Ovarian Anti-Müllerian Hormone Expression in Hyperprolific Sows: Associations with Reproductive Stage and Parity, with Elevated Expression in the Corpus Luteum During the Luteal Stage

Although anti-Müllerian hormone (AMH) is widely recognized as a marker of ovarian reserve, its expression in ovarian tissue of hyperprolific sows remains poorly characterized. This study investigated ovarian AMH expression across reproductive stages and evaluated its associations with ovulation rate and parity in hyperprolific Landrace × Yorkshire sows. Ovarian tissues from thirty-one sows were collected after slaughter and classified according to reproductive stage, parity, and ovulation rate. AMH expression was assessed in primordial, primary, secondary, and antral follicles, as well as corpora lutea, using immunohistochemistry and was quantified with the H-score method. Anti-Müllerian hormone was localized to granulosa cells and oocytes throughout follicular development, as well as to luteal cells in the corpus luteum. Expression within ovarian follicles did not differ among follicle types, reproductive stages, parity groups, or ovulation rate classes. In contrast, luteal cells exhibited significantly greater AMH expression during the luteal phase than during the follicular phase (p < 0.001). Antral follicles in primiparous sows appeared to show higher expression than those in multiparous sows, whereas no association was observed between AMH expression and ovulation rate. These findings demonstrate consistent ovarian AMH expression throughout follicular development and identify stage-dependent expression in luteal tissue. Notably, AMH expression was not associated with ovulation rate, indicating that AMH may reflect the size of the growing follicle pool rather than ovulatory capacity. The age-related trend observed in antral follicles supports the potential value of AMH as an indicator of reproductive longevity in hyperprolific sows.