Analysis of the combined effect of the spermatozoal degeneration allele (Sd) and homozygosity of the rose comb allele (R) on the duration of fertility of roosters (Gallus domesticus).

Roosters homozygous for the rose comb allele (R/R) are subfertile. Likewise, roosters bearing the dominant spermatozoal degeneration allele (Sd) are subfertile. The objective of the present research was to see whether these effects were cumulative. Domestic fowl were bred in order to obtain males representing the following genotypes: R/r+ sd+/sd+, R/r+ Sd/sd+, R/R sd+/sd+, and R/R Sd/sd+. Duplicate fertility trials were conducted with Single Comb White Leghorn hens. In each trial, ejaculates were pooled according to genotype. The insemination dose was 1 x 10(8) viable spermatozoa per hen, and eggs were collected over a 21-day interval following a single intravaginal insemination. Fertility over the 21-day period was 53 +/- 2.1 (SEM), 36 +/- 1.6, 21 +/- 2.1, and 11 +/- 1.2%, respectively. Therefore, the effect of homozygosity for the R allele and the presence of the Sd allele were cumulative in the depression of fertility.