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Changes in Horse Manure ConsistencyBy Kentucky Equine Research Staff · May 26, 2017

Loose manure and diarrhea in horses typically stem from one of three causes: antibiotic therapy, diet, or disease. Because of excessive water loss associated with diarrhea, affected horses can become dehydrated and have other problems, so horse owners should investigate changes in manure consistency immediately, calling in a veterinarian if necessary.

Antibiotics are a well-known trigger for loose manure because they eliminate many of the innate and beneficial microorganisms that reside in the horse’s hindgut.

In a recent study*, researchers concluded that “antibiotic-associated diarrhea (AAD) is attributed to the disruption of the normal flora of the hindgut, permitting proliferation of pathogenic microbes.”  In the study, not all horses were affected similarly.

Providing a probiotic supplement anytime antibiotics are given has been a traditional approach to help combat AAD, according to Catherine Whitehouse, M.S., a nutrition advisor with Kentucky Equine Research (KER), but ongoing research hopes to reveal more information. Veterinarians should always been kept in the loop when AAD is suspected in a patient, and horses should have access to clean, fresh water during antibiotic therapy to thwart dehydration.

Diet can be another catalyst for loose manure. “Overfeeding and the consumption of indigestible material, such as fibrous roughage, dirt, and sand, can lead to diarrhea in young horses,” said Whitehouse. “In adult horses, inappropriate or sudden dietary changes, such as differences in digestibility of feedstuffs and differences in the amount of feed offered, can also cause problems.”

Because microbes in a horse’s gut become accustomed to a consistent diet, dietary changes can have a profound effect on manure consistency. When the diet changes, the microbe population must shift to reflect the change. If the change happens too quickly, the microbes cannot handle the new feed properly, and loose stool or even diarrhea may be the result.

Whitehouse cautions that not every horse can handle every feedstuff, especially richer options. Protein-dense, rapidly fermentable fibers, such as alfalfa (lucerne), must be introduced to the diet slowly to avoid loose manure. Beet pulp is another feedstuff that should be gradually added to a diet.

If a horse has a significant change in manure texture right after a dietary change, this would not be unusual and will likely improve as the horse becomes adapted to the diet. If manure does not begin to solidify or become normal, a different diet might have to be formulated for the horse.

In addition to dietary causes, disease may trigger loose manure. “Horses are affected by both infectious and noninfectious causes of diarrhea and colitis, such as internal parasites and Salmonella. If disease is a suspected cause, it is best to let a veterinarian examine the horse immediately to determine the root of the problem,” advised Whitehouse.

Some horses with diarrhea benefit from the hindgut buffer EquiShure, which was designed to normalize the pH of the cecum and colon. 

*Harlow, B.E., L.M. Lawrence, M.D. Flythe, S.H. Hayes, G.L. Gellin, L.A. Strasinger, M. Brümmer, and A.L. Fowler. 2013. Microbial species richness of equine fecal microflora in horses challenged with antibiotics. Journal of Equine Veterinary Science. 33(5):331.