EFFECTS OF CREEP FEEDING, ZERANOL AND BREED TYPE
ON BEEF PRODUCTION
DAVID LOUIS PRICHARD
A DISSERTATION SUBMITTED 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
DigMe ItM Internet Archive
in 2010 with funding from
University of Florida, George A. Smathers Libraries with support from Lyrasis and the Sloan Foundation
The author wishes to express his sincere thanks to Dr. D. D.
Hargrove, Major Professor, for his guidance and suggestions during the
course of graduate study and in the preparation of this manuscript.
The author is indebted to Professor Don Wakeman and Dr. Marvin Koger
for their helpful suggestions and constructive criticisms of this
dissertation. Graditude is extended to Drs. John Moore, Gerald Mott,
Bill Ocumpaugh and Tim Olson for serving as committee members.
Appreciation is expressed to the following graduate students
for their help in the collection of data: Sergio Cesar, Anke van Dijk,
Kepler Euclides, Carlos Fontes, Mike Harrison, Alexis Pourrain, Joao
Restle, Barbara Robinson, Morse Solomon and Fred Tucker. Special
thanks are given to Tim Marshall for his friendship while coaching the
Livestock Judging Team together. The author wishes to thank Paul Dixon
and the BRU crew for their help in collecting data used in this
manuscript. The financial support of this project provided by
International Minerals and Chemical Corporation is greatly
appreciated. The author is indeed grateful to the Animal Science
Department for granting him an assistantship for graduate work.
Appreciation is extended to Cheryl Combs for typing this
manuscript. The author wishes, also, to express his sincere
appreciation to his wife, Caren, for her patience and unselfish love
and encouragement throughout this period of study.
TABLE OF CONTENTS
LIST OF TABLES .
LIST OF FIGURES .
ABSTRACT . .
REVIEW OF LITERATURE .
Factors Affecting Cal
Creep Feed .
Breed of Dam .
Breed of Sire
Sex of Calf .
Factors Affecting Cow
Creep Feed .
Breed of Cow .
Breed of Sire of
Sex of Calf .
Factors Affecting Fema
Breed and Age .
.le Reproductive Tract
ie . .
. . .
le Reproductive Tract
e . .
. . .
Factors Affecting Adipose Tissue
Nutritional Regime .
Breed . .
Factors Affecting Carcass Charact
Nutritional Regime .
Zeranol Implants .
Breed of Dam .
Breed of Sire .
STUDY I CALF AND COW PERFORMANCE .
Introduction . .
Experimental Procedure .
Results and Discussion .
Calf Performance .
Weights and Weight Gains
Frame and Condition Scores
Udder and Teat Scores .
Cow Performance .
Summary . .
STUDY II WEANLING HEIFER DEVELOPMENT AND
Introduction . .
Experimental Procedures .
Results and Discussion .
Reproductive Tract Development
ula ILy .
;tics and Compositi
Udder and Subcutaneous Fat
Carcass Characteristics and Composition .
Summary . . .
i~ > 4**
SUMMARY AND CONCLUSIONS ......... .......... ... 75
LITERATURE CITED . . . 79
VITA . . .. ... .92
LIST OF TABLES
1. NUMBER OF CALVES BY BREED OF SIRE, BREED OF DAM AND
SEX OF CALF . . ... .. 32
2. LEAST-SQUARES MEANS FOR CALF TRAITS . .... 36
3. WEIGHT GAINS OF LONG AND SHORT-TERM CREEP-FED CALVES ABOVE
THAT OF THE NONCREEP-FED CONTROLS, CREEP FEED INTAKE AND
CREEP FEED EFFICIENCY . .... ... 39
4. LEAST-SQUARES MEANS FOR AVERAGE DAILY GAIN FROM 146 TO 210
DAYS OF AGE BY CREEP TREATMENT, ZERANOL TREATMENT AND
BREED OF DAM . . 43
5. AVAILABLE DRY MATTER (KG) PER COW-CALF PAIR BY MONTH,
PASTURE AND CREEP TREATMENT WITHIN YEAR AND AVERAGE
MONTHLY RAINFALL . . 45
6. MEAN CRUDE PROTEIN PERCENTAGE BY MONTH, PASTURE AND CREEP
TREATMENT WITHIN YEAR . .... 46
7. MEAN IN VITRO ORGANIC MATTER DIGESTIBILITY PERCENTAGE BY
MONTH, PASTURE AND CREEP TREATMENT WITHIN YEAR 47
8. LEAST-SQUARES MEANS FOR COW TRAITS . .... 50
9. LEAST-SQUARES MEANS FOR REPRODUCTIVE TRACT CHARACTERISTICS 58
10. LEAST-SQUARES MEANS FOR UDDER AND SUBCUTANEOUS FAT
PARAMETERS . . 59
11. LEAST-SQUARES MEANS FOR EMPTY BODY WEIGHT, GASTROINTESTINAL
TRACT FILL, HOT CARCASS WEIGHT AND DRESSING PERCENT .... 61
12. LEAST-SQUARES MEANS FOR CARCASS CHARACTERISTICS ...... 69
13. LEAST-SQUARES MEANS FOR ESTIMATED CARCASS COMPOSITION 70
LIST OF FIGURES
1. Average daily creep feed intake . 37
2. Udder and subcutaneous adipocyte size distribution for
noncreep (NC), short-tem (SC) and long-term (LC) creep-
fed weanling heifers . . 62
3. Udder and subcutaneous adipocyte size distribution for
weanling heifers not implanted (NZ) and implanted (Z)
with zeranol . . .
4. Udder and subcutaneous adipocyte size distribution for
Brahman and Romana Red-sired weanling heifers .67
5. Udder and subcutaneous adipocyte size distribution for
weanling heifers from Angus and F1 Angus x Brown Swine 68
dams . . . .
Abstract of Dissertation Submitted to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
EFFECTS OF CREEP FEEDING, ZERANOL AND BREED TYPE ON BEEF
David L. Prichard
Chairman: D. D. Hargrove
Major Department: Animal Science
Two hundred calves, produced in 1981 and 1982, sired by
Brahman and Romana Red bulls and out of Angus and F1 Angus x Brown
Swiss reciprocal crossbred cows (F ) were stratified by breed type and
sex to the following creep treatments: no creep feed (NC); long-term
(LC), creep-fed from 56 d of age to weaning (210 d); and short-term
(SC), creep-fed from 146 d of age to weaning. Half of the steer and
heifer calves within each breed and creep treatment were implanted with
36 mg of zeranol at 56 and 146 d of age. Twelve heifers were chosen
randomly for slaughter each year from within creep and zeranol
treatments and breed groups.
LC and SC calves were heavier (P<.001) at 210 d of age than NC
calves (264 and 257 vs 231 kg), and LC calves were heavier (P<.001) at
146 d than NC calves. Cows with creep-fed calves gained more weight
during the breeding season than cows with noncreep-fed calves.
Pregnancy rate of dams was not affected (P<.46) by calf creep
treatment. Zeranol increased (P<.001) 146 and 210-d weights of
calves. Brahman-sired calves had heavier (P<.001) 146 and 210-d
weights and higher frame scores than Romana Red sired calves. Calves
out of Angus dams had lower (P<.001) 146 and 210-d weights but higher
(P<.03) 210-d conditions scores than calves produced by F1 dams.
Zeranol implanted LC and SC calves gained .18 and .14 kg/d more (P<
.001), respectively, from 146 to 210-d of age than did non-implanted
calves on the same creep treatments. Implanted NC calves gained only
.06 kg/d more (P>.10) than non-implanted NC calves.
Creep feeding did not increase (P>.19) size of the
reproductive tract in weanling heifers. The LC heifers had larger (P<
.04) udder and subcutaneous adipocytes than NC heifers. Zeranol
implants increased (P<.02) uterine weight and decreased (P<.02) percent
lipid in the udder. Brahman-sired heifers had more (P<.004) total udder
adipocytes than those sired by Romana Red bulls. Heifers out of F1
dams tended (P>.12) to have larger udder adipocytes than heifers
produced by Angus dams. Breed of sire and dam did not affect (P>.25)
To stay competitive in the purebred cattle industry, the
purebred producer often creep feeds his calves to obtain added weight,
added condition and possibly higher prices. Commercial cattlemen
generally do not creep feed their calves due to the high cost of feed.
However, when pasture conditions do not provide adequate nutrition,
commercial cattlemen may choose creep feeding as an emergency
program to supply added nutrients to the calf. It is essential for
commercial and purebred cattlemen to be able to properly select for
milking ability within their cow herds. However, many cattle producers
have overlooked the possibility that creep feeding may be masking the
cow's milking ability and impairing the future productivity of
replacement heifers. It has been theorized that creep-fed heifers
deposit excess fat in their mammary system, and that this may impair
milk production in later life. Little is known, however, about
differences in body composition and fat distribution patterns between
creep-fed and noncreep fed calves.
An area of interest, particularly to the commercial cattleman,
is the influence of growth stimulants on weight and condition of the
calf at weaning and on future reproductive performance of heifers
implanted preweaning. Research has shown that growth stimulants, as
well as creep feeding, significantly increase the weight of calves at
weaning. No data exist, however, concerning the interactions of growth
stimulants with creep feeding and their effect on calf performance.
Furthermore, no information is available on the interactions of each
and both of these management practices with differences in milk
production of various breeds of cattle.
The objectives of this study were to
1) evaluate the effects of and interactions among creep
feeding, zeranol implants and breed type on calf and cow
2) ascertain the effects of creep feeding, preweaning zeranol
implants and breed type on reproductive tract development,
fat deposition in the udder and body composition of
REVIEW OF LITERATURE
Factors Affecting Calf Performance
Creep Feed. Creep feeding is the supplemental feeding of calves
while they are nursing their dams. The basic function of creep feeding
is to increase preweaning calf performance, mainly weaning weight and
condition. The basis for this response is an increased intake of
energy during the nursing period.
Creep feeding increases the weaning weight of beef calves
(Furr and Nelson, 1959; Burns and Koger, 1&63; Marlowe et al., 1965;
Stricker et al., 1979). Furr and Nelson (1959) stated that the
response to creep feeding depends on the dam's plane of nutrition. They
observed an increase of 40 kg in weaning weight as a result of creep
feeding when mature Hereford cows were wintered on a low level of
nutrition, compared with a 24 kg increase in weaning weight for
creep-fed calves on dams receiving a high level of nutrition during the
winter. Anthony and Starling (1968) reported that creep feeding gave
greater calf gains when the dams also were supplemented.
Supplementation of only the cow increased her gain but not that of the
calf, while creep feeding the calf without supplementation of the dam
increased both calf and cow weight gain. Temple and Robertson (1961)
observed that calves creep-fed from 150 to 234 days of age gained 16 kg
more than controls in 1959, but less than the controls in 1960. The
authors claimed that conditions and management were identical for both
groups, but this is somewhat difficult to believe since this is one of
a few studies reporting a negative response to creep feeding. Martin
et al. (1981) reported that creep feeding improved (P<.05) weaning
weight in 7 of 10 years, and the overall average response was 15 kg (P<
.01). The range in response varied from a six kg disadvantage to a 41
kg advantage for creep-fed calves. The authors stated that the
negative response for year 6 could be explained by location of the
creep feeder and low feed intake. The feeder was not located near
water or shade, demonstrating the importance of proper placement of the
creep feeder for optimal feed consumption and weight gain. Martin et
al. (1981) also reported that creep feeding increased (P<.01) the
feeder grade of both steer and heifer calves from high Good to low
Choice. Cundiff et al. (1966), in an extensive study involving nearly
14,000 Hereford and Angus calves in Oklahoma, stated that creep feeding
improved 205-day weight by an average of 12.8 kg. They noted that
creep feeding reduced the seasonal effect on weaning weight, in that
seasonal deviations from the overall mean were less than when there was
no creep feeding. The advantage for creep feeding appeared to be
greater for calves born in summer and autumn.
Sticker et al. (1979) conducted a study using Hereford
cow-calf pairs grazing Fescue-Ladino clover pastures. The authors
reported that creep feeding increased (P< .01) average 205-day weight
from 185 to 210 kg, calf feeder grade from average Choice to high
Choice and wither height from 96 to 100 cm.
From the producer's point of view the important issue is not
whether creep feeding improves weaning weight but whether or not it is
economical (Preston and Willis, 1974). Hunsley et al. (1967) conducted a
4-year study in which 314 calves were either creep-fed on an ad libitum
or limited (.9 kg/head/day) basis, or not creep-fed from about 3 to 8
months of age. Creep feeding was profitable in all 4 years. Similar
results in favor of creep feeding were obtained by Hammes et al. (1959)
and Wilson et al. (1966).
Burns and Koger (1963) creep-fed, on an ad libitum basis, Angus,
Brangus, Hereford and Santa Gertrudis calves for 57 days prior to weaning
and reported no monetary advantage for creep feeding. The high cost of
creep feeding under pasture conditions is best illustrated by Kuhlman
et al. (1961) in Oklahoma. Creep feeding calves out of mature cows from
60 to 245 days of age increased weaning weight by 32 kg, but the calves
consumed 399 kg of feed. Calves from young cows on the same feeding
regime gained 45 kg but ate 429 kg of feed. Stricker et al. (1979)
reported that calves creep-fed from late April to late October consumed
an average of 316 kg of feed; gained 34 kg more than noncreep-fed calves
and required 9.3 kg of creep per kg of gain above noncreep-fed calves.
Preston and Willis (1974) stated that the uneconomical nature of creep
feeding was apparent when one considered that feed conversions during
final fattening in the feedlot (6 to 8:1) were much less than the range
of values (7-19:1) reported for creep feeding.
Almquist (1968) reported creep feeding to be uneconomical with
heifers (whose growth improvement was only 8%) unless pasture savings
were included, since feed costs were higher than the value of the extra
weight gain. The growth response of steers to creep feeding was 24%
and was economical on the basis of feed conversion alone. Almquist con-
cluded that in areas where pasture land has a relatively high value,
creep feeding can be economic if full account is taken of savings in
pasture rental, since creep-fed calves reach a specified weight much
Zeranol Implants. One of the most economical management prac-
tices available to cattlemen in the past 15 years has been the use of growth
promoting implants. One of the growth promoting implants available and
approved for use is zeranol (zearalanol). Zeranol is an anabolic agent
approved by the Food and Drug Administration for use in feedlot steers and
also has been cleared for use in suckling calves, weaned calves, growing
beef cattle and feedlot heifers. Zeranol is a derivative of zearalenone, a
metabolic product isolated, crystallized and produced from a selected strain
of fungi identified as Gibberella zeae (Fusarium graminearum) (Shipchandler,
Numerous research reports have clearly shown the effect of zeranol
on growth rate of calves implanted at about 90 days of age (Perry et al.,
1970; Thomas et al., 1970; Utley and McCormick, 1976). Ralston (1978) con-
ducted a study using 454 Hereford and Holstein x Hereford calves to evalu-
ate the effectiveness of zeranol on 205-day weights of castrated and intact
male calves. Calves implanted with zeranol at birth and again at 90 days
of age produced gains to weaning at 205 days equal to gains by calves im-
planted with diethylstilbestrol. Zeranol implants did not reduce gains of
intact males. Zeranol was equally effective in crossbred and Hereford calves.
It was noted that Holstein-sired calves from low producing dams received
increased growth stimulus similar to straightbred calves from high producing
dams. Ralston theorized that the propensity to gain from hybrid vigor plus
that of the implant might cause added stress to the calf when the milk
supply was limiting; however, no evidence of stress was observed. The author
also noted that zeranol implants reduced (P<.01) testicular weights and
generally reduced masculinity.
Corah (1980) reported that two 36 mg implants of zeranol, one
at birth and one at 4 months of age, improved weaning weight by 8.2 kg
over one implant of zeranol given either at birth or 4 months of age.
In a separate study, the author found that calves implanted one or two
times with zeranol gained 10 and 24.5 kg more than non-implanted
calves during a period of 150 days prior to weaning. The author also
observed that implanted calves at weaning were leaner or had less
condition than non-implanted calves.
Davis (1980), using 286 Hereford and Hereford-cross steer and
heifer calves, reported that calves implanted with 36 mg of zeranol at
2 months of age gained 10 kg more in 200 days than did the
non-implanted calves. Giving a second zeranol implant prior to weaning
was not advantageous and response was not influenced by sex. Davis
stated that calves with more rapid gains and heavier weights at the
time of implanting had the greatest response to zeranol implants.
Zeranol did not compensate for poor performance on pasture if daily
gains were below .59 kg. Davis concluded that such factors as milk
production of the dam, pasture quality, supplements and genetic
potential of the calf for growth might influence the response from
Gerken et al. (1978) implanted zeranol in suckling heifer
calves at birth and 100 days of age or only at 100 days of age. They
reported that calves implanted twice gained 20 kg more than
non-implanted calves and calves implanted once gained 12.7 kg more
prior to weaning than the calves that did not receive an implant.
Lowman (1980) reported that calves implanted at 2 months of age and
weighing an average of 90 kg gained 6.5 kg more over a 100 day period.
Breed of Dam. Preweaning calf performance is highly
correlated with the milk producing ability of the dam. Many studies
have shown differences due to breed of dam for traits such as calf
weaning weight, condition score and frame score. Peacock et al. (1978)
conducted a crossbreeding program using Angus, Brahman and Charolais
cattle in a diallel design. They reported that average weaning weights
were 236, 181 and 177 kg, respectively, for straightbred Charolais,
Brahman and Angus calves, for an overall average of 198 kg. The mean
weight for all crossbred calves was 211 kg. Heterosis levels for
weaning weight for the F1 crosses were 12.2%, 2.1% and 7.1%,
respectively, for reciprocal Angus x Brahman, Angus x Charolais and
Brahman x Charolais combinations. There was no significant difference
due to breed of dam for condition score. The authors concluded that the
comparative performance of reciprocal F groups of calves indicated
that maternal ability of the three breeds of dams ranked in descending
order of Brahman, Charolais and Angus.
Gaines et al. (1966) reported that calves out of Hereford dams
weighed less at weaning and had lower feeder grades than calves out of
Angus or Shorthorn dams. When they made all possible crosses among the
three breeds, calves out of Hereford dams were 23 kg lighter than
calves from either Angus or Shorthorn dams. This difference probably
was due to the superior milk producing ability of the Angus and
Gregory et al. (1978a) observed a breed of dam effect on
weaning weight. The heaviest calves were those out of Brown Swiss dams
and the lightest were those out of Angus dams. Andrade (1980)
conducted a study in Florida using 2-year-old Angus, Brown Swiss and F1
Angus x Brown Swiss reciprocal crossbred heifers. He reported that
calves from Angus heifers had lower (P<.01) 205-day weights than calves
from the Brown Swiss and crossbred heifers. Smith et al. (1976)
suggested that breeds with greater growth potential responded better to
increased milk production of the dam. This was shown by Olson (1980),
using Angus, Brown Swiss and F1Angus x Brown Swiss reciprocal cross
cows. Calves from crossbred and Brown Swiss dams weighed more at
weaning than those from Angus. This reflects not only the milk
producing ability of the Brown Swiss but also the superior genes for
growth that were being contributed by the Brown Swiss and Fldams.
Euclides et al. (1983), using the same breeds of dam, reported that the
average daily milk production for Angus, Brown Swiss and F1Angus x
Brown Swiss reciprocal cross dams was 5.3, 8.3 and 6.8 kg,
respectively. They reported that calves out of Angus dams had higher
(P<.05) weaning condition scores than calves out of Brown Swiss dams
with the calves from crossbred dams being intermediate. The influence
of breed of dam on calf performance has been clearly documented by many
others (Cobb et al., 1964; Lawson and Peters, 1964; Long and Gregory,
1974; Koger et al., 1975). However, no difference in calf weaning
weight due to breed of dam was observed in straightbreds (Angus,
Brahman and Hereford) by Crockett et al. (1978). Gregory et al. (1966)
stated that little influence of breed of dam exists for preweaning calf
traits when British breeds are compared without F1Zebu crosses.
Breed of Sire. Due to the large numbers of combinations of
beef production resources and variations in market demands, one type of
cattle cannot fit all production systems. The availability of a
variety of cattle types offers the possible opportunity of matching
germ plasm resources with production requirements. Tnis opportunity is
somewhat limited because of the lack of direct comparisons of many
breeds (Mason, 1971).
Peacock et al. (1978) reported significant sire effects for
weaning weight and condition score. Charolais-sired calves were
heavier at weaning (223 kg) than Angus and Brahman-sired calves (199
and 198 kg, respectively). The authors also reported that crossbred
calves were heavier than straightbred calves at weaning. Calves sired
by Angus bulls had the highest condition score (9.9) followed by those
sired by Charolais (9.6) and Brahman (9.4) bulls. A significant breed
of sire by breed of dam interaction for condition score was
observed. Angus x Brahman calves had a condition score of 10.2 compared
to 9.8 for Brahman x Angus calves. Data from Pahnish et al. (1969)
supported this finding.
Smith et al. (1976) reported that calves out of Hereford and
Angus cows and sired by Charolais and Simmental bulls had faster
preweaning average daily gains and were heavier at 200 days of age than
those sired by Hereford, Angus, Jersey, South Devon and Limousin
bulls. Limousin and South Devon-sired calves had similar 200-day
weights to Hereford x Angus calves. Jersey-sired calves were
lightest at 200 days of age.
Crockett et al. (1978) conducted a study comparing
straightbred Angus, Brahman and Hereford and all possible
two-breed-of-sire rotational crosses. They reported that calves from
Brahman bulls were heavier at weaning than those from Angus bulls when
both were crossed with Hereford cows. There was no difference in
weaning weight among the straightbred groups.
Gregory et al. (1978b) observed that calves sired by Gelbvieh,
Maine-Anjou, Chianina and Brown Swiss bulls had superior (P<.01)
average daily gains and 200-day weights when compared to Angus x
Hereford and Red Poll-sired calves. Similar results were obtained by
Cundiff (1970), even though the magnitude of the differences was
smaller. Andrade (1980) and Euclides et al. (1983) reported that breed
of sire did not affect calf 205-day weight or weaning condition score,
in a comparison of Angus, Brown Swiss and F Angus x Brown Swiss bulls.
Olson (1980) reported that Brown Swiss-sired calves were heavier at
weaning than calves sired by Angus or F Angus x Brown Swiss bulls when
all possible matings were made. There was no difference in weaning
weight of calves out of Brown Swiss dams and sired by either Angus or
Brown Swiss bulls. Numerous other workers have shown breed of sire
effects for preweaning performance traits (Baker and Black, 1950;
Brown, 1961; Kincaid, 1962; Chapman et al., 1970; Koger et al., 1975).
Sex of Calf. The effect of sex of calf on preweaning
performance traits is extremely important in today's cattle production
scheme. For the cattleman to accurately assess his cow herd in terms
of production, he must rank his cows on a within sex of calf basis for
weaning parameters or he must use additive or multiplicative factors to
adjust to a constant sex basis. Koger et al. (1962 b) stated that sex
effects can be adjusted more accurately by using a multiplicative
factor rather than adding a constant.
Weaning weights are greater for bulls than heifers (Lasley et
al., 1961; Crockett et al., 1978; Nodot, 1980). Marlowe and Gaines
(1958), Brinks et al. (1961) and Pell and Thayne (1978) reported that
weaning weight differences between male and females were reduced when
males were castrated and that steers were intermediate in weight
between bulls and heifers. Brown (1961) stated that males were heavier
than females, but the magnitude of differences varied among breeds and
Condition score at weaning reflects the thrift and
adaptability of the calf as well as the maternal ability of the dam.
Peacock et al. (1978) reported that heifer calves were fatter at
weaning than steer calves. Preston and Willis (1974) pointed out that
for sex differences to occur the sex hormone influences must be
manifested; therefore, parameters taken before 150 days of age
may show no significant effect for sex of calf.
Factors Affecting Cow Performance
Creep Feed. Advantages other than weight gains and condition
scores of calves have been reported for creep feeding. Black and
Trowbridge (1930) and Jones and Jones (1932) reported that dams of
creep-fed calves out-gained dams of noncreep-fed calves during the
nursing period. Johnson and Fenn (1943), Foster et al. (1946) and
Nelson et al. (1955), however, found essentially no difference in
weight change of cows nursing creep-fed calves.
Burns et al. (1966) conducted a 4-year study with five breed
groups: Angus, Brahman, Brahman x Angus inter se, Hereford and Santa
Gertrudis. Creep feed was available to the calves about 60 days prior
to weaning. They reported that cows with creep-fed calves gained 24 kg
as compared to 23 kg for cows nursing noncreep-fed calves. The average
gain by breed group was 38, 32, 20, 19 and 10 kg, respectively, for the
Hereford, Angus, Santa Gertrudis, Brahman x Angus and Brahman cows.
The authors concluded that the breeds assumed to have the poorest
milking ability responded most to creep feeding in terms of cow and
calf weight gains. All responses appeared to be directly related to
creep intake, which probably was a reflection of the milking ability of
Stricker et al. (1979) conducted a 4-year grazing study with
Hereford cows and calves on Tall Fescue-Ladino Clover pastures to
determine if calf production could be economically increased by use of
nitrogen fertilization and(or) creep feeding. Pastures were fertilized
with nitrogen at the rates of 0, 112 and 224 kg/ha and half of the
calves received creep feed. Cows nursing creep-fed calves gained 61 kg
during the nursing period compared with 55 kg for cows with
noncreep-fed calves. Bcth groups of cows gained .65 kg per day during
the breeding season; however, 74% of the cows nursing creep-fed calves
became pregnant compared to only 55% for cows with noncreep-fed
calves. There was a significant creep by level of nitrogen
fertilization interaction for cow gain and pregnancy rate. As nitrogen
fertilization was increased, weight gain and pregnancy rate for cows
with noncreep-fed calves decreased, whereas weight gain and pregnancy
rate for cows with creep-fed calves remained fairly constant across all
three nitrogen treatments. The authors also reported that creep feeding
increased pasture carrying capacity by .9 animal unit months per ha
during the summer (lactation) phase.
Breed of Cow. Breed of cow can have a significant effect on
many traits relating to cow performance and total beef production. Rate
of reproduction in beef cattle is the most important trait influencing
the economy of beef production. Many researchers reported that
crossbred females were superior to straightbred cows for reproductive
rate (Koger et al., 1962a; Turner et al., 1968; Peacock et al., 1971;
Peacock and Koger, 1980). These authors compared Brahman, European and
Flreciprocal Brahman x European cows to evaluate the effect of breed
of cow on reproductive performance.
Crockett et al. (1973), from the Everglades area of south
Florida, reported birth rate for Angus cows to be 88.7% as compared to
73.7% for Brahman cows. Contrary to the above results, data from
Peacock et al. (1971) on straight breeding and reciprocal crossing of
Brahman and Shorthorn cattle on various pasture programs indicated
that the average pregnancy rate for Brahman cows was 71% vs 64% for
Shorthorn cows. Research in south central Florida (Peacock et al.,
1977) from straightbreeding and reciprocal crossing of Angus, Brahman
and Charolais cattle showed no differences in pregnancy rate for breed
of dam. The observed pregnancy rates for straightbred dams were 81.5%
vs 77.1% for the crossbred dams.
Weight and condition score changes due to breed of cow have
been reported by Kropp et al. (1973) and Holloway et al. (1975). These
authors used British, Holstein and British x Holstein crossbred cows
under range and drylot conditions. They concluded that weight and
condition score changes before, during and after lactation were
dependent upon the percentage Holstein breeding.
Wyatt et al. (1977b) compared the performance of
winter-calving 4 and 5-year-old Hereford, Holstein and Hereford x
Holstein cows on tall-grass native range and in drylot confinement.
Two levels (moderate and high) of a 30% protein supplement were fed
during the winter to groups of cows within each breed. A higher level
of supplementation (very high) was fed to an additional group of
Holstein cows. Drylot cows were fed cottonseed hulls and alfalfa hay
as roughage sources to simulate seasonal changes in energy content of
the diet of range cows. All cows, both on range and in drylot, except
the moderate and high Holsteins, regained their winter weight losses
during the subsequent lactation period. This suggests that the lower
supplement levels were inadequate for maintenance and productivity of
the larger, heavier milking Holsteins. A significant breed effect on
condition score was apparent both on range and in drylot, with
Holsteins having the lowest and Herefords the highest condition
Breed of Sire of Calf. Cartwright and Carpenter (1961)
suggested that milk production may be affected not only by the genotype
of the dam but also by the genotype of the calf. These researchers
conducted a study using Hereford and F1 Brahman x Hereford bull and
heifer calves. Nursing habits of calves were monitored for four
consecutive weeks. They observed that crossbred calves nursed more
frequently and for longer periods of time than Hereford calves. In
another phase of the study, weight gains during lactation of the
Hereford dams nursing either Hereford or crossbred calves were
correlated with 180-day weights of their calves. The absolute magnitude
of the correlation coefficient was greater for crossbreds (-.62) than
for Herefords (-.20). These data suggest that breed of sire of calf
may indirectly affect pregnancy rate through changes in cow weight
(Warnick et al., 1967).
Kaiser (1975) mated Guernsey cows to Angus, Friesian and
Brahman bulls and reported no significant change in cow weight at 12
and 26 weeks of lactation due to breed of sire of calf. He also
reported no influence of breed of sire of calf on the interval to first
postpartum estrus. Campos (1982) and J. Restle (unpublished data)
reported no breed of sire of calf effect on cow condition score or
pregnancy rate when comparing Angus, Brown Swiss and F Angus x Brown
Swiss reciprocal crossbred bulls.
Sex of Calf. Conflicting reports have been published as to
the effect of sex of calf on cow performance (milk production and
pregnancy rate). Cartwright and Carpenter (1961) correlated lactation
gains of Hereford cows with 180-day weights of their calves. They
reported that the correlation coefficient was greater for bull calves
(-.35) than for females (-.19). They concluded that bull calves
apparently nursed more vigorously, and that cow weight change possibly
could be influenced by sex of calf. Wettemann et al. (1978) stated that
suckling intensity increased the postpartum anestrous interval in range
Hereford x Holstein cows but did not influence body weight loss during
Melton et al. (1967) and Christian et al. (1965) found no
significant difference in dam's milk yield attributable to sex of
calf. However, Melton et al. reported that cows nursing bull calves
gave 53 kg more milk over a 175-day lactation than cows nursing heifer
calves. Pope et al. (1968) reported a significant advantage in milk
yield for cews nursing bulls alves. Rutledge et al. (1971), on the
other hand, observed that Hereford dams nursing heifer calves produced
significantly more milk than those nursing bull calves.
Nodot (1980) reported that Brahman cows nursing male calves
had a longer average calving interval than those nursing heifer calves.
Warnick et al. (1967) found that pregnancy rate was not influenced by
sex of calf in Angus, Brahman, Brangus, Hereford and Santa Gertrudis
Factors Affecting Female Reproductive Tract Development
Nutritional Regime. A positive relationship exists between
weight and age at which puberty is reached in the bovine female. If
the heifer is to reach puberty at an early age, the reproductive tract
must be fully developed. A major factor affecting the weight of a
heifer at a given age is nutritional level.
Hill et al. (1970), using 18 to 20-month old Angus and
Hereford heifers, studied the effects of undernutrition on ovarian
function and fertility in beef heifers. Undernutrition reduced the
follicle population and caused some unusual ovarian development by days
15 to 17 of the estrous cycle. No major differences in follicle
populations between control and undernourished heifers were detected
after mating or at the time of slaughter, although three undernourished
heifers had negligible numbers of medium size follicles (3-5 mm). The
authors concluded that a decline in follicle number and size after 10
to 12 days feed restriction was followed by a recovery in most heifers
at or soon after the next estrus.
Spitzer et al. (1978) fed two groups of yearling beef heifers
either a ration meeting N.R.C. recommendations for all nutrients or a
restricted diet with only one-third the recommended energy. Heifers on
the low energy diet had smaller ovaries than those on the
non-restricted diet (9,088 vs 14,296 mm3). No significant differences
among heifers on different diets were noted in either number of
follicles or follicular volume.
Cornwell (1981) fed Angus and Brahman heifers either at
maintenance level or above or below maintenance. She reported that
uterine horn diameter and ovarian size and weight were not affected by
level of nutrition. She did report, however, a significant breed by
level of nutrition interaction. The number of follicles for Brahmans
increased with level of nutrition. Angus heifers showed an increase in
number of follicles from the low level to maintenance level of
nutrition, but there was a decrease in follicle number from the
maintenance to the high level of nutrition. The author concluded that
the variation in number and size of follicles and in size and weight of
the ovaries indicated that nutritional level may influence the
production and(or) release of gonadotrophic hormones.
Breed and Age. Foley et al. (1964) examined the effects of
age, breed and live weight on ovarian and luteal tissue weights. They
reported mean ovarian weights of 2.25, 4.78 and 5.61 g, respectively,
for Holstein heifer calves that were 47, 103 and 165 days old. These
authors conducted a separate study using 83 pregnant Ayrshire,
Guernsey, Holstein and Jersey cows and heifers. They observed highly
significant correlations between total ovarian weight and age and live
weight (.70 and .65, respectively). Mean ovarian weights (all ages)
differed only slightly among the four breeds. The authors concluded
that physiological age was more important than chronological age and
weight in determining size and weight of ovaries in prepubertal
heifers. Furthermore, it appeared that age and weight had more affect
than breed on ovarian weights of normal pregnant cattle.
Cornwell (1981) reported that Angus heifers had more follicles
than Brahman heifers at similar ages. Angus heifers tended to have
larger follicles than Brahman heifers; however, Brahman heifers had
larger and heavier (P<.01) varies. The author reported no significant
difference in uterine horn diameter between the two breeds.
Sixty-five Holstein heifers were slaughtered at monthly
intervals in groups of five from birth through 12 months of age to
determine morphological and biochemical changes in their reproductive
organs (Desjardins and Hafs, 1969). Ovarian weight increased 2.7 times
faster than live weight. While no ovarian follicles were visible at
birth, their numbers increased to a maximum at 4 months (16), decreased
to 8 months of age (6) and remained relatively constant thereafter.
Similar data were reported by Erickson (1966). Desjardins and Hafs
(1969) also observed that uterine weight increased proportionately more
than did body weight from 1 to 12 months of age. The authors stated
that rapid increases in the size of ovaries and the number of follicles
suggested that a concurrent increase in ovarian secretary activity
might be expected. They further concluded that the increased rate of
uterine growth relative to body weight prior to puberty may be the
result of ovarian estrogen secretion. This theory was supported by
Factors Affecting Adipose Tissue Cellularity
Nutritional Regime. Adipose tissue metabolism, cellularity
and deposition in ruminants have been studied for their intrinsic
values and economic implications in animal production. For example,
the grading of carcasses in the U.S.A. is influenced by the amount of
intramuscular adipose tissue (marbling). Within certain limits, the
more marbling the higher the grade. In addition, the adipose tissue
serves a vital role as an energy source in cattle during lactation, yet
it has been implicated in the depression of milk yield in animals fed
high-concentrate diets (Vernon, 1980).
The relative contributions of adipocyte (fat cell) number and
size to the deposition of the excessive mass of adipose tissue
characteristic of obesity have been the subject of research for several
years in man, rats and mice (Hood and Allen, 1973). The problem of
hyperplasia versus hypertrophy of adipose tissue in relation to
subcutaneous, intermuscular and intramuscular fat deposition in beef
cattle is of great practical importance. However, limited and less
extensive information is available for beef cattle where adipose
cellularity has economic as well as scientific interest. Garbutt et
al. (1979) stated that the study of adipose cellularity in young beef
animals has been hampered by the limitations of identifying small
adipocytes as well as difficulty in finding homogeneous fat depots at
an early age. Researchers have questioned the time in an animal's
development when its adipocyte numbers become fixed, and whether
nutritional or environmental conditions near this fixation time can
alter fat cell production. In all species, adipose tissue develops by
hyperplasic growth until one or more specific periods in the animal's
development is reached, after which further increases in fatness result
primarily from cellular hypertrophy.
Hood and Allen (1973) showed that during growth of the bovine
animal, an increase in adipose tissue mass was accompanied by cellular
hypertrophy and hyperplasia. Hyperplasia of subcutaneous and perirenal
depots was nearly complete by 8 months of age or shortly thereafter.
However, hyperplasia was still an active process in intramuscular
adipose tissue at 14 months of age. Allen (1976) reported that, in
over-fattened cattle, a second population of small subcutaneous
adipocytes was observed, suggesting that hyperplasia may recommence
after a given period of time on a high energy diet.
Fat accumulation and adipose tissue cellularity changes in the
udder of over-conditioned bovine females have not been studied in
detail. Fat infiltration in the udders of beef and dairy heifers has
long been cited as the culprit of turning potentially good milkers
intc poor milkers by overfeeding during periods of early growth (Herman
and Ragsdale, 1946; Herman et al., 1948; Burt, 1956; Hansson, 1956).
Swanson (1960) conducted a study using twin dairy heifers
under one year of age. One of each pair was fed a normal growing
ration while its twin was fed heavily on concentrates until first
calving to produce rapid growth and fattening. The fattened heifers
weighed 32% more than the control heifers at 2 years of age; however,
the average fat-corrected-milk production by the fattened heifers in
the first lactation was only 84.8% of that of the controls. The
average production difference between the fattened and normal twins
remained through the second lactation. In addition, Swansor noted that
alveolar-secreting tissue had not filled the spaces in the framework of
the mammary gland of the fattened heifers. This may have been due to
excess fat within the mammary gland prior to the first lactation. Most
if not all of the excess fat was probably eliminated by the time the
second lactation had been completed, thereby leaving large open spaces
in the mammary gland void of secretary tissue.
Creep feeding beef heifer calves may result in over
conditioning. This practice has economic implications that may be
beneficial when selling feeder calves; however, many producers have
failed to consider the possible detrimental results of creep feeding
Holloway and Totusek (1973a,b) conducted an intensive study in
Oklahoma involving 206 Angus and Hereford heifer calves. Creep-fed
heifers consumed an average of 195 kg of creep feed per head, had no
permanent advantage in size, tended to produce less milk and lighter
calves at weaning, and had no apparent advantage in total productivity
over normal weaned noncreep-fed heifers. Similar results were reported
by Martin et al. (1970), Mangus and Brinks (1971), Kress and Burfening
(1972) and Hixon et al. (1982).
Martin et al. (1981) stated that what appears to be a simple
management practice to increase the weaning weight of calves turns out
to be a very complex problem when the future productivity of the heifer
calf is considered. They concluded that creep feeding can produce a
permanent detrimental effect on cow productivity, since fat deposition
in the udder during the preweaning period may hinder secretary tissue
Breed. Although breed has been used to provide an explanation
for differences in adipocyte size and number found in different
studies, there have been few if any studies specifically designed to
investigate variation due to breed. Yet such variations clearly must
occur, as shown by differences between beef and dairy cattle. Beef
cattle tend to mature and fatten at an earlier age than dairy cattle,
which tend to have more internal fat and less subcutaneous fat than
beef cattle (Callow, 1961).
Hood and Allen (1973) compared Holstein, Hereford x Angus and
Hereford steers in a study on the cellularity of bovine adipose tissue.
Perirenal and subcutaneous adipose tissues in Hereford x Angus steers
contained larger (P<.05) cells than the same tissues from Holstein
steers. Hereford steers had significantly smaller adipocytes than
either Holstein or Hereford x Angus steers; however, they were fed a
totally different diet (low energy roughage diet vs a high energy corn
diet). The number of adipocytes in subcutaneous fat of Holstein steers
was less (P<.05) than that in Hereford x Angus steers. Hood and Allen
(1975) reported similar findings from an updated study of the same
Factors Affecting Carcass Characteristics and Composition
Nutritional Regime. The effect of plane of nutrition on
carcass traits has been well documented (Wanderstock and Miller, 1948;
Brown, 1954; Klosterman et al., 1965; Moody, 1976). In general,
increasing the length of feeding and(or) the nutritional plane appears
to enhance carcass quality traits but lowers carcass cutability.
Grain-fed (high concentrate) beef generally has physical and sensory
quality traits superior to those of forage-fed beef (Meyer et al.,
1960; Chapman et al., 1961; Kropf et al., 1975; Bowling et al., 1977;
Harrison et al., 1978; Schroeder et al., 1980).
Rouquette et al. (1983) investigated the effects of creep
feed, stocking rate and electrical stimulation on carcass traits of
weanling Simmental-sired calves out of F Brahman x Hereford dams.
They reported that creep feeding did not produce any significant
improvement in physical or sensory traits of the carcass. However,
there was evidence that electrical stimulation of carcasses from
creep-fed calves had a greater effect on carcass characteristics than
on those carcasses from noncreep-fed calves. Rib steaks from
electrically-stimulated carcasses of creep-fed calves had higher (P<
.05) tenderness values than steaks from nonelectrically stimulated
Corah and Bishop (1975) examined the effects of creep feeding
oats on the carcass characteristics of weanling heifers and of steers
slaughtered after a period in the feedlot. Carcasses from creep-fed
heifers had significantly heavier hot carcass weights, higher dressing
percentages, larger ribeye areas and more fat cover than carcasses
from noncreep-fed heifers. The differences in carcass traits at
weaning between creep-fed and noncreep-fed heifers were not apparent in
the carcasses of steers that had been fattened in the feedlot. Similar
results were observed by Greathouse and Henderson (1968), Scarth et al.
(1968) and Martin et al. (1980).
The influence of plane of nutrition on relative tissue growth
is best illustrated from the results of Guenther et al. (1965) and from
Waldman et al. (1971). Both groups of researchers fed high
and moderate levels of nutrition. Guenther et al. (1965) fed half-sib
Hereford steers and estimated body composition at the start and as the
experiment progressed. Waldman et al. (1971) fed Holstein steers and
estimated composition using rib-cut dissection at slaughter. Both
groups of researchers concluded that steers on the high plane of
nutrition fattened more rapidly relative to muscle and bone growth than
those on the moderate plane. In addition, they concluded that body
composition in terms of fat, lean and bone tissue could be altered by
the plane of nutrition.
Corah and Bishop (1975) reported that carcasses from weanling
heifers fed creep feed approximately 160 days prior to slaughter had
less (P<.01) water and more (P<.01) fat than carcasses from
noncreep-fed heifers. There was no difference in percent protein.
Carcasses from noncreep-fed heifers had a higher percentage of bone
than those from creep-fed heifers. Creep feeding did not significantly
affect percent water, fat and protein in the carcasses of steer
comtemporaries slaughtered after a period in the feedlot. The apparent
difference in percent bone remained through the feedlot phase.
Zeranol Implants. Gregory and Ford (1983) evaluated the
effect of zeranol on the carcass traits of late maturing, intact bovine
males. They concluded that zeranol treatment effects on carcass traits
were of little consequence other than through zeranol treatment effects
on weight. Similar data have been reported for ram, ewe and wether
lambs (Wiggins et al., 1976) and steers (Borger et al., 1973).
Sharp and Dyer (1971) conducted a study to determine the
effects of zeranol on the carcass composition of growing ruminants.
Using heifers, steers and wether lambs in separate studies, they
observed no significant effect of zeranol on carcass quality traits.
However, in one study the percentages of protein and water in the
carcasses of steers were significantly increased with zeranol implants,
while the percentage of fat was reduced.
Breed of Dam. Characterization of breeds of cattle for
carcass characteristics and composition is of utmost importance with
today's widespread use of crossbreeding. Knowing the carcass
attributes of the breed of dam and breed of sire may help the producer
use available genetic material wisely to increase production
Peacock et al. (1979) compared the Angus, Brahman and
Charolais breeds in a 3 x 3 diallel mating scheme to evaluate breed and
heterosis effects on carcass characteristics of steers. They reported
that maternal effects for Angus dams were positive for quality grade
but negative for estimated retail yield and slightly negative for
carcass weight. Effects for Brahman dams were positive for estimated
retail yield but negative for carcass weight and quality grade. The
effects for Charolais dams were positive for carcass weight,
intermediate for quality grade and negative for estimated retail
yield. Peacock et al. (1982) observed that additive maternal effects
for Angus dams were nonsignificant for all measured carcass traits.
Effects for Brahman dams were significantly positive for ribeye
area/100 kg carcass weight and negative for fat over the ribeye. The
additive maternal effects for Charolais dams were significantly
positive for fat over the ribeye and negative for ribeye area/100 kg
carcass weight. Significant maternal heterosis effects were observed
only for chilled weight and fat over the ribeye for first cross Angus x
Brahman dams and for chilled carcass weight in Angus x Charolais dams.
Hargrove et al. (1983) conducted a study to evaluate the
carcass characteristics of Angus, Brown Swiss, F, F2 and backcross
steers. They reported that steers out of Brown Swiss dams had heavier
hot carcass weights and larger ribeye areas than steers out of Angus
dams. Steers produced by F1 dams were intermediate for hot carcass
weight and ribeye area. There was a tendency for carcasses from steers
out of Brown Swiss dams to have lower quality grades than those out of
either Angus or F dams. The superiority of the Angus breed for
carcass quality grade over other breeds has been observed by other
researchers (Hedrick et al., 1975; Luckett et al., 1975; Young et al.,
1978; Koch et al., 1982).
Several studies (Cole et al., 1964; Solomon et al., 1981;
Adams et al., 1982) have confirmed that distinct differences in carcass
compositional components exist between breeds of cattle. The preceding
authors reported that carcasses from Angus cattle were fatter and had
less lean and bone on a percentage basis than those from Brahman
cattle. Cole et al. (1964) also compared dairy type cattle to British
and Zebu cattle and reported that carcasses from Holstein steers were
very similar in composition to those from Brahman steers. However,
data used in these particular studies were collected from steers and
heifers which were slaughtered at a constant end point of live weight,
days on feed or age. LeVan et al. (1979) reported that breed had no
marked effect on relative distribution of carcass retail lean, fat or
bone when straightbred Angus and Charolais steers were compared at
similar percentages of the corresponding breed average mature weight.
Solomon (1983) compared carcass components of Angus and Brahman bulls
slaughtered at similar percentages of mature cow weight. Solomon
reported no major breed differences in predicted carcass lean, fat and
bone based on the 9-10-11 rib cut. He concluded, based on overall
carcass composition that the bulls were slaughtered at similar points
in their respective growth curves and were compared on an equivalent
Breed of Sire. Peacock et al. (1979), using Angus, Brahman,
Charolais and crossbred steers, reported that the direct effects of
Angus breeding from either the sire or dam were positive for quality
grade, intermediate for retail yield and negative for carcass weight.
Breed effects for the Brahman were slightly positive for carcass
weight, with negative effects for retail yield and carcass quality.
The direct effects of Charolais breeding were positive for carcass
weight and retail yield, but negative for quality grade.
Crockett et al. (1979) found that carcasses from steers with
Brahman, Beefmaster or Brangus sires had higher marbling scores, more
fat over the ribeye and smaller ribeye areas than those with Limousin,
Maine-Anjou and Simmental sires. Other studies indicated that Brahman-
sired cattle ranked low in breed group comparisons for marbling score
and quality grade (Damon et al., 1960; Luckett et al., 1975; Young et
Koch et al., (1982) mated Angus and Hereford cows to Angus,
Hereford, Tarentaise, Pinzgauer, Brahman and Sahiwal bulls. They
reported that Brahman-sired steers had the heaviest carcass weights and
Sahiwal-sired steers the lowest carcass weights at a constant age.
Dressing percentages at a common carcass weight were lower for
Pinzgauer crosses (62.0%) and higher for Brahman and Sahiwal crosses
(63.8 and 64.0%) than for Hereford x Angus (63.2%) or Tarentaise
crosses (63.2%). Several reports have attributed advantages in dressing
percentage for Brahman cattle to lower gastrointestinal tract weights
and contents than other cattle breeds (Carpenter et al., 1961; Ramsey
et al., 1965; Tucker, 1981). Koch et al. (1982) reported that
differences in carcass composition were greatest at a common weight
because that contrast emphasized differences in rates of maturity.
They observed that Brahman crosses had a significantly higher retail
product percentage (71.0%) than other breed groups, except for
Tarentaise crosses (70.2%). Hereford x Angus crosses had the lowest
retail product percentage (66.9%). They found, in addition, that at a
common fat thickness Brahman and Sahiwal crosses had less fat trim than
Tarentaise and Pinzgauer crosses because of significantly lower kidney
and pelvic fat percentages. Other studies reporting breed of sire
effects of carcass traits and tissue components of cattle slaughtered
at some common end point include Koch et al. (1976) and Winks et al.
CALF AND COW PERFORMANCE
Gross income in the cow-calf phase of the beef industry is
highly dependent on the production of heavy weight calves at weaning.
Creep feeding and implanting with growth stimulants are two means of
increasing preweaning gains (Cundiff et al., 1966; Scarth et al., 1968;
Utley and McCormick, 1976; Stricker et al., 1979; Corah, 1980; Lowman,
1980; Ochoa et al., 1981). Little is known about the combined effects
of growth stimulants with creep feeding and variations in the milk
producing abilities of the dam on calf performance.
Advantages other than weight gain of calves have been reported
for creep feeding. These included increased weight, condition and
pregnancy rate of the dam (Jones and Jones, 1932; Stricker et al.,
1979). Creep feeding, however, has been implicated in the possible
altering of the maternal rank (weaning weight of calf) of cows within a
herd (Burns et al., 1966; Ochoa et al., 1981). Furthermore, it has
been suggested that creep feed is utilized best by calves suckling dams
with limited milk production (Christian et al., 1965).
The objective of this study was to evaluate the effects of and
interacticns among creep feeding, zeranol implants and breed type on
calf and cow performance.
This project was conducted at the Beef Research Unit,
Gainesville, from April 1 through September 1, 1981, and 1982. The
research unit is located in north central Florida (latitude 29" 40'N)
and the climate is considered semitropical. Average maximum and
minimum temperatures for the 1981 and 1982 experimental periods
respectively were 32.8 and 19.3C and 31.3 and 19.1C. Monthly rainfall
averages during the experimental periods (April-September) in 1981 and
1982 were 80.9 and 170.3 mm, respectively. Soils in the research unit
vary from moderately well drained to very poorly drained. The major
soil type is Leon fine sand.
Two hundred calves, sired by Brahman and Romana Red bulls and
out of Angus and F1 Angus x Brown Swiss reciprocal crossbred dams
(table 1), were stratified by breed type and sex to the following creep
treatments: (1) no creep feed (NC); (2) long-term creep (LC),
creep-fed from an average age of 56 d to weaning (210 d ); and (3)
short-term creep (SC), creep-fed from an average age of 146 d to
A commercial creep feed with 14% crude protein, not more than
8% crude fiber, not less than 2.5% crude fat and 9000 U.S.P. units of
vitamin A per .45 kg was fed. Creep feeders were located near shade
and water. Alternate calves within sex, breed type and creep treatment
subgroups were implanted with 36 mg of zeranol at about 56 d of age
and reimplanted 90d later.
A 60-d breeding season from about April 1 to June 1 was used.
Calves were identified and weighed and bull calves castrated within 24
of birth. Calves were weaned on September 1, when their average age
was 210-d, and weaning weights of all calves were adjusted to this age.
Cows were palpated for pregnancy at weaning time.
TABLE 1. NUMBER OF CALVES BY BREED OF
SIRE, BREED OF DAM AND SEX OF CALF
Breed of dam
Breed Angus F1 Angus x Brown Swiss
sire Steer Heifer Steer Heifer
Brahman 18 30 26 37
Romana Red 8 21 30 30
Cows and calves were maintained in pastures consisting
primarily of Pensacola bahiagrass (Paspalum notatum Flugge) and white
clover (Trifolium repens L.). Brood cows were wintered on corn silage
(IFN 3-20-506) plus molasses (IFN 4-04-696) and protein supplement to
meet NRC requirements from early December until about March 15, when an
adequate quantity of clover was available in the pastures.
PastLres were monitored for both quantity and quality of
available forage. Quantity of available forage was estimated using a
simple-disk meter (.5m2 ) as described by Santillan et al. (1979).
Hand-plucked samples of grass and clover were obtained from each
pasture once a month from April through August. The ratio of grass to
clover was estimated visually each month. Grass and clover samples
were analyzed (AOAC, 1980) for crude protein using a Technicon
Autoanalyzer II and in vitro organic matter digestibility (IVOMD) was
determined using the procedure described by Moore and Mott (1974). The
estimated ratio of grass to clover was combined with the crude protein
and IVOMD determinations from the samples to obtain mean pasture crude
protein and IVOMD percentages.
Cow-calf pairs within the LC and SC creep treatments were
randomized to one of two replicates (pastures). Cow-calf pairs in the
NC groups were considered one replicate and placed in a single pasture.
The same four pastures were used both years for the LC and SC creep
groups; however, the two pastures used for the LC creep treatment in
1981 were used for the SC creep treatment in 1982. A different pasture
was used for the NC group each year. Stocking rates across both years
varied from 1.17 to 1.69 cow-calf pairs per ha.
Data were analyzed by least squares, fixed model procedures
analyses of calf traits included the fixed main effects of creep,
analyses of calf traits included the fixed main effects of creep,
zeranol, breed of sire, breed of dam, sex, year and pasture. Fixed
main effects used in the model for cow traits included creep, zeranol,
breed of cow, breed of sire of calf, sex of calf, year and pasture.
Age of calf at the beginning of the trial was used as a covariate
(linear, quadratic) in final calf and cow models, except for 146 and
210 d weight which were age adjusted variables. Dam age (linear,
quadratic) was included in preliminary analyses; however, it was
removed from the calf model due to lack of significance. All cows in
this study were 4 yr of age and older, with the exception of six
which were 3 yr of age. All two and three-factor interactions were
included in the preliminary analyses. Only significant interactions
remained in the final models. Linear contrasts of the least-squares
means for creep treatment were computed for calf and cow traits
affected (P<.10) by creep treatment. Dry matter (kg) available per
cow-calf pair, mean pasture crude protein percentage and mean pasture
IVOMD percentage were used as covariates in independent analyses in an
attempt to account for pasture differences. However, pasture nested
within creep treatment and year was used in the final models.
Cow response traits for the calf model were 146 and 210-d
weights and conditions scores, preweaning average daily gain, frame
score and heifer udder and teat scores. Cow response traits included
cow weight change -from the beginning (which was also the start of
long-term creep feeding) to the end of the breeding season, from the
end of the breeding season to July 1, and from July 1 (start of
short-term creep feeding) to weaning. Other dependent variables
included condition scores at the beginning and end of the breeding
season and at weaning and pregnancy rate. A range of 1 to 17 was used
for condition scores of both cows and calves (Andrade, 1980). Frame
scores were from 1 to 5 (Wakeman, 1978). Udder and teat size were
subjectively scored, where 1 = below average, 2 = average, and 3 =
Results and Discussion
Weights and Weight Gains. Least-squares means for calf
preweaning performance traits are shown in table 2. Mean 210-d weight
was 252 kg. Long-term (LC) and short-term (SC) creep-fed calves were,
respectively, 33 and 26 kg heavier (P<.001) at 210 d than noncreep-fed
calves (NC). The LC calves were 7 kg heavier (P<.08) than SC calves
at 210 d. The LC calves were heavier (P<.001) at 146 d and had a
higher (P<.001) average daily gain from 56 to 146 d than SC and NC
calves. Both SC and NC calves were considered to be noncreep-fed at
this time, since the SC calves did not receive creep feed until they
averaged 146 d of age. The SC and NC calves had comparable 146-d
weights (177 and 174 kg) and average daily gains from 56 to 146 d of
age (1.02 and 1.00 kg). The higher (P<.001) average daily gain of the
LC calves from 118 to 146 d of age accounted for their heavier 146 and
210-d weights and greater average daily gain from 56 to 146 d. The LC
calves were consuming an average of about .7 kg of creep feed/d at
118 d of age and about 1.15 kg/d by .46 d of age (figure 1). There was
no difference (P>.10) among creep treatments for average daily gain
from 56 to 118 d of age. This is of interest since most purebred
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56 70 84 98 112 126 140
DAYS OF AGE
Average daily creep feed intake.
cattle producers who creep feed begin when their calves are about 2 mo
of age. Prior to the time calves are about 4 mo of age, however,
the producers may be obtaining very little benefit in terms of calf
weight gain. The LC and SC calves had higher (P<. 01) average daily
gains from 146 to 210 d of age (1.20 and 1.25 kg, respectively) and
from 56 to 210 d of age (1.14 and 1.11 kg) t an did NC calves (.90 and
.96 kg). The SC calves gained faster (P<.08) from 146 to 210 d of age
than did the LC calves. This may have been a compensatory response,
since the LC calves had higher average daily gains from 118 to 146 d of
age. Similar advantages for creep feeding calves from about 60 d of age
to weaning were reported by Kuhlman et al. (1961), Stricker et al.
(1979) and Martin et al. (1981). Burns et al. (1966) reported a 14.kg
advantage due to creep feeding calves for 60 d prior to weaning at 215
d of age. The 14 kg advantage observed by Burns et al. is about half
as much as was obtained in this study for an equivalent time period.
Average weight gains of LC and SC calves above the gains of
the NC calves, creep feed intakes and creep feed efficiencies are
presented in table 3. The LC calves gained 28 kg more weight from 56
to 210 d of age than did the NC calves. They consumed an average of
about 187 kg of creep feed during this time and required 6.7 kg of
creep feed/kg live weight gain above the NC calves. The SC calves
gained 22 kg more than the NC calves and had a creep efficiency of 5.3.
Efficiency of creep utilization for gain did not differ (P<.10) between
LC and SC calves.
Calves implanted with zeranol were 9 kg heavier (P<.001) at
146 d of age and 16 kg heavier (P<.001) at 210 d than non-implanted
calves (table 2). Zeranol implanted calves gained .08 kg/d more (P<
LU L 0
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.001) from the first implant date to the date of the second implant (56
to 146 d of age) than did the non-implanted calves and .12 kg/d more (P<
.001) from the second implant to weaning. These findings are in
agreement with Corah (1980), who reported an increase in weight gain of
about 10 and 24 kg, respectively, for one and two implants preweaning.
Zeranol implanted LC and SC calves gained .18 and .14 kg/d
more (P<.001), respectively, from 146 to 210 d of age than did the
non-implanted calves on the same creep treatments, whereas implanted
NC calves only gained .06 kg more (P<.10) than non-implanted calves.
The additional growth response obtained from zeranol was expressed
to a greater degree when nutrition was increased, a finding similar to
that reported by Davis (1980).
Calves produced by F1 Angus x BroWn Swiss reciprocal crossbred
dams (F1) were heavier (P<.001) at 146 and 210 d of age and had higher
average daily gains (P<.01) during all periods except from 146 to 210 d
of age than calves from Angus cows (table 2). Similar advantages in
weaning weight of calves produced by Angus x Brown Swiss crossbred and
straightbred Angus cows were reported by Andrade (1980) and Olson
(1980). There was no significant creep treatment by breed of dam
interaction for any calf trait, which would suggest that there was an
additive effect of creep feed and milk consumption on preweaning weight
gain. LC calves nursing F1 dams gained an average of .18 kg/d more
from 56 to 210 d of age than NC calves nursing F1 dams, compared to a
.17 kg/d higher average daily gain for LC than for NC calves nursing
Angus dams. Comparable differences in average daily gains between SC
and NC calves from 146 to 210 d of age, the period in which the SC
calves received creep feed, were .32 kg/d for SC calves nursing F1 dams.
The F1 dams produced about 1.5 kg/d more milk than did the
Angus dams (Euclides et al., 1983). Ereed of dam was confounded in
this study with breed composition of calf. All calves nursing F, dams
were 1/4 Brown Swiss 1/4 Angus and 1/2 either Brahman or Romana Red
breeding. Calves nursing Angus dams were 1/2 Angus and 1/2 either
Brahman or Romana Red. Calves nursing the F1 dams had more growth
potential than those nursing Angus dams (Gregory et al., 1978b;
Andrade, 1980; Euclides et al., 1983). The additive response for
growth rate obtained from creep feed and milk consumption was partially
confounded in this study by the fact that calves with greater growth
potential were nursing the dams with higher milk production. These
data do not concur with the findings of Christian et al. (1965); Burns
et al. (1966) and Ochoa et al. (1981), who suggested that creep feeding
tends to mask the milk production differences among ccws, anc that
calves nursing poorer milking dams may compensate by eating more creep
feed than those nursing high producing dams. Wyatt et al. (1977a) also
stated that as milk intake of the calf increases the non-milk inputs,
forage and creep feed, are reduced.
Zeranol implants increased (P<.03) the rate of gain from 146
to 210 d of age more in calves nursing Angus dams than in those nursing
F1 dams (table 4). Non-implanted calves nursing F1 dams gained an
average of 1.10 kg/d from 146 to 210 d of age as compared to an average
daily gain of 1.02 kg/d for non-implanted calves nursing
Angus cows. Zeranol implanted calves nursing Angus dams,
however, gained slightly faster than implanted calves nursing F1 dams
(1.19 and 1.17 kg/d, respectively). The interaction of creep, zeranol
and breed of dam affected (P<.03) average daily gain from 146 to 210 d
of age. The greatest response to zeranol for average daily gain from
146 to 210 d of age was shown by SC calves nursing Angus dams and by LC
calves nursing Angus and F1 dams (table 4).
Brahman-sired calves were heavier (P<.001) at 146 and 210 d of
age and had higher (P<.02) average daily gains from 56 to 210 d of age
than calves sired by Romana Red bulls.
Steer calves were heavier (P<.001) at 146 and 210 d of age and
gained faster in all periods (P<.001) than heifer calves (table 2).
The zeranol effect on 210-d weight was greater (P<.09) in steers than
heifers. Implanted steers were 22 kg heavier than non-implanted
steers, whereas the 210-d weight of implanted heifers was 11 kg
heavier than that of those not implanted with zeranol. Davis (1980),
on the other hand, reported that there was no significant zeranol
treatment by sex of calf interaction effect on calf weaning weight. The
breed of dam by sex of calf interaction affected 146-d (F<.05) and
210-d (P<.06) weights. Steer calves nursing F dams were 25 and 33 kg
heavier at 146 and 210 d of age, respectively, than heifers nursing F1
dams. Comparative advantages for steers nursing Angus dams over
heifers nursing dams of the same breed were 14 and 20 kg.
Pasture, nested within creep treatment and year, affected (P<
.003) average daily gain from 56 to 118, 118 to 146, and 146 to 210 d
of age. Pastures were monitored each month for quality and quantity of
available forage. Available dry matter (kg) per cow-calf pair, mean
pasture crude protein percentage and mean pasture IVOMD percentage were
used in independent analyses in an attempt to account for variability
due to effect of pasture. However, due to reduced R2 values and lack
of agreement between actual means and least-squares means, these
crn (M C-
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U C L
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covariables were dropped from the final analyses in favor of the total
effect of pasture. Values for available dry matter per cow-calf pair,
mean pasture crude protein percentage and mean pasture IVOMD percentage
are presented in tables 5, 6 and 7 respectively. Large variations in
available dry matter per cow-calf pair, mean pasture crude protein and
mean pasture IVOMD existed across months and years in this study. The
data presented in table 5 would indicate that quantity of available
forage was not limited in any pasture during this study. The low crude
protein and IVOMD values in July and August of 1982 (tables 6 and 7)
would suggest that quality of forage might have been limited for
optimal calf performance during this period.
Frame and Condition Scores. Least-squares means for frame and
condition scores are presented in table 2. Creep feeding did not
affect (P<.20) frame score at weaning. Stricker et al. (1979), on the
other hand, reported that creep feeding resulted in an increased frame
size. The LC calves were fatter (P<.001) at 146 d or age than calves
not receiving creep feed, and LC and SC calves were fatter (P<.001)
than NC calves at 210 d. There was no difference (P<.16) in condition
at 210 d between LC and SC calves.
Zeranol implants did not affect (P>.20) frame score at weaning
or condition score at either 146 or 210 d of age. These results are in
agreement with those of Davis (1980) and Gerken et al. (1978). Corah
(1980), however, reported that calves implanted at birth with 36 mg of
zeranol and again at 4 mo of age had less condition at weaning than
Calves produced by F1 dams were larger framed (P<.001) than
those out of Angus dams, but had lower condition scores at 210 d (P<
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.03). The F, dams produced more milk as cited earlier, but were
nursing calves with one-fourth Brown Swiss breeding. These calves were
larger framed and later maturing, thus, did not fatten as early as the
one-half Angus calves nursing Angus dams. Brahman-sired calves had
larger frames (P<.001) than those sired by Romana Red bulls.
Steer calves had higher frame scores (P<.001) and lower
condition scores at 146 (P<.08) and 210 d (P<.001) than heifer calves.
Breed of dam by sex of calf interaction affected (P<.06) frame score.
Steers and heifers nursing F1 dams had larger frames ( 3.5 and 3.0,
respectively) than those nursing Angus dams (2.8 and 2.6). There was a
greater difference between the two steer groups than between the two
groups of heifers.
Udder and Teat Scores. Udder score at weaning, which was a
subjective measure of udder size, was affected by creep treatment (P<
.02) and breed of sire (P< .002) The LC heifers had a higher average
udder score (2.0) than the SC and NC heifers (1.7 and 1.8,
respectively). The higher udder score of the LC heifers might reflect
increased fat deposition in the udder. Hansson (1956), Swanson (1960)
and Martin et al. (1981) have suggested that fat infiltration in the
udder, as a result of overfeeding heifers during periods of early
growth, may negatively affect future maternal performance.
Brahman-sired heifers had a higher (P<.002) average udder
score than those sired by Romana Red bulls. This may be due in part to
more fat being deposited in the udder of the Brahman-sired heifers and
(or) excessive amounts of skin which is characteristic of the Brahman
breed, but not of the Romana Red.
Teat size was affected (P<.001) only by zeranol treatment.
Average teat size was greater in implanted than non-implanted heifers,
a finding similar to that of Lowman (1980).
Least-squares means for cow weight change, condition score and
pregnancy rate are presented in table 8. Cow condition score at the
beginning of the breeding season did not differ (P>.57) among the three
assigned calf creep-treatment groups. However, cows with LC calves
gained more (P<.09) weight during the 60-d breeding season and had a
higher (P<.02) average condition score at the end of the breeding
season than those nursing NC calves. Other authors have suggested that
increasing cow weight gain and condition during the breeding season, by
creep feeding the calves, may result in a subsequent increase in
pregnancy rate (Jones and Jones, 1932; Stricker et al., 1979). In this
study, however, pregnancy rate was not affected (P>.46) by creep
treatment of calf (89.5% for the non-creep group vs 92.7% for the
creep-fed group) even though a difference did exist in cow weight
change and condition sccre.
Creep treatment of the calf did not affect (P>.11) cow weight
gain from the end of the breeding season to July 1, the start of
short-term creep treatment, but cows nursing SC and LC calves gained
more (P<.001) weight from July 1 till the calves were weaned on
September 1. There was no difference (P> .28) in cow condition score
at weaning due to creep treatment of calf.
Cow weight gain, condition score and pregnancy rate were not
affected by zeranol implants in their calves. In this study, zeranol
implanted calves gained more rapidly throughout the nursing period than
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did non-implanted calves. Since zeranol implants in calves had no
affect on cow weight gain, condition score or pregnancy rate, the
increased weight gain of the calf apparently did not place an added
stress on the cow.
Angus cows gained less (P<.02) weight from the beginning of
the breeding season to July 1 but had higher (P<.001) condition scores
than did F1 cows. The F1 cows had a higher (P<.07) pregnancy rate than
Angus cows (96.6 vs 86.8%). Previous studies with the same two breed
groups have reported no difference in the pregnancy rates (Olson, 1980;
Euclides et al., 1983).
Cows with Brahman-sired calves gained more (P<.09) weight
during the breeding season than those with Romana Red-sired calves.
There was no difference, however, in weight gain during the breeding
season of calves sired by the two breeds of bulls (table 2). Breed of
sire of calf did not affect (P>.19) cow condition score or pregnancy
rate. Sex of calf did not affect (P>.55) cow weight gain or condition
score; however, cows with heifer calves had a higher (P<.10) pregnancy
rate than those with bull calves.
It can be concluded that calves receive very little benefit
from creep feed prior to 120 d of age. Creep feeding calves from about
5 mo of age until weaning at 7 mo results in more efficient utilization
of creep feed and almost as much increase in weight gain as creep
feeding from 2 mo of age. The effect of creep feed intake on
preweaning weight gain may be additive with milk intake in calves with
above average growth potential. Increased levels of nutrition, from
creep feed and milk, may result in increased growth response to
zeranol. Pregnancy rate in the cow herd is not increased by creep
feeding the calves, when cows have adequate nutrition during the
A 2-yr study was conducted to evaluate the effects of creep
feeding, preweaning zeranol implants and breed type on calf and cow
performance. Two hundred calves sired by Brahman and Romana Red bulls
and out of Angus and F1 Angus x Brown Swiss reciprocal crossbred (F1 )
dams were stratified by breed type and sex to three creep treatments:
(1) no creep feed (NC); (2) long-term creep (LC), creep-fed from 56 d
of age to weaning (210 d); and (3) short-term creep (SC), creep-fed
from 146 d of age to weaning. Alternate calves within sex, breed type
and creep treatment were implanted with 36 mg of zeranol at about 56 d
of age and reimplanted 90 d later. The LC and SC calves had higher (P<
.001) 210 d weights than NC calves (264 and 257 vs 231 kg
respectively). The LC calves had higher (P<.001) 146 d weights than NC
calves. Frame score was not affected (P>.20) by creep treatment. The
LC calves had higher (P<.001) average daily gains from 118 to 210 d of
age and superior 146 and 210-d condition scores than did NC calves.
Cows with creep-fed calves gained more weight during the breeding
season than cows with noncreep-fed calves. Pregnancy rate was not
affected (P>.46) by creep treatment. Zeranol implants increased (P<
.01) both 146 and 210-d weights (184 vs 175 kg and 259 vs 243 kg) and
average daily gains during all periods to weaning. Cow weight gain,
condition score and pregnancy rate were not affected (P>.14) by zeranol
treatment of calves. Brahman-sired calves had higher (P<.005) 146 and
210-d weights and frame scores than Romana Red-sired calves. Calves
out of Angus dams had lower (P<.001) 146 and 210-d weights, frame
scores and average daily gains from 56 to 146 and 210 days of age, but
higher ( P<.03) 210-d condition scores than calves out of F1 dams. The
F1 cows gained more weight (P<.007) during the breeding season, had a
lower (P<.001) condition score and a higher pregnancy rate (96.5 vs
86.8%) than the Angus cows. Cows with heifer calves had a higher (P<
.10) pregnancy rate than those with steer calves.
WEANLING HEIFER DEVELOPMENT AND COMPOSITION.
The effects of creep feeding and preweaning growth stimulants
on future reproductive performance and maternal ability of replacement
heifers are of concern to many cattlemen. Most commercial cattlemen
sell some of their weaned heifers as feeder-stocker calves. By using
creep feed and growth stimulants, cattlemen can sell these heifers at
heavier weignts and for more total dollars.
Excessive conditioning or fattening of suckling heifers may
influence subsequent development of desired maternal traits (Holloway
and Totusek, 1973b). A detrimental effect of above average maternal
environment during the early life of heifer calves on their subsequent
producing ability has been shown by Mangus and Brinks (1971), Kress and
Burfening (1972) and Beltran (1978). Swanson (1960) and Holtz et al.
(1961) suggested that over-conditioned dairy heifers deposited excess
fat in their mammary system, which impaired future milk production
The effects of growth stimulants on the future reproductive
performance of heifers are controversial. An important issue from the
producer's point of view is not whether creep feeding and growth
stimulants improve weaning weight, but how these practices affect
future productive potential of replacement heifers.
The purpose of this study was to evaluate the effects of creep
feeding, preweaning zeranol implants and breed type on reproductive
tract development, fat deposition in the udder, and body composition of
The preweaning creep feeding and zeranol treatments and breed
types compared in this study were described in study I. Calf and Cow
Performance. Twenty-four weanling heifers were used in this study.
These heifers were selected so that one heifer was chosen from each
creep treatment, zeranol treatment, breed of sire, and breed of dam
Heifers were slaughtered one day following weaning. The
gastrointestinal tract from each heifer was cleaned of digesta for
determination of empty body weight. Carcasses were quality and yield
graded after e 24-h chill at 1 to 2"C. The 9-10-11 rib section from
the right side of each carcass was removed and physically separated
into fat, lean and bone tc estimate separable carcass components, as
outlined by the procedure of Hankins and Howe (1946). The soft tissue
components (lean plus fat) of the 9-10-11 rib section were thoroughly
mixed, ground and analyzed for chemical composition by AOAC (1980)
procedures. Chemical determinations of the soft tissue components were
used to estimate edible fat, protein and moisture, according to the
prediction equations developed by Hankins and Howe (1946).
Reproductive tracts were removed from each heifer at time of
slaughter. Ovaries were weighed, measured and follicles greater than 3
mm were counted. Uterine weight (horns and body of uterus) was
recorded and the outside diameter of the right uterine horn was
measured at the bifurcation. The udder was removed and weighed. Half
of each udder was ground and sampled for percent lipid. Percent lipid
was determined using the Soxhlet Ether Extraction procedure according
to AOAC (1980).
Adipose tissue samples were taken from the udder and
tail-head region of each heifer. The subcutaneous sample from the
tail-head region was taken 5 cm to the right of the tail-head. Three
thin slices (approximately 200 mg) were obtained from each tissue
sample using a Stadie-Riggs microtome. Slices were fixed with 5ml of
3% osmium tetroxide and 3 ml of 50 mM collidine-HCL buffer solution
(pH 7.4), as described by Hirsch and Gallian (1968). The connective
tissue matrix surrounding the adipocytes was solubilized with 8 M urea
as described by Etherton et al. (1977). Adipocytes were rinsed through
a 250-pm nylon mesh screen, with distilled water containing .01%
triton x-100 (pH 10) into 200 ml volumetric flasks. A NaCI solution
(.154 M) was added to increase volume to 200 ml. DLplicate 10 ml
aliquots were removed from each flask, added to 190 ml of a 45% sucrose
solution, counted and sized using a Coulter Counter Model TA II. A
560-vm aperture was used. A 77.8-vm standard of corn pollen was used
to determine the volume of each of the instrument's 16 channels.
Standard particles and fixed adipocytes were assumed to be spherical.
Data were analyzed by least-squares, fixed model procedures
using the Statistical Analysis System (SAS, 1979). The model used to
analyze all response variables included the fixed main effects of year,
creep treatment, zeranol treatment, breed of sire and breed of dam.
Age at the time of slaughter was used as a covariate. All
interactions were pooled and remained in the error term. Linear
contrasts of the least-squares means for creep treatments were computed
for all response variables affected (P<.10) by creep treatment.
Results and Discussion
Reproductive Tract Development. Least-squares means and P
values for reproductive tract characteristics are shown in table 9.
Creep treatment did not affect (P>.19) the ovarian weight, ovarian
size, uterine horn diameter or follicle number of weanling heifers.
Long-term (LC) and short-term (SC) creep-fed heifers tended (P>.11) to
have heavier uterine weights than noncreep-fed (NC) heifers. No
comparable data were found in the literature. Cornwell (1981) fed
long-yearling heifers on three levels of nutrition and reported no
significant effect of nutritional level on ovarian size or weight or on
uterine horn diameter. Research by Hill et al. (1970) and Spitzer et
al. (1978), using long-yearling and yearling heifers, respectively,
indicated that ovarian size was reduced when heifers were on a
restricted plane of nutrition.
Heifers implanted with 36 mg of zeranol at 56 and 146 d of age
had a greater (P<.03) uterine horn diameter and heavier (P<.02) uterine
weight than non-implanted heifers. There was no effect (P>.20) of
zeranol implants on ovarian weight or size or on number of follicles.
Breed of dam did not have an effect (P> .17) on the
development of the reproductive tract of the weanling heifers.
Brahman-sired heifers had a greater ovarian weight (P<.04) and size (P<
.02) than Roman Red-sired heifers. Uterine horn diameter, uterine
weight and follicle number were not affected (P>.14) by breed of sire.
The differences in ovarian weight and size due to breed of sire may
have been due to differences in size of the heifers. Brahman-sired
Cj ) o
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heifers weighed more (P<.02) at slaughter than Romana Red-sired heifers
(233 vs 211 kg). Foley et al. (1964), using dairy cattle of all ages,
reported a highly significant correlation (.65) between weight of both
ovaries and live weight. They stated that age and live weight appeared
to have more effect on ovarian weight than did breed. However, the LC
heifers in this study were heavier (P<.02) at slaughter than NC
heifers, yet there were no differences in ovarian size and weight due
to creep treatment. Therefore, the differences found in ovarian size
and weight between the Brahman and Romana Red-sired heifers might have
been due to genetic differences, independent of body size.
Udder and Subcutaneous Fat. Creep feeding did not increase (P>
.25) udder weight, percent lipid or total lipid in the udder (table
11). Though not significant, the least-squares means would indicate a
tendency for heifers to deposit more fat in the udder as length of
creep feeding increases. Furthermore, the subjective udder scores,
presented in study I were higher for LC than for NC heifers. The NC
heifers had a greater (P<.02) number of adipocytes/g of udder tissue
than LC and SC heifers; however, the total number of adipocytes in the
udder was not affected (P>.58) by creep treatment. The LC heifers had
larger (P>.04) udder and subcutaneous adipocytes than NC heifers (166.0
and 166.7 pm vs 152.7 and 148.8 Pm, respectively). The SC heifers
tended (P>.15) to have larger udder and subcutaneous adipocytes than NC
heifers. Subcutaneous adipocyte number/g of tissue was not affected (P>
.49) by creep treatment. Figure 2 illustrates the size distribution of
adipocytes by creep treatment. The LC and SC heifers had higher (P<
.10) percentages of total adipccyte volume composed of adipocytes
greater than 160 mw in diameter than did NC heifers, whereas NC heifers
LO :*- r-%
CM o i-
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had the highest (P<.05) percentage of total adipocyte volume made up of
adipocytes less than 129 Pm in diameter.
Data reported by Hood and Allen (1973), Allen (1976) and
Garbutt et al. (1979) indicate that adiposity in cattle may be
influenced by nutritional treatment during periods of growth and
development. Allen (1976) stated that changes in bovine cellular
hypertrophy and hyperplasia are dependent on the location of the fat
depot. He indicated that intramuscular lipid accumulation is more
dependent on cellular hyperplasia than are subcutaneous depots. The
results of this study would indicate that cellular hypertrophy had
occurred in the udder and subcutaneous fat depots of creep-fed
heifers. Therefore, any increase in lipid accumulation in these fat
depot areas would be due primarily to adipocyte hypertrophy rather than
Zeranol implants did not affect (P>.98) udder weight. Percent
udder lipid was lower (P<.02) in heifers implanted with zeranol;
however, total udder lipid was not affected (P>.68). Implanted heifers
had more (P<.07) adipocytes/g of udder tissue and tended (P>.14) to
have smaller udder adipocytes than non-implanted heifers. Total udder
adipocytes did not differ (P>.22) between implanted and non-implanted
heifers (8.55 and 7.06 x 10 respectively). Zeranol treatment did not
affect (P>.65) number of subcutaneous adipocytes/g of tissue; however,
implanted heifers had smaller (P<.10) subcutaneous adipocytes than
non-implanted heifers. Size distribution of udder and subcutaneous
adipocytes by zeranol treatment is shown in figure 3.
Heifers out of Angus dams had smaller (P<.08) udders and less
(P<.10) total fat in the udder than those out of F1 dams (2.91 vs 3.49
31wImOnA 7V101 JO LN30l3d
O 0 O 0 O 0 0 0
I- ro re) CMi CM' -
kg and 2.37 vs 2.86 kg). This difference in udder size was not
detected from visual estimates presented in the first study. Breed of
dam did not affect (P>.44) percent lipid in the udder. Total udder
adipocytes and udder adipocytes/g of tissue were not affected (P>.35)
by breed of dam. Heifers out of F1 dams tended (P<.12) to have larger
udder adipocytes than those produced by Angus dams. Subcutaneous
adipocyte size anc number were unaffected (P>.61) by breed of dam.
Brahman-sired heifers had heavier (P<.001) udders (3.85 vs
2.55 kg) and more total fat in their udders (3.15 vs 2.08 kg) than
Romana Red-sired heifers. Percent lipid in the udder, however, was
unaffected (P>.78) by breed of sire. Number of udder adipccytes/g of
tissue was not affected (P>.31) by breed of sire. But as a result of
more total fat in the udder, Brahman-sired heifers had more (P<.004)
total adipocytes than those sired by Romana Red bulls. Romana
Red-sired heifers, however, tended (P>.14) to have larger udder
adipocytes than Brahman-sired heifers. In addition, Romana Red-sired
heifers had fewer (P<.08) adipocytes/g of subcutaneous adipose tissue
but larger (P<.09) subcutaneous adipocytes than those sired by Brahman
Breed type has been used to provide an explanation for
differences in adiposity in several studies; however, there have been
few studies specifically designed to investigate variations in
adipocyte size and number among breeds. Hood and Allen (1973, 1975)
reported that perirenal and subcutaneous adipose tissue in 14-mo old
Hereford x Angus steers contained larger cells than the respective
tissues from Holstein steers of similar age and live weight. In
addition, they observed that a higher percentage of the total adipocyte
volume for Hereford x Angus steers was in larger cell diameter ranges
than for the same tissues from Holstein steers. Figures 4 and 5
illustrate the distribution of udder and subcutaneous adipocytes for
breed of sire and breed of dam.
Carcass Characteristics and Composition. Least-squares means
for carcass characteristics and composition are shown in tables 11, 12
and 13. The LC heifers had heavier (P<.005) empty body weights and
less (P<.02) gastrointestinal tract (GIT) fill than NC heifers. The LC
heifers also had heavier (P<.002) hot carcass weights and higher (P<
.02) dressing percentages than NC heifers. The LC heifers had heavier
(P<.10) empty body and hot carcass weights than SC heifers, but there
was no difference (P>.21) in GIT fill or dressing percent between
heifers of the two creep treatments. The SC heifers did not differ (P<
.10) frcm NC heifers for empty body weight, GIT fill, hot carcass
weight or dressing percentage.
Yield grade was not affected by creep treatment; however,
carcasses from LC heifers had more (P<.05) KPH fat, greater (P<.003)
fat thicknesses and larger (P<.04) ribeyes than NC and SC heifers.
Carcasses from SC and NC heifers did not differ (P>.17) for KPH fat,
fat thickness cr ribeye area. When expressed on a per 100 kg of hot
carcass basis, ribeye area was not influenced (P>.84) by creep
treatment. Creep treatment did not affect (P>.47) marbling sccre,
carcass maturity, lean color or fat color. Similar effects of
long-term creep feeding on the carcass characteristics of weanling
calves were reported by Scarth et al. (1968), Corah and Bishop (1975)
and Martin et al. (1980). Rouquette et al. (1983), on the other hand,
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found no differences in carcass characteristics between long-term and
Carcasses from LC heifers had a lower percent edible protein
(P< .05) than carcasses from NC and SC heifers (table 13). Creep
treatment did not affect (P>.26) percent edible fat or moisture in the
carcass. The LC heifers had a higher (P<.04) percent separable fat and
tended (P <.1) to have a lower percent separable lean content of the
carcass than SC and NC heifers. Carcasses from SC heifers had a higher
(P<03) percent bone than carcasses from LC heifers, but did not differ
(P>.17) from those of NC heifers. Contrary to the above, Corah and
Bishop (1975) reported no difference in percent protein of carcasses
between noncreep-fed and creep-fed heifers slaughtered at weaning.
Furthermore, they observed that carcasses from noncreep-fed heifers had
a higher percent bone than those from creep-fed heifers.
The SC heifers sacrificed in this study were probably not
completely representative of the SC treatment group. SC and NC heifers
did not differ (P<.11) with respect to any carcass trait including
slaughter height and hot carcass weight. However, in the population
from which these heifers were chosen, SC calves were heavier (P<.001)
at 210-d of age than NC calves.
Zeranol implants did not affect (P>.20) empty body weight, GIT
fill, hot carcass weight or dressing percent. Implanted heifers had
higher (P>.02) cutability carcasses (lower yield grade number) than
non-implanted heifers. Percent KPH and fat thickness were not affected
(P>.20) by zeranol treatment, but ribeye areas were larger (P<.06) in
the implanted heifers. The larger ribeye accounted for the lower yield
grade number of the carcasses from implanted heifers. Marbling score
and fat color were not affected (P>.41) by zeranol treatment. However,
zeranol implants increased lean color (P<.05) and maturity (P<.006),
and overall maturity (P<07). Bone maturity was not affected (P>.17)
These results indicate that zeranol affects carcass traits
associated with body weight, and may increase maturity rate, as
measured by characteristics of the muscle. Gregory and Ford (1983),
using late maturing bull calves, concluded that zeranol treatment
effects on carcass characteristics were of little consequence other
than through increases in body weight.
Estimated edible fat, protein and moisture in the carcass were
not affected (P>30) by zeranol implants. Zeranol, however, did cause
a decrease in the percent separable fat (P<.09) and an increase (P<
.008) in the percent separable lean in the carcass. Percent separable
bone was not affected (P>.23) by zeranol treatment. Similar results
for estimated carcass components, using yearling steers, were reported
by Sharp and Dyer (1971).
Breed of dam did not affect (P>.23) empty body weight, GIT
fill, hot carcass weight or dressing percent. Carcasses from heifers
out of Angus dams had more (P<.08) ribeye area per 100 kg of hot
carcass and tended (P.11) to have less KPH fat than those out of F1
dams. This resulted in a tendency for carcasses from heifers out of
Angus dams to be higher (P<.12) yielding than those out of F1 dams.
Carcass fat thickness, maturity, lean color and fat color were
unaffected (P>48) by breed of dam. Estimated edible and separable
carcass components were not affected (P>.19) by breed of dam.
Brahman-sired heifers had heavier empty body (P< .009) and hot
carcass (P <.02) weights than Romana Red-sired heifers. Breed of sire
did not affect (P>.18) GIT fill, dressing percent, quality and yield
grade components, or estimated carcass composition. These results are
in agreement with Koch et al. (1982) who mated Angus and Hereford cows
to various breeds of bulls and reported no differences in carcass
characteristics between Brahman and Sahiwal-sired steers, other than
Brahman-sired steers had heavier carcass weights.
These data indicate that an increase of subcutaneous fat in
long-term creep-fed heifers is due primarily to adipocyte hypertrophy.
Creep feeding also increases adipocyte size in the udder. Heifers
implanted preweaning with zeranol have a Icwer percent lipid in the
udder and smaller udder and subcutaneous adipocytes than non-implanted
heifers. Zeranol implants increase ribeye area and percent separable
lean and decrease percent separable fat in the carcasses of weanling
Effects of preweaning creep feeding and zeranol implants on
reproductive tract development, udder and subcutaneous fat deposition,
and carcass composition were studied in 24 weanling heifers sired by
Brahman and Romana Red bulls and out of Angus and FI Angus x Brown
Swiss reciprocal crossbred cows. Creep treatment did not affect (P>
.19) ovarian weight, ovarian size, uterine horn diameter or follicle
number. Heifers from the three creep treatments did not differ (P >.25)
in udder weight or percent lipid and total lipid in the udder. The
noncreep-fed (NC) heifers had a greater (P<.02) number of adipocytes/g
of udder tissue than long-term creep fed (LC) and short-term
creep-fed (SC) heifers. The LC heifers had significantly larger udder
(166.G vs 152.7 um) and subcutaneous adipocytes (166.7 vs 148.8 um)
than NC heifers. The LC heifers had heavier (P<.10) empty body and hot
carcass weights than SC and NC heifers. Carcasses from LC heifers had
m re (P<.04) separable fat, less (P<.11) separable lean and less (P<
.05) edible protein than carcasses from SC and NC heifers. Heifers
implanted with zeranol had a greater (P<.03) uterine horn diameter and
heavier (P<.02) uterine weight than no -implanted heifers. Percent
lipid was lower (P<.02) in heifers implanted with zeranol. Total udder
adipocytes did not differ (P>.22) between implanted and non-implanted
heifers; however, implanted heifers had smaller (P<.10) subcutaneous
adipocytes than non-implanted heifers. Implanted heifers had higher (P<
.02) cutability carcasses (lower yield grade number) than non-implanted
heifers. Zeranol implants increased carcass lean color (P<.05) and
maturity (P<.006) and overall maturity (P<.07). Zeranol decreased (P<
.09) percent separable fat and increased (P<.008) separable lean in the
carcass. Breed of dam did not have an effect (P>.17) on development of
the reproductive tract of weanling heifers. Heifers out of Angus dams
had smaller (P<.08) udders and less (P<.10) total fat in the udder than
those out of I dams. Heifers out of F1 dams tended (P<.12) to have
larger udder adipocytes than heifers produced by Angus dams. Estimated
edible and separable carcass components were unaffected (P>.19) by
breed of dam. Brahman-sired heifers had a greater ovarian weight (P<
.04) and size (P<.02) than Romana Red-sired heifers. Brahman-sired
heifers had mcre (P<.004) total udder adipccytes; whereas, Romana
Red-sired heifers tended (P>.14) to have larger udder adipocytes.
Breed of sire did not affect (P>.18) estimated carcass composition or
quality and yield traits.
SUMMARY AND CONCLUSIONS
A 2-year study was initiated to evaluate the effects of creep
feeding, preweaning zeranol implants and breed type on calf and cow
performance and on weanling heifer development and composition. Two
hundred calves sired by Brahman and Romana Red bulls and out of Angus
and F, Angus x Brown Swiss reciprocal crossbred (F1) cows were
stratified by breed type and sex to the following creep treatments: no
creep feed (NC); long-term creep (LC), creep-fed from 56 d of age to
weaning (210 d); and short-term creep (SC), creep-fed from 146 d of age
to weaning. Half of the steer and heifer calves within each breed and
creep treatment were implanted with 36 mg of zeranol at 56 and 146 d of
age. Twenty-four of the weanling heifers were sacrificed to evaluate
the effects of creep feeding, zeranol implants, and breed on
reproductive tract development, udder and subcutaneous fat deposition
and carcass composition.
The LC and SC calves had higher 210-d weights than NC calves
(264 and 256 vs 231 kg). The LC calves had higher 146-d weights,
higher average daily gains from 118 to 210-d of age, and higher
condition scores at 146 and 210-d than NC calves. Frame score was not
affected by creep treatment. Cows with creep-fed calves gained more
weight during the breeding sea on than cows with noncreep-fed calves,
but pregnancy rate was not affected by creep treatment. Zeranol
implants increased both 46 and 210-d weights (184 vs 175 and 259 vs
243 kg) and average daily gains during all periods to weaning. Cow
weight gain, condition score and pregnancy rate were not affected by
zeranol treatment of calves. Brahman-sired calves had higher 146 and
210-d weights and frame scores than RomEna Red-sired calves. Calves
out of Angus dams had lower 146 and 210-d weights, frame scores and
average daily gains from 56 to 46 and 210 d of age, but higher 210-d
condition scores than calves out of F1 dams. The F1 cows gained more
weight during the breeding season, had a lower condition score, and a
higher pregnancy rate (96.6 vs 86.8%) than the Angus cows. Cows
nursing heifer calves had a higher pregnancy rate than those nursing
Creep treatment did not affect (P>.19) ovarian weight, ovarian
size, uterine horn diameter or follicle number. Heifers from the three
creep treatments did not differ (P >.25) in udder weights or percent
lipid and total lipid in the udder. The NC heifers had a greater (P <
.02) number of adipocytes/g of udder tissue than LC and SC heifers. The
LC heifers had significantly larger udder (166.0 vs 152.7 um) and
subcutaneous adipocytes (166.7 vs 148.8 um) than NC heifers. The LC
heifers had heavier (P <.10) empty body and hot carcass weights than SC
and NC heifers. Carcasses from LC heifers had mcre (P<.04) separable
fat, less (P <.11) separable lean and less (P<.05) edible protein than
carcasses from SC and NC heifers. Heifers implanted with zeranol had a
greater (P <.03) uterine horn diameter and heavier (P <.02) uterine
weight than non-implanted heifers. Percent lipid was lower (P <.02) in
heifers implanted with zeranol. Total udder adipocytes did not differ
(P >.22) between implanted and non-implanted heifers; however,
implanted heifers had smaller (P <.10) subcutaneous adipocytes than
non-implanted heifers. Implanted heifers had higher (P< .02) cutability
carcasses (lower yield grade number) than non-implanted heifers.
Zeranol implants increased carcass lean color (P< .05) and maturity (P
.006) and overall maturity (P <07). Zeranol decreased (P <09) percent
separable fat and increased (P< .008) separable lean in the carcass.
Breed of dam did riot have an effect (P >.17) on development of the
reproductive tract of weanling heifers. Heifers out of Angus dams had
smaller (P< .08) udders and less (P< .10) total fat in the udder than
those out of F1 dams. Heifers out of F1 dams tended (P< .12) to have
larger udder adipocytes than heifers produced by Angus dams. Estimated
edible and separable carcass components were unaffected (P> .19) by
breed of dam. Brahman-sired heifers had a greater ovarian weight (P>
.04) and size (P<.02) than Romana Red-sired heifers. Brahman-sired
heifers had more (P <004) total udder adipocytes; whereas, Romana
Red-sired heifers tended (P> .14) to have larger udder adipocytes.
Breed of sire did not affect (P> .18) estimated carcass composition or
quality and yield traits.
It can be concluded that calves receive very little benefit
from creep feed prior to 120 d of age. Creep feeding calves from about
5 mo of age to weaning results in more efficient utilization of creep
feed and almost as much increase in weight gain as creep feeding from 2
mo of age. The effect of creep feed intake on preweaning weight gain
may be additive with milk intake in calves with above average growth
potential. Increased levels of nutrition, from creep feed and milk, may
result in increased growth response to zeranol. Little benefit, in
terms of increased pregnancy of the cow herd, is obtained from creep
feeding when cows have adequate nutrition during the breeding season.
The increase of subcutaneous fat in long-term creep-fed
heifers is due primarily to adipocyte hypertrophy. Creep feeding also
increases adipocyte size in the udder. Heifers implanted preweaning
with zeranol have a lower percent lipid in the udder and smaller udder
and subcutaneous adipocytes than non-implanted heifers. Zeranol
implants increase ribeye area and percent separable lean and decrease
percent separable fat in the carcasses of weanling heifers.
Work is continuing on the long-term effects of preweaning
creep feed and zeranol treatments on the future productivity of beef
Adams, N. J., G. C. Smith and Z. A. Carpenter. 1982. Performance,
carcass and palatability characteristics of Longhorn and other
types of cattle. Meat Sci. 7:67.
Allen, C. E. 1976. Cellularity of adipose tissue in meat animals.
Fed. Proc. 35:2302.
Almquist, H. T. 1968. Supplemental calf feeding trials. Feedstuffs.
Andrade, V. J. 1980. Effect of nutritional level during late gestation
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