EFFECTS OF THE PLUMAGE-REDUCING NAKED NECK (NA) GENE ON THE PERFORMANCE OF FAST-GROWING BROILERS AT NORMAL AND HIGH AMBIENT-TEMPERATURES

A population segregating for the naked neck (Na) gene was used to evaluate the gene's effect on fast-growing broilers at high (32 C) and normal (23 C) temperatures. An experimental stock comparable to those of modem broilers was established by backcrosses to commercial sire lines. Matings between heterozygous (Na/na) males and females produced normally feathered (na/na) birds, and heterozygous (Na/na) and homozygous (Na/Na) naked neck birds for the experiments. Compared with na/na birds, the Na/na and Na/Na birds had about 20 and 30% less feather mass (relative to body weight), respectively, at both temperatures. At normal temperatures, naked neck broilers averaged 2,000 g BW, 290 g of which was breast meat, at 6 wk of age, compared to 1,895 and 257 g, respectively, for their normally feathered full-sib counterparts. The effects were more pronounced at the high temperature; the Na/Na broilers averaged 2,018 g with 284 g of breast meat at 8 wk of age, as compared to 1,723 and 215 g, respectively, in the na/na broilers. The heterozygous naked neck birds exhibited intermediate performance. Reduced plumage was associated with lower skin mass due to reduced fat deposition within it. The advantages associated with reduced plumage increase with broiler size and ambient temperature. The heterozygous naked neck broilers were superior to normal broilers at normal temperatures, with even greater superiority at the high temperature. Further reductions in plumage, as seen in Na/Na birds, increases this advantage.