252. Effects of a Pre-breeding Immunomodulatory Feed Supplement on Ovarian Development in Beef Heifers with Divergent Antral Follicle Count.

Abstract Previous work with an immunomodulatory supplement administered to beef cows before and during a superovulation protocol increased the number of transferable embryos. The objective of this study was to evaluate the role of an immunomodulatory supplement (OG; OmniGen-AF) on ovarian function in beef heifers with divergent follicle counts. Across two years, 240 Angus heifers were fed a total mixed ration either with OG supplement (n = 120) or without OG (n = 120) for 50 days before breeding. Individual feed intakes were recorded via Insentec feeding systems. The OG supplement was provided daily at 6 g/45.4 kg heifer body weight and the amount delivered was adjusted at the midpoint of the study to reflect heifer growth. Antral follicle count (AFC) was measured via ovarian ultrasonography. From each year, five heifers per supplement treatment were selected within low (11.01 ± 1.53) or high (35.95 ± 1.49) AFC groups. This created four experimental groups: LAFC-OG, LAFC+OG, HAFC-OG, and HAFC+OG (n = 10/group). Selected heifers were synchronized, artificially inseminated, and slaughtered on d 16 post-insemination. Reproductive tracts were collected, and ovarian measurements including surface AFC and luteal weight were recorded. Blood samples were collected on d 16 post-insemination and analyzed for progesterone and anti-Müllerian hormone (AMH). Data were analyzed via the MIXED procedure of SAS v9.4 with pregnancy status, follicle group, treatment, and the interactions as fixed effects and year as a random effect. Luteal weight was not different in response to main effects or their interactions (P > 0.40). Surface AFC was greater (P < 0.01) in high AFC heifers compared with low AFC heifers and tended (P = 0.09) to be greater in OG supplemented heifers compared with non-supplemented heifers. Anti-Müllerian hormone concentrations were greater (P = 0.05) in heifers receiving OG compared with non-supplemented heifers and in high AFC heifers compared with low AFC heifers (P < 0.01). Serum progesterone concentrations exhibited a three-way interaction, such that pregnant, low AFC heifers receiving OG had greater (P = 0.04) progesterone concentrations compared with all other groups, which were similar. Pre-breeding supplementation with OG enhanced ovarian function in beef heifers, as evidenced by increased AMH concentrations across AFC groups. The observed increase in serum progesterone, independent of luteal weight, in pregnant, low AFC heifers receiving OG suggests improved steroidogenic efficiency. These effects likely reflect enhanced granulosa and luteal cell health, potentially through modulation of immune signaling and protection of the endocrine environment from cytokine-mediated suppression. These results warrant investigation into the molecular pathways by which immunomodulation supports early conceptus development. USDA is an equal opportunity provider and employer.