Diarrhea is defined as an increase in the amount of manure expelled, whether it is passed with more frequency or a change in the quality of the manure from formed to soft and/or watery.

Diarrhea may be caused by eating inappropriate or unfamiliar feed; by bacteria or viruses, or diseases of the colon. If the horse is very ill and/or has a fever, the veterinarian must collect fecal material for culture to eliminate the possibility of a bacterial infection which could be spread to other horses and/or humans. Other possible causes of acute diarrhea are foal heat, arsenic poisoning, phosphorus poisoning, plant poisoning, parasitism (especially Trichostrongyles) and Potomac horse fever.

A particularly dangerous diarrhea results from overeating grain. This type of diarrhea creates serious body-wide disturbances that can be life threatening and/or result in founder.

Any horse with severe diarrhea requires veterinary attention to detect and quickly treat dehydration and electrolyte changes/imbalances. Horses with diarrhea are fed hay and water only, but are allowed access to water in order for the bowel to “rest”. In severe cases, fluids can be given intravenously, although some horses are able to tolerate fluids by stomach tube. Appropriate electrolyte concentrations must be added to basic fluids and water to correct specific disturbances.

In addition, a variety of preparations are available to aid equine diarrhea that are analogous to the familiar human Kaopectate. Again, these are given by the veterinarian via a stomach tube. The horse may also be given activated charcoal to help with absorption of toxins in the intestinal tract.

Oral antibiotics should not be used to treat diarrhea in horses. This is mainly due to the horse’s large intestine containing a complex and delicately balanced population of bacteria and other organisms essential to the digestion of a plant diet. Oral antibiotics will not only kill the “bad” bacteria but the beneficial ones as well. This may result in a chronic diarrhea that is difficult to reverse.

Chronic diarrhea is a special case. It can be caused by diseases of the intestine such as cancer (lymphosarcoma quite often) or by deficiencies in the intestinal tract that make it impossible for the horse to absorb some nutrients (malabsorption syndrome). Chronic diarrhea can also result after an acute problem with diarrhea, if the organisms in the intestinal tract have been imbalanced as a result of either the diarrhea or its treatment.

Chronic diarrhea as a result of cancer or malabsorption syndrome may be impossible to treat. However, chronic diarrhea that is the result of imbalances in the organisms normally present in the intestines, can be approached from several different angles-all of which require considerable time and patience in order to produce a hope for some degree of success.

Rheaform is an oral medication particularly effective against protozoa, one of the classes of microorganisms in the large intestine. Presentation of an abnormally high number of protozoa upon examination of the feces under a microscope can be effectively treated with Rheaform to eliminate or control the diarrhea.

Should Rheaform prove ineffective, or its use not indicated, simply allow the horse time in a turn out with exposure to the normal organisms in the manure of healthy horses. This may eventually result in the affected horse’s return of normal manure. A diet high in complex fiber will also aid in obtaining better-formed manure (hay, straw, and bran are appropriate; grass is not).

Finally, if all else fails, a procedure called transfaunation can be tried. This involves tubing the horse with fluid obtained by straining normal manure or normal intestinal contents from a horse that was killed or died. This fluid is very rich in normal intestinal organisms, and a sufficient number survive their trip through the stomach of the treated horse which will be detectable in the manure within the next 24 to 48 hours. Transfaunation requires numerous repetitions to be effective.

Foal heat (scours): most foals experience the foal heat diarrhea (scours), which often causes unsightly hair loss around the tail. As soon as the scours become obvious, wash and dry the area thoroughly; then pick up the foal’s tail and squirt some mineral oil underneath it. As the foal swishes his tail, he will scour the oil on his hind end preventing the hair loss.