The role of the fetal gonads and placenta in steroid production, maintenance of pregnancy and parturition in the mare.

This article explores the impact of removing the fetal gonads on steroid hormone production and the progression of pregnancy in horses. Results indicate that the removal of these reproductive organs caused a drop in maternal estrogen levels, but didn’t affect progestagen levels, the hormone necessary for maintaining pregnancy. Despite this, the pregnant horses carried the fetus to full term.

Objective of the study

• This study aimed to determine the role of fetal gonads in strengthening pregnancy by examining the differences in hormone levels and pregnancy outcomes in mares with gonadectomized foetuses.

Methodology

• The researchers removed the fetal gonads in some mares and compared changes in hormone concentration and pregnancy progression to normal mares and those with sham-operated fetuses.

Finding 1: Impact on Steroid Production

• The removal of fetal gonads led to a notable decrease in both conjugated and unconjugated estrogens in the maternal plasma. However, it showed no effect on progestagen levels, another important hormone for pregnancy.

Finding 2: Impact on Labour

• Mares with gonadectomized foals had much lower levels of the hormone 13,14-dihydro-15-oxo-PGF-2 alpha (PGFM) during labour, leading to weaker uterine contractions than those in control mares. This hormone is associated with labour contractions.

Finding 3: Impact on Pregnancy

• Despite the hormonal changes due to gonadectomy, pregnancy in the mares was maintained until parturition, which suggests that estrogen produced by the fetal gonads might not be the only factor involved in maintaining pregnancy.
• On the downside, 3 out of the 4 foals born from the gonadectomized fetuses were dysmature and died during or soon after birth, indicating that fetal gonads might play an essential role in fetal development.

Finding 4: Role of Estrogens

• The study also delved into the production of estrogens by the feto-placental unit from a biosynthesis perspective, discussing the potential role of these hormones in fetal development during the mare’s pregnancy.