Birth weight of Nellore calves: heritability and sex x sire interaction

Abstract

Experimental data were obtained from the herd book of Campo Experimental de Terenos, and it refers to birth weight of 861 calves born during 1965 through 1977. The heritability was estimated by four models; the first model was the complete one; in the second model the effects that showed no significant influence on birth weight were drawn; the third model was used to analyze males and females separately and included the same variables as the complete model; the fourth model included the variables used in the second model. Year, sex and dam previous condition (cow that calved or not in the previous year and first calf heifers) affected birth weight (P<.01). The approximate mean weights of the males and females were 25.04 and 23.40 kg, respectively, for the different models. Cows that failed to conceive in the previous year produced calves, approximately, .70 kg heavier, at birth, than calves from heifers and from cows that calved in the previous year. Birth season, and cow's age did not affect birth weight. The heritability estimates of birth weight for the different models were as follows: .73 ± .15 for the first model; .70 ± 15 for the second one; .90 ± .20 and .90 ± .21, for males and females, respectively, on the third model; and .82 ± .20 and .81 ± .20, for males and females, respectively, on the fourth one. We can conclude, by these results, that sex does not affect sire evaluation for birth weight.