305. Evaluating the influence of moderate differences in body condition on successful ovulation induction and fasted glucose metabolism in broodmares.

Abstract Ovulation induction is commonly used in equine breeding management to improve reproductive efficiency, yet some mares fail to respond for reasons that remain unclear. Metabolic factors, including reduced insulin sensitivity and increased body condition, influence estrus dynamics in mares and are associated with reduced success of ovulation induction in women, who share similar patterns of folliculogenesis to mares. While these relationships are well characterized in obese mares and overweight women, it remains unclear whether more subtle variation within commonly observed body condition ranges have similar effects. The majority of broodmares have a moderate body condition score (BCS), and the influence of moderate differences in body condition on metabolism and reproductive performance is not well studied. The objective was to evaluate whether moderate differences in body condition influenced fasted glucose metabolism or ovulation rates following ovulation induction. We hypothesized that moderately obese mares would exhibit increased fasted insulin concentrations and a greater incidence of anovulation following ovulation induction. Light breed mares (n = 13) were grouped according to BCS and cresty neck score (CNS) into lean (n = 6; BCS = 4.1 ± 0.1; CNS = 1.0 ± 0.3) or moderately obese (n = 7; BCS = 5.8 ± 0.3; CNS = 2.3 ± 0.4) groups. Mares were fasted overnight prior to the collection of a blood sample and plasma was analyzed for glucose and insulin concentrations. Follicular development and uterine edema were monitored using transrectal ultrasound. Prior to ovulation induction, mares underwent at least one ovulation (confirmed by the presence of a corpus luteum) to ensure that each mare had transitioned from anestrus. Once a dominant follicle (35 to 40 mm) and uterine edema were present, an intramuscular injection of deslorelin acetate (1mL; 1.8 mg/mL) was used to induce ovulation. Mares then underwent an ultrasound every 24 hours until a corpus luteum was observed. Data were analyzed in R Studio. Statistical significance was considered at P ≤ 0.05. All mares ovulated within 48 hours following the injection of deslorelin acetate (LN = 6; MO = 7; P = 1.0), with some mares from both groups ovulating within 24 hours (LN = 2; MO = 3). Fasted glucose (LN: 84.5 ± 3.4 mg/dL; MO: 90.0 ± 1.1 mg/dL) and insulin (LN: 4.8 ± 0.9 mU/mL; MO: 4.9 ± 0.8 mU/mL) concentrations were not different between groups (P ≥ 0.13). Similarly, follicle size (LN: 38.0 ± 0.6 mm; MO: 37.4 ± 0.6 mm) and uterine edema score (LN 2.7 ± 0.2; MO: 2.6 ± 0.2) at ovulation induction were not different between groups (P ≥ 0.52). In this study, moderate differences in broodmare body condition were insufficient to alter successful ovulation induction or fasted glucose or insulin concentrations.