Heterosis, Breed Maternal and Breed Direct Effects in Red Poll and Hereford Cattle2,3

Abstract

Individual heterosis (HiRH), breed maternal (GmR and GmH) and breed direct (GiR and GiH) genetic effects were estimated from a two-breed diallel experiment of the Red Poll (R) and Hereford (H) breeds. Data were collected on 539 calves born (521 normal presentations), 484 calves weaned and 474 completing the postweaning growth phase. Significant heterosis effects, expressed as a percent of the straightbred mean, were 8.0% for birth weight and 7.9% for both preweaning average daily gain and 200-d weight. Heterosis effects on postweaning growth traits of females were 15.7% for 168-d gain, 12.0% for 368-d weight and 2.9% for 368-d height. Heterosis effects on postweaning growth traits of intact males were 9.1% for 168-d gain, 6.5% for 368-d weight, 2.3% for 368-d height and 9.6% for scrotal circumference. Breed maternal effects were significantly greater for calves with Red Poll dams for birth weight, preweaning average daily gain, 200-d weight and for postweaning gain of female calves receiving a high silage diet. However, bull calves from Hereford dams grew more rapidly postweaning; bull calves received a diet of higher energy density. Estimates of GiR exceeded GiH for survival, preweaning average daily gain, 200-d weight and 368-d height. However, GiH exceeded GiR for calving difficulty, birth weight and 168-d postweaning gain in both heifers and bulls. Breed maternal effects were higher for the Red Poll, while breed direct effects were higher for the Hereford.