Effects of repeated daily injections of prostaglandin F2alpha on ovaries in mares.

This research study examines the effects of repeated daily injections of Prostaglandin F2alpha (PGF2alpha), a hormone-like substance, on horses’ ovaries. The results showed that the duration between ovulations increased for mares receiving multiple injections after ovulation, but not for those receiving an injection during estrus or shortly after ovulation.

Experiment Design

• The research was conducted in two experiments with different groups of pony mares. The mares’ reactions to Prostaglandin F2alpha injections were observed under different conditions. The Prostaglandin F2alpha dosage was either 1.25 mg once daily or 1.25 mg ten times daily.
• In the first experiment, seven groups were formed, with 2 or 3 mares in each group. Some received no injections at all, serving as controls, while others were given either 5 or 10 daily subcutaneous (SC) injections of Prostaglandin F2alpha, starting on various days post-ovulation.
• The second experiment followed a similar design, with nine groups of 4 mares each. Some were used as controls, while others were given different numbers of Prostaglandin F2alpha injections, either during estrus or at varying times after ovulation.

Results and Findings

• The study found that the interovulatory interval, the number of days between ovulations, was longer in mares who received ten daily injections starting on days 7 and 13 post-ovulation compared to the control mares. The interval increased from 24.5 days to 33.5 and 49 days.
• The results also showed that the interovulatory interval was longer for mares that received ten daily injections of Prostaglandin F2alpha starting on day 13 post-ovulation but was shorter for those that received the injections on day 1 post-ovulation. The interval decreased from 25 days to 14.5 days for those given injections on day 1, and increased to 40 days for those given injections on day 13.
• The lengthening of the interovulatory interval was not due to any apparent changes in peripheral LH concentration or any effect on the diameter of the largest ovarian follicle, as one might expect. This suggests that Prostaglandin F2alpha prevented ovulation by working directly at the ovarian level on the follicle.

Implications of the Study

• The findings indicate a direct effect of Prostaglandin F2alpha on the ovaries, notably extending the interovulatory interval. This could have implications for the management of horse reproduction, particularly in controlling or inducing ovulation.
• Future research could delve further into the physiological mechanisms of Prostaglandin F2alpha’s influence on the ovaries and follicles and the potential applications of these findings in veterinary medicine and animal breeding.