HERBAL TREATMENT FOR DIARRHEA by Jeff Grogmet DVM. B Sc (Agr)

Suppose your dog suddenly develops diarrhea but is not vomiting. Try slippery elm, a herb that contains fiber as well as mucilage.
Mucilage helps soothe irritation and inflammation of the mucous membranes, and lining of the gastrointestinal tract GIT.
Bacteria use fiber as a food source so it normalizes the intestinal flora. Slippery elm is available as a loose powder or in capsules. 
Another soothing herb for diarrhea is marshmallow. Like slippery elm, it contains mucilage to coat the GIT.
It is especially useful in inflammatory conditions such as gastritis, enteritis, or colitis. It desensitizes nerve endings in the intestinal wall thereby reducing spasms. Marshmallow comes in capsules.

Dogs of Canada November 2006 issue