Interactions between the naked neck gene, sex, and fluctuating ambient temperature on heat tolerance, growth, body composition, meat quality, and sensory analysis of slow growing meat-type broilers

Influence of the Naked Neck gene, NA, on heat tolerance was evaluated in slow growing meat-type chickens in interaction with sex. Standard male Ross broilers were used as rapid growth controls. Fluctuating temperature was used to simulate day–night variations, i.e. 17 °C to 23 °C in normal and 27 °C to 33 °C in hot conditions. Male and female chickens were weighed twice and once a week, respectively, and Gompertz function was fitted to our data to calculate theoretical age at 1 kg (A1K) and 2 kg (A2K). Carcass, abdominal fat, breast and leg yields were measured (CY, AFY, BRY, and LY). Meat quality was evaluated 24 h post-mortem with pH and colour (L, a⁎, b⁎) of the breast, and 72 h post-mortem with breast meat drip loss (DL). Rectal temperature and its variation were measured at the maximum and minimum ambient temperature at 1 and 2 kg (RT2min, RT2max, and ΔBT2 kg). Hematocrit (HCT, ΔHCT) were measured at the same stages. Organoleptic characteristics of breast and leg muscles were studied for females from both ambient temperatures.Significant genotype × sex × temperature interaction was observed for A2K, AFY, RT2max, ΔBT2 kg, and ΔHTC2 kg. Hot condition did not affect ΔBT2 kg and A2K in homozygous NA birds; ΔBT2 kg was markedly increased in all other genotypes for males but not for females. Significant genotype × environment interactions were found only for A2K and CY. Sex × temperature interactions were found for all traits except for A1K, b⁎, pH, and ΔHCT2 kg. In both conditions, males reached 2 kg at the same age (69 d) while females reached this weight 11 d latter in hot than in normal condition. Heat decreased CY in males (− 1.0%) and increased it in females (+ 1.4%). Meat was paler in males and darker in females in the hot condition leading to a difference in meat brightness between males and females only in the hot condition. Concerning sensory analysis, genotype × temperature interaction was significant for meat consistence, both in leg and breast muscles.Effects of the NA gene on susceptibility to heat stress were smaller in slow growing animals than in broilers. However, heat tolerance was still improved in homozygous NA slow growing birds, as shown by the limited change in diurnal variation of body temperature. Furthermore, the NA gene improved breast meat percentage.In contrast to broilers, where females should be recommended for production in hot climates, the present study would rather suggest that naked neck males from slow-growing meat-type ‘label’ chicken lines should be preferred.