Important cause of early pregnancy losses in mares pinpointed

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An incorrect number of chromosomes appeared responsible for nearly a quarter of early pregnancy losses in mares examined in a British study.

Amanda de Mestre and her colleagues, writing in the journal Scientific Reports, said the first eight weeks of pregnancy was a critical time, during which most pregnancy losses occurred.

Despite intensive management strategies, between 5% and 10% of confirmed pregnancies in mares ended in this period.

The study team noted that an abnormal number of chromosomes, known as aneuploidy, is a common finding in human miscarriage, yet is rarely reported in domestic animals.

Early pregnancy loss in mares has no diagnosis in more than 80% of cases, with the remaining 20% being diagnosed as either infectious in nature (around 4%) or non-infectious (around 16%).

The researchers set out to characterise aneuploidies associated with these early losses.

DNA from clinical cases of spontaneous miscarriage (within 14 to 65 days of gestation) and healthy control placentas (from various gestational ages) was examined.

Aneuploidy was detected in 12 of the 55 early losses, representing 21.8% of the cases examined.

In contrast, no aneuploidy was detected among the healthy control placentas examined.

“The equine pregnancies assessed here were all clinically recognised, therefore incidence of aneuploidy in equine pregnancy is predicted to be higher than the 22% we report,” they wrote.

The authors noted that aneuploidy in mares occurred at a similar rate to that seen in human miscarriages.

“Rodents are currently used to study how maternal ageing impacts aneuploidy risk, however the differences in reproductive biology is a limitation of this model,” they wrote.

They suggested the horse could be used as an alternative to rodent models to study mechanisms resulting in aneuploid pregnancies.

The study team comprised de Mestre, Charlotte Shilton, Anne Kahler and Claire Wathes, all with the Royal Veterinary College in London; Brian Davis and Terje Raudsepp, with Texas A&M University; James Crabtree, with Equine Reproductive Services (UK) Ltd in North Yorkshire, England; James Crowhurst, with Newmarket Equine Hospital in Suffolk, England; and Andrew McGladdery, with Rossdales Equine Practice, also in Suffolk.

Shilton, C.A., Kahler, A., Davis, B.W. et al. Whole genome analysis reveals aneuploidies in early pregnancy loss in the horse. Sci Rep 10, 13314 (2020).

The study, published under a Creative Commons License, can be read here

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