The effect of the naked neck gene, Na, on growth and carcass composition of broilers raised in two temperatures

Eight-week-old broilers of the three genotypes, normally feathered (na+/na+), heterozygous naked neck (Na/na+), and homozygous naked neck (Na/Na), were compared for growth performance and body composition characteristics at two environmental temperatures, 21 C in the cool room and 38 C in the hot room. Birds maintained in the cool room attained significantly greater live, New York dressed, and eviscerated weights than did birds maintained in the hot room, while consuming 93% more feed and achieving 84% greater weight gain. However, there were no significant differences in feed conversion ratios. Percent yield was 3% greater for birds in the hot room. In the cool room, na+/na+ birds were heavier than Na/Na birds for body weight measurements while in the hot room the reverse was true. In both temperatures the na+/na+ and Na/na+ birds were similar. For New York dressed percent yield, the Na/Na and Na/na+ were similar and had greater yield than na+/na+ birds in the cool room. The same trend held for birds in the hot room but to a much less degree. Eviscerated yield showed no genotype X temperature interactions. Body composition data indicated that Na/Na birds contained more moisture, similar protein, less lipid (particularly in cool room), and more ash (particularly in hot room) than the na+/na+ birds. Overall, in the hot environment, the Na/Na birds achieved significantly greater body weights than na+/na+ birds while containing less lipid but more moisture and ash.