The objective of this study was to compare age at first calving (AFC) and cow weight at calving (CWC) of straightbred Nellore and crossbred 1/4 Charolais + 3/4 Nellore (1CHA3NEL), and 5/8 Charolais + 3/8 Nellore (5CHA3NEL) cows, and birth weight of calf/CWC (BWR) and weaning weight of calf at 270 days/CWC (WWR) ratios of straightbred Nellore and crossbred 1CHA3NEL, 5CHA3NEL, Canchim (5/8 Charolais + 3/8 Nellore) and 7/16 Charolais + 9/16 Nellore (7CHA9NEL) calves. Analyses of variance were carried out by the least squares method, with models that included the effects of year and season of birth, and genetic group of cow for AFC; year, season, and age of cow at calving, and genetic group of cow for CWC; and year, season, and age of cow at calving, and sex and genetic group of calf for BWR and WWR. Genetic group affected all studied traits. The least squares means for AFC and CWC were 1073.0 ± 9.0 days and 425.4 ± 1.4 kg for the Nellore, 1043.5 ± 3.6 days and 447.4 ± 1.7 kg for the 1CHA3NEL, and 966.1 ± 5.2 days and 486.4 ± 2.7 kg for the 5CHA3NEL cows, respectively. The least squares means for BWR and WWR were 66.5 ± 0.9 and 438.3 ± 6.2 g/kg for the Nellore, 69.6 ± 0.4 and 415.4 ± 2.5 g/kg for the 1CHA3NEL, 75.1 ± 0.5 and 515.9 ± 3.3 g/kg for the 5CHA3NEL, 72.6 ± 0.7 and 469.0 ± 4.9 g/kg for the Canchim, and 73.9 ± 0.8 and 501.8 ± 5.8 g/kg for the 7CHA9NEL calves, respectively. The additive direct effect of the Charolais, as a deviation of the Nellore, and the heterotic individual effect of the Charolais and Nellore breeds were -138.40 ± 23.24 and -73.89 ± 24.34 days for AFC, and 112.30 ± 11.40 and -12.23 ± 9.08 kg for CWC, respectively. The additive direct, additive maternal, heterotic individual and heterotic maternal effects were 0.6 ± 9.0, -11.1 ± 4.9, 5.9 ± 5.6, and 13.1 ± 3.9 g/kg for BWR and 94.3 ± 66.4, -277.0 ± 32.8, -19.0 ± 39.9, and 206.4 ± 29.6 g/kg for WWR, respectively. The results show that as higher was the percentage of cows Charolais genes, the smaller its AFC, the higher its CWC, and the smaller the BWR and WWR ratios; and the as higher the expected heterozygosity in the cow, the smaller its AFC, and the higher the BWR and WWR.
beef cattle; crossbreeding; productive efficiency; cows
