Relative efficacy of conventional sperm parameters and sperm penetration bioassay to assess bull fertility in vitro

Frozen semen samples from 10 bulls were thawed and actively motile sperm recovered using a swim-up technique. Calcium ionophore A23187 at 0.5 μM concentration was used for 1 min to induce the acrosome reaction in the sperm. Mature female golden hamsters were superovulated with 50 IU of equine chorionic gonadotrophin followed 56 h later with 75 IU of human chorionic gonadotrophin. The cumulus mass was recovered 17 h after hCG treatment by puncturing the oviducts in the infundibulum region. Subsequently, cumulus cell mass and zona pellucida were digested by 0.1% hyaluronidase and 0.1% trypsin, respectively, to yield zona-free hamster eggs (ZFE). A sperm penetration bioassay was performed by coincubating capacitated sperm at 5×106 concentration and ZFE for 3 h at 38°C in an air incubator. The conception rate of the bulls was based of an average of 82.6 cows per bull with pregnancy status confirmed by rectal palpation. It was found to be strongly correlated (p<0.01, r=0.723) with fertilization percentage, whereas percent motile sperm, percent viable sperm and percent sperm with intact acrosomes were not significantly correlated with the conception rate (r=0.210, −0.021 and −0.468, respectively). Results of the present study suggest that the sperm penetration bioassay can be reliably used to test the fertilizing potential of bull sperm in vitro.