The objective of this study was to evaluate the effects of genetic and non genetic factors on cow weight at calving (CWC) of Nellore and 1/2 Canchim + 1/2 Nellore cows, mated to Canchim (5/8 Charolais + 3/8 Zebu) and Charolais breed bulls, respectively, and also on the gestation length (GL) of their calves, and the weights (W) and ages (A) at first insemination (FI), conception (FCo), and calving (FC) of 1/2 Canchim + 1/2 Nellore heifers. The least squares method was used, with models that included the effects of year and month of calving, age of cow and origin of cow (for the Nellore cows only) for the analyses of CWC, breeding season, age of cow, origin of cow and sire of calf (random) for the analyses of GL, and year and season of birth and the interaction year x season for the analyses of the traits of the heifers. Year of calving and origin of cow affected CWC. The cows calving from August to November were lighter than the cows calving in December and from May to July. Cow weight linearly increased with age of cow. For the crossbred Canchim x Nellore calves, gestation length was longer for males than for females. The CWC least square means were 450±2 kg (Nellore cows) and 502±2 kg (1/2 Canchim + 1/2 Nellore cows) and the GL least square means were 291.0±.4 days (1/2 Canchim + 1/2 Nellore calves) and 285.7 ± .2 days (1/2 Charolais + 1/4 Canchim + 1/4 Nellore calves). The least square means were 372±2 kg (WFI), 376±2 kg (WFCo), 442±3 kg (WFC), 810±5 days (AFI), 831±6 days (AFCo), and 1116±6 days (AFC) for the 1/2 Canchim + 1/2 Nellore heifers. The heritabilities of GL, as a trait of the calf, were equal to .17±.14 (1/2 Canchim + 1/2 Nellore) and .69±.31 (1/2 Charolais + 1/4 Canchim + 1/4 Nellore).
beef cattle; females; fertility; heritabilities; weights
