Sperm Penetration of Pig Eggs in Relation to the Timing of Ovulation and Insemination

Summary. The influence of four post-ovulatory ages of egg on the proportion of eggs penetrated by spermatozoa was studied in the pig. The time of ovulation was controlled by an injection of human chorionic gonadotrophin (hcg) given during pro-oestrus. Gilts in oestrus were inseminated 0, 4, 8 or 12 hr after the estimated time of ovulation, and eggs recovered from the oviducts in vivo either 2 or 3 hr later. Eggs were examined from thirteen gilts in each of the four insemination groups. A total of 515 eggs was recovered, giving an overall recovery rate of 86%. Spermatozoa were found attached to or in the zona pellucida of twenty-eight of 117 eggs (24%) recovered 2 hr after insemination and in the perivitelline space of four of these eggs, but none was fertilized. Of 398 eggs recovered from forty animals 3 hr after insemination, 208 eggs (52%) from thirty-one animals had spermatozoa attached to or in the zona pellucida. Twenty-four of these eggs had spermatozoa in the perivitelline space, and 143 (36%) were fertilized. These findings demonstrate that boar spermatozoa can reach and penetrate the zona pellucida of pig eggs within 2 hr of insemination, and can enter the ooplasm and cause resumption of meiosis within 3 hr of insemination. There was no indication that post-ovulatory age as such influenced the number of spermatozoa in the zona pellucida or the proportion of eggs fertilized.