Inducing labor in humans might be commonplace, but performing the same procedure in pregnant mares is tricky business. If the timing’s off, the foal isn’t likely to be strong enough to survive. But French researchers say that monitoring mares' progesterone levels—combined with veterinary and breeding experience—could be the key to timing inductions successfully.

“Monitoring progesterone levels, which fall at the end of gestation, in association with the classical criteria for estimating foaling time, provides a practical way to predict—with a little bit of experience—the night of foaling,” said Daniel Tainturier, PhD, DVM, head of the biotechnology and reproductive pathology department at Oniris/National Veterinary School of Nantes in France. Tainturier’s research team presented their work at the 2014 French Equine Research Day held March 18 in Paris.

While most mares do not need induction, inducing labor can be useful when it’s important to have veterinary staff available at the time of foaling or if assisted birth is necessary, Tainturier said. Assisted births are required when dystocia—a difficult birth—occurs.

In his study, Tainturier and his team evaluated 41 late-term pregnant mares of a variety of horse and pony breeds. First, they tested and determined each mare's specific baseline progesterone level. They then examined the mares for signs of imminent foaling—in particular, the presence of thick, white colostrum in the teats—and began comparing the mares' current blood progesterone levels to their baseline levels