Ask an Expert

Diagnosing Diarrhea

August 10, 2010

There are a multitude of reasons why your horse might be experiencing diarrhea and several options to cure it.


My 27-year-old Quarter horse gelding seems to have chronic diarrhea. The amount varies but he always has manure stains and some amount of buildup on his buttocks and fetlock. I am concerned they may be an indicator of something other than “old age.” My vet thinks it’s just an aging digestive tract that isn’t as efficient as it was. I try to control it by adding beet pulp to his senior feed as suggested by the vet, but it still occurs. Is this something I should be concerned about or could this be an indicator of something more serious than “old age”?


Aging in horses brings many changes, and without the benefit that your regular veterinarian has in knowing you and your horse’s history, care and living conditions, diet, current physical condition and your geographic location, I can only speak in generalities. Chronic diarrhea is an increase in the fluid volume of feces that lasts longer than three weeks, which creates a manure that looks more like that of cattle than the typical “road apples” that horses produce. This can leave the buildup on buttocks, legs, and tail, as you have stated is happening.
Usually, chronic diarrhea is a problem within the large intestines (colon) and it can have varied causes based on age, breed and use of the horse. For an older horse such as yours, possible causes include drug-induced diarrhea (NSAIDs such as Bute or Banamine, or antibiotics), sand in the colon, Inflammatory Bowel Disease, gastroduodenal ulcers (ulcers in the stomach or upper small intestine), stress-induced diarrhea, internal parasites (especially with parasite resistance to our currently available dewormers on the rise), chronic liver disease, Salmonellosis (a bacterial infection that can be passed to humans), Potomac fever, fungal diarrhea, neoplasia (cancer), and in many cases, idiopathic diarrhea, meaning we don’t know specifically what causes it and we can only treat it symptomatically. Unfortunately, even with a variety of diagnostic tests available, it can often be difficult to pinpoint an exact cause for the chronic diarrhea, although these tests can rule out specific disease processes.

My recommendation would be to discuss with your veterinarian your concern that it might be more than old age digestive system changes. Let your veterinarian know that you would like to pursue ruling out other causes, those that your vet believes would be next most likely to be causing the problem, given your horse’s chances of being exposed to a certain cause. For example, if your horse is not receiving NSAID’s such as Bute for arthritis, nor is it receiving any antibiotics, then that is not a likely cause of the diarrhea. Let your vet know that you are not questioning their judgment, but instead you want to help provide them with more information from selected diagnostic tests about your horse’s condition, which can be used to better treat and hopefully resolve the problem. And if you both decide that more diagnostic tests are unnecessary at this time, then discuss other dietary changes that you can try to see if they help dry up or reduce the amount of diarrhea that is occurring.

— Dr. Nannette Chastine, member of the American Association of Equine Practitioners