Evaluation of an intravaginal triptorelin acetate gel for inducing ovulation in mares

The objective of these studies was to investigate the efficacy of an intravaginal triptorelin acetate (TA) gel as an ovulation-inducing agent in mares. In Exp. 1, 24 mares were blocked using a combination of parity and age and randomly assigned to 1 of 3 treatment groups: 5 mL TA gel (TA5), 10 mL TA gel (TA10), or 5 mL vehicle gel only (CON). Following the appearance of a follicle ≥ 25 mm, a blood sample was obtained for measurement of LH from each mare every 24 h until treatment administration. When a follicle ≥ 35 mm was observed, treatments were administered intravaginally. Following treatment, blood samples were collected for measurement of LH and ovaries were scanned via ultrasonography every 12 h until 48 h post-ovulation. Mares in both TA5 and TA10 tended ( = 0.08) to experience a brief surge in LH by 12 h post-treatment. There was a treatment by time interaction ( < 0.005). The interval from treatment to ovulation was not different between groups ( > 0.05). We hypothesized that duration of elevated LH was not sufficient to induce ovulation in most mares. In Exp. 2, 23 mares were blocked by parity/age and randomly assigned to 3 treatment groups: the CON ( = 7) and TA5 ( = 8) treatment groups remained the same, but the TA10 treatment was split into two 5-mL doses administered 24 h apart (TA5×2; = 8). Blood collection and ultrasonography occurred every 12 h on detection of a follicle ≥ 25 mm in diameter. Once a follicle ≥ 35 mm was detected, treatment was administered and ultrasonography and blood collection for measurement of LH occurred every 6 h until 48 h post-ovulation to get a more robust characterization of the effect of TA on LH and a more accurate timeframe in which ovulation was occurring. Mares in both TA5 and TA5×2 had an increase ( < 0.05) in LH by 6 h post-treatment, which was declining by 12 h post-treatment. Following the second dose in TA5×2, another rise in LH occurred, but to a lesser magnitude ( > 0.05) compared with the initial dose. Again there was a treatment by time interaction ( < 0.005) and in Exp. 2 the interval from treatment to ovulation was shorter in TA5 (61.5 ± 8.8 h) and TA5×2 (61.5 ± 9.6 h) compared with CON (123.1 ± 21.7 h; < 0.01). In Exp. 2, administration of TA gel increased LH concentrations and hastened the interval from treatment to ovulation in mares, without an advantage in the timing of ovulation noted between the 5 or 10-mL doses, or administration of two 5-mL doses given 24 h apart.