male meat producing animals should be impeded. The current economic conditions have caused beef producers to become more acutely aware of the importance of maximizing production 1

PAGE 13

2 efficiency, with their ultimate goal being to produce quality lean tissue (muscle) at the least possible cost. As a result, much interest has been generated regarding the use of young intact males in modern beef production systems. Such interest stems from the fact that bulls gain weight more rapidly, utilize feed more efficiently and produce higher yielding carcasses with less fat and more red meat than steers and heifers (Field, 1971; Seideman et al 1982). In fact, if only half of the cattle finished in U.S. feedlots were finished as bulls rather than as steers a savings of millions of dollars in feed costs would result, since approximately 13% less feed would be required per unit gain by bulls. Nevertheless, increased production efficiency obtained through the use of intact males has often been offset by management problems, particularly with animal behavior (Seideman et al 1982). Furthermore, meat production from intact males has often encountered strong resistance from packers, since bulls have been shown to produce carcasses which are less tender and have lower quality grades, darker lean color and coarser-textured lean. All of these factors result in lower consumer acceptance of this product at the retail level than steers and heifers (Field, 1971). Although several problems associated with producing meat from young bulls exist, perhaps some, if not all, of these problems can be corrected and thus, the utilization of young bulls might become more widespread in beef production systems. Many producers use breed differences as a means of altering production characteristics of beef cattle. In Florida, producers utilize the characteristics of British (e.g., Angus) and Zebu (e.g.. Brahman) breeds, in addition to continental breeds, in their cattle

PAGE 14

3 operations in order to capitilize on the hybrid vigor resulting from crossing of these diverse breeds. A number of studies (Luckett et al 1975; Peacock et al., 1980, 1982; Solomon et al 1981b; Adams et al 1982) described substantial differences in production and growth traits, carcass and meat characteristics, and compositional factors between Angus and Brahman cattle (steers and heifers). Few studies have been conducted to characterize the performance, growth, carcass, and compositional factors, as well as meat palatability characteristics of purebred bulls representing these diverse breed types. Recent advances in meat technology may enhance bull beef quality and acceptability. Reviews by Cross (1979) and West (1982) indicated that electrical stimulation of prerigor carcasses usually will improve tenderness, enhance lean color and marbling, in addition to reducing heat-ring formation of beef. As a result of these considerations, these studies were undertaken to 1) compare the qualitative and quantitative characteristics of carcasses from purebred Angus and Brahman bulls slaughtered at different live weights; 2) evaluate palatability, histological, compositional and biochemical characteristics of the longissimus muscle from carcasses representing these diverse breed types; 3) determine the effect of carcass electrical stimulation on the carcass quality-indicating factors and meat palatability; 4) evaluate the use of slaughtering at similar percentages of the mature cow weight as a technique for comparing bulls, of such diverse origins, on an equal compositional basis;

PAGE 15

4 5) ascertain the plausibility of histologically and (or) biochemically classifying animals relative to their optimum slaughter potential by the use of skeletal muscle fiber characteristics and (or) associated properties of muscle nucleic acids.

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REVIEW OF LITERATURE Production and Carcass Traits Sex Effect A number of studies which have been reviewed by Field (1971) and Seideman et al (1982) have identified the bovine intact male for its superiority over its castrate counterpart in average daily gain (17% greater), in feed consumed per kilogram of gain (13% less) and in the production of leaner, higher yielding carcass with 35% less body fat. Arthaud et al (1977) reported that at all ages studied (12, 15, 18 and 24 mo at slaughter), bulls gained weight more rapidly, were more efficient in converting feed to live weight and produced carcasses with lower fat percentages than steers. One of the most prominent characteristics of the intact male is redistribution of body fat and increased body musculature (Seideman et al., 1982). Galbraith et al (1978) and Crighton (1980) indicated that the increased musculature and superior growth performance of bulls were associated with a positive nitrogen balance which was ascribed to the protein anabolic effects of testicular hormones. These differences in growth and lean deposition alone appear to favor the production of meat from intact males since a lower priced, leaner product could be realized. Nevertheless, even with these advantages, the use of intact males has often been offset by management problems, particularly with animal behavior or by strong resistance from packers, retailers and consumers. 5

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6 Part of the industry resistance to young bulls is caused by difficulty of removing the hide. Bull hides are generally thicker, heavier and more difficult to remove than hides from heifer and steer carcasses (Seideman et al 1982). This problem increases the processing costs significantly and reduces the acceptability and the value of the product (Cross and Allen, 1982) to the packer. Furthermore, discrimination has resulted because of several other reasons, including negative connotations associated with the terms "Bull or Bullock," and price differences between carcasses from bulls and steers. The price difference is a result of lower USDA quality grades of bulls and the belief that beef from intact males has lower consumer acceptance at the retail level because of differences in lean color, texture, fat distribution, size of cuts and palatabil ity. Field (1971), citing 13 research studies performed during the 1960's, reported that the average dressing percentage and fat thickness for bulls vs steers were 59.7% and 9.3 mm vs 59.6% and 14.3 mm, respectively. Seideman et al (1982) concluded that bulls had .2% lower dressing percentages than steers, based on their review of literature. Champagne et al (1969) and Landon et al (1978) found that dressing percentages were similar between bulls and steers; however, this was dependent on the age at castration of the steers. Field (1971), Arthaud et al (1977), Jacobs et al (1977), Landon et al. (1978) and Crouse et al. (1983) reported that bulls had less subcutaneous fat, larger ribeye muscles, less kidney fat and, thus, lower USDA yield grades than steers. These authors also reported that bulls had less marbling and, thus, lower USDA quality grades than steers when fed for comparable periods on the same diet. Cross and

PAGE 18

7 Allen (1982) presented data from 16 research studies. Their report showed that bulls had a mean marbling score of "slight-typical" and a mean USDA quality grade of "Average-Good" while steers had "modest-minus" marbling and "Low-Choice" quality grade. Smith and Merkel (1982) reported mean marbling scores of "slight-typical" for bulls and "small -pi us" for steers in their review of 21 research studies. These authors indicated that bulls and steers fed for comparable periods on the same diet will differ in marbling by approximately 1 to 1 2/3 scores and in USDA quality grade by about 2/3 to 1 full grade. Seideman et al (1982) concluded that when compared to steers bulls would, on the average, produce carcasses with lower quality grades, darker lean color and coarser-textured lean with less marbling, less quantities of subcutaneous fat and a higher incidence of dark cutting lean. Cross and Allen (1982) identified 9 previous studies which indicated that lean color of bull beef was darker and less desirable than that of steer beef. Glimp et al. (1971) found carcasses from bulls to be more mature physiologically on the basis of bone ossification and lean color than carcasses from steers of the same chronological age. Crouse et al (1983) reported similar findings; however, bulls in their study were 1 month older chronologically than steers. Sex by chronological age interactions were observed by Arthaud et al. (1977) for secondary sex characteristics and physiological maturity. At 12 mo of age, differences between bulls and steers in maturity scores and lean color were negligible, but at older ages, bull carcasses consistently exhibited more advanced maturity and darker lean color.

PAGE 19

8 Field (1971) suggested that because of their temperament, bulls may be more easily stressed than steers and, therefore, are more likely to become dark cutters. Kousgaard (1981) reported that 18-23% of the young bulls that they studied had 24 h postmortem muscle pH values greater than 6.0, indicative of dark cutting beef, and as a result had significantly darker colored lean than steers. Price and Tennessen (1981) investigated dark cutting in young bulls and reported that 73% of the bulls that were mixed with unfamiliar animals prior to shipment were dark cutters while only 2% of the bulls that were not mixed with unfamiliar animals prior to shipment were dark cutters. Kousgaard (1981) found that holding bulls for two nights prior to slaughter increased the incidence of dark cutters by 5% as compared to holding them for only one night (23% vs 18%). Boccard et al (1979) reported that the pigment content of muscle from bulls was not always higher than that of steers, but rather that differences were breed dependent. Arthaud et al (1977) found that muscle from Angus bulls had higher myoglobin concentrations than that from Angus steers of the same chronological age. Field (1971) reported no difference in myoglobin concentrations in muscles of bull and steer carcasses. A comparison (Field, 1971) of percentage of retail yield and percentage of separable lean and bone in bull and steer carcasses revealed that bulls had an average advantage over steers of 2.6% in estimated chuck, rib, loin and round. Champagne et al (1969) found a difference of 4.8% between yield values of bull and steer carcasses when actual carcass cutout was used. They concluded that the USDA yield grade formula underestimates true yield of bull carcasses by

PAGE 20

9 approximately 2%. Berg and Butterfield (1976) reported that although differences in percentage of bone are small, bull carcasses possess higher muscle to bone ratios than steer carcasses. Jacobs et al (1977) reported that on a boneless basis, bull carcasses contained 58% less crude fat and 23% more crude protein than steer carcasses. Bull carcasses yielded 5.5% more boxed beef than steers, and trinnmed waste fat was 17% less than in steers. Bull carcasses were worth 32% more to the retailer than were steer carcasses due to reduced in-store trimming losses and higher retail yields. Landon et at. (1978) also reported that percentages of total retail cuts were greater for bulls than for steers. Cross (1982) reported that the boxed beef and retail segments of the meat industry place price constraints on young bulls with too little fat (less than 5.1 mm) and on those that produce carcasses that are too large (over 363 kg). Seideman et al. (1982) considered the inadequate fat cover and excessively heavy carcasses characteristic of bulls to be serious disadvantages of their production. Breed Effect A comparison by Peacock et al (1980) of purebred Angus and Brahman steers fed a concentrate diet for an average of 176 d revealed no difference in average daily gain (ADG) due to breed type. However, in a follow up study (Peacock et al 1982), where they compared feedlot gain and carcass traits of purebred Angus and Brahman steers fed a concentrate diet for an average of 174 d and slaughtered at a constant weight (411 kg) and age (439 d). Brahman steers gained less weight per day than Angus steers. Bailey et al (1982) reported no difference in ADG due to breed type when bulls from widely divergent

PAGE 21

10 breed types, which included Bos taurus and Bos indicus x Bos taurus crosses, were fed to a constant age (400 d). In a recent study by Adams et al (1982) where they compared performance and carcass characteristics of purebred Angus and Brahman steers fed a high energy diet for 157 and 179 d, respectively, Angus steers gained weight much more quickly, and consequently were on feed 22 fewer days than Brahman steers. Angus steers were also heavier than the Brahman steers at the beginning and also at the end of the experiment. Similar results were reported by Cole et al (1964) when Angus and Brahman steers were full fed to a constant live weight (408.2 kg) or age (20 mo), whichever came first. A number of studies have reported differences in dressing percentage (DP) between Angus and Brahman cattle. Peacock et al. (1980) reported that Brahman steers dressed slightly higher than Angus steers. Solomon et al (1981b) reported similar findings when comparing Angus and Brahman heifers. Butler et el. (1956) in a study comparing yearling Hereford and Brahman x Hereford steers fed either high or low concentrate diets for 140 d found that steers w^ith Brahman breeding had higher DP than those without Brahman breeding. They suggested that the difference in DP between Bos indicus and Bos taurus cattle probably was due to difference in the capacity and amount of intestinal tract content (fill) at the time of slaughter. This has since been substantiated by Tucker (1981). Adams et al (1982) found Angus steers to have higher DP than Brahman steers; however, they pointed out that the Angus steers were much fatter at slaughter than the Brahman steers. On the contrary. Cole et al. (1964) observed no difference in DP between Angus and

PAGE 22

11 Brahman steers fed to a constant live weight (408.2 kg) or age (20 mo), whichever came first. Beef is graded on a composite evaluation of both quality and yield factors and is merchandized according to the final quality and yield grade. Quality grades (USDA, 1975) attempt to categorize carcasses into similar palatability groups whereas yield grades are used for the prediction of the percentage of boneless, closely trimmed retail cuts from the round, loin, rib and chuck (USDA, 1965). Carcass quality strongly influences the net income of packers, the price of meat and possibly consumer demand. Bone, lean and overall maturity scores combined with marbling scores determine the USDA quality grade. The amount of fat thickness over the ribeye muscle at the 12th rib measured at a point three-fourths the distance from the chine bone, ribeye area at the 12th rib, estimated percentage of kidney, pelvic and heart fat (KPH) and hot carcass weight determine the USDA yield grade. Carcass quality characteristics of Angus and Brahman heifers were compared by Solomon et al (1981b), Darker, more mature colored lean was observed for carcasses from Angus heifers than for those from Brahman heifers. These authors did point out that the Angus heifers were chronologically 1 mo older at slaughter than the Brahman heifers. No difference due to breed type was detected for bone maturity scores. Bone maturity, which is the degree of ossification within the bone structure, is used to determine stages of physiological maturity (i.e., degree of the animal's maturation). Research conducted by Luckett et al (1975), Peacock et al. (1980, 1982), Solomon et al (1981b) and Adams et al (1982) revealed that

PAGE 23

12 carcasses from Angus cattle received higher quality grades because of superior marbling scares when compared to carcasses from Brahman cattle. This probably results from selection practices wherein the breeders of British cattle (e.g., Angus) have succeeded in developing animals that will store a large amount of fat in their muscle at a young age. Although distinct breed differences exist between Angus and Charolais steers (Guenther, 1977) when compared at similar slaughter weights, age or days on feed, Le Van et al (1979) indicated that differences in marbling scores, quality grades and percentage of carcass cutability between Angus and Charolais steers were relatively minor when the cattle were slaughtered and compared at similar percentages of the corresponding breed average mature weight. Bailey et al (1982) reported no difference in marbling scores and quality grades due to breed type when bulls representing different genotypes were slaughtered at a constant age (400 d). The breed groups included Bos taurus and Bos indicus x Bos taurus crosses. In the study by Solomon et al (1981b), carcasses from Angus heifers were slightly heavier and had larger ribeyes than those from Brahman heifers. However, no difference in fat thickness or KPH was observed. Thus, carcasses from Brahman heifers received higher numerical yield grades than those from Angus heifers. Adams et al (1982) found that carcasses from Angus steers, which were heavier, had more subcutaneous fat, more KPH and larger ribeye areas and, consequently, received higher yield grades than carcasses from Brahman steers. However, in that same study, when carcass traits were adjusted to a constant carcass weight (279.4 kg), ribeye area was no longer

PAGE 24

13 significantly different between the two breeds, but fat thickness was still greater for carcasses from Angus steers. Luckett et al (1975), working with purebred steers of Angus and Brahman breeding fed a high concentrate diet for 100 to 114 d, found that carcasses from Brahman steers had considerably less subcutaneous fat and smaller ribeyes than those from Angus steers. Results from a study conducted by Le Van et al (1979) comparing Angus and Charolais steers revealed that differences in growth rate and yield grade factors were relatively minor when cattle were slaughtered and compared at similar percentages of the corresponding breed average mature weight. Several studies (Cole et al., 1964; Solomon et al 1981b; Adams et al 1982) have confirmed that distinct differences in carcass compositional components (i.e., percentage of lean, fat and bone) between Angus and Brahman cattle exist. Carcasses from Angus cattle were usually considerably fatter and had less lean and bone on a percentage basis than those from Brahman cattle. However, data used in these particular studies were collected from steers and heifers which were slaughtered at some constant endpoint (e.g., live weight, age, or days on feed). Le Van et al (1979) reported that breed had no marked effect on relative distribution of retail lean, fat or bone throughout the animal's body when Angus and Charolais steers were compared at similar percentages of the corresponding breed average mature weight. Palatability Traits Sex Effect As far as meat quality is concerned. Palmer (1963) reported that sex or sex condition generally has little effect on tenderness, but when it does the difference is only marginal and may not be detectable

PAGE 25

14 by the average consumer. This may be true for young animals, but the generalization may not apply to mature males. This is reflected in the work of Hedrick et al. (1969), Hunsley et al. (1971), Prost et al (1975) and Arthaud et al (1977), indicating that chronological age had a more adverse effect on tenderness in bull beef than in steer beef. Hedrick et al (1969) reported that Warner-Bratzler shear force values and sensory panel scores indicated that steaks from bulls less than 16 mo of age were comparable in tenderness to steaks from steers and heifers of similar age. However, steaks from more mature bulls were less tender. Flavor and juiciness scores were not significantly affected by sex or sex condition. Arthaud et al. (1977) reported similar results for bulls and steers on a low energy diet. However, they found that when the animals were on a high energy diet bulls were always less tender than steers, regardless of age. It has been proposed (Boccard et al., 1979; Cross et al 1982) that decreases in meat tenderness associated with advancing chronological age in bulls may be linked to concomitant increases in collagen (a type of connective tissue) content and subsequent cross-linking. Prost et al (1975) observed that bovine intact males had consistently more intramuscular connective tissue (collagen) than fem.ales. Boccard et al. (1979) and Cross et al. (1982) investigated the influence of sex on the amount of total, soluble and insoluble collagen in bovine muscles. They found that the collagen content of muscle was higher in bulls than in steers, regardless of age or breed type. Boccard et al (1979), working with Afrikaner and Friesland bulls and steers, reported that collagen solubility decreased markedly between 12

PAGE 26

15 and 16 mo of age, only in the case of bulls. Cross et al. (1982), on the other hand, observed that collagen solubility decreased considerably between 9 and 15 mo of age for bulls and between 9 and 12 mo for steers. Animals used by Cross et al (1982) represented four breed types (Charolais, Simmental Hereford and Angus). Goll et al (1962) suggested that differences in bovine collagen solubility between sexes might arise from the fact that a lipid coating over the collagen molecules, in addition to the frequency of cross-linkages within and among the collagen molecules, was more prevalent in males than in females. Boccard et al. (1979) and Cross et al. (1982) proposed that the connective tissue toughness in bulls, which inadvertently would affect meat palatability may be linked to sexual development and may be subject to some endocrine function(s) in the animal. Furthermore, these authors found that differences in muscle collagen were biologically related to age as well as breed type and closely linked to the onset of puberty. The bulk of scientific evidence reviewed by Field (1971) and Seideman et al (1982) indicated that meat from intact males was usually less tender and more variable than meat from steers or heifers; however, it generally was not less desirable in flavor or juiciness. The report by Reagan et al (1971) suggested that much of the observed variability in palatability among steaks from bullock carcasses was the result of variations in tenderness properties. These differences in tenderness perhaps could be caused by myofibrillar shortening (cold shortening) or connective tissue as previously discussed. Furthermore, it is becoming increasingly apparent that subcutaneous fat thickness is related to beef tenderness through its effect as an insulator to reduce

PAGE 27

16 the rate of chilling and the related muscle fiber cold shortening phenomenon (Smith et al 1976; Dolezal et al 1982). If some minimum subcutaneous fat thickness could assure that beef from young bulls would have "acceptable" palatabil ity then utilization of young bulls in modern beef production systems might become more widespread. Breed Effect The possibility that breeding influenced meat tenderness was first suggested by Carpenter et al (1955) when they recognized that as the percentage of Brahman breeding increased, tenderness of steaks and roasts of steers decreased. Since this first observation, convincing evidence of a relationship between breeding and tenderness has been provided (Burns et al 1958; Cole et al 1958; Huffman et al 1962; Luckett et al., 1975; Peacock et al., 1980, 1982; Leak, 1981; Solomon et al 1981b; Adams et al 1982). In all of these studies cited above, carcasses from Angus cattle produced meat which was more tender than carcasses from Brahman cattle. Palmer (1963) reported that meat from carcasses with Brahman breeding was generally less tender than that from carcasses with European ancestry. However, he did note that certain individual Brahman sires produced progeny above average in tenderness and that, by the same token, certain individual sires of the European breeds produced progeny lacking in tenderness. King et al (1958) found that the variability in tenderness of steaks from steer carcasses was closely related to particular sires and, thus, these findings indicate the possibilities for producing tender meat through judicious selection and breeding. Palmer (1963) reported that breed of sire had a pronounced effect on

PAGE 28

17 meat tenderness with Angus, Hereford and Shorthorn progeny being more tender than progeny of Brahman and Brahman x Shorthorn sires. Alsmeyer (1960) reported that cattle with high percentages of Brahman breeding were less tender than cattle of predominantly European origin. Furthermore, he noted that the percentage of Brahman breeding accounted for more variability in panel tenderness ratings than did cattle of European ancestry. Carcass Electrical Stimulation It is obvious from the literature that meat from young bulls is usually tougher and more variable in tenderness, and darker in color than that from steers. As previously discussed, differences in tenderness perhaps could be caused by myofibrillar shortening (cold shortening) due to inadequate subcutaneous fat cover often encountered with young bulls or by connective tissue. Perhaps some of these problems associated with using young bulls for block beef could be corrected with the aid of postmortem handling techniques. One such postmortem technique might include carcass electrical stimulation (ES). For the most part, ES has been demonstrated to increase the palatability of beef (Grusby et al 1976; Savell et al lS78b; Bouton et al., 1980; Stiffler et al 1982) and improve lean color and lean maturity as well as reduce heat-ring formation (Savell et al., 1978b, 1979; McKeith et al., 1981; Knight, 1982). Riley et al (1982) investigated the effects of ES and subcutaneous fat thickness on the tenderness of the longissimus muscle of bulls and steers. They found that ES produced the greatest improvement in tenderness of steaks from young bulls with less than 7.6 mm fat cover, but even with this improvement meat tenderness from bulls did

PAGE 29

i not equal that of steers. These authors suggested that differences in tenderness was probably caused by cold shortening. On the other hand, they reported that ES had essentially no effect on the tenderness of bulls and steers when the fat thickness exceeded 7.6 mm. Crouse et al (1983) found no effect of ES on the tenderness of meat from bulls. Furthermore, they found that loin steaks from bulls were more than one sensory panel score inferior when compared to those from steers. Crouse et al (1983) suggested that the variation in tenderness associated with sex condition was related to the connective tissue component rather than cold shortening, since the average fat thickness was 8.1 mm for bulls and 12.1 mm for steers. Thus, the role of temperature decline was likely not rapid enough in bulls to induce cold shortening. The literature strongly indicates that ES alleviates the cold shortening type of tenderness problem in meat (Chrystall and Hagyard, 1976; Davey et al 1976; Bouton et al., 1980; Hagyard et al 1980; Eikelenboom et al 1981). Other researchers believe that benefits of ES are not solely related to the prevention of cold shortening. Postulated mechanisms include structural alterations of muscle fibers (Savell et al 1978a; George et al 1980; Will et al., 1980; Voyle, 1981; Sorinmade et al 1982), increased lysosomal enzyme activity (Sorinmade et al 1978; Dutson et al., 1980) and decreases in the number or strength of the collagen crosslinkages (Judge et al., 1980). Stiffler et al (1982) recognized that the percentage of change in tenderness values caused by ES was quite variable, when the type of beef being investigated was considered. They concluded that this

PAGE 30

19 source of variation was associated with the initial, or inherent, tenderness of the nonstinulated meat, especially from animals (steers and heifers) less than 42 mo of age (i.e., the greater the initial toughness, the greater the effect of stimulation). Muscle Fiber Types The development of highly specific enzyme stains has permitted the identification and subsequent evaluation of individual fiber types within a muscle (Moody and Cassens, 1968; Ashmore and Doerr, 1971; Cassens and Cooper, 1971). The muscle fiber is the basic unit of skeletal muscle and comprises 75 to 90% of the total muscle mass (Hegarty, 1971). Early anatomical studies (Ranvier, 1873; Needham, 1926) have classified muscle fibers as red, white, or intermediate based on their gross color. Physiologically, muscles are recognized as slow or fast, depending on the speed of contraction (Guth and Samaha, 1969), while histochemical studies have led to recognition of three types of muscle fibers, i.e., types A, B and C (Stein and Padykula, 1962) or types I, II and intermediate (Dubowitz and Pearse, 1960). Despite the differences in fiber classifications, white fibers can be equated with type A or II or fast; the red fibers are equivalent to type B or I or slow, while type C fibers are intermediate. Ashmore and Doerr (1971) and Ashmore et al. (1972) have shown that all fibers are red at birth having high succinic dehydrogenase and nicotinamide adenosine dinucleotide-diaphorase (NADH) activities, but some show high and others show low ATPase activity. On this basis, they classified them into a-red (aR) and p-red (gR) fibers, respectively, with the PR fibers being true red fibers. On the other hand, the aR fibers have the capacity to transform from an aerobic

PAGE 31

20 state of metabolism to an anaerobic state, thus becoming a-white (aW) fibers having high ATPase activity. Not all aR fibers become aW fibers; some remain as aR fibers, which are intermediate in physiological and metabolic parameters. The BR fibers remain red throughout their lifespan. The number of muscle fibers comprising a muscle is believed to be genetically determined and firmly established at birth or shortly thereafter in cattle (Hegarty, 1971). Subsequent increases in muscle size during preand postweaning development are due to the enlarging or growth of individual muscle fibers and the transformation of the aR to the aW fiber type (Ashmore et al 1972). Transformation is primarily concerned with changes in energy-producing enzymes, and is accompanied by a rapid increase in fiber size (Ashmore et al 1972). Furthermore, these authors postulated that selection of heavily muscled animals for breeding stock and progressive elimination of sustained muscle activity could lead to selection of animals with a high proportion of aW fibers. Several studies (Mahyuddin, 1976; Suzuki et al 1976; Dreyer et al., 1977; White et al 1978; Spindler et al 1980; Solomon et al 1981a) have presented evidence which indicates that during muscle growth the percentage of aR fibers decreases while the percentage of aW fibers increases. The histochemical (Dubowitz, 1970; Brooke, 1970), ultrastructural (Gauthier, 1970), biochemical (Beatty and Bocek, 1970) and ontogenetic differences (Cosmos, 1970) in the three types of muscle fibers have been reviewed in great detail. Cassens and Cooper (1971) also reviewed and described the morphological and biochemical characteristics of

PAGE 32

21 these fibers at length. In summary, a VI or "white" fibers are generally characterized as being large in diameter, have a well developed sarcoplasmic reticulum, and are high in glycogen, creatine phosphate, ATP and contraction speed, but are low in myoglobin, mitochondrial numbers, lipid content, blood supply, oxidative metabolic activity, RNA and protein turnover (Gauthier, 1970; Ashmore and Addis, 1972; Cassens and Cooper, 1971). The aR or "red" fibers are just the opposite while the 3R or "intermediate" fibers are intermediate in these characteristics. Each fiber type differs in its growth potential, growth impetus, function and metabolic capabilities (Ashmore and Addis, 1972). Hammond (1932) noted that the sizes of muscle fibers in sheep increased with age, exercise, and nutrition. He also noted that fibers were largest in male animals, intermediate in castrated males and smallest in females. Other workers (West, 1974; Dreyer et al 1977; Guenther, 1977; Moody et al 1980; Solomon et al., 1981a) reported that size of muscle fibers was affected by animal age, weight, breed type, sex, genetic conditions or nutrition. Stein and Padykula (1962), Ashmore et al. (1972) and Johnston et al (1975) reported that the aW muscle fibers were generally the largest in diameter, the 3R fibers smallest, and the ctR fibers intermediate in size. Cassens et al (1969) and Ashmore and Addis (1972) reported that since the number of fibers in a muscle is relatively fixed at birth, muscle size is directly proportional to the degree to which aR fibers transform into ctw fibers. The fibers may conceivably reach their full growth potential later in life or at heavier body weights than either BR or cR fibers and thereby delay the onset of the "fattening phase" of growth.

PAGE 33

22 Along this line, Solomon et al (1981a) observed that smallframed, early maturing Finnish Landrace crossbred lambs had more aW fibers and fewer aR fibers in the LD muscle vihen compared at similar slaughter weights (32 and 41 kg) than large-framed, late maturing Suffolk crossbred lambs. They suggested that breed, or more specifically the stage of physiological maturity, may have contributed to a shift from aR to aW fibers during growth. Furthermore, they observed that the small -framed lambs had larger LD fiber diameters than the large-framed lambs at both slaughter weights. Dreyer et al (1977) evaluated the semimembranosus and semitendinosus (dark and light sections) from earlier maturing Friesland and later maturing Afrikaner bulls fed ad libitum and slaughtered at similar ages from birth to 24 mo inclusive. For the muscles studied by these authors, Friesland bulls had more aW fibers and fewer "R fibers than the Afrikaner bulls when compared at similar chronological ages, which also would suggest that breed, or physiological maturity, may contribute to the conversion of aR to aW fibers during growth and maturation. Furthermore, they found that the earlier maturing Friesland bulls had larger fiber diameters than the later maturing Afrikaner bulls in the muscles investigated. Johnston et al. (1981) presented evidence which also suggested that feeding system may affect the degree to which aR fibers transform into aW fibers. Bartlett et al, (1979) compared Angus with Charolais calves at 25 d of age and found that the Angus calves had a higher percentage of aW and aR fibers, while the Charolais calves had a higher percentage of 3R fibers.

PAGE 34

23 In a previous study by Johnston et al (1975), no significant effect due to breed type (Angus vs Charolais steers) was detected for the percentages of LD muscle fiber types when steers were fed for the same length of time. Although these authors did not state exactly what age the steers were before going on feed or after the removal from feed, the steers were described as being similar in age and weight and derived from similar nutritional regimens. These authors did observe larger fiber diameters and fiber areas for all three fiber types associated with the Charolais steers than for the Angus steers. Guenther (1977) reported that the variation in total amount of muscle in cattle of different maturation rates and body size (Angus vs Charolais) was due to differences in the total number of muscle fibers rather than the size or diameter of muscle fibers. Similar conjectures were made by Ashmore and Robinson (1969) and Burleigh (1980). Guenther (1977) noted that the Angus steers used in his study had larger fiber diameters than the Charolais steers when compared at similar ages from 1 mo to 15 mo inclusive. Hegarty et al (1973) noted that two different types of pigs (early vs late maturing) had the same muscle weights, but developmental ly, the muscles were at different stages of maturity. Muscle Nucleic Acids Some animals have the ability to grow faster than others and produce much greater amounts of muscle in a shorter period of time. The cellular effect of genetic selection for growth rate has been studied in different meat animal models. Some investigations compared different breeds of cattle (Ashmore and Robinson, 1969; La Flamme et al., 1973; Lipsey et al 1978; Trenkle et al., 1978; Eversole et

PAGE 35

24 a1., 1981), pigs (Powell and Aberle 1975; Harbison et al 1976) and chickens (Moss, 1968). Growth of animals is characterized by an orderly increase in the mass of tissues and organs as v/ell as changes in form and body composition. Enesco and Leblond (1962) indicated that normal growth occurs in successive stages characterized by an increase in cell number, increases in both cell number and cell size and finally, an increase in cell size alone. In meat animals, growth of the major tissues (bone, muscle and lipid) is most important with skeletal muscle having the greatest economic value. Postnatal skeletal muscle growth is characterized by an increase in muscle cell size rather than an increase in the number of cells (MacCallum, 1898; Ashmore and Addis, 1972; Ashmore et al 1972). Total cell numbers appear to be fixed since muscle cells do not divide beyond a certain stage of embryonic development (Stockdale and Holtzer, 1961; Ashmore and Addis, 1972). Since the amount of deoxyribonucleic acid (DNA) per mammalian diploid nucleus is constant (6.2 pg), DNA can be used successfully as an index of cell (nuclei) number in tissues composed of mononucleated cells (Vendrely, 1955). Deoxyribonucleic acid is the component found almost exclusively in the nucleus of the cell that is the basis of genetic information and controls synthesis of proteins. The ratio of protein to DNA (i.e., cytoplasm to nucleus) has been shown (Winick and Noble, 1965; Robinson, 1969) to provide an index of cell size. Enesco and Leblond (1962) presented evidence which indicated that increases in both of these constituents contributed to the growth of young rats. Thus, a distinction between growth caused by hyperplasia and that contributed by hypertrophy could be obtained.

PAGE 36

25 In tissues composed of multinucleated cells, such as skeletal muscle, one cannot calculate cell number and size directly from DNA and protein. However, Cheek et al (1971) suggested that in skeletal muscle the amount of DNA is indicative of the number of nuclei in muscle and the protein:DMA rate measures the average amount of cytoplasm associated with one nucleus within the muscle fiber. This ratio of nuclei to cytoplasm may be of significance in growth of muscle fibers. At least 70% of muscle DNA is due to nuclei within the myofibers; thus, cell number can be estimated from the quantity of DNA in a sample of muscle, adjusted to total muscle mass (Cheek et al 1971). In addition to DNA, ribonucleic acid (RNA) is a part of the genetic mechanism of the cell and represents a critical part of the mechanism for cell differentiation and growth. Ribonucleic acid reflects the activity per ribosome (Burleigh, 1980) and may serve as an index for the extent to which protein synthesis occurs. A high ratio of RNA to DNA has been interpreted as a greater capacity for synthesis of protein (Winick and Noble, 1965; Millward et al 1973) and may be indicative of growth potential (Sarkar et al 1977). Despite the absence of cell division, total DNA increases in muscle during growth and development (Moss, 1968). The source of this replicating DNA appears to be proliferative satellite cells (HacConnachie et al., 1964; Moss and Leblond, 1971). Swatland (1971) concluded that hypertrophy in muscle fibers is accompanied by an increase in the number of nuclei which are derived from fusion with proliferative satellite cells. A certain amount of DNA is needed to control the process of protein synthesis and deposition in the muscle (Cheek et

PAGE 37

26 al., 1971). In actively growing muscles, muscle cells contain many nuclei (DNA units), each controlling the extent and rate of synthesis over its domain by providing synthesis machinery, i.e., RNA and riboscmes (Thompson and Heywood, 1974). Hormones, nutrition and exercise can, within limits, modulate the extent of the activity of the muscle nuclei in providing the apparatus associated with protein synthesis (Trenkle, 1974; Cheek and Graystone, 1978; Goldberg et al 1980). Several investigators (Ashmore and Robinson, 1969; Powell and Aberle, 1975; Harbison et al., 1976; Lipsey et al 1978; Trenkle et al., 1978; Eversole et al 1981) presented evidence which indicates that larger (heavier) muscles have more total DNA and total RNA than smaller (lighter) ones. Therefore, the differences in total nucleic acids encountered by these authors when comparing different breed types were usually attributed to differences in muscle weights between the breeds since nucleic acid concentrations per gram of muscle tissue were generally not significantly different. Trenkle et al (1978) also recognized that full fed steers, which were accumulating protein in their muscle at a faster rate than limited fed steers, also had higher RNA:DNA ratios suggesting a greater capacity for synthesis of protein by these steers. Muscle protein deposition is not just simply a process of synthesis. Millward et al (1976) and Laurent and Millward (1980) presented evidence which indicated that a sizeable portion of the protein synthesized is degraded. Laurent and Millward (1980) established that this rate of degradation is higher in the faster growing muscle cells. The net protein accretion between synthetic and degradative processes represents the actual protein acquisition in

PAGE 38

27 muscles (Millward et al 1976; Goldberg et al 1980; Laurent and Millward, 1980). As an animal reaches physiological maturity, the rates of synthesis and degradation become equal and there is no further net protein deposition in muscle (Millward et al 1976; Laurent and Millward, 1980; Lindsay, 1982). At this point, the ratio of protein to DNA is at its highest level (Robinson, 1969, Burleigh, 1980) and the absolute rates of synthesis and degradation, although still appreciable, have declined to a rate much lower than that occurring during rapid muscle growth (Millward et al 1976; Goldberg et al 1980; Laurent and Millward, 1980).

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STUDY 1 PRODUCTION TRAITS AMD CARCASS COMPOSITIONAL CHARACTERISTICS OF YOUNG PUREBRED ANGUS AND BRAHMAN BULLS SLAUGHTERED AT SIMILAR PERCENTAGES OF MATURE WEIGHT Introduction A considerable amount of interest has been stimulated regarding the use of young bulls in modern beef production systems. Such interest stems from the fact that bulls gain more rapidly, utilize feed more efficiently and produce a higher yielding carcass (more retail product) with less fat and more red meat than steers (Field, 1971; Seideman et al., 1982). However, as Seideman et al (1982) explained in their review, increased production efficiency obtained through the use of intact males has often been offset by management problems, particularly with animal behavior. Furthermore, meat production from intact males has encountered strong resistance from packers, since bulls, on the average, have been shown to produce carcasses with lower quality grades, darker lean color and coarser-textured lean resulting in lower consumer acceptance at the retail level than steers (Field, 1971). Therefore, when young bull carcasses are officially graded by USDA graders, the standards require the grade designation to also include the word "Bullock." Although several problems associated with producing meat from young bulls exist, perhaps some or all of these problems can be reduced or alleviated and, thus, meat from young bulls could help satisfy the demand for lean beef. 28

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29 A number of studies (Cole et al., 1964; Luckett et al 1975; Peacock et al 1980, 1982; Solomon et al 1981b; Adams et al 1982) described substantial differences in production traits, carcass characteristics and compositional factors between Angus and Brahman cattle (steers and heifers). Except for research on size and condition (Long et al 1979) and on selected slaughter and carcass traits (Jenkins et al 1981) of serially slaughtered bulls representing a five-breed dial lei which included Angus and Brahman, few studies have been done to characterize performance and carcass compositional characteristics of purebred bulls representing these diverse breed types. Therefore, this study was conducted (1) to compare production, compositional and carcass characteristics of purebred Angus and Brahman bulls, and (2) to evaluate the use of slaughtering at similar percentages of the mature cow weight as a technique for comparing bulls, of such diverse origins, on an equal compositional basis. Materials and Methods Seventy-eight purebred bulls (10 to 18 mo at slaughter) were used over a two year period (table 1) to ascertain the effects of breed (Angus or Brahman) and slaughter weight (60, 80, 90, 100% of the average mature cow weight for the respective breed) on production traits and carcass compositional characteristics. All the bulls came from the University of Florida registered Angus and Brahman herds in which all female replacements during a 30 year period were generated within the herd with new genetic material obtained from outcross herd sires and frozen semen. The dam's nature weights for the respective breeds were 456.3 kg for Angus and 515.3 kg for Brahmans.

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30 TABLE 1. ALLOTMENT OF EXPERIMENTAL ANK^LS % Mature weight^ Breed^ 60 80 90 100 Angus Year I S 5 5 5 Brahman 5 5 5 Year II 5 Angus 5 1 5 6 Brahman 5 6 8 2 Age ranged from 10 to 18 mo at slaughter. Percentages of the average mature cow weight for the respective breed.

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31 Each year, the fall-calved Angus bulls grazed summer annual forage (Tifleaf-1 Millet) after which bulls representing the 60% group were slaughtered. The remaining Angus bull calves were then placed in the feedlot and fed a shelled corn-protein supplement diet (table 2) until they reached their appropriate slaughter weight. Winter-calved Brahman bulls were fed the concentrate diet (table 2) after being weaned to simulate gains the Angus bulls achieved on forage. After slaughtering the Brahman bull calves representing the 60% group, the remaining bulls were fed the same diet (table 2) to their designated slaughter weight. Bulls were slaughtered when they reached or came close to their designated target weight. Actual live weights at slaughter for Angus bulls were 293, 381, 412, and 463 kg and for Brahman bulls were 316, 420, 463, and 516 kg. After slaughter, carcasses were weighed and then Chilled at 0-2 C. Live weights and hot carcass weights were used to calculate dressing percentage. At 24 h postmortem, the left side of each carcass was ribbed between the 12th and 13th rib and quality and yield characteristics were evaluated by University of Florida personnel. Skeletal, lean and overall maturity were combined with marbling score to determine quality grade (USDA, 1975). Other quality traits evaluated were lean color (7 = very dark red, 1 = dark pink), texture of lean (7 = extremely coarse, 1 = very fine), lean firmness (7 = extremely soft, 1 = very firm) and presence of heat-ring (4 = extreme, 1 = none). Fat thickness over the ribeye at a point three-fourths the distance from the chine bone, ribeye area, estimated percent kidney, pelvic and heart fat, and hot carcass weight were used to determine the yield grade.

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32 TABLE 2. DIET COMPOSITION Ingredient Year 1, % Year 2, % Corn, whole, shelled (IFN 4-02-931) 80 92 Sugarcane pulp, dehy, pelleted (IFN 1-04-686) 4 Cottonseed hulls (IFN 1-01-599) 4 8 Commercial supplement 12^ ^ Imperial Beef Concentrate 52% changed to Purina Custom Mix 38% (crude protein equivalent approximately 54%) three months into study. Moor Man's Beef Finisher with monensin (crude protein equivalent approximately 80%) fed at rate of 227 g per day, modified midway through study by changing crude protein equivalent to approximately 54%.

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33 The 9-10-11 rib section from the right side of each carcass was removed at 24 h postmortem, by the procedure outlined by Hankins and Howe (1946), vacuum packaged and stored at -18 C for subsequent physical separation and chemical analysis. The 9-10-11 rib cuts were physically separated into lean, fat and bone, after being thawed at 2 C. The soft tissue components (lean plus fat) were then thoroughly mixed and ground together and stored frozen (-18 C) until analyzed by AGAC (1980) procedures for chemical composition. The chemical determinations made on the soft tissue components were used to predict carcass composition using the equations developed by Field (1971). Crude protein was determined as nitrogen (Semi automated method; AOAC, 1980) x 6.25. In addition, a sample (2.54 cm in thickness) from the anterior end of the longissimus muscle at the 13th rib end from the left side of each carcass was removed, closely trimmed of external fat and connective tissue, then finely ground and thoroughly mixed. Chemical determinations for moisture, ether extractable lipid and protein were also performed on these muscle samples. Data were analyzed by the regression procedure of the Statistical Analysis System (SAS, 1979). A 2 x 4 x 2 factorial model involving breed, weight group and year was used to analyze all response variables. F-tests were used to determine the effects of breed, weight group and year on the parameters investigated. The Duncan's multiple range test (SAS, 1979) was used to "test differences among slaughter weights. Results and Discussion Live animal traits and dressing percentages are presented in table 3. Angus bulls were (P<.05) younger and lighter at slaughter than

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34 TABLE 3. LEAST-SQUARES MEANS FOR LIVE ANIMAL TRAITS AND DRESSING PERCENTAGES BY BREED, WEIGHT GROUP AND YEAR Item N Age d Live wt. kg ADG,^ kg/d Dressing % Main Effects Breed (B) Angus 37 415.2^ 387.2^ 1.08 56.6^ Brahman 41 442.5^ 428.9^ 1.03 59.2^ Weight group (W) % 60 20 334.7^ 304. 7*^ .76^ 54.5'' 80 17 442.6^ 400.3^ 1.10^ 58 4^ 90 23 457.9*^ 437.7^ 1.15^ 58 8^ 100 18 482 1^ 489 6^ i. • cyj 5Q Year (Y) 1 40 418. o'^ 405. o'^ 1 11^ 58 1 2 38 440.7^ 411.2^ 1.00^ 57.7 Interactions^ BxW * BxY NS NS WxY NS NS BxWxY NS NS NS Average daily gain, b c d e Means within a main effect group in the same column bearing f different superscripts are different (P<.05). ^ = P<.05; NS = nonsignificant (P>.05).

PAGE 46

35 Brahman bulls, as expected based on the nature of the experimental design which took into account differences in maturation rates due to breed types. Interactions (P<.05) between breed and weight group (BxW) for age and live weight (table 4) indicated that Angus bulls from the 80, 90 and 100% weight groups were approximately 1 mo younger (14.8 vs 15.9 mo) and 48 kg lighter at slaughter than Brahman bulls from the respective weight groups (table 4), However, Angus bulls representing the 60% group were only 1 d younger, on the average (334 vs 335 d), and 23 kg lighter at slaughter than Brahman bulls from the 60% group. These data suggest that the Brahman bulls required longer times to reach the 80, 90 and 100% weight groups than did the Angus bulls. As slaughter weight increased, age and live weight increased (P<.05) as anticipated. Year also had an effect (P<.05) on age and weight at slaughter. Bulls comprising the second year group were older (22 d) and heavier (6 kg) at slaughter than those used the first year. A weight group by year (WxY) interaction was noted for live weight (table 5). Bulls used for the first year study v/ere slightly heavier at the 60% weight but lighter at the 80 and 100% weights than those for the second year. Weights for the 90% group were similar from one year to the next. Part of these differences in live weight for the different years may be associated with the difference in number of bulls between breeds in the 80 and 90% groups (table 1). Average daily gain was not affected (P<,05) by breed type but was influenced by weight group and year (table 3). Average daily gain for the 60% group was calculated by subtracting the weight at weaning from their v/eight before going into the feedlot and dividing the total number of days that transpired during this time. Average daily gain

PAGE 47

35 to E &Si •r— •> to TD to -i•1Q. c 1— o I o +-> CD res c 31 i•1T3 rro fO SZ3 cn 1o +-> •r— S3 to i> o (_> DJ3 TD O cn > "r• 5 0) CD -a <: 4-> •> ^ a. cn 3 •ro CJ s3 cn a 00 ^asf CO <: ;i>!3LO • (U > OJ • to ro r-i I— t I— t ^ ;! O CO cu LT) XI LO I— ( "Id1—1 LO O o ro CO CM vo LO cn o CO CO 'If V* o. i• (O +-> CO cn c CD Qi o o O o O o o o fO >, o .— LO LO CO CO cr> cr> o o r— Sf— 1 f — t -•-> •1OJ (O c: res C1.4-> o CD O O E +- ^cn-rc c c •1— (13 to SfO ra sz Sto o (/> B 1/) B m B lO B cn cu 0) 43 -C 3 3 sz 3 •r> SO) CD 0 CC O Qi C SC S_ c: S<=c ca (0 j3 O "O

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37 TABLE 5. WEIGHT GROUP BY YEAR INTERACTIONS^ FOR LIVE WEIGHT, AVERAGE DAILY GAIN AND LEAN TEXTURE Weight Live wt. h ADG, Lean nrniin "L M I U U 10 Year ka ka/d 60 1 >J\J\J • J 84 1 8 60 2 300.4 .68 2.3 80 1 388.7 1.21 3.1 80 2 411.8 .99 2.5 90 1 437.9 1.21 3.5 90 2 437.6 1.09 2.5 100 1 484.5 1.18 3.3 100 2 494.7 1.13 2.6 ? Significant at the P<.05 level. Average daily gain. Refer to table 8 for codes.

PAGE 49

38 for the remaining weight groups was calculated by subtracting the v^eight before going into the feedlot from their final slaughter weight and dividing by the total number of days that passed. Increasing slaughter weight was associated with an increase in ADG, which was significant, however, only from the 60 to the 80% group. Arthaud et al (1977), studying production and carcass traits of Angus bulls and steers fed different energy levels and killed at four ages 1 1 (12, 15, 18, or 24 mo) found that bulls, regardless of diet (high or low energy) had increasing ADG from 12 to 15 mo of age, but then ADG decreased from 15 through 24 mo. The bulls representing the 60 and 80% groups in the present study were 11 and 15 mo of age at slaughter, respectively. After 15 mo (80% group), the ADG did not decrease for the bulls in the present study as did the bulls and steers used by Arthaud et al (1977). Average daily gains for bulls in the different weight groups were affected by breed (table 4). Brahman bulls (60% group) which were fed a concentrate diet to simulate gains achieved by Angus bulls on forage actually gained 17% more weight per day than the Angus bulls (table 4). However, for bulls representing the 80, 90, and 100% groups, Angus bulls gained v/eight faster than Brahman bulls. Bulls from the second year, for the most part, gained (P<.05) less weight per day than those used the first year (table 3). However, this difference due to year was not consistent for all weight groups (table 5) and both breeds (table 6). Bulls used the first year were substantially superior in ADG (table 5) than those used for the second year study for all the weight groups except the 100% group, where ADG were similar. Angus bulls from the first year study tended to gain weight j

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39 TABLE 6. BREED BY YEAR INTERACTIONS^ FOR AVERAGE DAILY GAIN, DRESSING PERCENTAGE, QUALITY GRADE AND HEAT-RING SCORES ADG^, Dressing Quality HeatBreed Year kg/d % grade^ ring^ Angus 1 1.19 57.3 12.1 2.3 Brahman 1 1.03 58.8 10.8 2.5 Angus 2 .96 55.9 13.2 2.1 Brahman 2 1.03 59.5 10.7 3.0 ? Significant at the P<.05 level. Average daily gain. ^ Refer to table 8 for codes.

PAGE 51

40 more rapidly than Brahman bulls from year one (table 6). On the contrary. Brahman bulls from the second year gained slightly more weight per day than Angus bulls used the second year. The differential response of breed, weight group and year on ADG resulted in a three-way interaction (P<.05) of these main effects (table 3). Perhaps these differences in ADG and, thus, live weight may be attributed to the changes in diet composition from the first year to the second (table 2). These changes were an increase in the percentage of shelled corn (from 80 to 92%) and cottonseed hulls (from 4 to 8%) with sugarcane bagasse pellets being removed from the diet. In addition, the commercial protein supplement was changed from an intermediate crude protein equivalent of approximately 54% used the first year to one containing a high crude protein equivalent of approximately 80% the second year. The supplement used the second year in turn had to be switched back to one containing an intermediate crude protein equivalent of approximately 54% midway through the study. The reason for making this switch during the course of the experiment was because the bulls were not utilizing the high levels of nonprotein nitrogen in the supplement sufficiently for growth. In fact, the Angus bulls, which went into the feedlot 3 mo earlier than the Brahman bulls, because of their earlier calving and, thus, earlier weaning dates only had one mo to benefit from this diet modification. The Angus bulls were slaughtered 28 d after making the switch in crude protein. However, the Brahmans were only in the feedlot for 56 d prior to the supplement switch. The breed by year (BxY) (table 6) interaction (P<.05) noted for ADG indicated that the Angus bulls gained less weight per day the

PAGE 52

41 second year than the first, suggesting a breed effect on diet utilization for growth. This difference appears to be related to the diet supplement modification during the second year. Peacock et al (1980), in a study comparing feedlot performance and carcass traits of purebred Angus and Brahman steers fed a concentrate diet for an average of 176 d, found no difference in ADG due to breed type. Bailey et al (1982) reported no difference in ADG due to breed type when comparing bulls from widely divergent breed types, including Bos taurus and Bos indicus x Bos taurus crosses fed a concentrate diet and slaughtered at a constant age (400 d). However, in a study by Peacock et al. (1982), where they compared feedlot gain and carcass traits of purebred Angus and Brahman steers fed a concentrate diet for an average of 174 d and slaughtered at a constant weight (411 kg) and age (439 d). Brahman steers gained less weight per day than Angus steers. A recent study by Adams et al (1982) substantiated these findings. These authors compared performance and carcass characteristics of purebred Angus and Brahman steers fed a high energy diet for 157 and 179 d, respectively. Their intent was to slaughter individual steers as they attained a U.S. Choice finish (visually appraised). Brahman steers were lighter than the Angus steers at the beginning and also at the end of the experiment. Angus steers gained weight much more rapidly, and consequently they were on feed 22 fewer days than the Brahman steers. Similar results were also reported by Cole et al. (1964), who compared Angus and Brahman steers full-fed to a constant live weight (408.2 kg) or age (20 mo), whichever came first.

PAGE 53

I 42 In the present study where young Angus and Brahman bulls were fed to a percentage of the mature cow weight for each respective breed, the type of diet appeared to interact with breed relative to growth characteristics. This may be true for only bulls, but could have possibly affected the results other workers have found for steers. Angus bulls had lower (P<.05) DP than Brahman bulls (table 3). This was true at each designated slaughter weight; however, the difference in DP between the two breeds decreased (table 4) with increasing weight. Furthermore, a greater difference in DP between breeds was observed the second year than the first (table 6). Perhaps these differences reflect the diet compositional differences from one year to the next and modifications made during the individual study. Solomon et al (1981b) found that Brahman heifers dressed slightly higher than Angus heifers fed different levels of nutrition for 217 d. Butler et al. (1956), in a study comparing yearling Hereford and Brahman X Hereford steers fed high or low concentrate diets for 140 d, found that steers with Brahman breeding had higher DP than those without Brahman breeding. They suggested that the difference in DP between Bos indicus and Bos taurus cattle was probably due to differences in the capacity and amount of intestinal tract content (fill) at the time of slaughter. Adams et al (1982) in their study found Angus steers to have higher DP than Brahman steers, but the Angus steers were much fatter at slaughter than the Brahman steers. On the contrary. Cole et al (1964) observed no difference in DP between Angus and Brahman steers fed to a constant live weight (408.2 kg) or age (20 mo), whichever came first.

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43 For the most part, increasing slaughter weight resulted in higher DP, however, the only significant difference found for DP was between the 60 and 80% group. This agrees with the study by Arthaud et al (1977), who evaluated production and carcass traits of Angus bulls and steers fed either high or low energy diets and slaughtered at four ages (12, 15, 18, or 24 mo). Means for yield grade factors by breed, weight group and year are presented in table 7. Except for hot carcass weight and numerical yield grade, neither fat thickness, ribeye area nor percentage of KPH were affected by breed (table 7). Brahman carcasses were heavier (P<.05) than Angus carcasses as expected from the experimental design. However, equal fatness and ribeye measurements at the heavier weights resulted in higher yield grades being assigned to Brahman carcasses. In the study by Peacock et al (1982), Brahman carcasses ended up slightly heavier (9 kg), with less subcutaneous fat and smaller ribeyes than Angus carcasses. Adams et al (1982) found that carcasses from Angus steers had more subcutaneous fat, more KPH and larger ribeyes, thus higher yield grades, than Brahman steers. However, in that same study when carcass traits were adjusted to a constant carcass weight (279.4 kg), ribeye area was no longer different between the two breeds, but fat thickness was still greater for carcasses from Angus steers. Luckett et al. (1975), working with straightbred steers of Angus and Brahman ancestry fed a high concentrate diet for 100 to 114 d, found that carcasses from Brahman steers had considerably less subcutaneous fat and smaller ribeyes than those from Angus steers.

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44 v> c o •M O n3 SQ) +-> X CQ CM < z <: a. o CD zc C3 Q UJ UJ a: CO >CO 00 q; o t— o < OH CJ Q _J UJ I— I >ai o Um •X. 00 UJ <: ZD cr oo I I— oo <: >o o o 0) n3 Q. O Sai o en +-> cno O O CO CD OJ sco E S. CO K CO <: oo oo n OJ CO CM TO CO o oo CM UD cri o CM CO o CM CO CO CM o U3 CM O J3 m I— I rtJ ^ LO r-l CM J3 cr> t— I IJD J3 00 03 00 CO CM CO to CM CM 03 UD JO O LO LO Ln LO LO CM (T3 VO I— 1 LO 00 o CM CM o o 3: to tn OJ c o x: +J -t-> Ll. s_ >> o iC7) Q_ 4_> CD CJ CD +-> 4— 4— •rn3 "O -M O cz ^ to o •r~ CO 4— 4-* •r— CX C •r~ o> ^ l/l S— OJ a. CJ r3 (/) LO 4-* C o CD •r^ CJ O *4— (O ^S•r~ (1) "O +J c CJ> c >> (O (U 1 .o o QJ +-> £Z O) x: -M OJ 4— O Ol CJ c o C o LO 3 o o A* CL. +-> CJ 4-> CJ 4 fd x: c: o c x> c •r-C rO II (J CO •r— LO > I/) o Q-LO O) Qo o O Xi to •ra)

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45 Solomon et al. (1981b), comparing purebred Angus and Brahman heifers when fed different planes of nutrition for 217 d, found that carcasses from Angus heifers were slightly heavier and possessed larger ribeyes than those from Brahman heifers. However, no difference in fat thickness or KPH was observed, thus carcasses from Brahman heifers received higher numerical yield grades than those from Angus heifers. Results from a study conducted by Le Van et al (1979), comparing Angus to Charolais steers revealed that differences in growth rate and yield grade factors were relatively minor when cattle were slaughtered and compared at similar percentages of the corresponding breed average mature weight. This is in agreement with the results from the present study. As carcass weight increased, fat thickness, KPH and final yield grade increased (table 7), indicating that heavier carcasses were probably fatter than lighter carcasses. This is in agreement with the work reported by Arthaud et al (1977), Jones et al (1978) and Solomon et al. (1981b). Ribeye area, as a measure of muscling, increased at each successive weight interval only for the Brahman bulls from the second year group (figure 1). On the contrary, for both years of Angus bulls and the first year Brahman bulls, ribeye area increased rapidly from the 60 to the 80% group, changed little or decreased between 80 and 90% and then increased from the 90 to the 100% group. Other than this three-way interaction (BxWxY) for ribeye area, year had no significant effect on yield grade factors. Conceivably, the increased growth rate for the second year Brahman bulls may be related to the continued increase in ribeye area detected only for this group of bulls. Furthermore, perhaps this difference may reflect the protein supplement modifications made during the individual study.

PAGE 57

46 o Angus Year 1 • Angus Year 2 ^ Brahman Year 1 Weight group, % igure 1. Effects of breed, weight group and year on ribeye area.

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1" .',•:*_.. ,^ 47 Quality characteristics of the longissimus muscle at the 13th rib when ribbed at 24 h postmortem, and bone maturity scores are presented in table 8. Lean maturity scores were lower for Angus carcasses at the 60 and 80% weights than for Brahman carcasses at these same weight percentages (table 4), indicating more youthful color. However, at the 90 and 100% weights, lean maturity scores were higher for Angus carcasses than for Brahman carcasses at these heavier weights suggesting more mature (physiologically) lean. Nevertheless, lean maturity scores for all the bulls averaged A which indicates that physiologically the bulls were still fairly young. In fact, the actual average age of all the bulls was 14.3 mo (table 3). Solomon et al (1981b) found that the lean from Angus heifers was more mature in color than that from Brahman heifers. These authors did point out that the Angus heifers were chronologically 1 mo older at slaughter than the Brahman heifers. Increasing slaughter weight was associated with an increase in lean maturity scores for Angus bulls (table 4). Lean maturities for carcasses from Brahman bulls appeared to decrease or change very little as weight increased. Based on these results, it appears that Brahman bulls changed very little physiologically in lean maturity. Overall carcass maturity scores tended to follow patterns characterized for lean maturities from the respective breeds. Adams et al (1982) reported no difference in overall maturity scores when comparing carcasses from Angus and Brahman steers fed for 157 and 179 d, respectively. Year had no effect (P>.05) on lean or overall maturity scores (table 8).

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48 o 4c: o +J o >X X >X X CQ X ca i>o o Q.O o 5cn l-> sz aio •rCO ^ z: ;2: 2: ^ z +: 2:2: 2:2:2:2:2:2:* 2:2: 00 c/o 00 00 00 oo 00 ^2:2:^* ^2:2:* t/) oo 00 oo to 2:* -K 2: 2: z: ^ -K cx)co cTiLnLncoLO vT CM rO LO ..... < LT) SCM CO CM CM 1— .—1 ra CO LD cn 00 0 CM in < S1 — 1 00 CO CM CM r—i ra ra ro 0 CO CO < i1 — 1 CM CO CM 1— t— 1 ra ra ra jQ LO CM t— 1 CM VO CM 0 ir-* CO CM CO CM hI— 1 ro ra 0 CO cr> 0 d00 00 • < 0 0 CO CO CM CM Ol. 1 — 1 ra CTv CO in CM CO cy> < sCM CO CM CM CM •r— 3 -M ra E ra GJ a >> •rS3 +-> ra o CQ >> --> il 3 01 ra I— 5ja CJ s> ra o z OJ XI ra s_ C7) >> -(- ra 3 oi. o o o ra S3 +-> X (D +J C ra a E cn ra I ra OJ o ra £_ croc/) o O) c u Q-'ira 3 jC sO -M -M S-I= cn 3 II +J O) U 1 — So ra I— 10 •> (U = +-> -o C C -r•I-rO ra o > E ca. cu -a ra o o > C. r-i < 0 T3 i0 ra II 0) • CM "O I— 1 0 • • • S0 M +-> ra j= ra sScr> &• o a o) E "b o c C o O -r-IE ra 41•a It II c >> >> ra I — I— CO +-> +-> "O c: ra ra c II ra ssra 0) > II II I— in 1 iwo t3 SCO CO S+-> -> QJ E c to 01 E ic: ra •.•!•!o o II I— nc •!O II II II II 'ic ro CM CM r— 1 CD 'r•>c c; c c Q> .i — -r-r— SO) O) (L) (_) S_ 1 — OJ Qj OJ QJ z C'oorararara Ut/J(/)tJ(/jLn c: — IIXIO-OOOO tj ra iQ.Q.Q.ca.11 •• > X) ra •— t -Q Luci.ECMr^r^r^^* ra TD o) <+cnx: -t— -r-j ^

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49 Bone maturity, which is the degree of ossification within the bone structure used to determine stages of physiological maturity (degree of the animal's maturation), was influenced by breed, weight and year. Brahman bulls had lower {P<.05) carcass bone maturity scores (table 8) than those from Angus bulls, indicating that Brahman bulls were more youthful physiologically. These results are probably associated with the understanding that Brahman are a later maturing breed type in comparison to Angus which are earlier maturing based on growth rates. As carcass weight increased, concomitantly scores for bone maturity increased. Arthaud et al (1977) found that except at 12 mo, where maturity scores were lower, bulls evinced similar skeletal, lean and overall maturity with advancing chronological age as steers. Solomon et al. (1981b) observed that with increasing live weight at slaughter due to level of nutrition, bone, lean and overall maturity scores all increased, indicating advancing physiological maturity associated with higher levels of nutrition. Furthermore, these authors pointed out that even though the heifers receiving the highest level of nutrition also received higher maturity scores, chronologically the heifers from this group were 2 weeks younger than those heifers from the intermediate (level of nutrition) group and only 3 d older than those heifers representing the lowest (level of nutrition) group. These authors indicated that plane of nutrition, rather than chronological age appeared to influence the physiological age of the animals. Bulls from the second year possessed slightly lower (P<.05) bone d maturity scores than those used the first year. Although there were

PAGE 61

50 differences in maturity indices, all carcasses were within the "A" maturity score and would qualify for the "Bullock" grade. In addition, advancing maturity within the "A" score has no effect on final quality grade. Significant BxW interactions were detected for marbling scores and quality grades. Marbling scores and quality grades improved (P<.05) with advancing slaughter weight (table 4) for only the Angus bulls {Jr^^ to Sl^^ and St to 6", respectively). No change (P>.05) due to weight was encountered for either marbling or quality grades for the Brahman bulls (Pd^^ to Pd^^ and St" to St", respectively). Most carcasses were in the USDA "Standard" grade. Only Angus carcasses from the 90 and 100% groups reached the "Good" grade (table 4). Previous research comparing Angus and Brahman cattle conducted by Luckett et al (1975), Peacock et al (1980, 1982), Solomon et al (1981b) and Adams et al (1982) revealed that Angus carcasses received higher quality grades because of superior marbling scores when compared to carcasses from Brahman cattle. Results from the study conducted by Le Van et al (1979) revealed that differences in marbling scores between Angus and Charolais steers were relatively minor when cattle were slaughtered and compared at similar percentages of the corresponding breed average mature weight. Bailey et al (1982) found no difference in marbling and quality grade due to breed type when comparing bulls from distinctly different breed origins, including Bos taurus and Bos indicus x Bos taurus crosses. Perhaps hybrid vigor due to crossbreeding Bos indicus with Bos taurus may also eliminate substantial differences (e.g., in marbling and quality grades) otherwise encountered when comparing the purebreds from these genetically different animals.

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51 However, in the present study, when purebred bulls were compared at similar percentages of mature weights, the Brahman bulls produced carcasses with less marbling than did the Angus bulls; a situation probably resulting from selection practices. It appears that the breeders of British cattle (e.g., Angus) have succeeded in developing animals that will store a large amount of fat in their muscle at a young age. Quality grades were higher the second year than the first for only the Angus bulls (table 6). No major difference (P>.05) due to breed type, weight group or year was observed for lean color or firmness. The majority of carcasses had firm, light cherry-red colored lean in the ribeye. The lean from Angus carcasses, however, was finer-textured (P<.05) with less evidence of heat-ring formation (P<.05) than lean from Brahman carcasses, especially for the second year (tables 4, 6 and 8) and probably accounts for the lean maturity differences previously discussed. Heat-ring is the appearance of dark lean color at the periphery of the ribeye muscle resulting from different chill rates within the muscle. It appears from this study that heat-ring formation may be a function of size of the carcass as well as fatness. Lean from the second year group of bulls was slightly finer in texture than lean from first year bulls, except in the case of the 60% group (table 5) where it was just the reverse. Furthermore, bulls from the first year 60% weight group possessed the finest-textured lean for the entire two year study. Predicted carcass components based on the 9-10-11 rib cut and longissimus muscle chemical composition are listed in table 9. There were no major differences (P>.05) in predicted carcass composition

PAGE 63

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53 (percentages of fat-free lean, fat and bone) due to breed type. These data suggest that based on overall carcass composition the bulls were slaughtered at similar points in their respective growth curves and, therefore, were compared on an equivalent basis. Cole et al. (1964), Solomon et al. (1981b) and Adams et al (1982) reported significant differences in percentages of carcass lean, fat and bone between Angus and Brahman cattle. Carcasses from Angus cattle were fatter and had less lean and bone on a percentage basis than those from Brahman cattle; however, data used in these studies were collected from steers and heifers which were slaughtered at some constant (similar) endpoint (e.g., live weight, age or days on feed). As carcasses became heavier, they contained lower percentages of fat-free lean and bone, and more fat (table 9), which agrees with findings reported by Hedrick (1968) and Berg and Butterfield (1976). According to the results from the present study, these bulls produced lean, acceptable weight carcasses. Year had no significant effect on predicted carcass components. One might have expected some differences due to year since it was involved in various interactions for production and carcass traits (tables 3, 7 and 8). Longissimus muscles from Angus bulls contained more (P<.05) lipid (%) and less (P<.05) protein {%) than those from Brahman bulls (table 9). The percentage of intramuscular fat increased from the 60 to the 80% group, decreased slightly between 80 and 90%, and once again increased from the 90 to the 100% group. Perhaps the changes associated with increasing slaughter weight for ribeye area can in part be attributed to similar changes recognized for the percentage of intramuscular fat (figure 2). The changes in percentage of intramuscular

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55 fat parallel those for ribeye area and marbling score. This suggests that part of the increase in size of ribeye may result from fat accretion and not actual muscle growth. Longissimus muscle from bulls representing the first year group possessed less extractable lipid {%) than those from the second year group (table 9). Several studies have found percentages of intramuscular fat to be highly correlated with marbling scores. This trend was more evident for the carcasses from Angus bulls than for carcasses from Brahman bulls (table 4). In general, the results from the present study suggest that slaughtering purebred bulls from different genetic backgrounds (e.g., Angus and Brahman) at similar stages in their respective growth curves appears to offset many of the compositional and carcass trait differences otherwise encountered if slaughtered at some constant (similar) endpoint (i.e., age, live weight, or days on feed). Furthermore, carcasses from these bulls fed to the selected slaughter weight produced lean, acceptable weight carcasses. Breed appeared to be related to indices of quality, i.e., some were more deficient in quality than others. Summary Seventy-eight purebred bulls (10 to 18 mo at slaughter) were used over a two year period to ascertain the effects of breed (Angus or Brahman) and slaughter weight (60, 80, 90 or 100% of the average mature cow weight for the respective breed) on production traits, carcass characteristics and composition. Angus bulls grazed summer annual forage (millet) for three mo after weaning while Brahman bulls were fed to simulate gains the Angus achieved on forage. The 60% group of

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56 bulls from both breeds was slaughtered after this postweaning feeding period. The remaining bulls were then placed in a confinement feedlot and fed a shelled corn-protein supplement diet until they reached their appropriate slaughter weight. Slaughter weights for Angus bulls were 293, 381, 412 and 463 kg and for Brahman bulls were 316, 420, 463 and 516 kg. The 9-10-11 rib section was used to estimate composition. Carcasses from Angus bulls received higher quality grades (St^ vs St") based on differences in marbling scores (Tr^ vs Pd~), and lower yield grades (1.8 vs 2.1) than carcasses from Brahman bulls. All the carcasses qualified for the USDA "Bullock" grade. There were no significant differences in predicted carcass composition due to breed type. The percentage of intramuscular fat increased between the 60 and 80% group, decreased slightly between 80 and 90% and once again increased from the 90 to 100% group. Ribeye area, as a measure of muscling, for both years of Angus bulls and the first year Brahman bulls, increased rapidly from 60 to 80%, changed little or decreased between 80 and 90%, and then increased between 90 and 100%, except for the Brahman bulls from the second year where the increase in ribeye area was continuous. The influence of year on production and carcass traits appeared to be associated with the change in diet composition from the first to the second year. Data suggest that carcasses from these bulls fed to selected slaughter weights produced lean, acceptable weight carcasses. However, the carcasses from the Brahman bulls were more deficient in marbling than those from Angus bulls. Furthermore, slaughtering purebred bulls representing different genetic backgrounds at similar

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57 stages in their respective growth cycles appears to offset many of the compositional and carcass trait differences otherwise encountered if they are slaughtered at some constant (similar) endpoint (i.e. age, live weight or days on feed).

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STUDY 2 EFFECTS OF BREED, SLAUGHTER WEIGHT, YEAR AND CARCASS ELECTRICAL STIMULATION ON THE QUALITY AND PALATABILITY OF BEEF FROM YOUNG PUREBRED BULLS Introduction Renewed interest in producing "lean beef" has promoted the use of young bulls in beef production systems. Such interest stems from the fact that bulls gain more rapidly, utilize feed more efficiently and produce a higher yielding carcass (more retail product) with less fat than steers (Field, 1971; Seideman et al 1982). Nevertheless, real or anticipated problems associated v/ith tenderness, dark lean color, low quality grades and the traditional reluctance of retailers to market "Bull" beef have delayed the use of young bull carcasses as a source of market beef. The possibility that breeding influenced tenderness was first suggested by Carpenter et al (1955) who detected that as the percentage of Brahman breeding increased, tenderness of steaks and roasts decreased. Since this first observation, several studies (Burns et al., 1958; Cole et al 1958; Huffman et al 1962; Luckett et al., 1975; Peacock et al 1980, 1982; Solomon et al 1981b; Adams et al., 1982) have found that meat from Angus cattle (steers and heifers) was more tender than meat from Brahman cattle. However, little work, if any, has been done to characterize the palatability of meat from intact males representing these diverse breed types. Electrical stimulation, for the most part, has been demonstrated to increase the palatability of beef (Stiffler et al 1982) and 58

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59 irriprove lean color and lean maturity as well as reduce heat-ring formation (McKeith et al 1981). Perhaps, with the aid of postmortem handling techniques, such as ES, some of the problems associated with using young bulls (especially of Brahman origin) for block beef may be reduced or completely alleviated. Therefore, this study was undertaken to characterize the palatability of meat from carcasses of young purebred Angus and Brahman bulls slaughtered at different live weights and to determine the effect of ES on the carcass quality-indicating factors and meat palatability. Materials and Methods Seventy-eight Angus and Brahman purebred bulls that were 10 to 18 mo of age were slaughtered at four weight groups: 60, 80, 90 and 100% of the average mature cow weight for the respective breed. Bulls were slaughtered over a two year period to determine the effects of breed, weight, year and postmortem electrical stimulation on carcass and meat characteristics of young bulls (table 10). Angus bulls grazed summer annual forage (millet) for three mo after weaning while Brahman bulls were fed, after being weaned, a concentrate diet to simulate gains achieved on forage by the Angus bulls. The 60% group of bulls from both breeds was slaughtered after this postweaning feeding period. The remaining bulls were then placed in a confinement feedlot and fed a shelled corn-protein supplement diet until they reached their designated slaughter weight. Slaughter weights were 293, 381, 412 and 463 kg for Angus and 316, 420, 463 and 516 kg for Brahman. Details about the diets, origin of bulls, production and carcass traits have been reported by Solomon et al. (1983). The right side of each carcass was stimulated with 500 volts (AC) for 20-2 sec impulses within 1 h after bleeding. The left side of

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60 TABLE 10. EXPERIMENTAL DESIGN^ % Mature weight^ Breed 60 80 90 100 Angus Year I 5 5 5 5 Brahman 5 5 5 5 Angus Year II 5 1 5 6 Brahman 5 6 8 2 All right sides from each animal were electrically stim1^ ulated (500 volts for 20-2 sec impulses). ^ Age ranged from 10 to 18 mo at slaughter. Percentage of the average mature cow weight for the respective breed.

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61 each carcass was not stimulated and served as the control. Electrical stimulation was performed by attaching cables to the stunning probes of a Boss Hog Stunner (Model 1004A). Metal probes on the ends of the cables were inserted into the round near the Achilles tendon and into the neck at the first thoracic vertebrae and adjacent to the ligamentum nuchae. All sides were chilled at 0-2 C for 24 h postmortem and then both sides from each carcass were ribbed. Quality grade factors, (USDA, 1975), in addition to lean color (7 = very dark red; 1 = dark pink), lean texture (7 = extremely coarse; 1 = very fine), lean firmness (7 = extremely soft; 1 = very firm) and presence of heat-ring (4 = extreme; 1 = none) were evaluated by University of Florida personnel. A 15.24 cm section of the short loin, starting at the 13th rib and extending approximately to the third lumbar vertebrae, was removed from both sides of all carcasses at two days postmortem. A 10.16 cm medial section of the bottom round muscle was also removed from both sides of all carcasses at two days postmortem. These boneless samples were wrapped with an inner coat of saran wrap and an outer coat of polyethylene freezer paper. They were held in a 0-2 C cooler until five days postmortem, and then placed in a -15 C freezer until being cut into sections for selected evaluations. The sections cut were 2.54 cm thick steaks from the short loin (figure 3) and 1.91 cm thick steaks from the bottom round. Two loin steaks/side were designated for sensory panel evaluation. One loin and one bottom round steak/side were allocated for WarnerBratzler shear force determinations. All the steaks were handled and cooked according to the procedure outlined by the AMSA (1978) guidelines.

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62 Posterior end Anterior end Figure 3. Location of samples from the short loin for various analyses.

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63 Loin steaks were broiled using a Farberware Open-Hearth broiler. Steaks were turned at 40 C internal temperature and removed from the broiler at 70 C. Internal temperature was monitored using copperconstantan thermocouples attached to a recording potentiometer. Samples (1x1x2.5 cm) were removed from steaks allocated for sensory panel and evaluated by an 8 member trained sensory panel for flavor (8 = extremely intense; 1 = extremely bland), juiciness (8 = extremely juicyi 1 = extremely dry), tenderness (8 = extremely tender; 1 = extremely tough) and amount of panel -detectable connective tissue (8 = none; 1 = abundant). Bottom round steaks were braised in an oven preheated to 177 C. They were removed from the oven once they reached an internal temperature of 85 C. Temperatures were monitored in the same manner as for the loin steaks. The loin and bottom round steaks designated for shear force measurements were allowed to cool to room temperature (25 C) before coring. A minimum of 6 cores (1.27 cm diameter) were removed from these steaks parallel to the muscle fiber orientation for shear force determinations using a Warner-Bratzler shear device. A 2.54 cm thick section from the short loin (figure 3) was used to determine fragmentation index and sarcomere length. Fragmentation index was evaluated using the procedure described by Davis et al. (1980). Sacromere length was determined by the laser technique outlined by Cross et al. (1981). A split-plot model was used to analyze all the response variables which may have been affected by ES. The model included fixed wholeplot effects for breed, weight group, year and their corresponding interactions. Subplot fixed effects for ES and the interactions

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64 associated with ES and the whole-plot effects were also included. Data were analysed by the regression procedure of the Statistical Analysis System (SAS, 1979). F-tests were used to determine the effect of treatments on the parameters under investigation. The Duncan's multiple range test (SAS, 1979) was used to test differences among slaughter weights. Results and Discussion Carcass Traits and Composition Details about carcass characteristics and composition of the bulls as influenced by breed, slaughter weight and year have been reported by Solomon et al. (1983). Generally carcasses from both breed groups were equivalent in composition even though Angus bulls were slaughtered at lighter weights. Quality Factors Results of the analysis of variance and subsequent F-tests for carcass and lean quality factors are summarized in table 11. Means for lean carcass quality factors by main effects of breed, weight group, year and stimulation treatment are presented in table 12. Lean maturity of the LD muscle were within the "A" maturity score for all carcasses. However, scores increased from the 60 to the 80% group and then remained constant (table 12). An interaction (P<.05) of breed and weight group suggested that the change in lean maturity over time v/as not the same in the breed groups (tables 11 and 13). Lean maturity scores for carcasses of Angus bulls representing the 60 and 80% groups were lower than those carcasses of Brahman bulls from these same v;eight groups, indicating more youthful color (table 13). However, at the 90 and 100% weights this

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67 TABLE 13. BREED BY WEIGHT GROUP INTERACTIONS^ FOR QUALITY FACTORS Breed Weight group, % Lean maturity Overall, maturity Marbl ing^ Qual itv grade Heatr ring Angus Brahman Angus Brahman Angus Brahman Angus Brahman 60 60 80 80 90 90 100 100 A^l a" a" A^^ J48 .56 A^' a12 A^2 A^5 A^^ A^l Tr^5 Pd^^ 03 89 Pd^^ SI 17 11.6 10.7 12.6 10.8 13.1 10.7 13.3 10.7 2.0 3.1 2.1 2.7 2.4 2.5 2.0 2.8 ^ Significant at the P<05 level. Refer to table 12 for codes.

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68 was reversed. Lean maturity was higher for Angus carcasses than for Brahman carcasses at these heavier weights, suggesting more mature lean color. Bone maturity scores (amount of bone ossification) were lower (P<.05) for Brahman carcasses than for Angus carcasses (table 12). These scores increased from the 60 to the 80% group, remained constant from the 80 to 90% group and then increased from the 90 to the 100% group. Bone maturity scores were lower (P<.05) for the carcasses from 29 the second year (A ) when compared to those from the first year 34 \ (A ). When bone and lean maturity scores were combined to get the overall maturity, the effect of breed and weight group were the same as those detected for lean maturity scores (tables 11, 12, and 13). Solomon et al (1981b) found that the lean from Angus heifers was more mature in color than that from Brahman heifers. However, no difference due to breed was observed for bone maturity. These authors did point out that the Angus heifers were chronologically 1 mo older at slaughter than the Brahman heifers. The heifers used in their study were fed three different planes of nutrition for 217 days. Furthermore, Solomon et al (1981b) observed that with increasing live weight at slaughter due to level of nutrition, bone, lean and overall maturity scores all increased. Marbling scores were higher (P<.05) for the carcasses of the Angus bulls than for those from the Brahman bulls (table 12). Marbling scores also increased from the 60% group to the 80% group and then leveled off. However, an interaction (P<.05) of breed and weight group was found for this characteristic. As shown in table 13, marbling score increased for the carcasses of Angus bulls as weight group

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69 increased but did not increase for the carcasses from Brahman bulls. Since carcass fatness was equal among the breeds in the different groups (Solomon et al., 1983), this lack of marbling increase in the carcasses from Brahman bulls suggests that these bulls did not have the same genetic ability to deposit intramuscular fat as the Angus bulls. Marbling score was found to be higher {P<.05) in carcasses the second year than the first (table 12). However, for both years the means for marbling score were within the "Traces" score. Carcasses from Angus bulls received higher (P<.05) quality grades than did those from Brahman bulls (table 12). A significant breed by year interaction (not presented in tabular form) for quality grade indicated that Angus carcasses from the second year received higher quality grades than those from the first year, whereas no difference in quality grades due to year was detected for carcasses from the Brahman bulls. The quality grades for the carcasses in the 90 and 100% groups were higher (P<.05) than those for the 60% group. Quality grade increased as weight group increased for the Angus bulls, but stayed constant for Brahman bulls. This would be expected since marbling score increased as weight increased, particularly for the Angus bulls. The mean values indicate that most of the carcasses were within the "Standard" grade. However, some of the carcasses from the Angus bulls had sufficient marbling to grade U.S. "Good." Previous research comparing Angus and Brahman cattle conducted by Luckett et al (1975), Peacock et al (1980, 1982), Solomon et al (1981b) and Adams et al (1982) indicated that Angus carcasses received higher quality grades because of superior marbling scores when compared to carcasses from Brahman cattle.

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70 No major difference (P>.05) due to breed type was observed for lean color or lean firmness. Lean firmness increased (decreasing score) from the 60 to the 80% group. This may be due to increased fatness firming up the muscle as weight increased. The majority of carcasses had firm, light cherry-red colored lean in the ribeye. Lean texture was affected by breed, weight group and year (tables 11 and 12). The lean from Angus carcasses was finer-textured than that from Brahman carcasses. Texture was finer for the 60% group than for the ether groups. However, all were acceptable, i.e., not coarse. A significant weight by year interaction (not presented in tabular form) for lean texture was detected. Lean from the second year group of bulls was slightly finer in texture than lean from the first year group in all the weight groups except in the case of the 60% group where it was just the reverse. Furthermore, bulls from the first year 60% weight group possessed the finest-textured lean for the entire two year study. The carcasses from Brahman bulls had more heat-ring (higher scores) than those from Angus bulls (table 12). As shown by the BxW interaction (tables 11 and 13), the greatest difference in heat-ring between breeds occurred in the 60% group. The magnitude of the heat-ring scores indicated that most carcasses showed evidence of heat-ring as expected from the lack of outside fat to retard surface chilling rate (Savell et al., 1978b). The general trend was for lean, bone and overall maturity scores, in addition to marbling scores and quality grades, especially for Angus carcasses, to increase with increasing carcass weight. No prevailing trends were observed for lean color, texture, firmness or heat-ring

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71 with advancing weight, except that lean from carcasses representing the 60% group was less firm {P<.05) than the lean from heavier weight carcasses. Differences in lean characteristics could be attributed to animal age differences. It appears from these data that only some of the problems normally associated with meat from young bulls were encountered, i.e., lower USDA quality grades and heat-ring formation. Other problems were absent: dark cutting muscle; coarse muscle texture with a dark appearance; and, exceedingly heavy carcass weights. Postmortem electrical stimulation improved (P<.05) lean maturity and, thus, overall maturity scores (table 12). This resulted in more youthful maturity scores being assigned at 24 h postmortem to sides which had been stimulated. Furthermore, stimulated sides had brighter lean color (P<.05) with a finer lean texture (P<05) than nonstimulated sides. These findings are in agreement with other ES studies (Riley et al., 1982; Savell et al 1982) where carcasses from young bulls were evaluated within 24 h postmortem. Savell et al (1978b) concluded that the accelerated glycolytic rate caused by ES enhanced the quality-indicating factors of the lean when evaluated at 18 to 24 h postmortem. Calkins et al. (1980) recognized that although ES had a significant effect on lean maturity and color at 24 h postmortem, beyond this time little difference, if any, was observed between stimulated and nonstimulated sides. Probably, this is why several scientists did not find any improvement in lean maturity and color associated with ES when lean characteristics were evaluated at 48 h postmortem (Grusby et al 1976; Strickland et al., 1979; Calkins et al 1980; Nichols and

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72 Cross, 1980). However, in a recent study by Crouse et al (1983), where they evaluated the effects of ES on carcass characteristics of young bulls at 48 h postmortem, these authors found that ES sides were lighter in color and exhibited more youthful lean maturity scores than control sides. A breed by stimulation treatment interaction (P<.05) was noted in the present study for lean color (figure 4 and table 11). Nonstimulated sides from Brahman carcasses had darker lean color than nonstimulated sides from Angus carcasses. Although ES improved lean color for both breeds, more of an improvement was detected for Brahman carcasses than for Angus carcasses. This suggested that muscle for the Brahman bulls was more reactive to ES than that from Angus bulls or that much of the darkness in lean color for Brahman carcasses was caused by rapid chilling and this effect was eliminated by electrical stimulation. Longissimus muscle from nonstimulated carcasses tended to be firmer than those from stimulated carcasses. This was not true for all weight groups, as shown by the interaction (P<.05) of weight groups and stimulation treatment (table 11). This interaction (not in tabular form) indicated that no difference in lean firmness between stimulated and control sides was observed for carcass representing the 60% group (both exhibiting moderately firm lean). However, as carcasses became heavier, lean became firmer only for the nonstimulated sides while remaining moderately firm for ES sides. Savell et al. (1978b) and Salm et al. (1981) reported that ES significantly enhanced the lean firmness and texture of beef. The present study as well as the study by Knight

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74 (1982) found that, in general, stimulation caused the meat to be finer in texture, but less firm than that from the controls. Even with the changes in lean characteristics induced by ES, no improvement (P>.05) in marbling scores or quality grades was detected (table 12). All the carcasses qualified for the USDA "Bullock" grade since maturities did not exceed A'^^'^. Stiffler et al. (1982), in summarizing data from research at Texas A & M University, reported that ES of beef carcasses increased marbling scores by 11% and, thus, increased quality grades. The effects of ES on marbling scores and quality grades are inconsistent. Some studies have shown an increase with stimulation; others show no change. Heat-ring formation was alleviated (P<.05) in the ribeye muscle of sides that had been stimulated (table 12). This decrease in heat-ring by stimulation was greater in carcasses from Brahman bulls than for those from Angus bulls (figure 4). Heat-ring is the appearance of coarse textured, dark colored lean on the outside of the exposed surface of the ribeye muscle which frequently has a sunken appearance near the outermost edge of its surface. This undesirable condition is seen most often in carcasses which have little subcutaneous fat cover (Savell et al., 1978b). Thus, a differential chilling rate between the outer and inner portion of the ribeye muscle results in the appearance of dark regions on the muscle surface. The outer portion chills faster and thus undergoes a slower glycolytic rate, pH decline and rigor onset than the inner portion of the muscle which is better protected (insulated) from cold temperatures. These dark areas are regarded as a disqualifying feature in the present carcass grading system, since if the USDA grader detects signs

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75 of incomplete chilling, such as heat-ring, the carcass cannot be graded. Electrical stimulation essentially eliminated this problem in the carcasses of the young bulls used in the present study. Due to the accelerated postmortem reactions associated with the use of ES, a more rapid color development and reduced heat-ring formation was observed which is in agreement with the studies reviewed by Smith et al (1980) and Stiffler et al (1982). Sensory Results of the analysis of variance and subsequent F-tests for sensory, shear force and histological characteristics are summarized in table 14. Means for sensory, shear force and histological characteristics of loin steaks and shear force values for bottom round steaks main effects are presented in table 15. Neither panel flavor nor juiciness scores for short loin steaks were influenced (P>.05) by breed, slaughter weight, year or stimulation treatment. Flavor and juiciness ratings for all treatment groups were scored as "slightly intense" and "slightly juicy," respectively, which is considered acceptable for these attributes. Loin steaks from carcasses of Angus bulls were rated more tender and contained less detectable connective tissue than those steaks from Brahman carcasses (table 15). Increasing slaughter weight from the 60 to 80% group was associated with an increase in steak tenderness and a decrease in detectable connective tissue for short loin steaks. The only exception was in the case of short loin steaks from carcasses representing the 80 to 100% weight groups used the first year (figure 5). In this instance, tenderness and connective tissue scores remained virtually unchanged between the 80 and 90% group, whereas tenderness

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76 o +-> to 0) o 5O CO s-M c X CO (/) 4-> U (U 3 h>Cn Q. r3 CJ o 3 SCT) CU > — OJ CO s QQ (U +-> CO CO CO CO (/> t/> CO oo CO u'i {yTyt CO 1/5 z: z z: z: 2: z: CO I/) CO to CO CO c/) -K z: 2: -)c 00 00 CO K Z CO CO X V Z3 o (/) ^ 10 (-> CT> O) 4-> c c +-> 0) 0 CO CJ /J (-) T3 s_ O) (O c s_ (/) (U •r0 &. -(-> 0 fO OJ +-> <+O) c 0 4(U I. sz SCJ ^ *-> 0 •r— (U > 0 -a C ra CJ E fO •r— c C OJ i. 0 (U c: =3 0 x: to s_ 4-> ^ 'rU1— CJ 00 1/1 -t-> 0 0 _l CQ •- c 0 C O) 10 0 O) s_ a' cu u> M c a 0 to •1— 0 +-> 0 to •rSC +-> •1— c 1/1 C 0 1— c X n X oo 2: TO c: • A I— X v" X II
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77 o O U3 C B 01 fo LTj o CT n o m kn ^ kn ^ ^ Q ja TJ ^ CM r vo CO c% CO 1^ ir> ir> ^ ^ o • ^ U3 o o CM vo r crv CO r~ o I/O lf> ^ ^ I— t CO vo a JO lo CM ^ I/) 00 c7\ o kn m IT) ^ ^ K£> ^ cn rCO Ln m LT) IT) in J3 o ^ ^ CM ^ CM ro cn lo m m m un ko vD ir> vo ^ A in CM PO CO CT> r** CO tn m ^ ^ lo -H CO c^ ^ o vo o^ in LO ro ^ CO ^ vo m m V ^ f— t ro m in in m vo f— in vo CO J3 CM VO m CO CO CO m in •a VO E 01 cn 1^ U1 Of VJ 1/1 vrt > i_ in u O if1c su O QJ GJ 1> V_ -O C r3 o c c o 13 Ol O ^ U_ ^ I — (_> t/> T3 v. .J m LiW O CO o V 0) U o o l s OJ at •-t E <0 C3>
l O •u i!-> ; c: >lT3 o Irt o > c= a 01 g TO • o u e a o -o M O U at X t+J <*>A u O) 4-> X O 1OJ X tII (U 01 t<*1^ u — • u C3 TO OJ c CJ 01 I. • C l_> CJ v OJ c: OJ O T3 3 CJ fO c OJ C =1 (U ro JZ OJ L. -•-••->-•-> o •M OJ II >> >i >i o > —.— .— i—t o ^ -o t/l c; a CJ c EES E i/t *T1 a CJ o u CJ O St. OJ *- M +j *j c r 01 1/1 X X X O CM s: 0) (U OJ c • Eg c: CJ J u M II 11 II ^ -*- o C7 E CJ o —1 CO 00 CO CO :i O CO TJ "O QJ CTiJ^ •—

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78 Year 1, tenderness O Year 2, tenderness Year 1, connective tissue Year 2, connective tissue so o O) c Q. >i io l/l c (U CO 60 80 Weight group, % 90 100 Figure 5. Effect of weight group and year on tenderness and connective tissue scores of short loin steaks.

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79 decreased and detectable connective tissue increased as carcass weight increased from the 90 to the 100% group. Perhaps this decrease in tenderness and concomitant increase in detectable connective tissue was associated with the increase in sexual development in these young bulls which is concurrent with an increase in collagen (a type of connective tissue) content and subsequent cross-linkage described by Cross et al (1982). Arthaud et al (1977) found steak tenderness to increase with increasing age (12 to 18 mo) and weight (314 to 453 kg) at slaughter; however, after this point meat tenderness decreased with advancing age and weight at slaughter. It has been proposed that connective tissue toughness in bulls, which inadvertently would affect meat palatability, may be linked to sexual development and may be subject to some hormonal function(s) in the animal (Boccard et al., 1979; Cross et al 1982). Carcass maturity scores indicated that bulls from the first year were physiologically more mature than those from the second year (table 12). Electrical stimulation had a significant effect on panel tenderness and detectable connective tissue scores (tables 14 and 15). With the use of ES, tenderness scores increased from "slightly tough" to "moderately tender" ratings. Connective tissue scores were improved from a "moderate" to a "traces" detectable amount. On the contrary, Riley et al. (1982), Savell et al (1982) and Crouse et al. (1983) reported that ES had essentially no effect on the palatability of steaks from USDA "Good" quality grade bulls with at least 7.6 mm subcutaneous fat cover or more. However, Riley et al (1982) did find that ES significantly improved the tenderness of steaks from USDA

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80 "Standard" and USDA "Good" grade bulls that had less than 7.6 mm fat thickness. The bulls used in the present study had an average quality grade of USDA "Standard" with 4.7 mm subcutaneous fat cover. The most dramatic and consistent effect of stimulation on panel tenderness and connective tissue scores was for steaks from the 60% group (figure 6). This group had the least amount of subcutaneous fat cover (2.2 mm) and, therefore, the longissimus muscle (short loin) may have undergone cold-induced shortening, resulting in meat toughening. In fact, in the present study, muscle fiber sarcomere length was considerably shorter (P<.05) from nonstimulated muscle representing the 60% group than from all the other groups (table 15). However, ES had no major influence (P>.05) on overall sarcomere lengths, although muscle from stimulated carcasses generally had slightly longer sarcomeres. The literature strongly indicates that ES alleviates the cold shortening type of tenderness problem in meat (Chrystall and Hagyard, 1976; Davey et al., 1976; Bouton et al 1980; Hagyard et al 1980; Eikelenboom et al 1981). Other research workers believe that benefits of ES are not solely related to the prevention of cold shortening. Postulated mechanisms include structural alterations of muscle fibers (Savell et al., 1978a; George et al 1980; Will et al 1980; Voyle, 1981; Sorinmade et al 1982), increased lysosomal enzyme activity (Sorinmade et al., 1978; Dutson et al., 1980) and decreases in the number or strength of the collagen cross-linkages (Judge et al., 1980). Stiffler et al (1982) recognized that the percentage of change in tenderness values caused by ES was quite variable, when the type of

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81 fif ^ ES, tenderness • Control tenderness ^ ES, connective tissue • Control, connective tissue -L 60 80 90 Weight group, % 100 Figure 6. Effect of weight group and stimulation treatment on tenderness and connective tissue scores of short loin steaks.

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82 beef being investigated was considered. They concluded that this source of variation was associated with the initial, or inherent, tenderness of the nonstimulated meat, especially from animals (steers and heifers) less than 42 mo of age (i.e., the greater the initial toughness, the greater the effect of stimulation). This may explain why £S had more of an effect on tenderness of steaks from the 60% group. Judge et al. (1980) claimed that ES lowered the shrinkage temperature of collagen by 0.6 C and that thermal stability of bovine intramuscular collagen may result from a diminution of collagen crosslinkages by ES. This may partially account for the lower (P<.05) amounts of connective tissue detected by the sensory panel in steaks from stimulated carcasses. Shear Force Short loin and bottom round steaks from Angus carcasses had lower shear values (P<.05) than those steaks from Brahman carcasses, except at the 80% slaughter point where this was reversed for loin steaks (figure 7). Loin steaks from carcasses of Brahman bulls showed a large decrease in shear force between the 60 and 80% weight groups, suggesting that this weight gain was associated with increased steak tenderness. Several studies (Luckett et al 1975; Peacock et al 1980, 1982; Solomon et al., 1981b; Adams et al 1982) have substantiated that meat from Angus cattle had lower shear values, implying more tender meat, than meat from Brahman cattle. However, Winer et al (1982) reported that beef derived from young bulls of widely divergent breed types, including Bos indicus x Bos taurus crosses, were not significantly different in tenderness.

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83 Weight group, % Figure 7. Effects of breed and weight group on shear force values of short loin steaks. J j

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84 The usual trend was for shear values to decrease as carcasses became heavier and fatter. However, shear values for short loin steaks from the first year had lower shear force values at the 60 and 80% weight groups than those from the second year (figure 8). After this, shear values increased from 80 and 90% and then remained the same from the 90 to 100% group, somewhat resembling trends for sensory scores discussed earlier. Nevertheless, meat from the first year group of bulls was generally more tender as indicated by lower shear values than meat form the second year group. This is in agreement with the findings detected by the sensory panel. Loin steaks from stimulated sides had lower (P<.05) shear values than those from control sides (4.31 vs 6.84 kg/1.27 cm, respectively), indicating a 37% increase in tenderness with the use of ES (figure 9 and table 15). These data pretty much agree with the findings detected by the sensory panel and also with previous research (Eikelenboom et al., 1981; Riley et al 1982) demonstrating a tenderizing effect of ES on meat from young, noncorpulent bulls. Meat from stimulated beef carcasses is, on the average, 15-46% more tender than that from nonstimulated carcasses depending on age, grade, and the nutritional status of the animal (Stiffler et al 1982). Again, the most dramatic and consistent effect of ES was for the shear values of steaks from the 60% group (figure 9). Since shear values exceeding 5.2 kg/1.27 cm core can be considered unacceptable in tenderness, short loin steaks for both Angus and Brahman bulls would be regarded as unacceptable or in some instances borderline in tenderness. The sensory panel results also confirm these findings. However, with the aid of ES, these tenderness problems were al leviated.

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85 Year 1 Weight group, % igure 8. Effect of weight group and year on shear force values of short loin steaks.

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86 o CM 0) o So s00 Oi JZ m 80 90 Weight group, % 100 Figure 9. Effect of weight group and stimulation treatment on shear force values of short loin steaks.

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87 Histological Longissimus muscles from Angus carcasses tended to have slightly longer sarcomeres (table 15) than those from Brahman carcasses, although this differ.ence was not significant. As carcasses became heavier, and subsequently fatter, sarcomere lengths increased. These differences in sarcomere lengths, although in some cases not significantly different, appear to be related to the amount of subcutaneous fat present, which may have protected the longissimus muscle from shortening due to cold temperatures during chilling as previously discussed. Longissimus muscles from the first year group had longer (P<.05) sarcomeres than those from the second year and thus may explain difference detected in shear values between these groups. Sarcomere lengths from stimulated sides appeared slightly longer than those from nonstimulated sides, however, this difference was not significant (P>.05). The effects of ES on sarcomere length are inconsistent. Some studies have shown an increase in sarcomere length with stimulation; others show no change. All four treatment groups (breed, weight groups, year and carcass electrical stimulation) had an effect (P<.05) on fragmentation index score. Steaks from Angus bulls, year one bulls and stimulated carcasses had lower fragmentation indices than steaks from Brahman bulls, year two bulls and nonstimulated carcasses, respectively. As slaughter weight increased, fragmentation index scores decreased. According to the coding system developed by Davis et al (1980), steaks with scores in these ranges (650 680) would be considered very tough. This was not apparent in the present study.

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88 The data from the present study suggest that meat from young bulls is generally tough and unacceptable but is improved if fed to heavier weights or if carcasses are electrically stimulated. Since shear values exceeding 5.2 kg/1.27 cm core are considered acceptable in tenderness, short loin steaks from both Angus and Brahman bulls would be regarded as unacceptable or in some cases borderline in tenderness. The sensory panel results also suggest borderline acceptability in tenderness for all groups. These data also suggests that the use of ES on carcasses from young bulls, especially for the types used in this study (averaging 414 kg live weight, 14.3 mo of age and 4.7 mm subcutaneous fat) eliminates several of the problems (e.g., tenderness, heat-ring formation, and coarse, dark colored lean) associated with these types of carcasses. Therefore, perhaps young bulls can be used successfully in the beef production system if, and only if, some kind of postmortem handling technique, such as electrical stimulation is used. However, while problems in the market place continue to exist because of the negative connotations associated with selling "Bull" beef, other alternatives will have to be utilized. Summary Seventy-eight purebred bulls (10 to 18 mo at slaughter) were used over a two year period to determine the effects of breed (Angus or Brahman), slaughter weight (60, 80, 90 or 100% of the average mature cow weight for the respective breed) and carcass electrical stimulation (500 volts, 20-2 sec impulses on the right side) on carcass and meat characteristics. Angus bulls grazed summer forage (millet) after weaning while Brahman bulls were fed to simulate gains achieved on

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89 forage by Angus bulls. Bulls were than placed in the feedlot for finishing to their designated slaughter weight (2S3, 381, 412, and 463 kg for Angus and 316, 420, 463, and 516 kg for Brahman). Carcasses from Angus bulls received higher quality grades (St"*" vs St") than those from Brahman bulls. Heat-ring formation and lean color problems normally associated with bullock carcasses were either eliminated or reduced by stimulation. Meat from Angus bulls was more tender than that from Brahman bulls as indicated by higher sensory panel scores for broiled loin steaks and lower shear values for braised bottom round steaks (4.96 vs 5.58 kg). However, a breed by weight group interaction (P<.05) was observed for loin steak shear values. At the 80% weight group, steaks from Brahman bulls had lower shear values than those from Angus bulls (6.31 vs 7.19 kg). For the other weight groups, shear force values for loin steaks from Angus bulls were lower than those from the Brahman bulls. Increasing slaughter weight from 60 to 90% was associated with an increase in panel tenderness scores for loin steaks. However, from 90 to 100% no change was detected. Stimulation increased the tenderness of loin steaks as determined by both panel scores and shear values (6.84 vs 4.31 kg) and of bottom round steaks (5.27 vs 4.84 kg shear force)

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STUDY 3 GROWTH TRAITS, CARCASS TRAITS AND MUSCLE DEVELOPMENT CHARACTERISTICS OF PUREBRED ANGUS AND BRAHMAN BULLS Introduction Animals from different genetic (breed) backgrounds have been reported to differ in growth characteristics and composition (Ashmore and Robinson, 1969; La Flamme et al 1973; Powell and Aberle, 1975; Harbinson et al 1976; Solomon et al 1981a, 1981b). However, in these studies the animals being evaluated were compared at the same endpoint (e.g., age, live weight or days on feed). Perhaps these differences would be mitigated had the animals been compared at some common stage of physiological maturation. The problem is that, as yet, no method exists which successfully identifies what point in the growth cycle the individual animal is in, without having to slaughter the animal Allen et al (1974) referred to physiological maturity as the relative stage of development of body processes, functions and composition of an animal. Boggs and Merkel (1979) described it as the point of maximum length of long bones and a leveling off of muscle growth, at which point there is an increase in fat deposition. Physiological maturity may occur at different chronological ages. Animal tissues undergo changes as animals advance in age. Thus, characteristics of various tissues such as ossification of cartilaginous areas, color of lean, changes in dimensions of anatomical units, and chemical composition have been used as indicators of physiological 90

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91 maturity. However, in meat animals these indicators, which are currently in use, do not develop uniformly within or between individual animals of the same chronological age (Boggs and Merkel 1979). Furthermore, since these indices are usually obtained after the animal is slaughtered, much time and money are already expended in growingfinishing the animal prior to the point at which the evaluation is made. In fact, if we have exceeded or fallen short of the optimum slaughter potential or physiological maturity of the animal, it is now too late to make any corrections. Since our goal is to slaughter animals when they reach their optimum slaughter potential, which is the point where they have maximum amount of lean tissue and a minimum amount of fat to assure quality and acceptability, then the need for an objective method to assess the optimum slaughter potential or point of physiological maturation of an animal is evident. Therefore, the objectives of this study were 1. to characterize the growth and developmental changes occurring in young bulls with special emphasis placed on the longissimus muscle; 2. to evaluate the use of slaughtering at similar percentages of the mature cow weight as a technique for comparing bulls, of such diverse origins, on an equal compositional basis; and 3. to ascertain the plausibility of histologically and (or) biochemically classifying animals relative to their optimum slaughter potential by the use of skeletal muscle fiber characteristics and (or) associated properties of muscle nucleic acids.

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92 Materials and Methods Thirty-eight purebred bulls (10 to 17 mo at slaughter) were used to determine the effects of breed (Angus or Brahman) and slaughter weight (60, 80, 90 or 100% of the average mature cow weight for the respective breed) on carcass composition and selected histological, biochemical, and compositional growth characteristics of the LD muscle (table 15). The dam's mature weights for the respective breeds were 456.3 kg for Angus and 515.3 kg for Brahmans. The fall -calved Angus bulls grazed summer annual forage (Tifleaf-1 Millet) for three mo after which bulls representing the 60% group were slaughtered. The remaining Angus bull calves were then placed in a confinement feedlot and fed a shelled corn-protein supplement diet until they reached their appropriate slaughter weight. Winter-calved Brahman bulls, after being weaned, were fed to simulate gains achieved by the Angus bulls on forage. After slaughtering the Brahman bull calves representing the 60% group, the remaining bulls were fed to their designated slaughter weight in a confinement feedlot on the same diet as the Angus. Details about the diets, origin of bulls, production and carcass traits have been reported by Solomon et al (1983). The bulls used for the present study represent the second year group of bulls evaluated by Solomon et al (1983). Bulls were slaughtered when they reached or came close to their designated target weight. Actual live weights at slaughter for Angus bulls were 293, 396, 411, and 469 kg and for Brahman bulls were 307, 427, 464, and 520 kg. After slaughter, carcasses were chilled at 0-2 C for 24 h, evaluated and sampled. The left side of each carcass was ribbed between the 12th and 13th rib and quality and yield characteristics were evaluated by University of Florida personnel.

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93 TABLE 16. EXPERIMENTAL DESIGN % Mature weight*^ Breed^ 60 80 90 100 Angus 5 1 5 6 Brahman 5 6 8 i Age ranged from 10 to 17 mo at slaughter. Percentages of the average mature cow weight for the respective breed.

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94 The separable lean, fat and bone components of the 9-10-11 rib section from the right side of each carcass was used to predict carcass composition using the equations developed by Field (1971). Details on the removal and handling of these rib sections have been reported by Solomon et al (1983). The entire longissimus, semitendinosus (ST), and psoas (PM) muscles from the left side of each carcass were physically removed, trimmed of external fat and connective tissue, weighed and measured. Measurements obtained were the length of the entire muscle from anterior to posterior insertion and the circumference at the widest location on each muscle. These three muscles were selected since they were considered to develop at a rate similar to that for the total body (Butterfield and Berg, 1966). Samples (approximately 1x1x5 cm) for muscle histological and biochemical characterization were obtained at 24 h postmortem of the LD muscle from the left side of each carcass at the 12th rib location (after measurements previously described were obtained). These samples were immediately covered with talc powder, then frozen and stored in liquid nitrogen. Because the LD muscle is considered to develop at a rate similar to that for the total body (Butterfield and Berg, 1966) and since this muscle represents a considerable proportion of the muscular tissue in meat animals, it was selected to study the progressive changes in skeletal muscle during growth. 3 A 1 cm section from each of these frozen samples was mounted on a cryostat chuck with a few drops of water so that muscle fibers were perpendicular to the cutting blade and allowed to equilibrate to -20 C. Sections (12 to 14 m thick) were cut with a Damon International CTF™ Microtome-Cyrostat. Serial sections were mounted on glass

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95 microscopic slides, allowed to air dry and stained with NADH-TR (Engel and Brooke, 1966) and myofibrillar ATPase reacted at alkaline pH (Guth et al., 1970). A cover slip was then placed over the tissue section using glycerol jelly to fix it into place. The slides were observed with a Nikon Photomicroscope. Several fields on each serial section stained with NADH-TR and myofibrillar ATPase were photographed at XIO with the bright field setting cn the light microscope. Also within each roll of film, a stage micrometer with .01 mm graduations was photographed. Enlarged photomicrographs (8.8 X 12.5 cm) were used to analyze and differentiate muscle fiber types. Fibers were classified according to Ashmore and Doerr (1971) on the basis of stain reactions into red (3R), intermediate (aR) and white (aW) types. All fibers inside a bundle containing 50 to 75 fibers were counted and then measured for cross-sectional area using a Numonics Model 1250 Planimeter. In addition to fiber area, the percentage of fibers of each of the three types was calculated by counting the total number of each type and dividing by the total number of fibers counted. Also from the stored, frozen LD samples, approximately 3 g of tissue was removed and minced with a razor blade. One gram of this minced tissue was homogenized in 20 ml ice cold .14 M KCl at 0-2 C using a Polytron homogenizer (Brinkmann Instruments) for 90 seconds. Aliquots of the homogenates were taken for analysis of RNA and DNA by procedures described by Sarkar et al. (1977). RNA and DNA were quantitated with orcinol and diphenylamine reagents, respectively. Another LD sample (2.54 cm thick), caudally located to the sample removed for histological and biochemical assays, was also removed.

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95 finely ground and thoroughly mixed. Chemical determinations (moisture, ether extractable lipid and protein) were performed (AOAC, 1980 procedures) on these longissimus samples. Protein was determined as total nitrogen ( Semi autona ted method, AOAC, 1980) x 6.25. Data were analyzed by the regression procedure of the Statistical Analysis System (SAS, 1979). A 2x4 factoral model involving breed and weight groups was used to analyze all response variables. F-tests were used to determine the effect of treatment on the parameters under investigation. The Duncan's multiple range test (SAS, 1979) was used to test differences among slaughter weights. Results and Discussion Least-squares means for production and carcass traits are presented in table 17. Angus bulls were approximately three weeks younger and 38 kg lighter at slaughter than Brahman bulls, which was expected due to the nature of the experimental design that took into account differences in maturation rates due to breed. A significant breed by weight group interaction was observed for age at slaughter (table 18). Increasing weight was associated with a continual increase in chronological age for the Angus bulls only. Brahman bulls representing the 80 and 100% groups were older than the Brahman bulls representing the 60 and 90% groups. The change in diet composition discussed by Solomon et al (1983) probably would account for these differences. A BxW interaction (P<.05) was detected for average daily gain (tables 17 and 18). Brahman bulls tended to grow more rapidly at the heavier (90 and 100%) weights than the Angus bulls and, consequently, reached their final slaughter weights in less time than the Angus bulls. Even though the Brahman bulls were always chronologically older

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93 +-> o (U c o o — L. ro IS V) 1/) 4-> +J O. c •f— S. 0 u Q. v% u 0 0 Q. •—1 3 l/t fC 4-* c: c 0 l-> 14(tJ > X to 0) • •-> 0 0 1— ^ ^ — 1 CJ M r— — 4 <0 •rI/) C f to (O OJ 1 E •rU. • (O l/l w O) c 0 ^ 0 1 1 •r<0 k> XI sTO A 10 4-> -> (I) Q. •rS Q.% 0 II 1— +J (U OJ C Sr— S> fO SO) 0 a> U X) -11/1 Mc i/J -I— 4-> T3 c c ro — C T0 cn E U-) •10 *r•f— 0 0 > +- to IT3 • 0. CU > 0 cu rtJ ^ 1 — u II +3 +J cn l/l CD •rC 3 OJ >> u ai->z: C -1c I/) •r0 +J C 4u fO 4X3 -0 (O ^ "O LO OJ -r0 iSQJ 0 xn "o a +-> Q. ra i-J cn ro = 0 V -0 fO •rCX Sr— II JC T3 u GJ (O 0 cu II > > TD f LU n. d) a. <)c CD ^

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99 TABLE 18. BREED BY WEIGHT GROUP INTERACTIONS^ FOR AGE, AVERAGE DAILY GAIN, CARCASS MATURITY AND RIBEYE AREA Breed Weight group, % Age, d ADG^ Maturity^ Lean Bone Ribeye ^ area, cm Angus Brahman 60 60 342.0 352.4 .67 .68 a32 54 A^^ A2 59.1 50.8 Angus Brahman 80 80 439.0 492.0 1.00 .98 ,50 52 A^^ a'^o 23 67.7 68.4 Angus Brahman 90 90 454.6 475.8 .99 1.19 .38 A^2 21 67.2 73.9 Angus Brahman 100 100 477.5 492.0 1.19 1.27 .55 .53 73.2 77.4 ? Average daily gain, kg/d. See table 17 for codes.

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100 than the Angus bulls, the Brahman bulls spent less time in the feedlot than did the Angus bulls when fed to the heavier weights. These differences were probably related to the modification in diet composition. Breed had no significant effect on subcutaneous fat thickness, ribeye area, or predicted composition of the carcasses. This is contrary to previous reports by Luckett et al (1975), Solomon et al (1981b), Adams et al. (1982) and Peacock et al (1982). These authors observed that Angus cattle (steers and heifers) were fatter, but also had larger ribeye muscles than Brahman cattle when compared at equal slaughter weights, ages, or days on feed. A BxW interaction (P<.05) was detected for ribeye area (table 17) in the present study. Ribeye area, as a measure of muscling, was larger in Brahman carcasses than in Angus carcasses, except at the 60% weight (figure ICa). At these lighter weights, Angus carcasses had bigger ribeyes than Brahman carcasses. However, when ribeye area is expressed on a constant (100 kg) carcass weight basis. Brahman bulls actually had smaller ribeyes (15%) than Angus bulls. Thus, the differences due to breed for ribeye area were, in fact, due to differences in carcass weights Significant BxW interactions were also observed for lean and bone maturity scores (tables 17 and 18). Lean maturity scores for the 60, 80, and 90% groups were higher for Brahman carcasses than for Angus carcasses, indicating more mature lean color for Brahmans. However, at the 100% weight this was reversed. Bone maturities (amount of bone ossification) revealed that Brahman bulls were slightly less mature (physiologically) at slaughter than Angus bulls, even though they were chronologically older. However, Angus bulls in the 60% group produced

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Figure 10. Growth of the longissimus muscle in relation to breed (Angus • • ; Brahman *) and weight group (WG) percentages.

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102

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103 carcasses that were less physiologically mature than those from the Brahman bulls. Solomon et al (1981b) found that Angus heifers were physiologically more mature, as measured by lean and bone maturities, than Brahman heifers when fed different planes of nutrition for 217 days. These authors did point out that the Angus heifers were chronologically one mo older at slaughter than the Brahman heifers. As slaughter weight increased, all the bulls tended to grow more rapidly and subsequently deposit more fat {%) and less lean (% fatfree). However, the rate at which these carcass components were changing appeared to be slowing down at the heavier weights (table 17). The general trend was for lean and bone maturity scores to increase with advancing weight, suggesting progressing maturation physiologically. These findings agree with previous research by Solomon et al (1981b). The most obvious difference observed between the two breeds was in marbling scores. Carcasses from Angus bulls consistently had more marbling (P<.05) than those from Brahman bulls, suggesting a situation probably resulting from selection practices over the years. However, based on carcass composition, the data from this study suggest that the bulls, although they may have distributed their fat differently, were slaughtered at similar points in their growth cycles and, thus, were compared on an equivalent compositional basis. Least-squares means for longissimus, semitendinosus and psoas muscle measurements are listed in table 19. No difference (P>.05) in the percentage of LD, ST, or PM per side weight was observed between breeds. However, all three muscles were heavier in Brahman carcasses than in Angus carcasses, reflecting heavier carcass weights for Brahmans.

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104 to CO o a m CO I— I to to (0 o _J UJ to S Q. d: o e> LxJ I— I _l UJ O 3 to ZD Q s: z a: o Q 00 QC 2= CO s: CO to to U.I UJ q; _j u <0 o o o en Cl o SC3 CD o O OJ iCQ Scn c Qj o t— t tn cn ix> 00 in o • • • • CO tn ^ CO cn u -o -o o tn 00 vo 00 cr> •— < • • • • ro afo 00 CO J3 o ja CO O CO 00 tf> C\J 00 o • • • • CO ^ O 00 CO O J3 -Q LT) cn CO ^ • • • • CO CO cn 1-^ CsJ CT> O cn CT> 00 Lf) o • • • • CO 'iCM 00 CO X> J3 oo tn CM vo I — ^ I— I IT) • • • • CO •tjo •-< 00 CO O OJ O O) to ^ O U3 3<— t CO i-< CM 00 CM CO CO o ja "O o "O CO CM "vl<— I tn o C7> 00 • • • • t- CM r-^ O CO CO u ^ u ja tJ cn LO o •— • f->. CO CO CM O J3 jQ J3 CM O O ^ 1— t I CO vo CO CM u CM cn ID c— I cn t— I • • • 1— 1 CM vT) O CO CO J3 in cn CM to lO ^ 00 l£5 00 CO CM J3 -O -O tJ i£> r-^ 00 CM CO CM CO CM • • • • I— I CM tf) CM o ja u o u cn CO cn ^ CX3 00 O CO r-H LO CM o u o ja ^ o XI I— I CO lo cn o iTi CO CM o tn CM a ja ja ^ CM t-l CM CM t— 1 cn I— t in cn u 00 .— I CO cn cn CM CO cn • • • • f-H CO o tn CM JQ O CO 00 00 cn cn CM in CM O in CM E E E o o o (1) • OJ • 0) +-> tj ^/) -t-> u 4-> o 35 c =J S c: c: E QJ CO E a E QJ 1/5 CD O 1O 3 c: +-> 3 M 3 to 4CD O O c I/) O • EI icn +J O) -ra -rn3 +J QJ -r3 _I t_> E a* 3 _j o O 3: _1 <_3 o cu lO _j to Ci. Sra 10 +-> CL u to sOJ CL c: Q) SOJ cn c: ita (U ja CL O i~ o 0) c •r— rtJ B OJ QJ — ^ o E in (O o QJ to • V QJ cu Q-C +-> l/J +-> {= c: c O O QJ •rs-M U) QJ O C 4(O n3 i+iQJ -rOJ 4-> c QJ XJ o 2: o

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105 The LD muscle was longer in carcasses from Brahman bulls than in those from Angus bulls. Abraham et al (1968), as cited by Carpenter (1973), found that length of loin was slightly longer in carcasses from Brahman steers which weighed 54 kg less (hot carcass weight) than those from Angus steers. Neither muscle circumference for all three muscles, measured at the widest location, nor muscle lengths for the ST or PM were affected (P>.05) by breed type in the present study. As carcasses became heavier, all three muscles became heavier, longer, and thicker. No definitive trends were detected for percentages of LD or ST per side weight. Thus, in all probability, these two muscles were probably growing at a rate similar to that of the total carcass. However, for the PM muscle, its percentage per side tended to decrease with increasing carcass weight, suggesting that this muscle may have been growing at a slower rate than the total carcass. This observation disputes the findings of Butterfield and Berg (1966), who indicated that the PM muscle has a high-average growth impetus, similar to that of the LD and ST muscle and the total carcass. Nevertheless, it appears that comparing Angus and Brahman bulls, on the basis of percentage of dam's mature weight for the respective breed, minimizes differences often encountered because of dissimilarities in physiological growth and maturation between these breeds. The majority of DNA is found in the cell nucleus and RNA in the nucleolus. These nucleic acids are carriers of genetic information in the cell, in addition to having structural and metabolic functions (Lehninger, 1975). The amounts of DNA and RNA in muscle are a measure of the numbers of cells (nuclei) and ribosomes, respectively, that are present (Burleigh, 1980). Several authors have demonstrated that

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106 measurement of total protein, DNA and RNA and their respective ratios reflect changes in cellular growth of tissues (Enesco and Leblond, 1962; Winick and Noble, 1965; Robinson, 1969). Since the amount of DNA per mammalian diploid nucleus is constant (6.2 pg), DNA can be used as an index of cell (nuclei) number in tissues composed of mononucleated cells (Vendrely, 1955). Furthermore, the ratio of protein to DNA (i.e., cytoplasm to nucleus) has been shown to provide an index of cell size (Robinson, 1969). Enesco and Leblond (1962) revealed that increases in both of these constituents contributed to the growth of young rats. Thus, a distinction between growth caused by hyperplasia and that contributed by hypertrophy can be obtained by comparison of total protein, DNA and RNA and their respective ratios for tissues with mononucleated cells. In tissues composed of multinucleated cells, such as skeletal muscle, one cannot calculate cell numbers and size from DNA and protein concentrations. However, Cheek et al (1971) suggested that in skeletal muscle the amount of DNA is indicative of the number of nuclei in muscle and the proteinrDNA ratio measures the average amount of cytoplasm associated with one nucleus within the muscle fiber, which may be of significance in growth of muscle fibers. Longissimus muscle chemical composition and nucleic acid properties are presented in table 20. These values are given on a total wet tissue (muscle) basis (g/muscle). The LD muscle from Brahman bulls contained 26% more total protein, 19% more total DNA and, for the most part, 77% less total lipid than those from Angus bulls. However, at the 80% weight group, the LD muscle from Brahman bulls contained 18% more intramuscular lipid than those from Angus bulls (figure 10b).

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107 ZD Si I— t o _l LU 00 LU LU O. O a. Q < tO CQ CO _1 < o LU CO o CO o (U 43: o o o o. o s01 SI o CTOO CQ 0) s00 o c: fO E ea SCQ CD c: •4-> oo 00 CO 00 K -a -a 0 0 0 -0 f3 CO CO CO CM en CO CM CO vo 0 r— 1 00 LO CM vo n CO LO VO CM CO CO r— i 0 0 0 0 CM I— 1 1— ( 00 vo LO If) CM I— 1 t— 1 CM CO CM vo Lf) CM CO vo C7> CM CO 1 — 1 JD X) JD JD JD JD VO 1—1 >— ( CM CO 0 0 1 — 00 vo CM 00 00 0 in CO t— 1 to rO ra ro (O CJ t — 1 0 CO CM •—1 00 vo CT> in VO CO :!vo CM CO t— 1 CM 10 t-H CO 1^ vo CM I— 1 JD ns JD CM vo t-H VO CO CM Lf) CM 10 LO 00 0 CM LO a\ CvJ VO VO CM CO t— I cr> vo 1 — 1 0 CO 00 CM m CM CT> cn CO CO CO t— 1 I— 1 vo CM CO cn 0 t— ) LO I— 1 CO .— 1 c +-> o SCL -M o CD o •IQJ I— Q en fO rO ra +J +J +J --> O O O O SI— I— HQ. Q z: DC c a; +-> o sO) S(T3 I/) M Q. Su S c (U i. O) vV*•r~ "O C7> •rs_ n3 (U ri •r— 0) E re cu x: +-> c: 0 CL 10 rj 0 0 SA cn Q. -> u •4-> (U vtfO if0 (L) • 'r' d) MC r— T— u c n3— I/) CD E LO 13 -r0 E t/J ro • ^ C V cn 0 c 0. c x: I/) II -u 4-> ••1— c: t/> V/) S o) lo z: JD C MOJ ••• na 43 LO
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1C8 Increasing slaughter weight resulted in a concomitant increase (P<.C5) in total protein and intramuscular lipid for the LD muscle (table 20), which was expected since these values are based on total muscle weight which also increased. The rapid and continuous increase, in intramuscular lipid from the 80 to the 100% weight group associated with the LD muscle from Angus bulls (figure 10b), may have been attributed to both hyperplasic and hypertrophic growth of the adipose cells (Johnson, 1978). Total DNA only increased up to the 90% weight and leveled off. This was apparent for both breeds. These findings are in agreement with work conducted by Powell and Aberle (1975), Harbison at al. (1976), and Trenkle et al. (1978). The differences observed for muscle DNA content due to breed and weight group suggest that the LD muscle from Brahman bulls and heavier weight bulls contained more nuclei but not, in all probability, more muscle fibers than those from Angus bulls and lighter weight bulls. In fact, since postnatal skeletal muscle growth is characterized by an increase in muscle cell size (hypertrophy) rather than an increase in the number of cells (hyperplasia), these differences in DMA content were most likely associated with a difference in muscle nuclei number and (or) satellite cell number (MacConnachie et al 1964; Moss and Leblond, 1970). Swatland (1971) concluded that hypertrophy in skeletal muscle fibers is accompanied by an increase in the number of nuclei. This increase in nuclei results from fusion with proliferative satellite cells (Swatland, 1971), In addition, since the -connective tissue content of bovine muscle is relatively high (Boccard et al 1979), it may be assumed that connective tissue cells also contributed to the

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109 amount of DNA determined for the LD muscle. This may be true, even though connective tissue contains relatively few cells and, hence, relatively few nuclei. It is also a possibility that the rapid and continuous increase in intramuscular lipid accretion (figure 10b) associated with the Angus bulls may have contributed to the differences in DNA content observed between breeds. Perhaps this growth of adipose cells, conducive to hyperplasic and hypertrophic growth (Johnson, 1978), masked or diluted the biochemical growth properties of the muscle. Total RNA, proteinrDNA, and RNA:DNA ratios were not significantly influenced by genotype. However, in the case of total RNA content (P<.06) it was approaching significance. The LD muscles from Brahman bulls appeared to contain more RNA and possess slightly higher protein: DNA ratios than those from Angus bulls (table 20), but not significantly so. A BxW interaction (P<.05) was detected for the ratio of RNA to DNA. The RNA:DNA ratio was generally higher in Brahman LD muscles than in Angus LD muscles, except at the 100% weight group, where it was slightly lower (figure 10c). In multinucleated cells, such as skeletal striated muscle, the ratio of protein to DNA is indicative of relative amounts of cytoplasm associated with one nucleus (Robinson, 1979; Cheek et al 1971). Cytoplasm per nucleus provides an index of the cell numbers and cell size and, when measured during growth, an index of the rate of cellular hyperplasia and hypertrophy. In the present study, although proteinrDNA ratio tended to be higher in Brahman bulls than in Angus bulls, no significant difference was actually detected. Thus, the consistency of proteinrDNA ratio implies that the development of this muscle from

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110 Brahman and Angus bulls was similar and that the larger (heavier) muscles associated with Brahmans were not due to an increase in the cytoplasm per nucleus. Muscles from Brahman bulls probably contained more nuclei and more cytoplasm than those from Angus bulls with the ratios remaining practically the same. Based on the DNA content and protein:DNA data (table 20), growth of the LD muscle from the 60 to the 90% weight group was characterized by an increase in cellularity (nuclei) as well as by an increase in cell size. After the 90% weight, growth of the muscle appeared to take, place by an increase in cell size alone, and not by increasing cellularity. However, it cannot be deduced that the proposed increase in cellularity associated with muscle growth between the 60 and 90% weight groups was due to an increase in number of muscle cells because of the limitations associated with interpretation of nucleic acid values in skeletal muscle discussed previously. If RNA:DNA ratio is indicative of protein synthesizing capacity (Winick and Noble, 1965; Millward et al 1973), then perhaps it also might be regarded as an index of growth potential (Sarkar et al 1977). Based on RNA:DNA ratio. Brahman bulls in this study had the capacity to synthesize more protein than Angus, except at the 100% weight (figure 10c). At these heavier weights, it appeared that Brahman bulls had just about reached their optimum muscle growth potential, whereas Angus bulls may still have had an appreciable capacity to synthesize protein. However, upon evaluating an additional group of Angus bulls (Solomon, unpublished data) slaughtered at 110% of the mature cow weight (507 kg), it was determined that the Angus bulls had, in fact, reached their optimum muscle growth potential at the 100% weight.

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Ill Protein:RNA ratio was not affected (P>.05) by breed; nevertheless a BxW interaction (P<.05) was detected (figure lOd). Increasing live weight was generally accompanied by a decrease in protein:RNA ratio. This decrease appeared to be faster in the LD muscle from Angus bulls than in Brahman bulls. The distribution and areas of muscle fiber types in the LD muscle are shown by breed and weight group in table 21. Percentages and areas for all three muscle fiber types were not influenced (P>.05) by breed. Nevertheless, Angus bulls tended to have a few more aW fibers and a few less aR fibers than Brahman bulls. Dreyer et al (1977) evaluated the semimembranosus and semitendinosus (dark and light sections) from Afrikaner (a late maturing breed) and Friesland (an early maturing breed) bulls fed ad libitum and slaughtered at similar ages from birth to 24 mo. In all three muscles studied, these authors observed that the Friesland bulls had more aW fibers and fewer aR fibers than the Afrikaner bulls when compared at similar chronological ages. Solomon et al (1981a) reported that early maturing Finnish Landrace crossbred lambs had more aW fibers and fewer aR fibers in both the longissimus and semimembranosus muscles than late maturing Suffolk crossbred lambs when compared at similar slaughter weights. They suggested that breed, or more specifically physiological maturity, may have contributed to a shift from a R to aW fibers during growth. This may explain why only minor differences in fiber populations were detected due to breed in the present study, since this study was designed to compare bulls from two diverse breeds at similar stages of growth and maturation. Moreover, the results for carcass characteristics and compositional parameters (table 17) discussed previously

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113 suggested that the bulls v/ere slaughtered at similar points in their respective growth cycles. All three muscle fiber types were slightly larger in Brahman bulls than in Angus bulls, although no significant difference was detected. In a report by Guenther (1977), Angus steers had larger fiber diameters than Charolais steers when compared at similar ages from 1 mo to 15 mo. The three types of muscle fibers were not differentiated in their study. Dreyer et al (1977) found that Friesland bulls had larger fiber diameters than Afrikaner bulls when compared at similar ages from birth to 24 mo. Johnston et al (1975) presented evidence which indicated that Charolais steers had slightly larger fiber diameters and areas than Angus steers for all three muscle fiber types when steers were fed for the same length of time. They also pointed out that steers representing both breed groups were of similar age; however, they failed to mention their actual age. Guenther (1977) reported that the variation in total amount of muscle in cattle of different maturation rates and body sizes (Angus vs Charolais) was due to differences in the total number of muscle fibers rather than the size or diameter of muscle fibers. Similar conjectures were made by Ashmore and Robinson (1969) and Burleigh (1980). Total number of muscle fibers was not calculated in the present study. The percentage of aR fibers decreased while the percentage of aW fibers increased with increasing live weight (table 21 and figure 11), thus an increase in the conversion (%) of R to aW fibers. Ashmore et al. (1972) evaluated porcine, ovine and bovine muscles histochemically to determine growth patterns and concluded that qR fibers have the capacity to transform into aU fibers. Transformation is primarily

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114 1 I • Weight group, % Figure 11. Effect of weight group on the percentage of aR and aW fiber types in the longissimus muscle.

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115 concerned with changes in energy-producing enzymes, and is accompanied by a rapid increase in fiber size. Furthermore, they found that muscle size is directly proportional to the degree to which aR fibers transform into aW fibers. These authors also suggested that the aW fibers may conceivably reach their full growth potential later in life or at heavier body weights than either aR or BR fibers and thereby delay the onset of the "fattening phase" of growth. As slaughter weight increased, all three types of muscle fibers in the LD increased in size. This finding agrees with those of Dreyer et al. (1977) and Guenther (1977) who studied bovine muscle and Solomon et al. (1981a) who studied ovine muscle. It would appear from the results of the present study that physiological maturation may have affected the degree of conversion of aR to aW fibers (table 21 and figure 11). The cross-over point where the percentage of aR fibers equaled that of the aW fibers occurred just prior to reaching the 80% slaughter weight. Based on RNA:DNA and protein:RNA ratios (figure 10c and d), at approximately the same point on the growth curve, LD muscles from these bulls began to rapidly synthesize protein. The amount of muscle fiber conversion began to slowly level off after the 90% weight group which also was true for the capacity to synthesize protein. Thus, from these observations, it would appear that the LD muscle had just about reached its optimum growth potential, which means the remaining growth associated with the muscle would be in fat accretion. In conclusion, these results suggest that gross, histological, and biochemical characteristics of the LD muscle appear to relate to growth traits and carcass composition in young bulls. Various differences in

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116 carcass and muscle characteristics often encountered when comparing animals from different breed origins at the same endpoint (i.e., age, live weight or days on feed) were eliminated or minimized because differences in physiological growth and maturation were accounted for. Hence, chronological age is not an important factor in determining the optimum slaughter potential and final cellularity of skeletal muscle in cattle. Moreover, it would appear based on the results from this study that morphological and biochemical evaluations of skeletal muscle (i.e., the degree of conversion of aR to aW fibers and changes in nucleic acid properties during postnatal growth) successfully identifies what point in the growth cycle the animal is in. Summary Thirty-eight purebred bulls (10 to 17 mo at slaughter) were used to determine the effects of breed (Angus or Brahman) and slaughter weight (60, 80, 90 or 100% of the average mature cow weight for the respective breed) on growth traits, carcass traits and selected histological, biochemical and compositional growth characteristics of the longissimus muscle. Angus bulls grazed summer forage after weaning whereas Brahman bulls were fed to simulate gains achieved on forage by Angus. All bulls were then placed in a confinemeni feedlot for finishing to their appropriate slaughter weight (293, 396, 411 and 469 kg for Angus and 307, 427, 464, and 520 kg for Brahman). Histological evaluations of muscle fiber types and biochemical examinations of muscle nucleic acids were made on a section of the LD at the 12th rib area.

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117 No major differences due to breed were found for predicted carcass composition. The LD muscle from Brahman bulls contained more total DNA (2.27 vs 1.19 g), more total protein (768.22 vs 593.59 g) and generally less total lipid (70.56 vs 101.26 g) when expressed on a total muscle basis. Total RNA content and proteiniDNA, protein:RNA and RNA:DNA ratios were not influenced (P>.05) by breed. The percentages and areas for all three muscle fiber types were not affected by breed. As weight increased, muscle weights, total protein, lipid, RNA, RNA:DNA, protein:DNA and areas for the three fiber types increased. Total DNA content increased only up to the 90% weight group and then leveled off while the protein:RNA ratio decreased as weight increased. Furthermore, the percentage of aR fibers decreased while the percentage of aW fibers increased with increasing slaughter weight.

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SUMMARY AND CONCLUSIONS Seventy-eight purebred bulls (10 to 18 mo at slaughter) were used over a two year period to determine the effects of breed (Angus or Brahman), slaughter weight (60, 80, 90 or 100% of the average mature cow weight for the respective breed) and carcass electrical stimulation (500 volts; 20-2 sec impulses applied to the right side) on production traits, carcass compositional and quality-indicating factors and meat palatabil ity. In addition, selected histological, biochemical and compositional growth characteristics of the longissimus muscle were evaluated for the second year group of bulls. Angus bulls grazed summer forage (millet) after weaning while Brahman bulls were fed to simulate gains the Angus bulls achieved on forage. The 60% group of bulls from both breed groups was slaughtered after this postweaning feeding period. The remaining bulls were then placed in a confinement feedlot and fed a shelled corn-protein supplement diet until they reached their appropriate slaughter weight. Slaughter weights for Angus bulls v/ere 293, 381, 412, and 463 kg and for Brahman bulls were 316, 420, 463, and 516 kg based on the dam's mature weights for the respective breeds which were 456.3 kg for Angus and 515.3 kg for Brahmans. The 9-10-11 rib section was used to estimate carcass composition. Histological evaluations of muscle fiber types and biochemical examinations of muscle nucleic acids were made on a section of the LD at the 12th rib area. Carcasses from Angus bulls received higher quality grades (St"*" vs St") based on differences in marbling scores (Tr^ vs Pd^), and 118

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119 lower yield grades (1.8 vs 2.1) than carcasses from Brahman bulls. All the carcasses qualified for the USDA "Bullock" grade. Meat from Angus bulls was generally more tender than that from Brahman bulls as indicated by higher sensory panel scores for broiled loin steaks and lower shear force values for braised bottom round steaks (4.96 vs 5.58 kg). However, a significant breed by weight group interaction was detected for loin steak shear force values. At the 80% weight group, loin steaks from Brahman bulls had lower shear values typifying more tender meat than those from Angus bulls (6.31 vs 7.19 kg). For the other weight groups, shear force values for loin steaks from Angus bulls were lower than those from Brahman bulls. Mo major differences due to breed type were observed for predicted carcass components. The LD muscle from Brahman bulls contained more total DMA (2.27 vs 1.19 g), more total protein (768.22 vs 593.59 g) and generally less total lipid (70.56 vs 101.26 g) when expressed on a total muscle basis. Total RNA content and the ratios of protein to DMA, protein to RNA and RNA to DNA were not significantly influenced by breed. Nor v/ere the percentages and areas for all three muscle fiber types affected by breed. Ribeye area, as a measure of muscling, for both years of Angus bulls and the first year Brahman bulls, increased rapidly from 60 to 80%, changed little or decreased between 80 and 90%, and then increased between the 90 and 100% group, except for the Brahman bulls from the second year where the increase in ribeye area was continuous. The percentage of intramuscular fat increased between the 60 and 80% group for both breeds, decreased slightly between 80 and 90% for both breeds.

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120 and then either increased, in the case of the Angus bulls, or decreased for the Brahman bulls from the 90 to the 100% weight group. As live weight increased, muscle weights, total protein, total lipid, total RNA content, RNA:DNA, protein:DNA and areas for the three fiber types increased. Total DNA content increased only up to the 90% weight group and then leveled off while the protein:RNA ratio decreased as weight increased. Furthermore, the percentage of aR fibers decreased while the percentage of aW fibers increased with increasing live weight. Increasing slaughter weight from 60 to 90% was associated with an increase in panel tenderness scores for loin steaks. However, from the 90 to the 100% group, no change was detected. The usual trend was for shear force values to decrease as carcasses became heavier and, subsequently, fatter. The influence of year on production traits and carcass and meat characteristics appeared to be associated with the change in diet composition from the first year to the second. Carcass electrical stimulation increased the tenderness for loin steaks as determined by. sensory panel scores ("slightly tough" vs "moderately tender" rating) and shear force values (6.84 vs 4.31 kg) and for bottom round steaks (5.27 vs 4.84 kg shear force). Furthermore, heat-ring formation and lean color problems normally associated with bullock carcasses were either eliminated or reduced by stimulation. In conclusion, the data suggest that the bulls used in this study whan fed to selected slaughter weights produced lean, acceptable weight carcasses. However, the carcasses from the Brahman bulls were more

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121 deficient in intramuscular fat than those from Angus bulls. Meat from Brahman bulls was, for the most part, less tender than meat from Angus bulls. Nevertheless, the meat, from the bulls slaughtered at the lighter weights representing both breeds, was generally tough and unacceptable but was improved when bulls were fed to heavier weights. The use of electrical stimulation on carcasses from young bulls, especially for the types used in this study (averaging 414 kg live weight, 14.3 mo of age, and 4.7 mm subcutaneous fat), eliminated several of the problems (e.g., tenderness, heat-ring formation and coarse, dark colored lean) normally associated with these types of carcasses. Moreover, various differences in carcass and muscle characteristics often encountered when comparing animals from different breed origins at the same endpoint (i.e., age, live weight or days on feed) were either eliminated or minimized when differences in physiological growth and maturation were accounted for. It also appears that selected morphological and biochemical evaluations of skeletal muscle (i.e., the degree of conversion of aR to aW fibers and changes in nucleic acid properties during postnatal growth) can successfully identify what point in the growth cycle the animal is in.

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LITERATURE CITED Abraham, H.C., Z.L. Carpenter, G.T. King and O.D. Butler. 1968. Relationship of carcass weight, conformation and carcass measurements and their use in predicting beef carcass cutabilitv. J. Anim. Sci 27:604. Adams, N.J., G.C. Smith and Z.L. Carpenter. 1982. Performance, carcass and palatability characteristics of Longhorn and other types of cattle. Meat Sci. 7:67. Allen, C.E., E.H. Thompson and P.V.J. Hegarty. 1974. Physiological maturity of muscle and adipose cells in meat animals. Proc. Recip. Meat Conf. 27:8. Alsmeyer, R.H. 1960. The relative significance of factors affecting and (or) associated with slaughter, carcass and tenderness characteristics of beef. Ph.D. Dissertation. University of Florida, Gainesville. AMSA. 1978. Guidelines for cookery and sensory evaluation of meat. Amer. Meat Sci Assoc. AOAC. 1980. Official Methods of Analysis (13th Ed.). Association of Official Analytical Chemists, Washington, DC. Arthaud, V.H., R.W. Mandingo, R.M. Koch and A.W. Kotula. 1977. Carcass composition, quality, and palatability attributes of bulls and steers fed different levels and killed at four ages. J. Anim. Sci. 44:53. Ashmore, C.R. and P.B. Addis. 1972. Prenatal development of muscle fiber types in domestic animals. Proc. Recip. Meat Conf. 25:211. Ashmore, C.R. and L. Doerr. 1971. Comparative aspects of muscle fiber types in different species. Exp. Neurol. 31:408. Ashmore, C.R. and D.W. Robinson. 1969. Hereditary muscular hypertrophy in the bovine. I. Histological and biochemical characterization. Proc. Soc. Exp. Biol. Med. 132:548. Ashmore, C.R., G. Thompkins and L. Doerr. 1972. Postnatal development of muscle fiber types in domestic animals. J. Anim. Sci. 34:37. Bailey, CM., P.J. David, J.S. Dow, Jr., T.P. Ringhob and C.F. Speth. 1982. Growth and compositional characteristics of young bulls in diverse beef breeds and crosses. J. Anim. Sci. 55:787. Bartlett, J.E., J.J. Guenther, K.K. Novotney and R.D. Morrison. 1979. Myofiber number and type in baby calves as influenced by breed-type. J. Anim. Sci. 49(Suppl. 1):211. 122

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BIOGRAPHICAL SKETCH Morse Bartt Solomon, son of Louis Sumner and Muriel Alexander Solomon, was born in Waterbury, Connecticut, on March 9, 1953. He received his elementary and secondary education in Waterbury, Connecticut, graduating from Wilby High School in June, 1971. Mr. Solomon received a Bachelor of Science degree in chemistry and biological science, magna cum laude, from the University of Connecticut, Storrs (May, 1977). During completion of his B.S. degree, Mr. Solomon was selected to be a member of Phi Lamda Upsilon. While attending the University of Connecticut, Mr. Solomon was married to the former Betsy Lynn Abrahamson of Greenfield, Massachusetts, on August 15, 1976. The author began graduate studies as a graduate research assistant in meat science and muscle biology in the fall of 1977 at the University of Kentucky under the guidance of Drs. James D. Kemp and William G. Moody. He was selected to membership in Gamma Sigma Delta in 1978. In December, 1979, Mr. Solomon received a Master of Science degree in animal science from the University of Kentucky. Mr. Solomon continued his graduate studies in meat science and muscle biology in March, 1980, as a graduate research assistant to Dr. Roger L. West at the University of Florida, Gainesville. While residing in Florida, his wife gave birth to their son, Neil Adam Solomon, on June 4, 1981. Following completion of requirements for the degree of Doctor of Philosophy, Mr. Solomon will become a research scientist for the Meat 134

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135 Science and Muscle Biology Research Laboratory at the United States Department of Agriculture, Beltsville, Maryland.

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Rog4? L. West, Chairman Associate Professor of Animal Science I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Ja^^s F. Hentges, Jr. Pr/fessor of Animal Science I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Arno Z. Palnl^r ^ Professor of Animal Science I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Michae Associate ofessor of Animal Science I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Wendell N. Stainsby Professor of Physiology

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This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate School, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosohy. August, 1983 Dean for Graduate Studies and Research


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