Testosterone effects on mares during synchronization with altrenogest: FSH, LH, estrous duration and pregnancy rate.

This research explored the influence of injecting testosterone propionate in horses fed on altrenogest, focusing on its effects on their follicle-stimulating hormone (FSH) levels, estrous behavior, and fertility. The experiment found that testosterone manipulation did not significantly impact estrous behavior or fertility, hinting at its potential in aligning FSH surges during diestrus.

Research Objectives and Procedure

• The main objective of the research was to understand the impacts of a single application of testosterone propionate on mares – female horses – that were fed altrenogest for 14 days. The specific points of interest included alterations in FSH levels during the diestrus phase and how these changes influenced subsequent estrous characteristics and fertility.
• In the study, 12 mares were used, 7 out of which were injected with testosterone propionate at a dosage of 200 micrograms/kg of body weight on the 5th day of progestogen intake.
• Daily blood samples were collected and all mares were artificially inseminated at the first detected estrus post-progestogen regimen.

Findings of the Study

• Testosterone propionate injection led to a 50% decrease in plasma FSH content within 24 hours, an effect lasting up to the next 48 hours. However, after 4 days post-suppression, FSH amounts rebounded and were notably higher than the control values during the final 4 days of progestogen intake.
• The hormone dosage also triggered estrous behavior in 5 out of the 7 treated mares within a day post-injection.
• Upon halting progestogen intake, factors such as the interval to the inception of estrus, length of estrus, and the luteinizing hormone peak magnitude showed no notable variance between the treatment and control groups.
• A majority of the treated mares, 6 out of 7, and 3 out of 5 control ones, became pregnant post-breeding on the initial estrus following the progestogen course.

Implications of the Research

• The study implies that manipulating FSH patterns during the diestrus phase does not significantly change estrous characteristics or fertility in the next estrus. This potentially marks a therapeutic method to synchronize FSH surge events during diestrus in mares, providing a valuable insight in the field of veterinary medicine and reproductive biology.