Effects of follicular fluid at fertilization in vitro on sperm penetration in pig oocytes.

The effects of porcine follicular fluid (PFF) on sperm penetration of pig oocytes and on prevention of polyspermy were examined and characteristics of spermatozoa exposed to PFF were determined. The addition of PFF at the level of 1 and 10% to the prefertilization and fertilization media decreased penetration rates and the mean number of spermatozoa in penetrated eggs regardless of the origin of PFF. In the presence of BSA, supplementation of 0.1% PFF to prefertilization and fertilization media and 1% PFF to prefertilization media did not decrease the penetration rates but did increase monospermic penetration to 54 and 68%, respectively. When PFF was added to prefertilization media, the number of spermatozoa binding to the zona and the percentage of acrosome-intact spermatozoa decreased with increased PFF concentration (from 43.1 +/- 2.8 and 73.1 +/- 4.9% to 7.2 +/- 1.3 and 15.7 +/- 15.4%, respectively). At the end of prefertilization incubation, sperm agglutination was observed and the degree depended on PFF concentration. Supplementation of fetal calf serum to prefertilization and fertilization media blocked the effects of PFF on sperm penetration and binding of spermatozoa to the zona. These results indicate that the prefertilization incubation of porcine spermatozoa in suitable concentrations of porcine follicular fluid will effectively reduce both the number of spermatozoa that attach to the surface of pig eggs and the incidence of polyspermy.