PROCEEDINGS - American Society of Animal Science

marbling score (MARB) and were recorded using routine
post-harvest procedures. Steers and heifers were harvested
at an average age of 417 d (SD = 16.3). Animals were sired
by four registered Charolais bulls; the progeny were placed
into either high (n=210) or low (n=188) calving ease groups
based on their sires’ CE EPD. The sires were selected
primarily on their carcass EPD with no selection criteria for
CE EPD. The dams were crossbred commercial cows of
primarily British influence.
Carcass data was analyzed using a general linear
model (SAS Ver. 9.2, Cary, NC). The model included the
fixed effects of contemporary group (defined as the
combination of sex and harvest date), sire CE group, and a
linear covariate of harvest age. The formation of
contemporary groups in this manner resulted in 24 unique
groups. Least squares mean estimates were calculated for
each of the carcass traits using the model equation:
y ijkl = b j CG j + b k G k + b l HA l + e 1
where, y was the carcass trait measured on animals, CG was
the contemporary group, G was the sire group based on
sires’ CE EPD, HA was the harvest age of the individual,
and e was a vector of random residual errors specific to
each observation in y.
Results and Discussion
Summary statistics for carcass observation are
summarized in Table 1 for HCW, REA, FAT, MARB, and
YG. The USDA YG grade was calculated using HCW,
REA, and FAT (AMS 2001) .
Table 1: Summary statistics for progeny carcass traits 1
N Mean SD Min 2 Max 2
HCW 312 372.9 32.9 257.0 454.5
REA 398 92.5 8.3 65.2 120.3
FAT 398 1.34 0.41 0.41 3.05
MARB 398 3.95 0.70 1.80 7.00
YG 398 2.99 0.57 1.07 4.70
1
HCW = Hot Carcass Weight (kg); REA=Longissimus
Muscle Area (cm 2 ); FAT= Subcutaneous Fat depth (cm);
MARB=Marbling Score; YG= USDA Yield Grade
2
SD= Standard Deviation; Min= Minimum Value; Max=
Maximum Value
Least squares means for high and low sire CE EPD
groups are shown below in Table 2.
Table 2: Least squares means for progeny carcass traits 1
N LSM±SE 2 P-value 4
HCW
High 3 139 371.62±1.84 a < 0.03
Low 3 173 365.29±2.07 b
REA
High 210 92.89±0.54 a < 0.06
Low 188 91.11±0.71 b
Fat
High 210 1.28±0.027 a < 0.91
Low 188 1.28±0.035 a
MARB
High 210 3.93±0.047 a < 0.53
Low 188 3.89±0.061 a
YG
High 210 2.97±0.037 a < 0.69
Low 188 2.99±0.048 a
1
HCW = Hot Carcass Weight (kg); REA=Longissimus
Muscle Area (cm 2 ); FAT= Subcutaneous Fat depth (cm);
MARB=Marbling Score; YG= USDA Yield Grade
2
LSM= Least Squares Means
3 High= Calves sired by high calving ease sires;
Low=calves sired by low calving ease sires
4 P-value is representative of LSM group differences
a,b =group means without common superscript letter differ,
P< 0.05
Results of this analysis were unanticipated.
Typically, calving ease is closely correlated with birth
weight as shown by both Meijering (1984) and Koots et al.
(1994). Birth weight has also been shown to have a high
correlation with carcass weight (Eriksson et al. 2004)
Following these studies, one can hypothesize that low
calving ease sires would produce calves with heavier HCW
and larger REA. The results of this study contradict this
hypothesis. Average CE EPD for sires was 2.2 and -0.8 for
the high and low groups, respectively. Differences between
the calving ease groups (High - Low) were 1.8 cm 2 for REA
(P