Genetic parameters of beef traits of Limousin and Charolais progeny-testedAI sires

Sire selection efficiency depends on the knowledge of accurate genetic para meters. In France, artificial insemination (AI) sires are selected accordin g to their own performances and those of their progeny, which are both reco rded in test stations. Genetic parameters among progeny traits were estimat ed using multi-trait REML (restricted estimation of maximum likelihood) ana lyses in Charolais and Limousin breeds. The expected decrease in genetic va riability algebraically calculated among progeny traits due to the selectio n of sires was not observed. This selection was not a strict truncation. He ritabilities of traits measured on progeny are moderate for growth traits, morphology and live fatness scores (from 0.14 to 0.38) and slightly higher for dressing percentage and carcass fatness score (0.50 and 0.44, respectiv ely). Genetic correlations among progeny traits depended on traits, selecti on programme and breed. Carcass weight and morphology were highly genetical ly linked to corresponding live traits (live weight and conformation, respe ctively). They can, therefore, be easily improved through indirect selectio n in contrast to carcass fatness which has only a small genetic correlation with live traits. (C) Inra/Elsevier, Paris.