Changes in maternal hormone concentrations associated with induction of fetal death at day 45 of gestation in mares.

The study investigates how inducing fetal death in pregnant Standardbred horses on day 45 of gestation affects the levels of maternal hormones. It found that such a process leads to significant decrease in the levels of oestrone sulphate but has limited effect on progesterone, and that a viable embryo is needed to maintain oestrone sulphate levels.

Study Design and Methodology

• The researchers of the study set up two groups of pregnant Standardbred mares.
• On the 45th day of gestation, saline was injected into the fetal sacs of 10 mares (saline-treated group), while the other 10 mares received a sham treatment (sham-treated group).

Outcome and Findings

• Post-operative plasma oestrone sulphate concentrations were lower in saline-treated mares from day 48 to day 55 of gestation than they were in sham-treated mares.
• Plasma progesterone levels were generally similar between the two groups, although luteolysis, or the breaking down of the corpus luteum, occurred in 4 saline-treated mares.
• There was generally no difference in plasma CG profiles between the two groups, except that CG concentrations in saline-treated mares were generally lower than those of sham-treated mares.
• A loss of uterine and cervical tone was also observed in the saline-treated mares following the operation.

Interpretation and Conclusion

• The findings suggest that a viable embryo is necessary for maintaining maternal plasma oestrone sulphate concentrations.
• This study also introduces the possibility that luteolysis can occur in spite of high plasma CG concentrations after a fetal death.
• Further research could be focused on the consequences of these hormonal changes on the mares’ health and further pregnancies.