The pre-weaning performance of Nellore (N), Guzerá x N (GN), Red Angus x N (RN) and Marchigiana x N (MN) calves, from a crossbreeding experiment conducted at IAPAR Paranavaí Experimental Station, produced by artificial insemination, born between 1985 and 1998 within two birth seasons (January to April and July to December) was studied. The least squares method was utilized to analyze 721 observations of birth weight (PNT) and 686 of weaning weight (PDS) and average daily gain from birth to weaning (GMD<FONT FACE=Symbol>_</FONT>ND). For PNT, the effect of classes of Julian days with ten days interval between classes, showed to be more useful to explain birth seasons variations than the calf birth month, whose influence was very strong for PDS and GMD<FONT FACE=Symbol>_</FONT>ND. For the three evaluated traits, there was important effect (linear and quadratic) of age (days) of the dam of the calf, as a co-variable, as well as of the fixed effects of breed of sire or genetic group, calf birth year and calf sex. The genetic group x sex of calf interaction was significant for PNT, PDS and GMD<FONT FACE=Symbol>_</FONT>ND. The random effect of sire within genetic group was important for PNT, PDS and GMD<FONT FACE=Symbol>_</FONT>ND. The least squares means and respective standard errors, always in the sequence N, GN, RN and MN, were: 28.5 ± 0.38 kg, 29.0 ± 0.44 kg, 29.4 ± 0.46 kg and 31.3 ± 0.47 for PNT; 141.3 ± 1.47 kg, 147.6 ± 1.61 kg, 167.5 ± 1.72 kg and 162.0 ± 1.89 kg for PDS; and 0.510 ± 0.007 kg, 0.540 ± 0.008 kg, 0.627 ± 0.008 and 0.583 ± 0.009 for GMD_ND.
beef cattle; crossbreeding; growth traits; pre-weaning
