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Breakthrough in equine early pregnancy loss research

Stud Medicine
21 Aug 2020 BEVA

Research funded by the Thoroughbred Breeders’ Association has achieved a significant breakthrough in discovering a major cause for the early loss of pregnancy in equine mares.

A study led by Dr Mandi de Mestre, head of the equine pregnancy laboratory at the Royal Veterinary College, revealed that a chromosomal defect known as aneuploidy occurred in a substantial number of the cases of early pregnancy loss examined.

Dr de Mestre explains: “Aneuploidy involves having an abnormal number of chromosomes. It also arises in women and can either cause the pregnancy to be lost in the early stages or results in an imbalance that produces physiological differences. It’s similar to the cause of Down’s Syndrome in humans, for which there is now a screening process.”

Explaining the background to the study, Dr de Mestre says: “The idea first came up a good ten years ago when, talking to vets we realised around 80 per cent of cases of early pregnancy loss had no known cause, in other words in the first two months, when the foetus and placenta is forming and organs are developing. 

There was a big black hole in our knowledge, which was the starting point for the TBA giving a grant for us to first develop a method of studying these losses.

I have a fantastic team at the RVC and we worked very closely with vets at the Newmarket Equine Hospital, Rossdales in Newmarket and Equine Reproductive Services in Yorkshire on ways to be able to track the losses. As a result, we published a paper in 2016 that showed we had the tools to isolate cases, and that led on to the project we have just finished, which allowed us to address the question of what is actually causing the losses.”

Looking at the findings, Dr de Mestre says: “In counting the chromosomes, we found that in just over 20 per cent of the early pregnancy loss samples we examined, there was an abnormal number.

The significance goes back to our original starting point, where in 80 per cent of cases we had no idea what was causing the pregnancy loss, and we’ve been able to chip away at one-quarter of the sample, which we feel is a substantial leap forward in understanding what is the underlying reason for the failure of these pregnancies.

The next step will be to develop diagnostic tests and work out a cost-effective and timely way to be able to screen mares, so that owners can use the information to know what to do next. The reassuring thing is that if a mare has a pregnancy loss through aneuploidy, it doesn’t mean there is a long-term problem, because a good number of the mares in our sample did have foals afterwards.”

Dr de Mestre expresses her thanks to all those who have brought the study to fruition, saying: “This research has required huge efforts from everyone involved. Charlotte Shilton, with support from our wider team, has excelled identifying these aneuploid pregnancies.  We have also worked closely with the world-class geneticists at Texas A&M University, a large number of vets across the UK and Ireland who were really committed to the work, and breeders who agreed to participate in the research. And thanks too to the TBA for the funding, without which the research would not have been possible.”

The study is available online.