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

Least squares means, genetic and phenotypic standard deviations, and p henotypic coefficients of variation were estimated for growth, size, c ondition score, age at puberty, gestation length, and calving difficul ty as traits of individual females from 12 breed groups combined, for nine purebreds combined, and for the F-1, F-2, and F-3 generations of three composite populations to which the nine purebreds contributed. H eritabilities and genetic and phenotypic correlations were estimated f or growth and size traits, age at puberty, gestation length, and calvi ng difficulty of calves with darns of different ages. Coefficients of variation and genetic standard deviations were similar for composites and contributing purebreds for the traits evaluated. Generally, estima tes of heritability were similar for all breed groups combined, contri buting purebreds combined, and composites combined. Estimates of herit ability for calving difficulty were higher for calves with 2-yr-old da ms than for calves with dams greater than or equal to 3 yr old and wer e sufficiently high (.33 and .26) to be a useful selection criterion f or reducing calving difficulty. Estimate of heritability for age at pu berty was .31 and for gestation length was .45. The r(g) between birth weight and calving difficulty score was higher for calves with 2-yr-o ld dams (.59) than for calves with dams greater than or equal to 3 yr old (.44). The higher genetic correlation between birth weight and cal ving difficulty score (.59) in calves with 2-yr-old dams than between birth weight:and 368-d weight (.33) suggests opportunity to reduce cal ving difficulty by reducing birth weight while maintaining 368-d weigh t. The genetic correlation of gestation length with birth weight was i ntermediate (.30) and the genetic correlation between gestation length and calving difficulty score was not important (-.07) in calves with dams greater than or equal to 3 yr. Phenotypic correlations were gener ally lower than genetic correlations among growth and size traits and the phenotypic correlation was intermediate between birth weight and c alving difficulty score in calves with 2-yr-old dams (.43).