Direct and maternal additive and heterosis effects from crossing Bos indicus and Bos taurus cattle: cow and calf performance in two environments

Data on Brahman and Hereford cattle and their crosses were used to estimate direct and maternal additive and heterosis (dominance + epistasis) effects on cow productivity and calf preweaning growth traits. The cows, which wer e born in the subtropical environment at Grafton, Australia from 1983 to 19 85, had varying levels of Brahman/Hereford genes. At the start of this stud y in 1990, half of the cows were transferred to the temperate environment a t Ebor and the other half remained at Grafton. In both environments the cow s were mated to Brahman (B) Hereford (H) and first-cross B x H bulls over t hree mating seasons. The same individual bulls were used in both environmen ts. All the traits were influenced by a significant genotype by environment interaction, which was a cumulative effect of some or all of additive x en vironment, dominance x environment and epistasis x environment interactions . Weight of calf weaned per cow exposed to bull (used as an overall measure of cow productivity) was significantly influenced by a positive direct het erosis effect of 25.8% (relative to straightbred cows) and 33.2% at Grafton and Ebor, respectively. As traits of the calf, preweaning ADG and weaning weight were influenced by a significant negative Brahman direct additive ef fect at Ebor but not at Grafton. Direct heterosis effects were 10.8% and 10 .3% at Grafton and 9.7% and 9.1% at Ebor for preweaning ADG and weaning wei ght, respectively. Inclusion of epistasis effects in the model significantl y improved the accuracy of predicting calf performance of genotypes at Graf ton. Therefore it is recommended that, where data structure allows, epistas is effects should be included in crossbreeding models. (C) 1999 Elsevier Sc ience B.V. All rights reserved.