Multivariate restricted maximum likelihood estimation of genetic parameters for production traits in three selected turkey strains

Genetic parameters related to growth, carcass composition and egg production were estimated on three (two female and one male) commercial strains of turkey using the method of restricted maximum likelihood (REML). In order to account for the sexual dimorphism in turkeys, body weight (BW, measured at 12 and 16 weeks of age) was considered as a sex-limited trait. As many as seven traits were analyzed simultaneously in one strain. Egg numbers were normalized using a Box-Cox transformation. Three different,genetic models were used. The first one was a linear mixed model with a direct,genetic effect. Model 2 accounted in addition for a dam's environmental effect, while model 3 introduced a maternal genetic effect. The heritability estimates of BW were very high, especially for female traits (0.77 for female BW16 and 0.68 for male BW16 in strain B). Sexual dimorphism was less heritable (0.23, 0.16, and 0.14 for the 16 weeks body weight sex difference in the three strains considered). One of the female strains exhibited a strongly negative genetic correlation (-0.5) between female BW and egg number. The elevated values of the estimates probably originated from the method used, which accounted for the bias due to the sequential selection that had been carried out, and from the choice of the base population. Use of models 2 and 3 resulted in slightly lower heritability estimates than model 1, due to low maternal effects. The latter, however, offered a reasonable compromise between quality and computational cost of the evaluations.