Excessive Inbreeding Can Increase Mid- To Late-Term Pregnancy Loss

Inbreeding has little effect on mare’s early pregnancy loss, a study from the Royal Veterinary College and Cornell University has shown. However, inbreeding does affect mid and late-term pregnancy loss in mares, reports Equine Science Update. About 5 to 10 percent of equine pregnancies are lost early in gestation; 7 percent of equine pregnancies are lost between day 70 of gestation and 24 hours after birth.

Inbreeding is a common practice in production livestock to strengthen desirable traits within a population. However, excessive inbreeding can heighten the chance of reduced fertility, genetic disorders and overall population wellness.

The study team used DNA samples from 189 horses in the UK, including samples of embryonic membrane and fetal DNA from both early and late-term pregnancy loss. Hair and blood samples were taken from adult Thoroughbreds as controls.

They found that the Thoroughbred mares who lost their pregnancies in mid- to late gestation had significantly higher inbreeding metrics compared to the control horses; there was no significant difference in early gestation pregnancy loss.

The research offers insight that can assist horse owners in making informed mating decisions, reducing the possibility of abortion. They also encourage people to carefully consider breeding horses that are closely related, as the foal may inherit mutations that make it unable to survive.

Read more at Equine Science Update.