Identification of a sperm cell attribute responsible for subfertility of roosters homozygous for the rose comb allele.

Fertility, sperm metabolism, sperm filling of oviductal sperm storage tubules (SST), and sperm motility were compared in subfertile roosters homozygous for the rose comb allele (R/R) and fertile controls (r/r or R/r males). As expected, fertility of R/R males was less than that of controls (p < 0.0001). The metabolic rate of spermatozoa from R/R males was also lower than that of controls (p < 0.05). Likewise, filling of SST in vivo was lower (p < 0.0001) for spermatozoa from R/R males than for control spermatozoa. However, in vitro filling of SST was not different between genotypes (p > 0.05). Motility of spermatozoa from R/R males was less than that of controls (p < 0.001) as determined by an objective spectrophotometric assay. Previous researchers have concluded that subfertility associated with homozygosity for the rose comb allele is attributable to a sperm-specific phenomenon. However, the cellular mechanism(s) responsible for the subfertile status were not defined. In contrast to previous researchers, we have demonstrated that subfertility of R/R males is explicable in terms of reduced sperm transport through the hen's vagina; reduced sperm motility appears to be the major contributing factor.