ESTIMATION OF GENETIC-PARAMETERS OF EGG-PRODUCTION TRAITS OF LAYING HENS BY RESTRICTED MAXIMUM-LIKELIHOOD APPLIED TO A MULTIPLE-TRAIT REDUCED ANIMAL-MODEL

Variance components for egg production traits (No of eggs produced between 19 and 26, 26 and 38 and 26 and 54 wk of age), egg characteristics (average egg weight at 2 different ages and egg density) and body weight of hens at 40 wk of age were estimated in two strains of a breeding company by univariate and multivariate Restricted Maximum Likelihood (REML) applied to a Reduced Animal Model (RAM). To allow tridiagonalization of the coefficient matrix when RAM is considered, the approach of Thompson and Meyer (1990) using an imaginary random effect with negative variance was implemented. Canonical transformation was also employed. REML estimation, carried out on 15 random samples of almost-equal-to 7 000 recorded hens drawn from each of 2 data files corresponding to 2 different strains, showed a rather small genetic antagonism between the group of egg production traits and egg density on one hand and that of egg weights on the other hand. Weight of hens behaved differently in the 2 strains. It showed also that traits within these groups were positively correlated. Heritabilities obtained by univariate and multivariate analyses were very similar and were lower for egg production traits (from 0.09 to 0.27) than for egg characteristics or weight of hens (from 0.34 to 0.48).