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 A18 March 2019 The Horse | AAEP Wrap-Up behavior decreased significantly when compared to initial baseline values; ■ All treatments increased magnesium levels for all horses; ■ The increase in these values was greater in the headshaking horses than in the control horses with magnesium and boron supplementation. Horses suffering from trigeminal- mediated headshaking behavior might benefit from magnesium and boron supplementation, said Sheldon. However, she cautioned that this study included a very small number of horses and that the supplementation period was short. Consider Lesser-Known Parasite in Neuromuscular Disease Cases Historically, vets have reported finding parasites in the skeletal muscle of some horses with neuromuscular disease. One they've always written off as not actually related to the neuromuscular disorder is the protozoan parasite Sarcocystis fayeri. Monica Aleman, MVZ, PhD, Dipl. ACVIM, an associate professor of medicine and epidemiology at the UC Davis School of Veterinary Medicine, believes, however, that there's more to it. She recently studied S. fayeri's prevalence in horses with neuromuscular disease. "At UC Davis we've found large num- bers of S. fayeri in the skeletal muscle of diseased horses," she said. "There are also anecdotal reports of horses with lameness and stiffness (but no characteristic neuro- muscular signs such as incoordination or muscle wasting) responding to treatment with antiprotozoal drugs." She said confirming S. fayeri in horses' skeletal muscle is also important from a public health standpoint because it's toxic to humans consuming raw horse meat. So she evaluated samples from 392 equids treated for suspected neuromuscu- lar disease at UC Davis from 2000 to 2014 and found that: ■ 50 study horses had encysted S. fayeri in their skeletal muscle; ■ 35 of those 50 had concurrent con- firmed neuromuscular disease; ■ 51 (83.6%) of 61 muscle samples from those 35 affected horses contained encysted parasites; and ■ 10 horses with S. fayeri were treated with an antiprotozoal (Marquis), and their clinical signs resolved within 15 days. "This doesn't necessarily prove S. fayeri causes disease but is worth considering and performing further investigation," said Aleman. She said the findings indicate S. fayeri infection is significantly more prevalent in young adult horses (< 7) with neuromus- cular disease than in healthy horses. "Consider muscle biopsy in horses with neuromuscular disease of undeter- mined cause or the presence of clinical signs such as stiffness, muscle atrophy (wasting), dysphagia (difficulty swal- lowing), weakness, gait abnormalities, myositis (tying-up), or myalgia (muscle pain)," she said. In summary, said Aleman, neuromus- cular disease might be associated with S. fayeri infection in muscle because its presence in large numbers could affect muscle function. h Finding the Cause of Chronic Diarrhea From infectious disease to microbial imbalance in the gut, causes of chronic diarrhea in horses run the gamut. Vets gathered recently to share their approaches to dealing with the common issue. At the heart of it? Every horse and situation is different; pay close attention to details. Ashley Whitehead, DVM, DVSc, Dipl. ACVIM, senior instructor of equine clinical sciences at the University of Calgary, and Luis Arroyo, Lic. Med. Vet., DVSc, PhD, Dipl. ACVIM, associate professor at the University of Guelph's Ontario Veterinary College, both in Canada, moderated the discussion. They covered the importance of collecting a thorough patient history, conducting a comprehensive physical exam, and including details not normally considered in diarrhea cases, such as toxic pasture plants. Whitehead recommended performing basic diagnostics such as bloodwork to evaluate organ systems, electrolyte concentrations, protein levels, and for evidence of infection. In addition, fecal egg counts are helpful to rule out internal parasites. Vets might also consider conducting an enteric pathogens panel. But both moderators cautioned that horses shed some microorganisms intermittently or at different times during disease and, therefore, such panels might need to be repeated. Even then, fewer than 30% of these cases will be truly diagnosed. If there are concerns about Salmonella, the presenters advised taking sequential manure samples once daily for three days for PCR testing or once daily for five days for bacterial culture. Noninfectious causes of diarrhea might include sand accumula- tion, inflammatory bowel disease, and gastrointestinal (GI) lymphoma. Practitioners should also consider malabsorption issues, which they can diagnose using stall-side absorption tests for glucose. The vets reported that many chronic diarrhea cases might be associated with a dysbiosis, in which the bacterial population in the horse's hindgut is unbalanced due to the presence of pathogens or un- favorable intestinal conditions caused by diet changes, environment, or medication administration. Many of these horses exhibit no significant signs besides chronic diarrhea and otherwise appear normal. Both moderators said they have had success treating these horses using a technique called fecal transfaunation (transfer of bacterial flora from a healthy individual's stool to the affected individual, via naso- gastric tube). Physicians have successfully used fecal transfaunation to treat a range of GI conditions in people, and the method is growing in popularity in equine medicine. While no formal protocol exists for this process in horses, Arroyo shared a method he is using and studying. He also said his research group plans to compare the efficacy of fecal transfaunation to administration of particular probiotic strains to treat colitis (inflammation of the large bowel, or colon) cases. Based on feedback from the vets in this session, chronic diarrhea in horses is a common and frustrating problem. The consensus was some things work for some horses and not for others. Therefore, finding a solu- tion can be a trial-and-error process, especially in horses that otherwise appear normal and have no additional signs or obvious cause. The best results come from working with your vet and methodically ruling out possible causes, trying potential treatments one at a time, said the moderators. A vet or an equine nutritionist who can evaluate diet and identify potential dietary triggers can help. Whitehead cautioned that chronic diarrhea cases take time, patience, and substantial communication between veterinarian and owner. "A successful outcome may not be complete resolution of diarrhea, but an improvement that is acceptable to the owner," she added. —Clair Thunes, PhD

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