Research from the Royal Veterinary College (RVC) has demonstrated that a chromosomal defect is responsible for a significant proportion of horse pregnancies that fail within the first two months of development.
These findings 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. Up to 10% of
confirmed mare pregnancies end in the first two months, and in over 80% of those
cases the cause is unknown
In this study, researchers found that aneuploid pregnancies (in
which a copy of a whole chromosome is either duplicated or missing) are a key
cause of equine pregnancy loss.
The research team, 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. They 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 also occurs in humans. The study highlights the need to
reconsider this genetic condition both in pregnancy loss but also 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.
She added, ”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.
For more details, see:
Whole genome analysis reveals aneuploidies
in early pregnancy loss in the horse
Charlotte A. Shilton, Anne Kahler,
Brian W. Davis, James R. Crabtree, James Crowhurst, Andrew J. McGladdery, D.
Claire Wathes, Terje Raudsepp & Amanda M. de Mestre
Scientific Reports (2020) vol 10,
Article number: 13314
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