Evaluation of assay conditions for the zona-free hamster ova bioassay of boar sperm fertility.

The ability to penetrate zona-free hamster ova may be a very useful test of fresh and frozen boar sperm fertility. These studies were designed to optimize assay conditions prior to evaluation of the accuracy of the bioassay in predicting boar sperm fertility. The ability to penetrate zona-free hamster ova was greater in sperm washed on a Percoll gradient than in sperm washed by dilution and centrifugation. Penetrating ability was greater in sperm from the sperm-rich fraction than from the whole ejaculate but did not differ among different aliquots of the sperm-rich fraction and did not decrease when the prewashing interval was increased from 15 to 85 min. Frequency of collection of ejaculates (1, 3, or 5 times per week) did not affect the penetrating ability of the sperm. Penetration rate was greater when sperm were coincubated with zona-free hamster ova at 39 degrees C compared to 37 degrees C. Sperm from an infertile boar had reduced penetrating ability compared to sperm from fertile boars (11% vs 93%, P less than .001). These studies suggest that the zona-free hamster ova bioassay may be a useful assessment of fresh boar sperm fertility.