Relation between Holstein bulls’ proofs for milk in USA and the milk yield, age at first calving, calving interval and survival to third calving of their F 1 zebu progeny in Venezuela

Summary To determine the effect of USA Holstein bulls’ breeding value for milk yield on the performance of their female F 1 progeny in the lowland tropics of Venezuela, semen was chosen from 39 sires, representing bulls with the highest (class H, n = 21) or average (class A, n = 18) proofs for milk, available locally. The mean proofs of the H and A sires were 937 and 237 kg milk, respectively, when semen was purchased in 1989–93, and 212 and −386 kg when updated in 2001. Progeny from commercial zebu dams were kept grazing on three dual purpose farms, where herd average milk yields were 735, 1113 and 3524 kg per lactation. Records on milk yield, lactation length, calving interval, age at first calving and survival rate to first, second and third calving from 222 progeny (476 lactations) were analysed using mixed linear models. The effect of sire class approached significance (p = 0.07) for milk yield and survival rate to second calving, with H daughters superior to A progeny by 41 and 46%, respectively, and no significant disadvantage for any trait. Class × farm interaction was only significant for age at first calving. Rank correlations using USA proofs for milk and the adjusted mean values for bulls with =15 F 1 records were 0.72 (p < 0.01, milk yield) and −0.07 (calving interval). Differences between sires, within classes, were highly significant for age at first calving and calving interval. It was concluded that the use of Holstein bulls with high USA milk proofs is probably justified for producing F 1 daughters, but that evaluation for growth rate and daughter fertility under tropical grazing conditions may be advisable.