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.

This research experiment investigates the effect of combined Estradiol and Sulpiride treatment, and follicle ablation on the initiation of ovulation in mares. Particularly, it studies the hormonal production, aspects of secretion, and changes in the gene expression for the luteinizing hormone receptor of the first ovulatory follicles induced in comparison to those occurring naturally in the spring.

Study Design and Methods

• The study incorporated anovulatory mares treated with either 50mg of estradiol cypionate (ECP) alone or a combination of ECP and two 3g Sulpiride injections.
• Half of each group underwent a complete follicle ablation via transvaginal aspiration before ECP treatment.
• A regular scanning of the ovaries was conducted until detection of a follicle ranging between 32-35mm.
• Follicular fluid was recovered via aspiration for hormonal concentration analysis, and regular blood collection was performed to ascertain plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone, progesterone, and estradiol.

Results and Findings

• The average date to the first 35mm follicle appeared to be earlier in mares treated with Sulpiride. About 63% responded within 28 days of the first Sulpiride injection. Follicle ablation did not affect this ovarian response.
• Estrogen exhibited a stimulating effect on plasma prolactin for 16 days in ECP-Sulpiride treated mares. However, this did not seem to have any significant impact on the ovarian response.
• The plasma levels of luteinizing hormone, stimulated by Estradiol, were higher in treated mares that responded. This observation could be indicative of an optimized LH response in mares treated with ECP-Sulpiride, which could be attributing to the early occurrence of the ovulatory follicle.
• There were no observed effects of the treatment or ablation on follicular fluid concentrations of estradiol, progesterone, leptin, or insulin-like growth factor 1 (IGF-1), or on LH receptor gene expression. These findings reveal that the early induced follicles have achieved maturity equivalent to the naturally occurring ovulatory follicles in the spring.

Conclusions

• The study provides critical insights into the physiological interactions between hormonal treatments and early ovulation in anovulatory mares. This suggests that we can potentially manipulate ovulation in such mares, particularly during the spring transition.
• Furthermore, the impacts of treatments on various hormonal concentrations and LH receptor gene expression could be foundational in further studies exploring the intricate endocrine interactions that regulate ovulation in mares.