Reproductive hormones, antral follicle count, and transvaginal oocyte aspiration outcomes in mares receiving intravenous clomiphene citrate

Abstract

The likelihood of creating an in vitro produced foal is much lower in horses than in other species because of inefficient in vitro embryo production. Inability to superstimulate ovaries is a major factor that could be addressed by choosing a right compound; clomiphene citrate (CC), a selective estrogen receptor modulator, is a potential agent. Therefore, 2 experiments were performed; mares received 2,000 mg of intravenous CC, every 24 hours for 5 days to assess the effects on reproductive hormone concentrations, uterine and ovarian responses, and oocyte parameters. In Experiment 1, 6 mares received CC and were monitored for plasma CC concentrations, serum reproductive hormone concentrations, and ovarian responses. Transvaginal oocyte aspirations were performed and in vitro embryo production parameters were collected. In Experiment 2, 6 mares received CC; reproductive hormone concentrations and ovarian responses were compared to control group (n = 6). Concentrations of CC had positive correlations with antral follicle count and uterine edema (r = 0.60, p = 0.0004 and r = 0.47, p = 0.009, respectively), and a moderate negative correlation with follicle-stimulating hormone (r = – 0.48, p = 0.001). Compared to controls, there were no differences in reproductive hormone concentrations, ovarian responses, or oocytes recovered in mares receiving CC; average blastocyst rate of matured oocytes was 47.5% in treated mares.