Heterosis and breed effect on carcass traits of rams. 1. Carcass weight and component traits

Abstract

A three-breed diallel mating design was used to generate 632 rams comprising three purebreds (Dorset Horn, Merino and Corriedale) and their six contemporary F1 crossbreds in the CSIRO Sheep Crossbreeding Experiment to provide materials for studying the heterosis and breed effects on carcass traits of intact rams maintained under pasture grazing conditions. The rams were slaughtered at an average age of 21 months, at which time their average (¦ s.e.) carcass weight was 28.4 ¦ 0.2 kg. This paper, the first of a series, is concerned with estimation of the linear effects due to heterosis (h') and breed-transmitted effect (gI) and breed-maternal effect (gM) on cold carcass weight and weight components (edible meat, bones and excess fat trim) of the carcass. The results showed that, in general, gI was more important than gM. Whether evaluated as a purebred, or as a paternal or maternal breed, the Dorset Horn produced more edible meat per sheep than either the Merino or the Corriedale. In terms of excess fat trim, the Corriedale tended to be the most wasteful. A significant (P < 0.05) heterosis effect was observed on all traits under investigation, but its main impact was on excess fat trim, where the h1 varied with the specific breed combination and ranged from 10% to 30%, but averaged c. 24% for the whole population.