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Equine placentitis is on the rise
A recent increase in nocardioform placentitis serves as a good reminder to review the best ways to catch this infection early and how to treat it.


Treatment basics

Treatment of placentitis includes combating the infection, decreasing the inflammatory response and supporting and maintaining the pregnancy.

At the University of Florida, Macpherson and her colleagues have tested several treatment methodologies. Mares have been treated with combinations of antimicrobials (penicillin, gentamicin, trimethoprim sulfamethoxazole), anti-inflammatory drugs (pentoxifylline, flunixin meglumine) and altrenogest (synthetic progestin), designed to control the infection, delay premature delivery and improve the foal's health.

In her studies, Macpherson looked at various combinations of medications. "Long-term administration of trimethoprim sulfamethoxazole (TMS) and pentoxifylline (PTX) extended gestational length in mares with placentitis when compared with infected, untreated mares," she says. "However, foal survival was not improved in treated animals (TMS and PTX were present in fetal and placental tissues). When progestins (altrenogest) were added to the TMS and PTX treatment regimen, 10 of 12 mares (83 percent) delivered viable foals."

A more recent study explored the use of TMS alone or combined with anti-inflammatory agents (dexamethasone, aspirin) and progestins (altrenogest plus aspirin). In this study, Macpherson says, experimentally infected mares receiving only TMS were as likely to deliver viable foals (63 percent) as mares receiving TMS in combination with dexamethasone, aspirin and altrenogest (72 percent). "A caveat to the administration of a TMS-based therapy for mares with placentitis is that foal viability is not consistently improved with this therapy in clinical practice, as it is not consistently shown effective in vivo as it is in vitro," she says.

"We have used TMS a lot in one of the projects done at the University of Florida, where we've had a very high live-foal rate. About 83 percent of our foals survived after infection and treatment with TMS, PTX and altrenogest," Macpherson says. "TMS is a drug that has some limitations, particularly for streptococcal organisms. The No. 1 cause of placentitis is Streptococcus equi, so in order to combat it, we need a better armament of drugs."

New drug holds promise

Macpherson recently evaluated the use of a long-acting ceftiofur, a third-generation cephalosporin,7 which has excellent bacterial activity against streptococcal organisms as well as many gram-negative aerobes and some anaerobes. Ceftiofur sodium is a commonly used antimicrobial in equine practice, and its injectable formulation provides a practical method of administration.

The newer drug—ceftiofur crystalline free acid—has a broad appeal for equine practitioners not only because it is a potent antimicrobial against Streptococcus zooepidemicus but also because it is administered intramuscularly at four-day intervals and provides therapeutic drug concentrations in horses for 10 days after the second dose. In addition, studies showed that it did not cross the placenta at all, which was a big eye-opener.

"In many ways, this exciting new drug would appear to be the perfect antimicrobial treatment for mares with placentitis," Macpherson says. "But we have to continue to explore that drugs are passing the placenta and that we can use effectively."

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.


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2. Erol E, Sells SF, Williams NM, et al. An investigation of a recent outbreak of nocardioform placentitis caused abortions in horses. Vet Microbiol 2012;158:425-430.

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5. Coutinho da Silva MA, Canisso IF, MacPherson ML, et al. Serum amyloid A concentration in healthy periparturient mares with ascending placentitis. Equine Vet J 2013 [in press].

6. Coutinho da Silva MA, Cannisso IF, Pinto CRF, et al. Serum amyloid A concentration in mares with experimentally induced ascending placentitis. J Equine Vet Sci 2012;32(7):407.

7. Macpherson ML, Gigučre S, Hatzel JN, et al. 2012. Disposition of desfuroylceftiofur acetamide in serum, placental tissue, fetal fluids, and fetal tissues after administration of ceftiofur crystalline free acid (CCFA) to pony mares with placentitis. J Vet Pharmacol Ther 2012 [Epub ahead of print].


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