Sperm mobility determines the outcome of sperm competition in the domestic fowl

The aim of this study was to establish whether the mobility of sperm of the domestic fowl, as measured by an in vitro assay, predicted the outcome of sperm competition. Thirteen pairs of New Hampshire roosters, comprising one male categorized as having high-mobility sperm and the other as having average-mobility sperm, were used. Each male provided 25 times 106 sperm, which were mixed and artificially inseminated into between four and seven New Hampshire hens, each of which produced 2 to 11 offspring. The experiment was conducted twice, such that the same pair of males inseminated the same females. Paternity was assigned by using microsatellite markers. There was a clear effect of sperm-mobility phenotype on the outcome of sperm competition: in all 13 pairs the high-mobility male fathered the majority of offspring (73.3% overall; p < 0.0001). The proportion of offspring fathered by the high-mobility male within pairs varied significantly between male pairs (p < 0.0005). This effect was associated with the difference in sperm-mobility scores between males within pairs: there was a significant positive relationship between the proportion of offspring fathered by the high-mobility male and the ratio of mobility scores between males (p < 0.05). In addition, compared with their success predicted from the non-competitive situation, in the competitive situation high-mobility males were disproportionately successful in fertilizing eggs compared with average-mobility males. This may occur because female sperm storage is limited in some way and a greater proportion of high-mobility sperm gain access to the female's sperm storage tubules. There was no evidence that female effects accounted for any of the variation in paternity

Increased fecundity resulting from semen donor selection based upon in vitro sperm motility

Semen donors were selected from a population of 100 roosters based upon the extent to which sperm penetrated 6% (wt/vol) Accudenz from an overlay of extended semen. Semen donors categorized by average or high sperm motility (n = 5 per phenotype) were ejaculated weekly, their ejaculates pooled by phenotype, and pooled semen extended. A subsample of each sperm suspension was overlaid on 6% (wt/vol) Accudenz in a cuvette, the cuvette was placed in a 41 C water bath, and the absorbance of the Accudenz layer was measured after a 5-min incubation. The remainder of the sperm suspension was inseminated (n = 55 hens per phenotype). Each hen was inseminated weekly with 50 x 10(6) sperm for 14 wk. The hatchability of eggs laid by hens inseminated with sperm from the high motility phenotype was 10% greater (P or = 0.05) or a motility by dose interaction (P > or = 0.05). A posteriori comparison among means revealed that the maximal fertility obtained with sperm from average roosters was 9% less (P < or = 0.05) than that obtained with only 25% as many sperm from the high motility phenotype. These experiments demonstrated that the fecundity of artificially inseminated hens can be increased when sperm penetration of Accudenz is used as a selection criterion for semen donors