Melengestrol acetate as a tool for inducing early ovulation in transitional mares

Area of Science:

• Veterinary Science
• Reproductive Biology
• Equine Reproduction

Background:

• Vernal transition in mares is a critical period for reproductive management.
• Phototherapy is often used to prepare mares for the breeding season.
• Synchronizing ovulation is essential for efficient artificial insemination and breeding programs.

Purpose of the Study:

• To evaluate the efficacy of melengestrol acetate (MGA) in synchronizing and accelerating the first ovulation of the year in mares.
• To determine the optimal dosage of MGA for achieving reproductive synchrony.
• To assess the impact of MGA on estrus, follicular development, and ovulation rates.

Main Methods:

• Ultrasonographic monitoring of follicular growth, uterine edema, and ovulation.
• Rectal palpation to evaluate cervical tone.
• Administration of two MGA dosages (150 mg/day and 100 mg/day) for 10 days to mares in late transition.
• Use of prostaglandin to induce luteolysis post-MGA treatment.

Main Results:

• Ovulation occurred in 87.5% of mares treated with 150 mg MGA/day and 62.5% with 100 mg MGA/day, significantly higher than the 20% in control mares (P=0.03).
• The mean interval from treatment to ovulation was shorter in the 150 mg MGA/day group (13.1 days) compared to the 100 mg MGA/day group (25.6 days) (P=0.01).
• MGA treatment successfully hastened the first ovulation of the year in mares.

Conclusions:

• Melengestrol acetate (MGA) is effective in synchronizing and accelerating the first annual ovulation in mares.
• A dosage of 150 mg/day for 10 days appears more effective than 100 mg/day for hastening ovulation.
• MGA offers a valuable tool for reproductive management in mares, particularly for initiating the breeding season.