HERITABILITY, REPEATABILITY AND ENVIRONMENT EFFECTS IN HEREFORD CATTLE .1. WEANING WEIGHT AND CONFORMATION SCORE

A total of 9.177 calf records of Hereford cattle, collected from 1974 to 1988, in two herds (A and B), in Rio Grande do Sul, Brazil, were analyzed to evaluate the effects of dam age, sex of calf, year and month of birth on 205-day weight and conformation score (EC). Paternal half-sibs analyses and least-squares procedures were used to compute heritability estimates for P205 and EC. Year and month of birth were a significant source of variation (P<0.01) on P205 and EC. Sex of calf was significant (P<0.01) on P205, but was not for EC. Dam age effect was a significant source of variation (P<0.01) for P205 and EC. The sex by age of dam interaction was not significant( P>0.05) for P205 and EC. Least-squares means for herds A and B, respectively were: P205 = 186.5 and 147.4 kg; EC = 24.06 and 21.06 points. Heritability estimates were: P205 = 0.36 +/- 0.06 and EC = 0.27 +/- 0.05 in A herd, and P205 = 0.33 +/- 0.05 and EC = 0.06 +/- 0.02 in herd B. Repeatability estimates for P205 and EC were 0.31 +/- 0.02 and 0.25 +/- 0.03 in herd A, and 0.25 +/- 0.02 and 0.10 +/- 0.02 in herd B, respectively.