Physiological role of seminal components in the reproductive tract of the female pig.

In many species the appearance of oestrus is sufficient to ensure that the time of ejaculation, sperm transport and capacitation are balanced with the time of ovulation. In the pig these phenomena vary considerably and require additional regulatory mechanisms which are partly explained by seminal components. Boar semen is rich in oestrogens (up to 11.5 micrograms/ejaculate). Infusion of saline with the addition of oestrogens in physiological amounts increased the myometrial contraction frequency up to 2.5-fold. This effect is explained by a release of PGF-2 alpha immediately after oestrogen infusion. Such an infusion also raises peripheral oestrogen concentrations and an effect on LH release can be demonstrated. Additionally, PGF-2 alpha is measurable in uterine vein plasma after oestrogen infusion and is transferred into the follicular fluid. The effect of oestrogens on LH and follicular PGF-2 alpha is likely to contribute to the timing of ovulation in response to mating. A specific protein of Mr 100,000-110,000 has been detected in boar seminal plasma and it exerts a strong immunosuppressive effect. This protein may be involved in a protection of spermatozoa but also of early embryos against female immunological attack. The addition of such specific compounds to AI doses, in which seminal plasma is diluted, may improve prolificacy.