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 × environment
interactions were rare: genotype × environment was
observed only for body weight at 10 wk of age and wasclose 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 effi-
ciency, 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