Breed differences and heterosis effects for carcass and meat palatability traits in an Angus-Brahman multibreed cattle p...

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Breed differences and heterosis effects for carcass and meat palatability traits in an Angus-Brahman multibreed cattle population
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English
Creator:
Elzo, M. A.
Johnson, D. D.
Wasdin, J. G.
Driver, J. D.
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.

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University of Florida
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Breed Differences and Heterosis Effects for Carcass and Meat Palatability
Traits in an Angus-Brahman Multibreed Cattle Population


M. A. Elzo, D. D. Johnson, J. G. Wasdin, and J. D. Driver1



Estimates of additive breed genetic effects indicated that Brahman carcasses had higher dressing
percent, lower marbling, smaller ribeye area, and less fat over the ribeye than Angus. Brahman beef was
tougher, had more connective tissue, and it was less juicy than Angus beef. Heterosis increased hot
carcass weight, dressing percent, ribeye area, fat over the ribeye, and kidney, pelvic, and heart fat in
Angus-Brahman crossbred steers. Results indicated that crossbred animals with percentage Brahman up
to 50% showed limited negative impact on meat quality while maximizing meat yield due to heterosis.


Summary
Carcass and meat palatability characteristics
constitute key factors for the success of beef
cattle operations. Consumers prefer meat that
has certain desirable degrees of tenderness,
marbling, juiciness, and flavor. Cattle in the
Southern region of the US contain some
Brahman influence to help them cope with hot
and humid climatic conditions. However, meat
from Brahman cattle tends to be less tender than
meat from Bos taurus breeds, causing branded
beef products to restrict Brahman from their
beef products. Information on Brahman
purebred and crossbred cattle is needed for
objective evaluation of carcass and meat
palatability traits. This research quantified
additive genetic differences between Angus and
Brahman, estimated Angus-Brahman heterosis
effects, and estimated least squares means for
six carcass and six meat palatability traits using
data from 1367 steers from the Angus-Brahman
multibreed herd of the University of Florida
collected from 1989 to 2009. Estimates of
additive genetic breed differences between
Brahman and Angus indicated that Brahman
carcasses had higher dressing percent, lower
marbling, smaller ribeye area, and less fat over
the ribeye than Angus. In addition, Brahman
beef was tougher, had more connective tissue,
and it was less juicy than Angus beef Lastly,
heterosis increased hot carcass weight, dressing
percent, ribeye area, fat over the ribeye, and


kidney, pelvic, and heart fat in Angus-Brahman
crossbred steers. Results indicated that
crossbred animals with percentage Brahman up
to 50% showed limited ,i gi,,,i' impact on meat
quality while maximizing meat yield due to
heterosis.

Introduction
Carcass and meat palatability characteristics
constitute key factors for the success of beef
cattle operations. Consumers prefer meat that
has certain desirable degrees of tenderness,
marbling, juiciness, and flavor. This has led to
the establishment of over 60 branded beef
products in the United States (USDA, 2010).
Thus, it seems reasonable for cattle producers to
breed animals that take advantage of
opportunities presented by branded beef
programs while simultaneously breeding
animals that survive well under a variety of
environmental conditions. The Southern region
of the US with its hot and humid subtropical
environment presents serious challenges to beef
producers. Most cattle in this region contain
some percentage of Brahman to help them cope
with climatic conditions, particularly during the
summer season. However, meat from Brahman
cattle is known to be less tender than meat from
Bos taurus breeds. This has led to restrictions
on the percent of Brahman breeding by the
majority of branded beef products. Information


'Department of Animal Sciences, University of Florida, Gainesville, FL










on Brahman cattle and its crossbreds with Bos
taurus breeds is needed to objectively evaluate
their ability for carcass and meat palatability
traits relative to that of Bos taurus breeds. The
Angus-Brahman multibreed herd of the
University of Florida with cattle ranging from
100% Angus to 100% Brahman is well suited to
evaluate Angus, Brahman, and crossbred groups
of any Angus and Brahman fraction for each
carcass and meat palatability traits under Florida
environmental conditions. Thus, the objectives
of this research were to obtain estimates of
additive genetic differences between Angus and
Brahman, Angus-Brahman heterosis effects, and
to compute least squares means for breed groups
of calves ranging from 100% Angus to 100%
Brahman for six carcass and six meat
palatability traits using the complete Angus-
Brahman multibreed dataset of the University of
Florida.

Materials and Methods
Animals, date, and traits
Cattle were from a long-term genetic evaluation
study utilizing Angus, Brahman, and Angus-
Brahman cattle from the multibreed herd of the
University of Florida. The mating design used
in this herd was diallel, i.e., sires of six breed
groups (Angus (A), 4 A /4 B, Brangus (5/8 A
3/8 B), 2A 2B, 'AA 34B, and Brahman (B))
were mated to dams from these same six breed
groups. The dataset contained carcass and meat
palatability information from 1,367 calves born
from 1989 to 2009 (216 Angus, 182 % A '4 B,
224 Brangus, 341 V2A 2B, 206 'AA 34B, and 198
Brahman). These calves were the progeny of
213 sires (44 Angus, 27 % A '4 B, 42 Brangus,
26 /A 2B, 26 'AA 34B, and 48 Brahman) and
824 dams (145 Angus, 119 3 A /4 B, 127
Brangus, 174 V2A 2B, 107 'AA 34B, and 152
Brahman). Carcass traits were hot carcass
weight (HCW, lb), dressing percent (DP, %),
ribeye area at the 12th rib (REA, in2), fat over the
ribeye the 12th rib (FOE, in), kidney, pelvic, and
heart fat (KPH, %), and marbling score (MAB;
100 to 199 = practically devoid, 900 to 999 =
abundant). Meat palatability traits were Wamer-
Bratzler shear force (WBSF, lb), tenderness
score (TEND; 1 = extremely tough, 8 =
extremely tender), connective tissue score (CTI;
1 = abundant amount, 8 = none detected),


juiciness score (JUIC; 1 = extremely dry, 8 =
extremely juicy), beef flavor score (FLAV; 1 =
extremely bland, 8 = extremely intense), and
off-flavor score (OFLAV; 1 = extreme off-
flavor, 6 = none detected).

Reproduction, feeding, and management
Cows were synchronized in March, artificially
inseminated twice, and then exposed to a natural
service bull for 60 d. Calves were born from
mid-December to mid-March, and weaned in
September. Cows and calves were kept on
bahiagrass (Paspalum notatum) pastures
throughout the year with free access to mineral
supplementation. Winter supplementation
consisted of bermudagrass (Cynodon dactylon)
hay, cottonseed meal, and molasses. After
weaning steers were either taken directly to a
contract feeder (1989 to 2005; King Ranch
Feedyard, Kingsville, Texas), or to the
University of Florida Feed Efficiency Facility
(FEF) in Marianna, Florida for 100 d, and then
transported to a contract feeder (2006 to 2009;
Suwannee Farms, O'Brien, Florida). Steers at
the FEF were housed in pens and fed a
concentrate diet composed of whole corn,
cottonseed hulls, and a protein, vitamin, and
mineral supplement (FRM, Bainbridge, GA).
The FEF concentrate had 90 to 91.2% of dry
matter, 14.1 to 17. 3 % of crude protein, 1.5 to
1.7 Mcal/kg DM of Net Energy maintenance,
and 0.9 to 1.2 Mcal/kg DM of Net Energy gain.
Steers were provided a standard commercial
cor-protein diet with vitamins and minerals at
the feedlot until they reached a subcutaneous fat
thickness of approximately 0.5 in.

Carcass and meat palatability evaluation
At the end of the feeding period, cattle were
transported to a commercial packing plant (Sam
Kane Beef Processors, Corpus Christi, TX), and
harvested in a conventional manner under
USDA, FSIS inspection. After 24 h
postmortem, carcasses were ribbed and data
collected including HCW, DP, REA, FOE,
KPH, and MAB (USDA, 1997). After carcass
evaluation, carcasses were fabricated and a
wholesale rib was removed and transported to
the Meat Processing Center, University of
Florida. Two 1-in steaks were removed from the
12th rib end of the wholesale rib, one for










Wamer-Bratzler shear force determination and
one for sensory panel evaluation. Steaks were
frozen at 14 d post-mortem and remained frozen
until subsequent shear force and sensory
evaluation. A 7 to 11 member trained (AMSA,
1995) panel evaluated each sample for five
sensory attributes (TEND, CTI, JUIC, FLAV,
OFLAV).

Statistical analysis
Carcass traits (HCW, DP, REA, FOE, KPH, and
MAB) and meat palatability traits (WBSF,
TEND, CTI, JUIC, FLAV, and OFLAV) were
analyzed using single-trait mixed model
procedures that accounted for additive genetic,
non-additive genetic, and environmental effects,
and assumed a homogeneous residual covariance
structure. The model used for all traits
contained the fixed effects of year of birth, the
fixed regression effects of slaughter age of steer,
Brahman breed effect (as a function of the
Brahman fraction of the steer), and heterosis
effect (as a function of the heterozygosis of the
steer), and a random residual effect. Random
residual effects were assumed to have zero
mean, a common variance, and uncorrelated.
Brahman breed effects estimated the additive
genetic difference between Brahman and Angus.
Heterosis effects estimated the difference
between interbreed interactions (i.e., Angus-
Brahman and Brahman-Angus) and intrabreed
interactions (i.e., Angus-Angus and Brahman-
Brahman) at 1 locus. The procedure MIXED of
SAS (SAS Inst., Inc., Cary, NC) was used for
mixed model computations. The statistical
significance of solutions for effects in the model
was assessed with a t-test. Least squares means
were computed for all breed groups of steers
(Angus, 34 A /4 B, Brangus, V1A VB, 'AA 3/B,
and Brahman) using a linear combination of
additive genetic breed effects and non-additive
genetic heterosis effects. Figures depicting
trends for carcass and meat palatability traits
across breed groups of steers.

Results
Carcass traits
Table 1 presents estimates of additive genetic
Brahman minus Angus differences and non-
additive Angus-Brahman heterosis effects for
HCW, DP, REA, FOE, KPH, and MAB.


Additive breed differences indicate that
Brahman carcasses had significantly (P <
0.0001) higher DP, lower MAB, smaller REA,
and less FOE, but similar HCW and KPHF. In
contrast, heterosis effects increased HCW (P <
0.0001), DP (P < 0.017), REA (P < 0.0001),
FOE (P < 0.0001), and KPHF (P < 0.01), but it
did not affect MAB. The large effect of
heterosis on HCW (77.03 8.69, P < 0.0001)
overshadows the negative impact of the additive
difference between Brahman and Angus (-
105.97 7.68, P < 0.0001) for crossbred
animals under current market conditions. Table
3 shows least squares means and their standard
errors computed for six breed groups of steers
(Angus, 34 A /4 B, Brangus, V1A VB, 'AA 34B,
and Brahman). Trends resulting from these
steer group means are shown in Figure 1.
Crossbred steers tended to have heavier HCW
than Angus and Brahman steers due primarily to
heterosis effects, thus the heaviest carcasses
were those from Fl steers. A similar pattern
existed for KPH. Dressing percent tended to
increase linearly from Angus to VA VB, and to
remain at this level in steers with higher
Brahman percentages. Marbling score
decreased steadily from Angus to Brahman.
Ribeye area tended to increase slightly from
Angus to 1A VB, and then to decrease towards
Brahman. A similar trend existed for FOE.

Meat palatability traits
Table 2 shows estimates of additive genetic
differences between Brahman and Angus as well
as Angus-Brahman heterosis effects for WBSF,
TEND, CTI, JUIC, FLAV, and OFLAV.
Additive genetic breed differences suggest that
Brahman steaks were significantly (P < 0.0001)
tougher based on WBSF and sensory panel
TEND, and sensory panel members perceived
them to have higher levels of CTI (P < 0.0001)
and to have lower levels of JUIC (P < 0.001).
However, no differences between Brahman and
Angus were detected for FLAV and OFLAV.
Heterosis effects had no impact on any meat
palatability traits. Table 4 contains least squares
means for the six breed groups of steers (Angus,
34 A '4 B, Brangus, V2A V2B, 'AA 34B, and
Brahman), and Figure 2 shows trends for the six
meat palatability traits in this study. Means for
WBSF showed a clear upward trend from Angus










to Brahman, whereas the opposite trend was
observed for sensory panel tenderness. The
decreasing trend for CTI was similar to the one
found for tenderness. Juiciness showed a steady
decline from Angus to Brahman. As expected
from the non-significant additive genetic breed
and non-additive genetic heterosis effects,
means for FLAV and OFLAV showed no trend


from Angus to Brahman.










Table 1. Additive genetic breed differences and heterosis effects for six carcass traits


n Effect
1,359 Brahman Angus
Heterosis
1,359 Brahman Angus
Heterosis
1,357 Brahman Angus
Heterosis
1,328 Brahman Angus
Heterosis
1,353 Brahman Angus
Heterosis
1,275 Brahman Angus
Heterosis


Estimate
5.84
77.03
1.60
0.69
-105.97
0.26
-0.59
0.82
-0.15
0.10
-0.08
0.16


Standard Error
7.56
8.69
0.25
0.29
7.68
8.83
0.14
0.17
0.02
0.02
0.05
0.06


Pr > It
0.44
<0.0001
<0.0001
0.017
<0.0001
0.98
<0.0001
<0.0001
<0.0001
<0.0001
0.15
0.01


al00 to 199 = practically devoid, 900 to 999 = abundant.







Table 2. Additive genetic breed differences and heterosis effects for six meat palatability traits
Trait n Effect Estimate Standard Error Pr > |t|
WBSF, lb 662 Brahman- Angus 1.54 0.25 <0.0001
Heterosis -0.12 0.30 0.68
TEND, score" 352 Brahman -Angus -1.18 0.15 <0.0001
Heterosis 0.26 0.17 0.13
CTI, score 352 Brahman Angus -0.97 0.14 <0.0001
Heterosis 0.29 0.16 0.062
JUIC, score" 352 Brahman- Angus -0.40 0.12 0.001
Heterosis -0.09 0.14 0.54
FLAV, scored 352 Brahman Angus 0.05 0.09 0.56
Heterosis 0.18 0.10 0.08
OFLAV, score 352 Brahman Angus -0.04 0.07 0.57
Heterosis -0.10 0.08 0.22
a1 = extremely tough, 8 = extremely tender.
bl = abundant amount, 8 = none detected.
c1 = extremely dry, 8 = extremely juicy.
dl = extremely bland, 8 = extremely intense.
el = extreme off-flavor, 6 = none detected.


Trait
HCW, lb

DP, %

MAB, score

REA, in2

FOE, in

KPHF, %










Table 3. Steer breed group least squares means for six carcass traits


Trait Angus % A /4 B
HCW, lb 711.22b 751.19x
5.78c 2.70
DP, % 61.66 62.41x
0.19 0.09
MAB, score 446.51 420.15x
5.87 2.74
REA, in2 12.64 12.90x
0.11 0.05
FOE, in 0.50 0.52
0.01 0.01
KPH, % 2.14 2.20
0.04 0.02
al00 to 199 = practically devoid, 900 to 999
bLeast squares mean
CStandard error


Breed Group
Brangus V2 A/2 B
749.53x 791.16x
2.19 5.34
62.59x 63.16x
0.07 0.18
406.90x 393.79x
2.22 5.43
12.80 13.17x
0.04 0.10
0.49 0.53
0.01 0.01
2.19 2.26
0.02 0.04


abundant.


xSignificantly different from Angus (P < 0.0047 to P < 0.0001).


Table 4. Steer breed group least squares means for six meat palatability traits
Breed Group
Trait Angus 4 A /4 B Brangus 2 A /2 B '4 A3 B Brahman
WBSF, lb 7.59' 7.91y 8.11x 8.24Y 8.68x 9.13x
0.19g 0.09 0.07 0.19 0.10 0.18
TEND, score 5.80 5.64 5.48x 5.48 5.05x 4.62x
0.12 0.06 0.05 0.11 0.06 0.11
CTI, score 6.11 6.01 5.88x 5.92 5.53x 5.14x
0.11 0.05 0.04 0.10 0.06 0.10
JUIC, scored 5.31 5.17 5.12x 5.02 4.97x 4.91x
0.10 0.05 0.04 0.09 0.05 0.09
FLAV, scored 5.45 5.55 5.56 5.66 5.58 5.50
0.07 0.03 0.03 0.06 0.04 0.07
OFLAV, score 5.81 5.75 5.75 5.69 5.73 5.77
0.06 0.03 0.02 0.05 0.03 0.05
al = extremely tough, 8 = extremely tender.
b1 = abundant amount, 8 = none detected.
c1 = extremely dry, 8 = extremely juicy.
dl = extremely bland, 8 = extremely intense.
el = extreme off-flavor, 6 = none detected.
tLeast squares mean
gStandard error
xSignificantly different from Angus (P < 0.0244 to P < 0.0001)
YDifference from Angus close to significance (P < 0.0546)


V4A3/4B
754.11x
2.98
63.21"
0.10
367.17x
3.03
12.61
0.06
0.44x
0.01
2.16
0.02


Brahman
717.05
5.62
63.26x
0.19
340.55x
5.72
12.05x
0.11
0.35"
0.01
2.06
0.04












Hot Carcass Weight


Dressing Percent


800


760


720


680
ANGUS 0.75A BRANGUS 0.50A


0-2


0.25A BRAHM


64


63


62


61
ANG


jUS


0.75A BRANGUS 0.50A
0.75A BRANGUS 0.50A


0.I IBR
025A BRAHM


Breed group of calf



Marbling

500*

450-

400

350



ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM

Breed group of calf



Fat Over Ribeye

0.8


0.6


0.4


0.2
ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM

Breed group of calf


Breed group of calf



Ribeye Area
d


I '*
- 1 4 '

13,

S12'

I11


ANGl S 0.75A BRANGUS 0.50A 0.25A BRAHM
ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM


Breed group of calf



Kidney--Pelvic-Heart Fat


u, 2.3'
I
. 2.2"

S21."
z-l


ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM

Breed group of calf


Figure 1. Trends of least squares means (LSM) for carcass traits for steers ranging in breed
composition from 100% Angus to 100% Brahman


\






mlPl


.... ......... ......... ......... .........


'''


'


m











Warner-Bratzler Shear Force


9.0'
uC,
s 8.5'

S8.0'

C) 7.5'
-J


7.0 .........
ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM
Breed group of calf


Connective Tissue
"J -q


6

5


ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM
Breed group of calf


Flavor


5.5

5.0
ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM
Breed group of calf


Tenderness


O'


Off Flavor


5.5



ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM
Breed group of calf


Figure 2. Trends of least squares means (LSM) for meat palatability traits for steers ranging in
breed composition from 100% Angus to 100% Brahman


7


6


5


4 ......... I ......... I .........
ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM
Breed group of calf


Juiciness

6.0

5.5

5.0

4.5

4.0
ANGUS 0.75A BRANGUS 0.50A 0.25A BRAHM
Breed group of calf


"J




Full Text

PAGE 1

Summary Carcass and meat palatability characteristics constitute key factors for the success of beef cattle operations. Consumers prefer meat that has certain desirable degrees of tenderness, marbling, juiciness, and flavor. Cattle in the Southern region of the US contain some Brahman influence to help them cope with hot and humid climatic conditions. However, meat from Brahman cattle tends to be less tender than meat from Bos taurus breeds, causing branded beef products to restrict Brahman f rom their beef produ cts. Information on Brahman purebred and crossbred cattle is needed for objective evaluation of carcass and meat palatability traits. This research quantified additive genetic differences between Angus and Brahman, estimated Angus Brahman heterosis effect s, and estimated least squares means for six carcass and six meat palatability traits using data from 1367 steers from the Angus Brahman multibreed herd of the University of Florida collected from 1989 to 2009. Estimates of additive genetic breed differen ces between Brahman and Angus indicated that Brahman carcasses had higher dressing percent, lower marbling, smaller ribeye area, and less fat over the ribeye than Angus. In addition, Brahman beef was tougher, had more connective tissue, and it was less ju icy than Angus beef. Lastly, heterosis increased hot carcass weight, dressing percent, ribeye area, fat over the ribeye, and kidney, pelvic, and heart fat in Angus Brahman crossbred steers. Results indicated that crossbred animals with percentage Brahm an up to 50% showed limited negative impact on meat quality while maximizing meat yield due to heterosis. Introduction Carcass and meat palatability characteristics constitute key factors for the success of beef cattle operations. Consumers prefer meat t hat has certain desirable degrees of tenderness, marbling, juiciness, and flavor. This has led to the establishment of over 60 branded beef products in the United States (USDA, 2010). Thus, it seems reasonable for cattle producers to breed animals that t ake advantage of opportunities presented by branded beef programs while simultaneously breeding animals that survive well under a variety of environmental conditions. The Southern region of the US with its hot and humid subtropical environment presents se rious challenges to beef producers. Most cattle in this region contain some percentage of Brahman to help them cope with climatic conditions, particularly during the summer season. However, meat from Brahman cattle is known to be less tender than meat fr om Bos taurus breeds. This has led to restrictions on the percent of Brahman breeding by the majority of branded beef products. Information Breed Differences and Heterosis Effects f or Carcass a nd Meat Palatability Traits i n a n Angus Brahman Multibreed Cattle Population M. A. Elzo, D. D. Johnson, J. G. Wasdin, and J. D. Driver 1 Estimates of additive breed genetic effects indicated that Brahman carcasses had higher dressing percent, lower marbling, smaller ribeye area, and less fat over the ribeye than Angus. Brahman beef was tougher, had more connective tissue, and it was less juicy than Angus beef. Heterosis increased hot carcass weight, dressing percent, ribeye area, fat over the ribeye, and kidney, pelvic, and heart fat in Angus Brahman crossbred steers. Results indicated that crossbred animals with percent age Brahman up to 50% showed limited negative impact on meat quality while maximizing meat yield due to heterosis. 1 Department of Animal Sciences, University of Florida, Gainesville, FL

PAGE 2

on Brahman cattle and its crossbreds with Bos taurus breeds is needed to objectively evaluate their ability for ca rcass and meat palatability traits relative to that of Bos taurus breeds. The Angus Brahman multibreed herd of the University of Florida with cattle ranging from 100% Angus to 100% Brahman is well suited to evaluate Angus, Brahman, and crossbred groups of any Angus and Brahman fraction for each carcass and meat palatability traits under Florida environmental conditions. Thus, the objectives of this research were to obtain estimates of additive genetic differences between Angus and Brahman, Angus Brahman h eterosis effects, and to compute least squares means for breed groups of calves ranging from 100% Angus to 100% Brahman for six carcass and six meat palatability traits using the complete Angus Brahman multibreed dataset of the University of Florida. Mate rials and Methods Animals, date, and traits Cattle were from a long term genetic evaluation study utilizing Angus, Brahman, and Angus Brahman cattle from the multibreed herd of the University of Florida. The mating design used in this herd was diallel, i. e., sires of six breed groups (Angus (A), A B Brangus (5/8 A 3/8 B), A B, A B, and Brahman (B)) were mated to dams from these same six breed groups. The dataset contained carcass and meat palatability information from 1 367 calves born from 1989 to 2009 (216 Angus, 182 A B, 224 Brangus, 341 A B, 206 A B, and 198 Brahman). These calves were the progeny of 213 sires (44 Angus, 27 A B, 42 Brangus, 26 A B, 26 A B, and 48 Brahman) and 824 dams (145 Angus, 119 A B, 127 Brangus, 174 A B, 107 A B, and 152 Brahman). Carcass traits were hot carcass weight (HCW, lb), dressing percent (DP, %), ribeye area at the 12 th rib (REA, in 2 ), fat over the ribeye the 12 th rib (FOE, in), kidney, pelvic, and heart fat (KP H, %), and marbling score (MAB; 100 to 199 = practically devoid, 900 to 999 = abundant). Meat palatability traits were Warner Bratzler shear force (WBSF, lb), tenderness score (TEND; 1 = extremely tough, 8 = extremely tender), connective tissue score (CTI ; 1 = abundant amount, 8 = none detected), juiciness score (JUIC; 1 = extremely dry, 8 = extremely juicy), beef flavor score (FLAV; 1 = extremely bland, 8 = extremely intense), and off flavor score (OFLAV; 1 = extreme off flavor, 6 = none detected). Repro duction, feeding and management Cows were synchronized in March, artificially inseminated twice, and then exposed to a natural service bull for 60 d. Calves were born from mid December to mid March, and weaned in September. Cows and calves were kept on bahiagrass ( Paspalum notatum) pastures throughout the year with free access to mineral supplementation. Winter supplementation consisted of bermudagrass (Cynodon dactylon) hay, cottonseed meal, and molasses. After weaning steers were either taken directly to a contract feeder (1989 to 2005; King Ranch Feedyard, Kingsville, Texas), or to the University of Florida Feed Efficiency Facility (FEF) in Marianna, Florida for 100 d, and then transported to a contract feeder (2006 to 2009; Suwannee Farms, O Brien, F lorida). Steers at the FEF were housed in pens and fed a concentrate diet composed of whole corn, cottonseed hulls, and a protein, vitamin, and mineral supplement (FRM, Bainbridge, GA). The FEF concentrate had 90 to 91.2% of dry matter 14.1 to 17. 3 % o f crude protein 1.5 to 1.7 Mcal/kg DM of Net Energy maintenance and 0.9 to 1.2 Mcal/kg DM of Net Energy gain Steers were provided a standard commercial corn protein diet with vitamins and minerals at the feedlot until they reached a subcutaneous fat th ickness of approximately 0.5 in. Carcass and meat palatability evaluation At the end of the feeding period, cattle were transported to a commercial packing plant (Sam Kane Beef Processors, Corpus Christ i T X ), and harvested in a conventional manner und er USDA, FSIS inspection. After 24 h postmortem, carcasses were ribbed and data collected including HCW, DP, REA, FOE, KPH, and MAB (USDA, 1997). After carcass evaluation, carcasses were fabricated and a wholesale rib was removed and transported to the M eat Processing Center, University of Florida. Two 1 in steaks were removed from the 12 th rib end of the wholesale rib, one for

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Warner Bratzler shear force determination and one for sensory panel evaluation. Steaks were frozen at 14 d post mortem and rema ined frozen until subsequent shear force and sensory evaluation A 7 to 11 member trained (AMSA, 1995) panel evaluated each sample for five sensory attributes (TEND, CTI, JUIC, FLAV, OFLAV). Statistical analysis Carcass traits (HCW, DP, REA, FOE, KPH, and MAB) and meat palatability traits (WBSF, TEND, CTI, JUIC, FLAV, and OFLAV) were analyzed using single trait mixed model procedures that accounted for additive genetic, non additive genetic, and environmental effe cts, and assumed a homogeneous residual covariance structure. The model used for all traits contained the fixed effects of year of birth, the fixed regression effects of slaughter age of steer, Brahman breed effect (as a function of the Brahman fraction o f the steer), and heterosis effect (as a function of the heterozygosis of the steer), and a random residual effect. Random residual effects were assumed to have zero mean, a common variance, and uncorrelated. Brahman breed effects estimated the additive genetic difference between Brahman and Angus. Heterosis effects estimated the difference between interbreed interactions (i.e., Angus Brahman and Brahman Angus) and intrabreed interactions (i.e., Angus Angus and Brahman Brahman) at 1 locus. The procedure MIXED of SAS (SAS Inst., Inc., Cary, NC) was used for mixed model computations. The statistical significance of solutions for effects in the model was assessed with a t test. Least squares means were computed for all breed groups of steers (Angus, A B, Brangus, A B, A B, and Brahman) using a linear combination of additive genetic breed effects and non additive genetic heterosis effects. Figures depicting trends for carcass and meat palatability traits across breed groups of steers Results Carcass traits Table 1 presents estimates of additive genetic Brahman minus Angus differences and non additive Angus Brahman heterosis effects for HCW, DP, REA, FOE, KPH, and MAB. Additive breed differences indicate that Brahman carcasses had significant ly ( P < 0.0001) higher DP, lower MAB, smaller REA, and less FOE, but similar HCW and KPHF. In contrast heterosis effects increased HCW ( P < 0.0001), DP ( P < 0.017), REA ( P < 0.0001), FOE ( P < 0.0001), and KPHF ( P < 0.01), but it did not affect MAB The large effect of heterosis on HCW (77.03 8.69, P < 0.0001) overshadows the negative impact of the additive difference between Brahman and Angus ( 105.97 7.68, P < 0.0001) for crossbred animals under current market conditions. Table 3 shows least squares means and their standard errors computed for six breed groups of steers (Angus, A B, Brangus, A B, A B, and Brahman). Trends resulting from these steer group means are shown in Figure 1. Crossbred steers tended to have heavier HCW than Angus an d Brahman steers due primarily to heterosis effects, thus the heaviest carcasses were those from F1 steers. A similar pattern existed for KPH. Dressing percent tended to increase linearly from Angus to A B, and to remain at this level in steers with hi gher Brahman percentages. Marbling score decreased steadily from Angus to Brahman. Ribeye area tended to increase slightly from Angus to A B, and then to decrease towards Brahman. A similar trend existed for FOE. Meat palatability traits T able 2 shows estimates of additive genetic differences between Brahman and Angus as well as Angus Brahman heterosis effects for WBSF, TEND, CTI, JUIC, FLAV, and OFLAV. Additive genetic breed differences suggest that Brahman steaks were significantly ( P < 0.0001) tougher based on WBSF and sensory panel TEND, and sensory panel members perceived them to have higher levels of CTI ( P < 0.0001) and to have lower levels of JUIC ( P < 0.001). However, no differences between Brahman and Angus were detected for FLAV and OFLAV. Heterosis effects had no impact on any meat palatability traits. Table 4 contains least squares means for the six breed groups of steers (Angus, A B, Brangus, A B, A B, and Brahman), and Figure 2 shows trends for the six meat palatab ility traits in this study. Means for WBSF showed a clear upward trend from Angus

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to Brahman, whereas the opposite trend was observed for sensory panel tenderness. The decreasing trend for CTI was similar to the one found for tenderness. Juiciness showe d a steady decline from Angus to Brahman. As expected from the non significant additive genetic breed and non additive genetic heterosis effects, means for FLAV and OFLAV showed no trend from Angus to Brahman.

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Table 1. Additive gen etic breed differences and heterosis effects for six carcass traits Trait n Effect Estimate Standard Error Pr > |t| HCW, lb 1 359 Brahman Angus 5.84 7.56 0.44 Heterosis 77.03 8.69 <0.0001 DP, % 1 359 Brahman Angus 1.60 0.25 <0.0001 Heterosis 0.69 0.29 0.017 MAB, score a 1 357 Brahman Angus 105.97 7.68 <0.0001 Heterosis 0.26 8.83 0.98 REA, in 2 1 328 Brahman Angus 0.59 0.14 <0.0001 Heterosis 0.82 0.17 <0.0001 FOE, in 1 353 Brahman Angus 0.15 0.02 <0.0001 Heterosis 0.10 0.02 <0.0001 KPHF, % 1 275 Brahman Angus 0.08 0.05 0.15 Heterosis 0.16 0.06 0.01 a 100 to 199 = practically devoid, 900 to 999 = abundant. Table 2. Additive genetic breed differences and heterosis effects for six meat palatability traits Trait n Effect Estimate Standard Error Pr > |t| WBSF, lb 662 Brahman Angus 1.54 0.25 <0.0001 Heterosis 0.12 0.30 0.68 TEND, score a 352 Brahman Angus 1.18 0.15 <0.0001 Heterosis 0.26 0.17 0.13 CTI, score b 352 Brahman Angus 0.97 0.14 <0.0001 Heterosis 0.29 0.16 0.062 JUIC, score c 352 Brahman Angus 0.40 0.12 0.001 Heterosis 0.09 0.14 0.54 FLAV, score d 352 Brahman Angus 0.05 0.09 0.56 Heterosis 0.18 0.10 0.08 OFLAV, score e 352 Brahman Angus 0.04 0.07 0.57 Heterosis 0.10 0.08 0.22 a 1 = extremely tough, 8 = extremely tender. b 1 = abundant amount, 8 = none detected. c 1 = extremely dry, 8 = extremely juicy. d 1 = extremely bland, 8 = extremely intense. e 1 = extreme off flavor, 6 = none detected.

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Table 3. Steer breed group least squares means for six carcass traits Breed Group Trait Angus A B Brangus A B A B Brahman HCW, lb 711.22 b 751.19 x 749.53 x 791.16 x 754.11 x 717.05 5.78 c 2.70 2.19 5.34 2.98 5.62 DP, % 61.66 62.41 x 62.59 x 63.16 x 63.21 x 63.26 x 0.19 0.09 0.07 0.18 0.10 0.19 MAB, score a 446.51 420.15 x 406.90 x 393.79 x 367.17 x 340.55 x 5.87 2.74 2.22 5.43 3.03 5.72 REA, in 2 12.64 12.90 x 12.80 13.17 x 12.61 12.05 x 0.11 0.05 0.04 0.10 0.06 0.11 FOE, in 0.50 0.52 0.49 0.53 0.44 x 0.35 x 0.01 0.01 0.01 0.01 0.01 0.01 KPH, % 2.14 2.20 2.19 2.26 2.16 2.06 0.04 0.02 0.02 0.04 0.02 0.04 a 100 to 199 = practically devoid, 900 to 999 = abundant. b Least squares mean c Standard error x Significantly different from Angus ( P < 0.0047 to P < 0.0001) Table 4. Steer breed group least squares means for six meat palatability traits Breed Group Trait Angus A B Brangus A B A B Brahman WBSF, lb 7.59 f 7.91 y 8.11 x 8.24 y 8.68 x 9.13 x 0.19 g 0.09 0.07 0.19 0.10 0.18 TEND, score a 5.80 5.64 5.48 x 5.48 5.05 x 4.62 x 0.12 0.06 0.05 0.11 0.06 0.11 CTI, score b 6.11 6.01 5.88 x 5.92 5.53 x 5.14 x 0.11 0.05 0.04 0.10 0.06 0.10 JUIC, score c 5.31 5.17 5.12 x 5.02 4.97 x 4.91 x 0.10 0.05 0.04 0.09 0.05 0.09 FLAV, score d 5.45 5.55 5.56 5.66 5.58 5.50 0.07 0.03 0.03 0.06 0.04 0.07 OFLAV, score e 5.81 5.75 5.75 5.69 5.73 5.77 0.06 0.03 0.02 0.05 0.03 0.05 a 1 = extremely tough, 8 = extremely tender. b 1 = abundant amount, 8 = none detected. c 1 = extremely dry, 8 = extremely juicy. d 1 = extremely bland, 8 = extremely intense. e 1 = extreme off flavor, 6 = none detected. f Least squares mean g Standard error x Significantly different from Angus ( P < 0.0244 to P < 0.0001) y Difference from Angus close to significance ( P < 0.0546)

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Figure 1. Trends of least squares means (LSM) for carcass traits for steers ranging in breed composition from 100% Angus to 100% Brahman

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Figure 2. Trends of least squares means (LSM) for meat palatability traits for steers ranging in breed composition from 100% Angus to 100% Brahman