HERITABILITY, REPEATABILITY AND ENVIRONME NT 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 an alyzed 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 herit ability estimates for P205 and EC. Year and month of birth were a sign ificant source of variation (P<0.01) on P205 and EC. Sex of calf was s ignificant (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 a ge of dam interaction was not significant( P>0.05) for P205 and EC. Le ast-squares means for herds A and B, respectively were: P205 = 186.5 a nd 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 = 0.3 3 +/- 0.05 and EC = 0.06 +/- 0.02 in herd B. Repeatability estimates f or P205 and EC were 0.31 +/- 0.02 and 0.25 +/- 0.03 in herd A, and 0.2 5 +/- 0.02 and 0.10 +/- 0.02 in herd B, respectively.