In March 2002 I adopted a 1 year old female. She was on Authority, so I switched my 2 male 4 year olds to that food. In May I switched them to Science Diet Sensitive Stomach. Since then one of my males has had diahrrea for a month, other 2 are fine. Been to Vet twice fecal test negative, and stomach Xray fine. On Flagyl, Zeniquin, Eukanuba low-residue first time, then Panacur. Didn't stop, it's like water. It doesn't seem to be a parasite or infection, can it be from too much fiber in the food?
It could be from the food. Other possibilities include inflammatory bowel disease, pancreatic insufficiency, parasites, other metabolic disease. I recommend an intestinal biopsy at this point. Good luck, vetcare