Control of ovulation rate in swine

ABSTRACT Follicular recruitment and atresia are important processes associated with ovulation rate in swine. Follicle-stimulating hormone regulates granulosa cell division, differentiation, and steroidogenic function, and, as such, significantly influences follicular growth and development. Follicle-stimulating hormone is an inducer of follicular recruitment in swine and an inhibitor of granulosa cell apoptosis, and it seems to be a major regulator of ovulation rate in swine. Although local factors, such as growth factors and steroid hormones, might regulate follicular development by controlling the expression of gonadotropin receptors or by modulating other related processes, the dominant role of FSH cannot be ignored. Recent results indicate that androgens might be among the local factors regulating ovulation rate in swine. Administration of testosterone or the nonaromatizable androgen dihydrotestosterone increased the number of ovulations in gilts in a dose-dependent manner. Furthermore, administration of dihydrotestosterone increased the amounts of FSH receptor mRNA in pig preovulatory follicles. Steady-state amounts of FSH receptor mRNA are relatively high during the early follicular phase but decrease significantly as follicles grow and approach ovulation, suggesting that major changes in amounts of FSH receptor mRNA occur during late follicular development in pigs. Local ovarian factors that regulate follicular responsiveness to gonadotropins seem to be important components of the mechanisms that control ovulation rate in pigs.

Implications

Increasing ovulation rate has the potential to increase swine reproductive efficiency. Identification of important regulators of ovulation rate will help us to design systems for hormonal supplementation, nutritional manipulation, or genetic selection directed to improve the quantity and quality of oocytes released during the ovulatory process. Although our knowledge of ovulation rate in swine is far from complete, experimental results indicate that FSH and ovarian factors that regulate its actions (hormone receptors, growth factors and their receptors, steroid hormones, and enzyme activities) seem to be critical in determining the number of follicles that ovulate. Investigative efforts need to continue to focus on understanding FSH secretion and its action on target cells of the ovarian follicle to better control follicular development and ovulation rate.

Key Words: Ovarian Development, Ovulation Rate, Pigs

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J. Anim. Sci. 80(E. Suppl. 1):E36-E46