Penetration of hamster and pig zona-free eggs by boar ejaculated spermatozoa preincubated in vitro.

The hamster and pig zona-free eggs were successfully penetrated in vitro by boar ejaculated and washed sperm, which had been preincubated in vitro in a chemically defined medium supplemented with calf serum proteins. The fertilization results and rate of polyspermy were found to be mainly dependent on sperm concentration at preincubation and on the time of sperm preincubation and fertilization. However, the pig zona-free eggs were penetrated also by the freshly washed boar sperm, but as early as 8 hours after semination. In this case the spermatozoa probably also capacitate on the surface of the egg plasma membrane. The fertilization of zona-free eggs with preincubated sperm results in higher penetration rate and very high polyspermy as early as 4 hours after semination.