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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16 April 2019 The Horse | What they do have at birth are low amounts of antibodies that are not yet optimized for pathogens, says Bettina Wagner, DVM, PhD, professor and de- partment chair at the College of Veteri- nary Medicine at Cornell University, in Ithaca, New York. "Foals are just 'warming up,' getting their immune system and their immune cells ready to respond without actually having antibodies for a specific patho- gen," she says. "So far nobody knows what these early antibodies are directed against." Colostrum: The Super-Immunity Drink Mares produce several hundred millili- ters of colostrum before they start to pro- duce milk, says Wagner. Rich in nutrients, colostrum fills a newborn foal's digestive system with antibodies that represent the dam's "entire lifetime of exposure to pathogens," she says. That includes anti- bodies against microorganisms specific to that mare's environment—whatever might be circulating on her farm, as well as those against pathogens the mare has confronted or been vaccinated against in the past. Colostrum also contains cytokines—proteins that work like signals for the immune system. "The cytokines stimulate the foal's immune system to get started," Wagner says. While a mare's colostral antibodies re- flect everything her immune system's ever fought, some of these disease-fighters be- come less active over time, says Wagner. That's why it's essential to vaccinate the mare during her pregnancy to restimulate her immune response to pathogens such as equine herpesvirus (EHV), influenza virus, Clostridium tetani, and more. "Since the foal relies on the mare for its initial antibody response, proper vac- cination of the mare is an important step in providing the foal with the necessary antibodies," Horohov says. A Closing Gut & A Ticking Clock The tricky thing about swallowing an entire life's repertoire of antibodies is getting them where they belong—in the bloodstream. If they stay in the digestive tract, they're not much use. Fortunately, the newborn equine gut is "open" to absorb these antibodies and get them to their destinations in the body. There's a caveat, though: It's only open for about the first 18 hours of life. Then, the gut closes gradually over the next six hours, says Ibrahim Elsohaby, PhD, post- doctoral researcher at the University of Prince Edward Island, in Charlottetown, Canada, and the Faculty of Veterinary Medicine at Zagazig University in Egypt. At 24 hours after birth, the gut is com- pletely closed, and no more antibodies can get through the intestinal walls into the bloodstream. "By then, they're just good protein," Wagner says. "But they won't do anything for the immune system." Signs of Failure Sometimes it's obvious that failure of transfer of passive immunity (FTPI)— not getting enough antibodies through colostrum—has or will happen. The mare died; the mare and foal were separated; the foal didn't nurse within the first hours. But sometimes it's less obvious, says Wagner. "It can depend on the quantity of the colostrum or the quality," she says. "Maybe the mare didn't make enough for some reason or the foal wasn't efficient at suckling. Or, possibly, the quality was poor because of a low rate of antibodies present in the colostrum." A baby that hasn't gotten enough high- quality colostrum will start to get sick, usually within two to five days, she says. "The foal won't be as active, is not moving around much, won't seem alert, and might stop suckling and often develops a fever." Testing for Transfer If, for any reason, you doubt your foal got enough antibodies through colos- trum, you can—and should—run diag- nostic testing. "Confirming that adequate passive transfer has occurred and, if not, replacing it with another source, is criti- cal," says Horohov. Most commonly, the veterinarian will take a sample of the foal's blood and test it for sufficient antibody transfer. This is the most important test and is often per- formed routinely in healthy foals around 48 hours after birth. But if earlier on you're concerned about the quality of the mare's colostrum, The Best Defense If a foal is low on antibodies, he'll need to consume supplemental colostrum from a colostrum bank or, if 24 hours have passed since birth, intravenous plasma. AMY K. DRAGOO

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