Effects of Combined Estradiol-Sulpiride Treatment and Follicle Ablation on Vernal Transition in Mares: Evaluation of Plasma and Follicular Fluid Hormones and Luteinizing Hormone Receptor Gene Expression.
Authors: Oberhaus Erin L, Thompson Donald L, Foster Brittany A, Pinto Carlos R
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Transitioning anovulatory mares into cyclicity during late winter remains clinically challenging, prompting investigation into whether pharmacological intervention could accelerate the natural vernal transition. Researchers treated January-acyclic mares with estradiol cypionate (ECP) alone or combined with sulpiride—a dopamine antagonist that elevates prolactin—with half of each group undergoing complete follicle ablation via transvaginal aspiration beforehand. The sulpiride-supplemented protocol proved most effective, with 63% of treated mares developing a 35-mm follicle within 28 days of the first injection, significantly earlier than control animals; ablation produced no additional benefit, suggesting that stimulating endogenous hormonal pathways rather than mechanically resetting the ovary drives the response. Whilst plasma prolactin increased substantially for 16 days post-sulpiride, follicular fluid composition and LH receptor gene expression remained indistinguishable between artificially induced and naturally spring-occurring ovulatory follicles, indicating that ECP-sulpiride early induced follicles achieve equivalent developmental maturity. For practitioners seeking to advance reproductive cycling in late-winter mares—particularly for breeding schedules or performance athletes—ECP combined with sulpiride offers an evidence-based alternative to passive waiting, though the mechanism appears to operate through systemic hormonal milieu rather than local follicular effects.
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Practical Takeaways
- •ECP-sulpiride combination can reliably induce earlier ovulation in anovulatory mares during winter, potentially useful for breeding programs requiring early conception
- •The maturity of induced follicles is biochemically equivalent to naturally timed spring follicles, suggesting induced ovulations should be physiologically competent for breeding
- •Follicle ablation prior to treatment does not improve response, simplifying the practical protocol for practitioners
Key Findings
- •Sulpiride treatment combined with estradiol cypionate accelerated ovulatory follicle development, with 63% of treated mares responding within 28 days versus earlier natural spring response
- •Plasma prolactin was significantly elevated for 16 days in ECP-sulpiride-treated mares but did not correlate with ovarian response
- •Early induced follicles achieved hormonal and gene expression profiles equivalent to naturally occurring spring ovulatory follicles despite accelerated timeline
- •Follicle ablation had no effect on ovarian response to treatment