Equine

equine Research identifies a key reason for equine pregnancy loss

Research from the Royal Veterinary College (RVC) has demonstrated that a chromosomal defect is the reason why a signifcant proportion of horse pregnancies fail within the frst 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 diffcult 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 confrm 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 fndings 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.