Plasma concentrations of progestagens, oestrone sulphate and prolactin in pregnant mares subjected to natural challenge with equid herpesvirus-1.

This research involves studying the plasma concentrations of certain hormones in pregnant mares after they were exposed to equid herpesvirus virus-1 (EHV-1). It found that horses carrying virus-infected foetuses had similar endocrine patterns to those with normal foetuses, and that significant amounts of progestagen metabolites were found in their blood.

Research Method

• The study was conducted on multiple pregnant mares on two different stud farms. The mares were naturally challenged with EHV-1 and divided into three groups based on their serum complement fixation titres.
• Group A consisted of 11 mares that were not exposed to the virus and delivered healthy foals. Group B included 13 mares that were exposed to the virus but also delivered healthy foals. Group C had 23 mares, all of whom were exposed to the virus and delivered infected foals that were either stillborn or lived for less than 31 hours.

Findings

• The average gestational period (pregnancy term) for Groups A and B was 343 and 339 days respectively. However, in Group C (mares with infected foals), the gestational period was significantly shorter, averaging 294 days.
• Group C mares had significantly lower concentrations of progestagens (a type of hormone) before giving birth, except for two mares with values comparable to those in Groups A and B. One of these two mares gave birth to a live foal that survived for 31 hours.
• Chromatography tests revealed that the main progestagen metabolites at different stages of gestation were substances similar to 20 alpha-dihydroprogesterone and 5 alpha-pregnane-3,20-dione.
• An incubation of various fetal tissues (liver, placenta, gonads, kidney, brain) found no significant difference in the ability to metabolize labeled progesterone in the presence of NADPH between virus-infected and non-infected tissues.
• Concentrations of plasma oestrone sulphate (another hormone) in all mares were found to be related to the gestational period. Plasma prolactin levels were higher at birth in Groups A and B, but lower in Group C.

Conclusion

• The hormonal patterns in the peripheral blood of mares with EHV-1 infected foetuses are similar to those of mares carrying normal foetuses and probably are related to gestational age at the time of delivery.
• Significant quantities of progestagen metabolites are found in the plasma of late-term pregnant mares. This underlines the possible impact of hormones on pregnancy outcomes in mares, especially in the context of viral infection.