Pituitary and chorionic gonadotrophic control of ovarian function during early pregnancy in equids.

This research investigates the influence of different hormones on the ovarian function during early pregnancy in horses and donkeys and observes how these functions change when pregnancies involve transferred embryos from a different species (inter-species pregnancies).

Objective and Methodology

• The study aimed to understand how concentrations of Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), Chorionic Gonadotrophin (CG) and progesterone affect early pregnancy in mares and donkeys.
• The research involved measuring these hormone levels in both normal intra-species pregnancies and transferred extra-species conceptuses (embryos).

Findings

• In normal intra-species horse and donkey pregnancies, researchers noted a secondary rise in progesterone levels following the appearance of CG. However, FSH concentrations continued to fluctuate, regardless of CG production.
• In cases where donkeys were carrying transferred horse embryos, there was a sharp drop in FSH levels and a steep rise in progesterone levels, corresponding with abnormally high CG levels.
• When horses carried donkey embryos, they showed no CG production. In seven out of eight studied cases, there was also no secondary progesterone rise, but FSH levels fluctuated similarly to normal intra-species pregnancies.

Conclusions

• The research indicated that it was FSH, not CG, that stimulates secondary follicular growth during a normal horse or donkey pregnancy.
• The study also noted that the LH-like activity of CG triggers ovulation of these follicles to form secondary corpora lutea.
• Exogenous progestagen therapy was attempted in four cases where horses were carrying a donkey embryo, but pregnancy continued to term in only one out of eight mares, suggesting that this treatment was largely ineffective in these cases.