The aims of this research were to estimate the influence of age of dam at calving (AC), and julian date of birth (JDB) on weaning weight (WW) and preweaning average daily gain (ADG) of gyr calves and adjustment factors for them. It was analyzed 10,685 and 18,339 records, on WW and ADG of Gyr calves, from the Associação Brasileira dos Criadores de Zebu data set belonging to 1229 and 1979 contemporary groups (CG), respectively. AC, for males, was fitted as a segmented polynomial quadratic-quadratic-quadratic with stage changing at 4.1, 12.7 for WW and 4.0, 8.2 years old for ADG, and as a segmented polynomial quadratic-quadratic with state changing at 3.8 years old for female. JDB was fitted as a segmented polynomial quadratic-quadratic with state changing at 126 days for WW and 167 days for ADG. The results showed that the adjustment factors for AC must be done separately, for males and females and for JDB, each season must be considered, so that the differences among them can be better observed. The adjustment factors to AC, for males, ranged from 0.94750 to 1.08033 for WW and 0.991714 to 1.07916 for ADG and, for females from 0.90937 to 1.07415 for WW and 0.96055 to 1.14007 for ADG. The adjustment factors to JDB ranged from 0.9256 to 1.0340 for WW and 0.9112 to 1.0551 for ADG.
adjustment factors; Gyr cattle; preweaning average daily gain; segmented polynomial; weaning weight
