It contributed to mid and late-term pregnancy loss, but not early loss.

A new study has revealed that genomic inbreeding contributes to mid and late-term pregnancy loss (MLPL) in thoroughbred horses.

However the research, conducted by Royal Veterinary College (RVC), found that it had no contribution to early pregnancy loss (EPL).

The study saw researchers from RVC, in collaboration with Cornell University, analyse DNA samples from 189 horses, including a control group. The scientists studied the metrics of thoroughbred pregnancies that were lost in early, mid and late gestation.

Findings revealed thoroughbred pregnancies that were lost in mid and late gestation had significantly higher inbreeding metrics than in UK thoroughbred adults. In contrast, pregnancies which were lost early in gestation had no significant difference in inbreeding metrics to thoroughbred adults.

Inbreeding is commonly used in the breeding of livestock, to ensure that newborns carry desirable traits.

However, excessive inbreeding can increase the likelihood of uncovering homozygous recessive genotypes, which can be associated with a higher risk of retained placenta and lower semen quality in horses.

Five to 10 per cent of equine pregnancies result in pregnancy loss in the early stage of gestation. A further seven per cent are lost between Day 70 of gestation and 24 hours post parturition.

The findings of this study, which is the first to explore the effects of genomic inbreeding levels on late term pregnancy loss in horses. The researchers say that this highlights the importance of informed equine mating decisions to minimise the risk of miscarriages in thoroughbreds.

Dr Jessica Lawson, Alborada Trust Research Fellow at the RVC, said: “The take home from our work should be to carefully consider breeding choices that involve mating of highly related individuals as, ultimately, this may increase the chance of the foal inheriting mutations which may not be compatible with life.

“We are already working on the next step, looking to identify these changes so more specific advice can be provided in the future.”

The full study can be found in the Equine Veterinary Journal.

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