The biology of early pregnancy in the mare

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Our research aims at understanding the interactions of the very young equine embryo with its environment in the uterus of the mare during the first month of pregnancy, a time when 10-20% of pregnancies are lost for reasons that we don't understand. The success and failure of early pregnancy is of fundamental and economic importance in all the domestic animals but the horse is an especially good species in which to study its underlying physiology; the equine embryo can be flushed from the uterus throughout the second to fourth weeks without harming the mare and, also, has structural and functional features that are not found in the embryos of other species. One such feature is the embryo's production and use of steroid hormones that we believe to be very important in influencing its local environment. This 'steroidogenesis' and steroid metabolism is being studied in detail. Another unusual feature is a thin, tough, transparent capsule that envelops the hollow ball of cells (the conceptus) as it expands rapidly from a diameter of less that 0.2 mm to one of more than 20 mm during its first two weeks in the uterus. Having described the biochemical makeup of the capsule, we now want to test our idea that it is vital for attaching the conceptus to the lining of the uterus (the endometrium) where the placenta will later develop. We think that this adhesion involves particular sugar molecules in the capsule and protein molecules on the endometrium and will test this notion using the very latest biochemical and molecular techniques on tissues collected from pregnant mares. In order to discover what goes wrong when pregnancy fails, we use a model system of 'compromised' pregnancy; at the end of the second week of pregnancy we treat some mares with a prostaglandin that reduces progesterone production by the ovary. Despite the treatment, the conceptus can survive in the uterus for another 3-4 days after which it is recovered and compared with conceptuses from 'control' mares not treated with prostaglandin. The comparisons of conceptuses and uterine materials from normal and compromised pregnancies are gradually enabling us to pinpoint the differences in proteins and steroid hormone activities that are associated with pregnancy failure.