Moderate differences in body condition do not influence fasted glucose metabolism or ovulation induction in mares

Ovulation induction is widely used in equine breeding management. However, some mares do not respond to ovulation induction for reasons that remain unclear.

The objective was to evaluate whether body condition influenced fasted glucose or insulin concentrations and ovulation rates following ovulation induction. We hypothesized that moderate mares would exhibit increased fasted insulin concentrations and greater incidence of anovulation following ovulation induction.

Light breed mares (n = 13) were grouped according to body condition score (BCS) and cresty neck scores (CNS) into lean (LN; n = 6; BCS = 4.1; CNS = 1.0) or moderate (MO; n = 7; BCS = 5.8; CNS = 2.3) groups. Mares were fasted overnight and blood samples were analyzed for glucose and insulin concentrations. Follicular development was monitored using transrectal ultrasound. Before ovulation induction, mares underwent at least one ovulation to ensure transition from anestrus. Once a dominant follicle (35 to 40 mm) and uterine edema were present, ovulation was induced with intramuscular injection of deslorelin acetate (1 mL; 1.8 mg/mL) followed by daily ultrasound until a corpus luteum was observed.

All mares ovulated within 48 hours following ovulation induction, irrespective of their body condition. Fasted blood glucose concentrations (LN: 84.5 ± 2.5 mg/dL, MO: 90.0 ± 2.3; P = 0.13) and fasted insulin concentrations (LN: 4.8 ± 0.9 mU/mL, MO: 4.9 ± 0.8; P = 0.95) were not different between groups.

Moderate differences in body condition had no observable impact on fasted insulin concentrations or successful ovulation induction.