Prediction of fertility of bovine semen: Preliminary studies with the hamster egg penetration test

The ability of liposome-treated fresh and frozen spermatozoa from two bulls to interact with zona-free hamster oocytes was examined to show whether the in vitro test results would correspond with in vivo fertility as indicated by the 60 to 90 d nonreturn to service rates which, using frozen semen, were 77 and 59%, respectively. The motility of spermatozoa in washed suspensions was also rated. Hamster test results were obtained using three ejaculates from each bull both as fresh and frozen semen. The results with frozen semen corresponded with fertility. The averages of three hamster tests for oocyte penetration rates and mean number of spermatozoa per penetrated oocyte comparing spermatozoa from the bull with the higher fertility with spermatozoa from the bull with the lower fertility were 91% and 2.7 versus 56% and 1.4, respectively. Spermatozoa washed from frozen semen from the bull with the higher fertility interacted with hamster oocytes at the higher rate even when sperm motility was rated the same for both bulls. By contrast, fresh spermatozoa from the lower fertility bull interacted with hamster oocytes at a higher rate than spermatozoa from the higher fertility bull in six tests, comparing six ejaculates of fresh semen from both bulls. Comparing the higher fertility bull with the lower fertility bull, the average of six tests for oocyte penetration rates and mean number of spermatozoa per penetrated oocyte were 60% and 1.6 versus 89% and 3.0, respectively. This suggests that this hamster test cannot be used with fresh semen to predict relative levels of fertility of frozen semen. Also, the subjective rating of sperm motility did not correspond with the in vitro oocyte penetrating ability of the spermatozoa.