Further Studies on the Effect of the Recessive White Genotype on Early Growth Rate and Body Size

Abstract

Previous studies from this laboratory have demonstrated a relationship between the C+ and c alleles at the recessive white locus and body weight at 8 and 26 weeks of age. Similar studies have been conducted on the same randombred population 20 and 21 generations later. In addition, one experiment involved a comparison of colored and recessive white birds when grown on a low energy replacement starter vs. a high energy broiler starter.The 1981 progeny studied were produced by 100 females housed in single bird cages and inseminated with pooled semen from 20 males. The gene frequency for the recessive white gene (c) was .56 ± .023 and the recessive white segregates were approximately 35% of the progeny produced. The 8-week body weights of the recessive white progeny as a percentage of the colored phenotype (C+/−) was 88.8% for males and 92.5% for females. These body weight differences at 8 weeks were highly significant (P<.005). The recessive white genotype also reduced 26-week body weight of females and 38-week egg weight.As expected, there were highly significant differences (P<.001) in body weight at 4, 6, and 8 weeks of age due to rations. However, there was no evidence of a genotype × ration interaction. The observed differences between genotypes (C+/− vs. c/c) were similar regardless of the energy level of the ration.These results confirm and extend the earlier observations on the depressing effect of the recessive white genotype on early growth and support the conclusion that this relationship represents a pleiotropic effect of the gene and is not the result of linkage disequilibrium.