Intraperitoneal insemination, sperm transport and capacitation in the pig

Intraperitoneal insemination was studied in a total of 58 pigs, both to ascertain the success of this route of sperm deposition with the eventual use of frozen-thawed boar semen in mind and to estimate the timing of capacitation in the absence of uterine exposure of spermatozoa. Ovulation was controlled in mature gilts, and 5–20 ml freshly collected semen containing approximately 10⁸ spermatozoa per ml introduced through the peritoneum either by means of mid-ventral laparotomy or using a 3.5-in (ca. 9 cm) × 18-gauge hypodermic needle.Embryo development to the morula and blastocyst stage appeared chronologically and cytologically normal after intraperitoneal insemination, but the timing of semen deposition was critical: optimal levels of fertilization (60%) arose from insemination in the 12 h preceding ovulation. Fertility was never comparable to that found after natural mating due to the inefficiency of sperm transport into the oviducts and the absence of significant sperm reservoirs. The timing of sperm capacitation after intraperitoneal insemination was not reduced when compared with that found after insemination directly into the oviducts, indicating a negligible contribution of peritoneal exposure to this process. Spermatozoa were not phagocytosed in the oviducts, but rather descended to the uterus at the same time as the developing embryos or degenerating eggs, the sperm flagellum usually being separated from the head by this stage.