The Horse

APR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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TheHorse.com | The Horse April 2019 19 pneumonia and leaving the survivors' lungs literally scarred for life. "The foal is highly susceptible to infec- tious agents that require cell-mediated im- mune responses," Horohov says, including but not limited to R. equi, which infects and multiplies in macrophages (white blood cells that respond to infection). "Fighting these bacteria off requires activation of the macrophage by the cel- lular immune system and, specifically, the production of interferon-gamma (a key protein in immune response)," he says. "But foals are unable to produce interferon-gamma early in life." Researchers still don't understand exactly how foals acquire the ability to make interferon-gamma, Horohov adds. The all-too-frequent "diarrhea disease," caused by the Clostridium difficile bac- terium, also requires cellular immunity. Sometimes fatal, C. difficile attacks foals' digestive tracts, which lack established populations of beneficial bacteria that can fight off bad bacteria, says Angelika Schoster, DrMedVet, DVSc, PhD, Dipl. ACVIM, ECEIM, senior clinical lecturer at the University of Zurich's Vetsuisse Faculty, in Switzerland. Probiotics have been marketed to help prevent C. difficile infections in foals, but their effects are contradictory, she says. What seems to work best for improv- ing the immune system of the foal gut is "letting nature take its course," Schoster says. "Foals usually consume mares' feces during the first weeks of life, colonizing the gastrointestinal tract with good bacte- ria. Breeders shouldn't prevent foals from practicing this routine." Take-Home Message The equine immune system is well- designed to develop over time, starting with a warmup in the uterus and sup- ported by passive transfer of maternal an- tibodies in the first 24 hours after foaling. We can ensure optimum immune status by vaccinating the dam during pregnancy, then monitoring colostrum intake and looking for signs of failure of passive transfer in the first 72 hours. After those critical days, our job as breeders is to see that mares and foals have healthy, stable, normal environments with minimal stress. A veterinarian-designed vaccina- tion program completes the developing immune system profile. h

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