Effect of Introducing the Naked Neck Gene in a Line Selected for Low Residual Feed Consumption on Performance in Temperate or Subtropical Environments

The aim of this study was to investigate the possibility of combining the naked neck gene with a genetic background that has been optimized for feed efficiency of laying hens at moderate temperature. In 1997, the naked neck gene was introduced into a line selected for low residual feed intake. In 2003, after 6 generations of introgression, 8 males and 56 females heterozygous for the NA*NA mutation were used to generate all 3 genotypes (NA*N/NA*N, NA*NA/NA*N, NA*NA/NA*NA), in 2 hatches, for rearing in Taiwan and France, respectively, at 3-wk intervals. Growth performance, anatomical traits, laying traits, and feed efficiency were recorded in each country. In addition, comb and rectal temperatures were measured in Taiwan. Performance was generally lower and mortality of laying hens was higher in Taiwan (11%) than in France (1%). Genotype x environment interactions were rare: genotype x environment was observed only for body weight at 10 wk of age and was close to significance for egg weight. The laying performance was significantly decreased in Taiwan by about 25%. The naked neck genotype had a negative effect on body weight and a positive effect of clutch length and egg weight. It also affected heat dissipation traits such as wattle length and rectal and surface temperature measurements. There was a clear additive and negative effect of the NA*NA mutation on rectal temperature. Feed intake and residual feed intake were increased in the homozygous carriers of the NA*NA mutation, which may improve heat tolerance of the low residual feed consumption (R-) line. Feed efficiency tended to be better in NA*NA/NA*NA hens in both environments. Thus, the introduction of the NA*NA mutation in the R- background appeared to be favorable from the viewpoint of feed efficiency, but it did not improve laying performance in a subtropical environment. Other factors than temperature, such as diet composition and lighting regimen, may be involved.