Body measurements of crossbred calves sired by Simmental bulls divergently selected for progeny first-calf calving ease in relation to birth weight.
Simmental bulls (n = 27) were divergently selected on linear model first-calf calving ease expected progeny difference (CEPD) relative to birth weight expected progeny difference (BEPD) so that body measures of calves from sires whose progeny tended to be born either with more or less dystocia than expected from BEPD could be obtained. At birth, calf weight, head circumference, shoulder width, hip width, heart girth, cannon bone circumference and length, and body length were recorded for 204 calves. These measures had also been obtained from the Polled Hereford X Angus dams of the calves at their births. Sire differences (P less than .05) existed for calf cannon bone circumference and length before and after adjustment for gestation length and birth weight of the calf. Sire BEPD was positively associated with cannon and head circumferences independent of phenotypic birth weight and gestation length. No relationship existed between CEPD or threshold model first-calf calving ease expected progeny difference and any calf measure, either before or after adjustment for birth weight. Multivariate factor analysis was used to describe independent components of skeletal width, frame, and thickness after removal of birth weight effects; factors were not related to genetic merit for calving ease or observed calving performance. Independent of weight, newborn calf measures were not highly related to body measures at weaning or to dam birth measures. Body shape differences at constant weight existed in crossbred calves, but they were not related to sire genetic merit for calving ease or measured dystocia. Selection for calf body shape, independent of birth weight, would not reduce dystocia.
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Virginia Polytechnic Institute, Blacksburg.
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D000818:Animals; D000831:Animals, Newborn / Q000033:anatomy & histology* / Q000235:genetics; D001724:Birth Weight; D001947:Breeding; D002417:Cattle / Q000033:anatomy & histology* / Q000235:genetics; D002418:Cattle Diseases / Q000235:genetics; D003433:Crosses, Genetic; D004420:Dystocia / Q000235:genetics / Q000662:veterinary; D005260:Female; D007743:Labor, Obstetric; D008297:Male; D011247:Pregnancy; D012044:Regression Analysis; D014886:Weaning