Heterosis and Heterosis Retention for Reproductive and Maternal Traits in Nellore-Angus Crossbred Cows

Calving rate, weaning rate, birth weight, weaning weight, and ADG from 1997 to 2011 were investigated in Angus, Nellore, F_(1) Nellore-Angus, first generation 3/8 Nellore 5/8 Angus produced as following: (1/2 Nellore 1/2 Angus sires and 3/4 Angus ? Nellore dams, 3/4 Angus 1/4 Nellore sires and 1/2 Angus 1/2 Nellore dams, and ? Nellore 1/4 Angus sires and Angus dams), and second generation 3/8 Nellore 5/8 Angus cows. The objectives were to estimate heterosis in Nellore-Angus crosses for cow reproductive traits and maternal effects on traits of their calves. The F_(1) cows expressed 0.20 ? 0.02 heterosis for calving rate, while both first and second generation 3/8 Nellore 5/8 Angus expressed 0.13 ? 0.02. the first generation 3/8 Nellore 5/8 Angus produced out of 3/4 Angus 1/4 Nellore sires and 1/2 Nellore 1/2 Angus dams expressed 0.14 ? 0.03 heterosis for calving rate. The F1 Nellore-Angus expressed 0.23 ? 0.03 heterosis for weaning rate and the 3/8 Nellore 5/8 Angus produced out of 3/4 Angus 1/4 Nellore sires ? 1/2 Nellore 1/2 Angus dams and the second generation 3/8 Nellore 5/8 Angus expressed 0.14 ? 0.07 and 0.15 ? 0.05, respectively. No heterosis was expressed for birth weight in any breedtype group. Multiple attempts to analyze weaning weight and ADG and estimate heterosis resulted in excessive adjustments to least squares means. Young and oldest cows weaned lighter calves than others. F_(1) cows weaned heavier calves at most ages. Nellore-sired F_(1) calves were heavier at weaning than the reciprocal cross. Calves out of cows of intermediate ages had larger preweaning ADG than calves born to 2- and 3-yr-old and to aged cows. Generally, calves out of F_(1) Nellore-Angus cows had larger ADG than those out of cows of other breedtypes. Nellore-sired F_(1) heifers had lower ADG than Angus-sired F_(1) heifers. In general, bull calves had larger ADG than heifers. Non-F_(1) crossbred cows expressed slightly larger heterosis than what would be expected by the dominance model. Heterosis expressed by second generation 3/8 Nellore 5/8 Angus for calving and weaning rate did not appear to differ from the first generation.