GENETIC AND PHENOTYPIC (CO)VARIANCES FOR PRODUCTION TRAITS OF INTACT MALE POPULATIONS OF PUREBRED AND COMPOSITE BEEF-CATTLE

Least squares means, genetic (sigma(g)) and phenotypic (sigma(p)) Stan dard deviations, and phenotypic coefficients of variation (CV) were es timated for growth traits of intact males from 12 breed groups combine d, for nine purebreds combined, and for the F-1, F-2, F-3, and F-4 gen erations of three composite populations to which the nine purebreds co ntributed. Heritabilities (h(2)) and genetic (r(g)) and phenotypic (r( p)) correlations were estimated for growth traits, calving difficulty of calves with dams of different ages, and gestation length. Coefficie nts of variation and ag generally were similar for composites and cont ributing purebreds. Generally, estimates of h(2) were similar for all breed groups combined, contributing purebreds combined, and composites combined. Estimates of h(2) for calving difficulty were higher for ca lves with 2-yr-old dams than for calves with dams greater than or equa l to 3 yr old and were sufficiently high (.27 and .31) to be a useful selection criterion for reducing calving difficulty. Mean h(2) pooled within all breed groups ranged from .35 for 200-d weight and 368-d wei ght to .48 for 368-d height. Estimates of h(2) for subjective scores o f anatomical traits were only slightly lower than those for growth and size traits. The h(2) of scrotal circumference (.43) was similar to t hose for growth and size traits. Genetic correlations between birth we ight and calving difficulty were similar for 1) calves with darns of a ll ages, 2) calves with 2-yr-old dams, and 3) calves with dams greater than or equal to 3 yr old. The r(g) of gestation length with birth we ight was low (.21) and was .57 and .54, respectively, with calving dif ficulty score and with percentage calving difficulty for calves with d arns 2 3 yr old. Phenotypic correlations were relatively high among gr owth and size traits and were intermediate between birth weight and bo th expressions of calving difficulty in calves with 2-yr-old darns (.5 3 and .42) but were lower for calves with dams in other age classes.