Extraspecific donkey-in-horse pregnancy as a model of early fetal death.

This research studied the phenomenon of early fetal death in pregnancy using a model where donkey embryos were implanted into horse mares. The study reveals that the absence of endometrial cups in these hybrid pregnancies leads to an 80% abortion rate. The abortions coincide with abnormal implantation and a significant congregation of white blood cells in the uterus of the host mare. While the application of pharmaceutical interventions didn’t prevent the abortions, passive or active immunization methods were found to improved the rate of fetal survival, even leading to the birth of live offspring. The research concludes that a proper endometrial cup reaction is critical for successful pregnancy and that it triggers an immunoprotective response in horse mares toward their babies.

Model of Early Fetal Death

• The study used the transfer of donkey embryos to horse mares as a model to study early fetal death, an area of study that has significant implications for understanding reproductive health and pregnancy issues.

Observations from the Case of Extra-specific Pregnancy

• One notable finding from this unusual model was the non-development of endometrial cups in the cross-species pregnancy cases, which turned out to be associated with an extremely high rate of abortions.
• About 80% of the donkey fetuses implanted in horse mares were aborted by day 80 to day 100.
• The abortions were linked to abnormal implantation and a significant gathering of white blood cells (leucocytes) in the surrogate mare’s uterus.

Outcome of Different Treatments

• Attempts to prevent the high abortion rate using pharmaceutical treatments such as progestagen (allyl trenbolone) or purified horse chorionic gonadotrophin were unsuccessful.
• However, when passive immunization methods were used with serum taken from mares carrying intraspecific horse fetuses or active immunization with donkey lymphocytes, there was a marked improvement in fetal survival rates, and even some successful births.

Maternal Immune Responses

• The research also demonstrated that horse mares exhibited both cytotoxic (rejection type) and immunoprotective responses to the foreign donkey fetus when repeatedly bearing donkey-in-horse pregnancies.
• This observation suggests that the endometrial reaction seen in regular equine pregnancies, which was missing in the hybrid pregnancies, is crucial for stimulating the mare to generate a protective immune response toward her fetus in utero.