Published: 10 Aug 2020 | Last Updated: 10 Aug 2020 12:35:23

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Research from the Royal Veterinary College (RVC) has demonstrated that a chromosomal defect is the reason why a significant proportion of horse pregnancies fail within the first two months of development. This will pave the way for new diagnostic tests for, what could be, one of the most common causes of pregnancy loss in mares.

Pregnancy loss is a notoriously difficult condition for veterinary surgeons to manage, as the underlying cause is often unknown. In this pioneering study, researchers from the RVC have determined aneuploid pregnancies, which is when a copy of a whole chromosome is either duplicated or lost (similar to Down’s Syndrome screened for in human pregnancy), as a key cause of equine pregnancy loss.

The researchers, led by Dr Mandi de Mestre, Reader in Reproductive Immunology and Head of the Equine Pregnancy Laboratory at the RVC, collaborated with seven different veterinary practices to gain access to samples from across the UK and Ireland and found that around 20% of the pregnancies lost were aneuploid. Charlotte Shilton, RVC PhD student who performed the analysis, applied three different genetic approaches to confirm the results.

Work is now underway to identify the underlying cause of these aneuploid pregnancies, with early data from this study suggesting it is most commonly introduced via the egg or sperm. Until now, chromosomal defects such as aneuploidy have only been reported as a rare condition in young horses with developmental disorders.

This study explains why the condition is so rare in horses, with most embryos and fetuses possessing this genetic change dying very early in development, as is also observed in human pregnancy. The study highlights the need to reconsider this genetic condition both in pregnancy loss but also for early developmental disorders.

Dr Mandi de Mestre, Reader in Reproductive Immunology at the RVC, said: “Early pregnancy loss remains a very frustrating condition for clinicians to treat as the underlying cause is unknown in around 80% of cases. These findings will allow researchers to develop new diagnostic tests for pregnancy losses, which would offer hope to thousands of owners of breeding mares that suffer this condition.

“A diagnostic test would allow them to make informed decisions on treatment strategies and to advise on whether they should invest in further attempts to breed their mare benefiting both horses and their breeders alike in the future. I would like to thank both the Thoroughbred Breeders Association and our collaborators at Texas A&M University and the participating veterinary surgeons for their support on this project.

James Crabtree, Independent Veterinary Consultant in Equine Reproduction and Stud Medicine at Equine Reproductive Services, said: “This has been an important study to be involved in as the cause of pregnancy failure in any given mare is often without diagnosis and we have to make assumptions in order to best treat and manage our patients after pregnancy failure. The team at the RVC have been great to work with and very understanding of the challenges we face in practice while considering our clinical judgements and reasonings with care and attention. It has been a great privilege to work with the Royal Veterinary College on this research project and we look forward to further collaborations.”


10.1038/s41598-020-69967-z "Whole genome analysis reveals aneuploidies in early pregnancy loss in the horse" (92407416-0999-494b-a1e4-07e6ce4b34c8)

The full paper is available at Nature (Scientific Reports):

Notes to Editors

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About the RVC

  • The Royal Veterinary College (RVC) is the UK's largest and longest established independent veterinary school and is a Member Institution of the University of London. It was the first in the world to hold full accreditation from AVMA, EAEVE, RCVS and AVBC.
  • The RVC is the top veterinary school in the UK and Europe, and ranked as the world’s second highest veterinary school in the QS World University Rankings by subject, 2020.
  • The RVC offers undergraduate and postgraduate programmes in veterinary medicine, veterinary nursing and biological sciences.
  • In 2017, the RVC received a Gold award from the Teaching Excellence Framework (TEF) – the highest rating a university can receive.
  • A research led institution with 79% of its research rated as internationally excellent or world class in the Research Excellence Framework 2014.
  • The RVC provides animal owners and the veterinary profession with access to expert veterinary care and advice through its teaching hospitals and first opinion practices in London and Hertfordshire.


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