Genotype X environment interactions in preweaning traits of purebred and reciprocal cross Angus and Brahman calves on common bermudagrass and endophyte-infected tall fescue pastures

Preweaning data on 486 Angus, Brahman, and reciprocal cross calves (AB, BA) managed on common bermudagrass or endophyte-infected tall fescue were used to evaluate the interactions of forage type and sex of calf with direct effects, individual heterosis, and maternal effects. Calves were spring-born in 1988, 1989, 1990, and 1991 to five sires of each breed. Male calves were castrated at birth, and calves were not creep-fed. Average values of heterosis for birth weight, 205-d weight, weaning hip height, and weaning weight:height ratio (WT/HT) were important (P < 0.01) and consistent across forage environment. Heterosis for birth weight was larger in bull calves than in heifer calves (P < 0.05), whereas heterosis for other preweaning traits were consistent across sex of calf. Average maternal effects for WT/HT (P < 0.10) were important and consistent across forage environment. Maternal effects for birth weight were larger with bull calves than with heifer calves (P < 0.01). Maternal effects for weaning hip height favored the Angus dam managed on bermudagrass (P < 0.05) but not managed on fescue. A similar but nonsignificant trend occurred in maternal effects for 205-d weight. Direct effects for birth weight were larger in bull calves than in heifer calves (P < 0.01). Direct effects for weaning height were larger in calves managed on bermudagrass than in calves managed on tall fescue (P < 0.07). A similar but nonsignificant trend was evident in direct effects for 205-d weight. Direct effects for WT/HT were relatively small and unimportant. These data indicate that heterosis for preweaning traits reported in this research are relatively stable across the two forage environments but maternal and direct effects may vary with production environment.