The influence of taking uterine biopsies on the concentration of some steroids in the blood and in the uterus, on the ovarian activity, and on the sexual behaviour of the mare.

The study suggests that daily uterine biopsies can prompt sexual behavior in horses, accompanied by increased blood progesterone content and follicular growth. The findings indicate that the source of this progesterone is likely the uterus and not the ovaries.

Experimental Observations

• The study presents several points in support of the uterus as the progesterone source. It shows that after ovarian removal, there were no active corpora lutea (a hormone-secreting structure that develops in the ovary after an ovum has been discharged) suggesting that the ovaries are not responsible for the production of progesterone.
• The same sexual behaviours, including mating, occurred in horses that had their ovaries removed. This implies that the uterus plays some part in inducing these behaviours.
• The concentration of the compound “5.4,” which is thought to be easily convertible into progesterone, was found to be significantly higher in the uterine biopsies. This further supports the theory that the uterus, not the ovaries, is the main source of progesterone.
• Administering stilboestrol (a synthetic non-steroidal estrogen) was found to lower the progesterone level in the uterine biopsies and the blood. Progesterone production could thus be influenced by estrogen, but it is not likely originating from the ovaries.

Implications and Conclusion

• The lack of estradiol-17 beta (a type of estrogen) in ovarian follicles and the fact that horses without ovaries also exhibited estrous behaviors implies that estrogens might not be the responsible agents for these behaviors.
• The study concludes that uterine biopsies could instigate a physiological response in horses, leading to sexual behaviors, follical growth, and increased progesterone production.
• These findings suggest that the uterus could play a role in sexual behavior and steroid formation. Overall, this research contributes to the knowledge on reproductive physiology in horses, and potentially other species too.