What Are the Causes of Diarrhea in Horses?

Diarrhea in horses can lead to severe dehydration and other complications if left untreated. There are numerous potential causes of diarrhea in horses, ranging from simple changes in feed to complex bacterial infections. Common sense and good barn management can go a long way toward preventing diarrhea.

  1. Feed

    • Change in diet is a common cause of diarrhea in horses. Any change in grain or hay must be made slowly to avoid introducing gastrointestinal issues. Even changing access to pasture grass should be done slowly. Overfeeding can cause diarrhea, as can feeding poor-quality, moldy or spoiled hay and grain. A variety of molds and toxins can form in hay or grain that is not kept dry. Feed meant for cattle or sheep may contain antibiotics and growth hormones that cause diarrhea in horses. Hay containing blister beetles, often found in the first cutting of alfalfa in north Texas, Oklahoma and northeast New Mexico, may cause diarrhea. Horses may also have or develop allergies or sensitivities to feed ingredients. Feeding horses sand may result in sand accumulation in the intestines, leading to irritation of the intestinal lining and diarrhea.

    Medication

    • Antibiotics can cause diarrhea by killing off good bacteria in the intestines. Ask your vet about side effects anytime medication is administered to your horse. De-wormers given to horses with severe parasite infestations can cause diarrhea as a reaction to parasite die-off. A common equine painkiller, phenylbutazone (bute) can cause colon ulceration, leading to diarrhea and other complications.

    Stress

    • Stress, induced by excitement or fear, leads to a release of hormones that increase blood flow to the intestines. In this case, the severity of the diarrhea directly relates to the amount of stress the horse feels. Exercise that is too intense for the horse's condition or heavy exercise in extreme heat can cause diarrhea by raising the horse's core temperature to a point that intestinal organisms die. Diarrhea caused by stress will recede as stress levels lower.

    Reduced Intestinal Flora

    • Horses that are very young or very old may have diarrhea caused by low levels of intestinal organisms. Inadequate intestinal flora will increase a horse's sensitivity to changes in feed. Diarrhea itself can cause reduced intestinal organisms, making the horse more sensitive to feed issues and potentially leading to chronic diarrhea.

    Parasites and Bacteria

    • Severe parasite infestation can cause diarrhea. Common diarrhea-causing bacteria include Salmonella, Clostridia and Ehrlichia Risticii (Potomac horse fever). Infections caused by any of these three bacteria are potentially fatal.