Research finds cause of many failed equine pregnancies

  • A key cause of the loss of early pregnancies in horses has been identified. H&H hears from those involved in the research to find out more, as well as veterinary experts in their fields to understand the wider implications of the findings...

    A chromosomal defect is the cause of many equine pregnancies’ early failure, it has been found, in a discovery that could lead to new diagnostic testing.

    Researchers from the Royal Veterinary College (RVC) found that aneuploid pregnancies, where the number of chromosomes is abnormal with a copy of a whole chromosome duplicated or lost, is a key cause of pregnancy loss within the first two months. Early miscarriage has been difficult for vets to manage as its cause is often unknown.

    The researchers, led by Mandi de Mestre, reader in reproductive immunology and head of the equine pregnancy laboratory at the RVC, worked with seven vet practices to gain access to samples from across the UK and Ireland. They found that about 20% of the pregnancies lost were aneuploid.

    Until now, chromosomal defects such as aneuploidy have only been reported as a rare condition in young horses with developmental disorders.

    An RVC spokesman said: “This study explains why the condition is so rare in horses, with most embryos and foetuses 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 de Mestre said the team’s findings would help researchers develop diagnostic tests, “which would offer hope to thousands of owners of breeding mares”.

    “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 a mare, benefiting both horses and breeders,” she said. “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, an independent veterinary consultant in equine reproduction and stud medicine at Equine Reproductive Services, said the study is important as the cause of many pregnancy losses is unknown.

    “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,” he said.

    “It has been a great privilege to work with the RVC on this research project and we look forward to further collaborations.”

    British Equine Veterinary Association president elect Huw Griffiths told H&H the cause of early embryonic loss had been “the topic of much debate for some time”.

    He said: “The causal factors are varied, as are the possible treatments available. Increased knowledge regarding the cause of embryonic loss will help the stud vet make informed choices as to which mares are the most likely to have repeated issues, versus those who have a rare genetic mismatch.”

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