Role of sperm velocity variables associated with poultry breed in 'last male precedence'

It is well known that when a hen mates with multiple roosters, it is the sperm of the last male that usually fertilizes most of the eggs ('last male precedence'). Sperm quality varies between males within a breed, but also between breeds, and thus, sperm competitiveness after mating may depend on the breeds of the roosters involved. The aim of the present work was to identify differences in sperm competitiveness between breeds, especially with respect to motility. A multibreed mating model was used. Blue Andaluza (BA) and Black Castellana (BC) hens left for 21 days with BA and BC roosters, respectively, were then left with Black-barred Andaluza (Bb) roosters for another 21 days (experimental groups hBA-rBC-rBb and hBC-rBA-rBb). Bb roosters (as the second breed replacing the first) fertilized the majority of eggs in both the hBC-rBA-rBb and hBA-rBC-rBb groups. The percentage of offspring sired by BA roosters (8.0%) was higher (p < 0.05) than the percentage of chicks sired by BC roosters (2.1%). The fertility of the BC hens in the hBC-rBA-rBb group was higher (p < 0.01) than that of the BA hens in the hBA-rBC-rBb group. No difference in sperm concentration was seen between the breeds. Within the rapid sperm subpopulation (sperm velocity, >50 μm/s), Bb sperm showed a higher straight-line velocity (VSL) and average path velocity (VAP) (p < 0.05) than BC sperm. The VSL and VAP values for Bb and BA sperm were similar. In conclusion, the present results show that the sperm of the BA breed, traditionally regarded as of moderate fertility, compensates for this drawback via sperm movement characteristics that afford it an advantage in competition scenarios involving males of other breeds. The VSL and VAP of the rapid sperm subpopulation may play the most important role in securing last male precedence.