12 Aug 2020
“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” – Mandi de Mestre of the RVC.
Mandi de Mestre, reader in reproductive immunology and head of the equine pregnancy laboratory at the RVC.
Research from the RVC has demonstrated that a chromosomal defect is the reason why a significant proportion of horse pregnancies fail within the first two months.
It is now hoped 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.
But now researchers have determined aneuploid pregnancies – when a copy of a whole chromosome is either duplicated or lost (similar to Down syndrome screened for in human pregnancy) – as a key cause of equine pregnancy loss.
The researchers – led by Mandi de Mestre, reader in reproductive immunology and head of the equine pregnancy laboratory at the RVC – collaborated with seven veterinary practices to gain access to samples from across the UK and Ireland, and found that about 20% of the pregnancies lost were aneuploid.
RVC PhD student Charlotte Shilton, who performed the analysis, applied three different genetic approaches to confirm the results.
Work is now under way 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.
It also highlights the need to reconsider this genetic condition in pregnancy loss and for early developmental disorders.
Dr de Mestre 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 to best treat and manage our patients after pregnancy failure.
“The team at the RVC has 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.”
