If Giardia is the cause of severe diarrhea in dogs, the vet will probably prescribe a special diet. If the food is changed even if only as a preventive measure due to being in a high risk area for Giardia, you should make sure the food to choose contains as few carbohydrates as possible, because the Giardia in the intestines of dogs mainly thrive on the carbohydrates in dog food diets. The more you offer them the more comfortable they feel and grow optimally ... Your Vet should be able to tell you which dogfoods are best for this case. In addition, the following tip in case of a poor digestion (such as caused by Giardia): 1 teaspoon of psyllium   1 cup of probiotic yogurt To be given half an hour before the main meal. Initially before each meal then if successful it can be reduced day by day. This must not be used as a permanent solution .... the reason for the diarrhea is to be found by your Veterinarian. This recipe serves exclusively for a short time to let the bowel and the intestinal flora calm down. For dogs that are fed fresh meat, you should add some calcium because the psyllium rob the system of calcium, this is one of the reasons why the psyllium should be given half an hour before the normal food is given. One can also use this for constipation, in this case the psyllium is to be soaked in water for approx. 1 hour. See also link: http://www.pahema.com/ Enter psyllium as search top right .