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) standard deviations, and phenotypic coefficients of variation (CV) were estimated for growth traits of intact males from 12 breed groups combined, for nine purebreds combined, and for the F1, F2, F3, and F4 generations of three composite populations to which the nine purebreds contributed. Heritabilities (h2) and genetic (rg) and phenotypic (rp) correlations were estimated for growth traits, calving difficulty of calves with dams of different ages, and gestation length. Coefficients of variation and sigma g generally were similar for composites and contributing purebreds. Generally, estimates of h2 were similar for all breed groups combined, contributing purebreds combined, and composites combined. Estimates of h2 for calving difficulty were higher for calves with 2-yr-old dams than for calves with dams > or = 3 yr old and were sufficiently high (.27 and .31) to be a useful selection criterion for reducing calving difficulty. Mean h2 pooled within all breed groups ranged from .35 for 200-d weight and 368-d weight to .48 for 368-d height. Estimates of h2 for subjective scores of anatomical traits were only slightly lower than those for growth and size traits. The h2 of scrotal circumference (.43) was similar to those for growth and size traits. Genetic correlations between birth weight and calving difficulty were similar for 1) calves with dams of all ages, 2) calves with 2-yr-old dams, and 3) calves with dams > or = 3 yr old.(ABSTRACT TRUNCATED AT 250 WORDS)