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Finding the Cause of Chronic Diarrhea in Horses: Be Methodical

Finding the Cause of Chronic Diarrhea in Horses: Be Methodical
From infectious disease to microbial imbalance in the gut, causes of chronic diarrhea in horses run the gamut. Veterinarians 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 lively discussion on chronic diarrhea at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.
 
The conversation covered the importance of collecting a thorough patient history, conducting a comprehensive physical exam, and considering details not normally considered in diarrhea cases, such as toxic plants in the facility’s pastures. Whitehead recommended performing basic diagnostics such as blood work 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.
 
Veterinarians might also consider conducting an enteric pathogens panel, which tests for disease-causing organisms that affect the gut. However, both moderators cautioned that horses shed some microorganisms intermittently or at different times during their course of disease and, therefore, such panels might need to be repeated multiple times. Even then, less than 30% of these cases will be truly diagnosed. If there are concerns about Salmonella, the presenters recommended taking sequential manure samples once daily for three days for PCR testing or once daily for five days for bacterial culture. Sequential sampling is important due to intermittent shedding of the bacteria in the manure of infected horses.
 
Noninfectious causes of diarrhea might include sand accumulation, inflammatory bowel disease, and gastrointestinal lymphoma. Practitioners should also consider malabsorption issues, which they can diagnose using stall-side absorption tests for glucose.
 
The veterinarians 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 unfavorable intestinal conditions caused by diet changes, environment, or medication administration. Many of these horses exhibit no other significant signs than 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 nasogastric tube). Physicians have successfully used fecal transfaunation to treat a range of gastrointestinal 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 uses and is studying at his institution. 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.
 
The practitioners also discussed pre- and probiotics, but Arroyo cautioned that research results on the latter are not particularly promising. He has tried to culture several commercial products but has had little luck getting the products’ strains to grow, and sometimes other bacteria have grown instead. Veterinary scientists have shown Saccharomyces boulardii to be effective at reducing diarrhea caused by certain clostridial organisms, but it requires very high doses at concentrations that are hard to find in commercial products, he said. Because researchers believe bacterial diversity and richness to be important to the equine microbiome, products with single or limited strains are unlikely to be effective, he added. Prebiotics such as mannanoligosaccharides (MOS) and fructooligosaccharides (FOS), as well as mycotoxin binders, have been found to be more effective, he said.
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