P4/E2-based protocol for synchronisation of ovulation of mares during the breeding and non-breeding season.

The research examines the effects of a hormone protocol on syncing ovulation in mares during the breeding and non-breeding season, aiming to improve efficiency in insemination and embryo transfer programs. The hormone protocol showed potential as a useful tool in stimulating cyclicity and ovulation in mares during both seasons.

Background & Aim

• The study was driven by the challenges posed by irregular ovulation during the breeding season and the absence of ovulation during non-breeding season for mares, hampering efficient insemination and embryo transfer programs.
• The research aimed to assess the impact of a hormonal protocol (P4/E2-based) on the synchronisation of ovulation in mares during the breeding and non-breeding season, specifically observing its effects on ovarian and follicle behaviour.

Methodology

• A total of 8 mares in the breeding season (BS) and 10 mares in the non-breeding season (NBS) underwent the hormone protocol, which started (Day 0) with the insertion of an intravaginal device containing 1g of P4 and 7mg Estradiol Benzoate IM (EB).
• On Day 9, the device was removed and mares were injected with 0.25 mg of cloprostenol sodic IM and 2 mg of EB IM.
• Ovarian and follicular behaviour was tracked through daily transrectal ultrasounds from Day 0 until ovulation occurred. When the dominant follicle reached at least 35 mm, the subjects were injected with 0.25 mg of gonadorelin acetate IM to induce ovulation.

Results & Findings

• Ovulation time post-P4 removal was similar during the breeding season (173.1 ± 68.8 hours) and non-breeding season (192 ± 58.2 hours; p = 0.3507).
• There was no statistically significant difference in ovulation rate during the breeding season (88%) and non-breeding season (60%; p = 0.0978), or spontaneous ovulation during the breeding season (43%) and non-breeding season (0%; p = 0.6085).
• However, during the breeding season, the dominant follicle was smaller on Day 9 than in the non-breeding season, and the ovulatory follicle was also smaller during the breeding season than in the non-breeding season.

Conclusion

• The P4/E2-based hormonal protocol demonstrated efficacy in inducing cyclicity and ovulation in mares during both the breeding and non-breeding season.
• This suggests its potential as a practical tool for enhancing efficiencies in insemination and embryo transfer programs by synchronising ovulation in mares.