Growth performance and carcass quality of naked neck genotypes of chickens subjected to various dietary methionine levels under hot environmental conditions

A decline in feather coverage in chickens due to the presence of the naked neck (Na) gene may alter sulfur amino acid requirements under high ambient temperatures. The present study aimed to determine the growth performance and carcass traits of naked neck (NaNa; Nana) and normally feathered (nana) genotypes when fed diets supplemented with different levels of methionine under hot environmental conditions. A three-factorial experimental design (3 × 3) was used, comprising three genotypes (NaNa, Nana, nana) and three dietary methionine supplementation levels (0.30, 0.35, and 0.40%). A total of 108 male chicks aged 4 weeks (36 birds per genotype) were randomly assigned to three dietary methionine levels in individual cages (12 birds per subgroup). Dietary methionine level had no significant effect on body weight, body weight gain, or feed conversion ratio. However, increasing methionine levels significantly (p ≤ 0.01) increased breast muscle percentage, dressing percentage, and the relative weight of edible parts. On the other hand, the relative weight of abdominal fat decreased significantly (p ≤ 0.01) with increasing dietary methionine levels. Additionally, naked neck genotypes (NaNa; Nana) had significantly (p ≤ 0.01) lower abdominal fat percentages compared to the normally feathered genotype (nana). A significant interaction between genotype and methionine level was detected for relative weight of breast muscles, with a favorable effect of the Na gene observed at higher dietary methionine levels. Introducing the naked neck gene into chicken populations fed diets supplemented with higher levels of methionine is highly recommended under hot environmental conditions.