The objective of this work was to calculate correction factors for the effects of age of the dam (AOD), age of the calf (AOC) and Julian birth date (DOB) on the average daily gain (ADG) from birth to weaning period of animals of Nellore breed. The data were analyzed by restricted maximum likelihood, using the animal model. The model included the fixed effects of contemporary group (CG), AOD, AOC and DOB, and the direct effects (animal), maternal, permanent environmental and residue. The data were submitted to previous analysis for the definition of segmented polynomials to be used by means of SAS computing program where the covariates sets were created. In the ADG study in function of AOD, was observed a quadractic-quadractic effect, and the dams reached the maturity between the 5th and 7th years of age. The predicted ADG for the calves increased for the dams in the 4th and 6th years of age, as that the maximum gain was reached, decreasing from 6 up to 15 years of age, when the calves presented the lower gain rate. For AOC was observed a simple quadratic effect. The ADG presented an overall mean of .681 kg/day and decreased as the animal age increased (from 156th to 308th day of age). The Julian birth date showed a linear effect on the ADG, that decreased in the period from 220th to 365th day of the Julian calendar. These two effects (AOC and DOB) were the most difficult to model: the "knots" and the segments of obtained polynomials at each step were dependent and, or influenced by the used modeling for the other effects, suggesting multicolinearity problems and, or concentration of data in influent points. In function of these problems, a simplified modeling of the AOC and DOB effects was choose.
Julian births date; contemporaneous groups; calf age at weaning; dam age of weaning