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Purdue University, West Lafayette, IN 47907
Abstract
Evaluation of straightbred and crossbred performance and estimates of heterosis were obtained for birth weight, 120-day weight, 210-day weight, gain from birth to 120 days, gain from 120 to 210 days and 210-day feeder grade using straightbred and reciprocal crossbred calves from Angus (A) and Milking Shorthorn (MS) cows born over a 5-year period.
Percent heterosis was estimated as 100 times mean of crossbred calves minus mean of straightbred calves divided by mean of straight-bred calves. Linear contrasts (crossbred minus straightbred) were used to determine overall and within-sex heterosis estimates.
Significant year, sex and calving period effects were observed. Bull calves were 2.5 ± .4 kg heavier than heifers at birth and, as steers, this advantage increased to 6.9 ± 1.6 and 10.6 ± 2.2 kg at 120 and 210 days, respectively. Steers scores .2 ± .1 units higher than heifers in feeder grade. Calves born early in the fall calving season tended to have superior weights, gains and feeder grades as compared to later-born calves.
Breed-of-sire effects were significant only for birth weight and feeder grade. Calves from MS sires were 1.9 ± .4 kg heavier at birth than calves from A sires. Calves from A sires scored 1.3 ± .1 units higher in feeder grade at 210 days than calves from MS sires.
Breed-of-dam effects were significant for all calf traits. Calves from MS cows were superior for weight and gain traits and calves from A cows had superior feeder grades.
Significant sire breed x dam breed interactions were observed, indicating heterosis for 120- and 210-day weights, gain from birth to 120 days, and gain from 120 to 210 days.
Nonsignificant crossbred minus straightbred contrasts of .7 ± .4 kg at birth and .2 ± .1 units in feeder grade resulted in heterosis percentages of 2.3 and 1.6%, respectively. Significant crossbred minus straightbred contrasts of 4.7 ± 1.6 and 9.6 ± 2.2 kg in 120- and 210-day weights yielded heterosis percentages of 4.2 and 5.2%, respectively. Heterosis estimates of 4.0 ± 1.4 kg in gain from birth to 120 days, and 4.9 ± 1.0 kg in gain from 120 to 210 days yielded heterosis percentages of 4.9 and 6.9%, respectively.
Heterosis estimates and percentages for steer calves exceeded those for heifer calves for all traits. Nonsignificant heterosis estimates for male and female calves, respectively, were .9 ± .7 kg (2.7%) and .6 ± .5 kg (1.9%) for birth weight, and .3 ± .2 units (2.5%) and .1 ± .2 units (.7%) for feeder grade.
Significant steer heterosis estimates of 5.4 ± 2.2 kg (6.6%) and 6.4 ± 2.5 kg (5.5%) were observed for gain from birth to 120 days and 120-day weight. With heifers, nonsignificant heterosis estimates for these traits were 2.7 ± 1.9 kg (3.5%) and 3.3 ± 2.1 kg (3.0%), respectively.
Significant heterosis estimates were observed with both steers and heifers for gain from 120 to 210 days and 210-day weight. Heterosis estimates for steer and heifer calves, respectively, were 6.0 ± 1.6 kg (8.3%) and 3.9 ± 1.4 kg (5.7%) for gain from 120 to 2l0 days, and 12.3 ± 3.5 kg (6.6%) and 7.2 ± 2.8 kg (4.0%) for 210-day weight.
1 Journal Paper No. 6634, Purdue University Agricultural Experiment Station.
2 Data derived from the Purdue University contributing project to NC-1 regional project, Improvement of Beef Cattle Through Breeding Methods.
3 The authors express their appreciation to John R. Hodges and personnel at the Feldun-Purdue Agricultural Center for cow herd management and assistance in collection of data.
4 Associate Professor, Graduate Student, Professor and Associate Professor, respectively.
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