66.035 records from Nellore, Hereford, Angus and Nellore x Angus and Nellore x Hereford crossbred calves were analyzed to estimate the influence of cow age, age at weaning and the julian birth date on average daily gain from birth to weaning. The statistical analysis indicated that these three covariates had significant effects on this trait. Furthermore, the linear adjustment for age at weaning was not enough to remove this effect on the average daily gain. These results show that these environmental effects can be an important variation source for this trait in animal improvement programs.
age at weaning; beef cattle; crossbreeding; julian birth date
