The Horse

MAR 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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YOUR GUIDE TO THE 2018 AAEP CONVENTION A16 March 2019 The Horse | AAEP Wrap-Up ALEXANDRA BECKSTETT CLAIR THUNES, PHD Fevers Without Respiratory Signs: Consider Tick-Borne Disease W hen a horse spikes a fever without the nasal discharge, coughing, and other respirato- ry signs you'd expect to see with infectious disease, potential causes could be vast. In the Great Lakes region and eastern U.S., which are areas known to have the highest tick-borne-disease incidence in humans and animals, one suspect is tick- borne disease. To find out how prevalent tick-related fevers are in horses, Linda Mittel, MSPH, DVM, senior extension associate at Cornell University's College of Veterinary Medicine, in Ithaca, New York, studied causes of fever of unknown origin (FUO). In her case-control study she surveyed clientele from 15 practices in nine eastern states and Wisconsin, which are known to have high tick populations. She included in the study 52 horses that had experi- enced FUO and 52 healthy horses from the same farms as matched controls. She also included an additional 23 FUO cases without matched controls. Ticks were col- lected from each farm, IDed, and tested. Mittel obtained blood samples from each horse and tested for DNA of two of the most common causes of equine fever without respiratory signs—the bacteria Anaplasma phagocytophilum, which causes the tick-borne disease anaplasmo- sis, and Neorickettsia risticii, which causes Potomac horse fever—plus other bacteria and parasites. She also analyzed other DNA in each sample and found that: ■ Clinical signs reported in FUO horses were depression, coughing, lethargy, colic, lameness, abnormal feces, an- orexia, and jaundice; ■ One horse tested positive for N. risticii and 10 for A. phagocytophilum; and ■ Genetic sequencing revealed "lots of different organisms," she said. While these results confirmed, as expected, that Anaplasma is a common cause of FUO in these regions, "I was sur- prised and a little disappointed we didn't find something really cool," said Mittel. Her take-home was that not every FUO without respiratory disease is caused by ticks and to consider other organisms. She's doing follow-up panel tests to look for additional tick-borne diseases that cause these fevers. Managing Headshaking in Horses: A Magnesium Supplement Might Help Some severely painful headshaking cas- es are resistant to existing treatments and can compromise a horse's quality of life to the extent that euthanasia is necessary. But researchers recently determined that a new feeding regimen that includes mag- nesium supplementation could help. Shara Sheldon, PhD, and a research team from the University of California, Davis (UC Davis) School of Veterinary Medicine's Department of Medicine and Epidemiology, examined the effects of the mineral— because it plays a role in nerve impulses—with or without boron (which increases ionized magnesium in the blood) on horses with trigeminal-mediat- ed headshaking. These horses experience neuropathic (nerve) pain because the tri- geminal nerve, which supplies sensation to the face, is constantly on the brink of firing, said Sheldon. Researchers believe 1-4.6% of horses have the condition, 75% of cases occur in geldings, and any breed can experience it. Headshaking appears to occur more frequently in spring and summer. Vets haven't found one therapy to be entirely effective. But researchers have considered magnesium supplementation as a possible treatment; some have re- ported that headshakers have abnormally low serum levels of magnesium. In earlier work Sheldon showed that infusing intravenous magnesium sulfate reduced headshaking in affected horses by 29%. In her current study the goal was to see whether a similar reduction in headshaking would occur if she adminis- tered magnesium as an oral supplement. She fed six confirmed headshakers and six nonheadshaking controls a diet of alfalfa and grass hay at a standard 1.5% of each horse's body weight. She placed them randomly in three treatment groups: pelleted feed combination, pel- leted feed combo with magnesium, and pelleted feed combo with magnesium and boron. Each group of horses rotated randomly through each treatment and acted as their own controls, with a one-week washout period between treatments during which they consumed only hay. Prior to the supplementation period and one week after, Sheldon's team drew blood and assessed it for several factors. At the end of each treatment period, three trained evaluators scored each horse for headshaking behavior while working in all three gaits. The results showed that: ■ All treatment groups' headshaking KEVIN THOMPSON/THE HORSE The Latest Medicine Studies

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