Seasonal and individual effects on ovarian and endocrine responses of mares to a synchronization treatment with progestagen-impregnated vaginal sponges.

This study looks at how the treatment of mares with progestagen-impregnated vaginal sponges and prostaglandin affects their ovarian and endocrine responses. The findings indicate that seasonal changes and individual differences can impact the treatment’s effectiveness in synchronizing ovulation.

Research Parameters and Procedure

• The study was carried out with 8 saddle-type mares. They were treated with progestagen-impregnated vaginal sponges for 8 days.
• The treatment also included prostaglandin which was administered on the day of sponge removal.
• The entire treatment process was given on random days of the horse’s reproductive or estrous cycle in the months of April, May, July and September.

Main Findings

• The insertion of the sponge triggered a significant decrease in LH (luteinizing hormone) levels. However, when the sponge was removed, there was an immediate surge in LH and a significant FSH (follicle-stimulating hormone) rebound.
• Ovulation occurred approximately 11.8 days after the conclusion of the treatment.
• In April, the period between sponge removal and ovulation was prolonged (14 days compared with approximately 10 days in other months), signifying that seasonal changes could affect the effectiveness of the treatment.
• The study also noticed a prolonged estrogen preovulatory rise and reduced FSH levels in July, further indicative of the influence of seasonal changes.

Individual Differences and Other Correlations

• There were numerous individual differences seen among the mares, but none of those were significantly linked to the period from sponge removal to ovulation.
• In the three months where the response to treatment was not impacted by the season, a correlation was observed between the interval from end of treatment to ovulation and the progesterone and FSH levels at days 5.6 and 7.8 after sponge insertion.
• The study also concluded that for an accurate prediction of when ovulation will occur after such a synchronization treatment, various factors such as the season of the year, individual characteristics of the mare, and the time of treatment in the estrous cycle need to be considered.