Equine Gastrointestinal Microbiome Unfazed By Fenbendazole

Many common medications can negatively influence the microbes residing in the equine hindgut. Sweeping changes in the types and amounts of bacteria, fungi, and protozoa in the hindgut can be harmful to the horse’s well-being. Altered microbe populations often result in diarrhea and an abnormal or decreased production of volatile fatty acids, which horses use as energy.

“Examples of medications capable of disrupting the equine intestinal microbiome include nonsteroidal anti-inflammatory drugs such as phenylbutazone, or bute, and various antibiotics,” explained Laura Petroski-Rose, B.V.M.S., a Kentucky Equine Research veterinarian.

The effects of fenbendazole, a popular dewormer (or chemical anthelmintic) used for controlling parasites such as small strongyles, were recently reviewed by a group of veterinary researchers from the United Kingdom. Does orally administered fenbendazole alter the intestinal microbiome?

To answer this question, horses with fecal egg counts (i.e., the number of parasite eggs in a fecal sample) in excess of 200 eggs/gram of feces were identified. These horses were administered fenbendazole according to manufacturer instructions. Fresh fecal samples were subsequently collected from the hindguts and the microbiomes analyzed.

Compared to untreated horses with fecal egg counts of <200 eggs/gram of feces, no difference in microbial population of the hindgut was seen in dewormed horses.

“This suggests fenbendazole has no detectable effect on organisms other than its targets. Moreover, it does not appear to make a contribution to changing the resulting metabolom,” concluded the researchers. A metabolom is a complete roster of small-molecule metabolites found in a biological sample.

“While this is great news for fenbendazole, the delicate balance of the intestinal microbiome is prey to a large variety of other medications and influences, including diet changes,” noted Petroski-Rose.

To help maintain a healthy hindgut, Kentucky Equine Research offers two products designed to maintain a healthy pH, translating into a stable microbiome: EquiShure and Triacton.

“In addition to offering hindgut buffering agents, ensure your horse’s diet is appropriate, containing the necessary nutrients to meet, but not exceed, requirements,” Petroski-Rose advised.

To do this, schedule a consultation with a Kentucky Equine Research nutrition advisor today.

*Crotch-Harvey, L., L.A. Thomas, H.J. Worgan, et al. 2018. The effect of administration of fenbendazole on the microbial hindgut population of the horse. Journal of Equine Science. 29(2):47-51.