Is there evidence to support the use of biologic agents to treat endometritis in mares? Marco Alvarenga, DVM, MS, PhD, a professor at São Paulo State University, in Brazil, said he thinks so. Alvarenga presented on the topic at the 2022 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas.

Alvarenga focused his talk on platelet-rich plasma (PRP) as it can be used in a field situation.

In Brazil, he explained, embryo donor mares make up 50% of all breeding mares, experiencing artificial insemination several times a year. They often develop breeding-induced inflammation of the endometrium, or uterine lining.

“You have a lot of mares with this condition,” Alvarenga said. “And the idea is to avoid the inflammation.”

The key to the problem is these mares express more inflammatory cytokines (a type of protein) than anti-inflammatory cytokines.

Alvarenga said he’d been intrigued by a 2012 study that showed PRP decreases the expression of most inflammatory cytokines when administered 24 hours before artificial insemination (AI).

“The first experiment that we did in Brazil, we used PRP four hours after AI, and we observed that it was really good, that decrease of inflammatory cells,” said Alvarenga, adding that it also increased pregnancy rates. They followed that experiment with a study comparing PRP use before and after AI. “We observed that the treatment before AI was a little bit better to decrease the inflammation of the fluid accumulation,” he said.

In another experiment, “with even a small amount of platelets, we observed a huge decrease in the fluid accumulation for these mares,” said Alvarenga, with pregnancy rates increasing, as well.

Researchers have also observed that mares that received PRP had no bacteria eight days after AI, though Alvarenga said he doesn’t have a good answer as to why.

He said he’s looking forward to trying a product that’s being developed that would lyophilize (freeze-dry) PRP.

Alvarenga also touched on research into stem cells, which can reduce inflammatory cytokines. Based on clinical observation, he said he’d like to see studies involving the injection of stem cells into the cervix, for mares that can’t relax their cervix.

“Although much more must be explored in biological therapies to treat uterine problems in mare, the evidence so far is encouraging,” he concluded.