hCG is more effective than the GnRH agonist buserelin for inducing the first ovulation of the breeding season in mares.
Authors: Fanelli Diana, Tesi Matteo, Rota Alessandra, Beltramo Massimiliano, Conte Giuseppe, Giorgi Mario, Barsotti Giovanni, Camillo Francesco, Panzani Duccio
Journal: Equine veterinary journal
Summary
# Editorial Summary This randomised controlled trial compared two commonly used ovulation-induction protocols during the challenging transitional period when mares are emerging from winter anoestrus. Researchers allocated 62 mares to treatment with either the GnRH agonist buserelin or human chorionic gonadotropin (hCG) once a dominant follicle reached 35 mm diameter following sulpiride priming, then monitored daily for ovulation. hCG proved substantially superior, with 90.1% of treated mares (30/33) ovulating compared to only 38.0% (11/29) in the buserelin group—a clinically and statistically significant difference (P = 0.0001). Beyond the choice of hormone, ovulation success was markedly influenced by reproductive readiness: mares displaying both ultrasonic uterine oedema and strong behavioural acceptance of the teaser stallion for at least three consecutive days before treatment achieved a 78% ovulation rate, versus just 42.9% in mares lacking these signs. For breeding practitioners, this evidence suggests hCG should be the preferred agent for inducing first ovulations in transitional mares, and that careful clinical assessment of both uterine changes and oestrous behaviour can predict treatment success before committing to hormone protocols. The sharp difference in efficacy between these two standard approaches warrants reconsideration of transitional-phase management strategies, particularly in performance and commercial breeding operations where timing pressures often drive earlier intervention.
Read the full abstract on PubMed
Practical Takeaways
- •Use hCG rather than GnRHa buserelin for inducing first ovulation in transitional mares—expect ~90% success with hCG vs ~38% with buserelin
- •Wait for clear signs of physiological readiness (uterine oedema + full acceptance of teaser for 3+ days) before ovulation induction treatment to maximize success rates
- •Assess reproductive readiness with teasing and ultrasound evaluation of uterine tone before committing to treatment protocols
Key Findings
- •hCG induced ovulation in 90.1% (30/33) of mares compared to 38.0% (11/29) with GnRHa buserelin (P=0.0001)
- •Ovulation rate was significantly higher (78%) in mares showing uterine oedema and full behavioural oestrus for ≥3 days before treatment vs 42.9% without these signs (P=0.01)
- •Uterine oedema and sustained teasing acceptance were predictive markers for successful ovulation induction response
- •GnRHa efficacy in transitional mares during early breeding season is substantially lower than hCG