Data were available on crossbred meat lambs for 10 live-weight and growth traits (2585 lambs), 5 carcass traits (1884 lambs) and 10 dissection traits (944 lambs). These were the progeny born on an experimental farm over 5 years, from 102, 79 and 65 sires respectively for the three groups of traits. Genetic parameters were estimated from the sire components in a nested analysis of variance within breed of sire and year subclass, adjusting for sex, dam age, rearing type and other factors.
The heritabilities of the live-weight and growth traits were all low, the highest being average daily gain to slaughter (0·10, s.e. 0·06), and none was statistically significant. The heritabilities of the traits of carcass composition were much higher: percentage lean (0·41, s.e. 0·13), percentage fat (0·37, s.e. 0·13) and percentage bone (0·16, s.e. 0·10). Intermediate values were found for most other traits: killing-out percentage (0·16, s.e. 0·07), fat depth (0·21, s.e. 0·11), eye-muscle area (0·14, s.e. 0·10) and lean/bone ratio (0·13, s.e. 0·09).
Phenotypic and genetic correlations among the traits were also estimated. No major incompatibilities were found among the traits. The results are discussed in relation to the genetic improvement of lean meat production in sheep.