Genetic influences on growth and partition of fat between depots and its distribution in fowl carcasses.

Thirty-two Hubbard and 40 Egyptian Fayoumi (dual-purpose) chickens were slaughtered in series at 2-wk intervals between 2-8 wk and 2-10 wk of age, respectively. Genetic differences in the allometric fat growth equation constants were studied. Relative to total body fat (TBF), the breeds did not differ significantly in relative growth of non-carcass fat. The Fayoumi tended to lay down carcass fat at a faster rate than the Hubbard. As TBF increased, the proportion of non-carcass fat increased and that of carcass fat decreased in the Hubbard; these depots tended to grow at the same rate as TBF in the Fayoumi. The Hubbard had significantly higher relative rates of fat deposition in the thigh, drumstick, breast and lower rates of fat deposition in the wing and neck than the Fayoumi. As the Hubbard matured, their growth coefficients of carcass fat tended to decrease anteriorly from breast to neck and also from leg to wing. The specific growth rates in almost all parts of the Fayoumi did not differ significantly from that of the total carcass fat. The present study shows for the Hubbard, as compared to Fayoumi, distinct patterns of fat partitioning (higher non-carcass fat: carcass fat; higher intermuscular fat: subcutaneous fat) and distinct patterns of fat distribution (higher proportion of the total depot occurring in the prime cuts). The study also gives some indications of different fat deposition patterns in poultry as compared to ruminants (cattle and sheep).