Monitor Mares' Progesterone Levels before Inducing Labor

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.

The researchers injected half the mares with oxytocin upon noting a significant drop in the blood progesterone levels; all of those mares delivered healthy and viable foals within an hour of the injection, Tainturier said. The foals all stood and nursed within an hour of birth, as did the foals in the control group (whose dams did not receive oxytocin). Tainturier noted that two foals in the experimental group subsequently died for reasons unrelated to the induction: One was stepped on by the mother, and the other had severe genetic malformations.

“Progesterone levels allow us to practically predict the night of foaling and thereby induce labor while several people are present for the foaling in case of difficulty,” Tainturier said. “But often the signs of imminent labor are contradictory, so decisions must be made with professional experience as well. When in doubt, it’s better to monitor the mare for a night or two (before inducing).”

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.