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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Page 26 of 51 | The Horse April 2019 27 anthelmintic efficacy, estimating the extent of a horse's strongyle infection, and monitoring ascarids in foals and yearlings. Identifying Effective Drugs Even more important than check- ing shedding status with FECs is using them to check that your dewormers are working, Nielsen says. "After you have dewormed the horses you identified as having high FECs, go back and retest them" 14 days later, he says. "What you really want to know is how many eggs they are shedding after treatment." Anthelmintic resistance occurs when worms that survive a treatment breed and pass on to their offspring the ability to survive that drug class. Over time the proportion of the worm population that's able to survive the deworming treat- ment increases—that is, the worms have become resistant to the dewormer. High numbers of strongyle and/or as- carid eggs post-treatment indicate the de- wormer was not entirely effective, which can be caused by a number of factors. Aside from anthelmintic resistance, the horse owner might not have administered an adequate dose of product (e.g., they underestimated the horse's weight and gave a lower dose), or they administered it correctly but the horse spat it out. Understanding Resistance Nielsen reiterates that each horse in a herd is a biological sample of the same parasite population. "One horse in a herd won't have resis- tant worms without others also having (them)," he says. "If only one horse in a Visit us online at to learn more about Merck Animal Health and the equine products and programs that help keep horses healthy. Consult your veterinarian for the diagnosis, treatment, and control of parasitism. Do not use in horses intended for human consumption. When using Safe‑Guard ® (fenbendazole) Paste 10% concomitantly with trichlorfon, refer to the manufacturers labels for use and cautions for trichlorfon. Safe-Guard ® (fenbendazole) has a gentle mode of action and contains a molecule that makes it as safe as its name suggests. Now that's safe. The Science of Safe The Science of Healthier Animals 2 Giralda Farms • Madison, NJ 07940 • • 800-521-5767 Copyright © 2019 Intervet Inc., d/b/a/ Merck Animal Health, a subsidiary of Merck & Co., Inc. All rights reserved. 3270 EQ-HP AD Safe-Guard® Straight From the Research Herd The University of Kentucky, in Lexington, maintains two naturally breeding equine research herds ( that serve as invaluable resources for parasitol- ogy research. One herd harbors multidrug-resistant parasites and the other hasn't been dewormed since 1979. "The horses live in a very low-stress way," says Martin Nielsen, DVM, PhD, Dipl. ACVM, an associate professor and Schlaikjer professor of equine infectious disease at the university. "They are never moved from one place to another or ridden. They do not get dewormed, and they do have very, very high worm burdens. But they don't have parasitic disease. "The research herd reminds us that for the most part, horses are going to be fine," he continues. "You can be very laid-back about some parasites. But we never want to lose even one horse through preventable disease. That's why we use deworming products and strate- gies."—Jill Griffiths

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