GENETIC-ANALYSIS OF A SELECTION EXPERIMENT ON INCREASED BODY-WEIGHT AND BREAST MUSCLE WEIGHT AS WELL AS ON LIMITED ABDOMINAL FAT WEIGHT

1. Genetic parameters of body weight (BW), breast meat weight or yield (BRW, BRY) and abdominal fat weight or yield (FTW, FTY) were estimate d in males and females originated from an experimental line selected f or improving broiler carcase quality and its control line. 2. Mean her itabilities over both sexes of BW, FTW and FTY were 0.43, 0.56 and 0.6 3 respectively. Those of BRW and BRY were 0.53 and 0.65 respectively. 3. BW was unfavourably correlated with FTW (r(g) of 0.40) and to a les ser extent with FTY (rg of 0.12). BW was, as expected, highly correlat ed with BRW (r(g) 0.77), but a poor correlation was obtained with BRY (r(g) of 0.15). Selection for more breast yield should not reduce the leanness of the birds, with a genetic correlation between BRY and FTY of -0.15. 4. The variance explained by the maternal effects accounted for a rather small part of the total phenotypic variance (from 3% to 8 % according to the trait), but ignoring these effects led to a signifi cant overestimation of the heritabilities (by 11% to 19%). 5. Except f or BRY, the heritability estimates differed between sexes, only modera tely for BW hut more for BRW, FTW and FTY. However, estimated genetic correlations between sexes were high (between 0.94 and 0.99) and in tu rn heritabilities of sexual dimorphism of the various traits very low (between 0.02 and 0.07). 6. A significant improvement of the genetic l evel for growth and carcase composition had been obtained in the selec ted line, with a mean genetic gain per generation of 0.12 sigma(g), 0. 13 sigma(g) and - 0.30 sigma(g) for BW, BRY and FTY respectively.