New Drug Protocol Holds Promise in Treating Placentitis in Mares

When bacteria gain access to a pregnant mare’s reproductive tract causing placentitis, the outcome can be bleak. Infection and inflammation of the placenta are well-known causes of foal loss. However, swift recognition of clinical signs and a new drug protocol might change that.

Researchers at the University of Florida and the University of Georgia Colleges of Veterinary Medicine have identified what they believe will be a more effective way to combat placentitis by tackling it on three fronts using a combination of the non-steroidal anti-inflammatory firocoxib, the antibiotic trimethoprim sulfamethoxazole (TMS), and altrenogest (a progestin used to suppress estrus).

Jennifer Varner, a third-year veterinary student at the University of Georgia’s College of Veterinary Medicine, presented the team’s findings at the 65th American Association of Equine Practitioners Convention, which is currently underway in Denver. She explained that veterinarians have directed traditional placentitis treatment toward arresting bacterial infections using antimicrobials. However, one small study supported the idea that quelling the mare’s inflammatory response while preventing the onset of uterine contractions might be integral to saving foals’ lives. Her team’s study goal was to find a safe and effective combination of drugs to address inflammation, infection, and premature contractions.

In their study they inoculated 13 pregnant mares with Streptococcus zooepidemicus, which they introduced midway into the cervix when the mares were between 270-300 days of gestation. They then randomly assigned each mare to either a treated group or an untreated control group.

Varner’s team began administering the treated group firocoxib, TMS, and altrenogest at the first signs of placentitis, such as discharge and abnormal mammary gland development. Initial signs typically appeared within two days of infection, said University of Florida professor Margo Macpherson, DVM, MS, Dipl. ACT, who worked with the study’s mares and foals. The drug protocol then continued through delivery.

“We were interested in the effects this drug combo had on inflammatory mediators,” Varner said. “Therefore, cytokines and prostaglandin concentrations in fetal fluids and membranes were analyzed.” In brief, these markers were lower in treated mares than in untreated ones.

By the study’s end, all seven mares in the treatment group had delivered live foals, whereas only two mares left untreated delivered live foals.  Important to these findings, said Varner, was that all the surviving foals needed some type of supportive care after birth for at least several days. This included giving them antimicrobials prophylactically (preventively). Three of the foals were notably immature, determined by their birth-weight-to-fetal-membrane-weight ratio and clinical signs.

In conclusion, the researchers determined this drug combination helps modulate the inflammatory response and dials down the release of prostaglandins that stimulate uterine contractions that lead to preterm births. The authors said this study supports the use of firocoxib, TMS, and altrenogest in mares with placentitis.