Here are the possibilities for the soft stools:
1. Inflammatory bowel disease (inflammation within the intestines leading to inadequate absorption of food)
2. Exocrine pancreatic insufficiency (inadequate levels of digestive enzymes leading to poor digestion and absorption of food)
3. Irritable bowel syndrome (intestinal condition that responds to fiber supplementation)
4. Intestinal bacterial overgrowth (usually a result of something else, such as dietary intolerance, eating things that should not be, stress, etc)
5. Intestinal parasites (such as Giardia, cryptosporidium, coccidia, etc)
If there has not been any weight loss and he is doing well otherwise, more serious conditions like intestinal cancer are less likely.
Here's what I would do:
-- Purchase a probiotic (beneficial intestinal bacteria) such as Culturelle (usually available at human pharmacies) and give 1 capsule daily for at least a couple of weeks.
-- Feed either a commercial low residue intestinal diet like Iams Intestinal Diet or Prescription Diet i/d (available at your vet's office) or a combination of boiled skinless/boneless chicken breast with cooked white rice in 3 part rice to 1 part meat ratio. Either diet should be fed in small amounts frequently throughout the day. Don't give chicken broth. Continue the diet for at least 10 days and if diarrhea stops, gradually switch back to regular diet. Don't give treats
or any other food.
-- Give 1 caplet of Immodium AD twice daily for 3-4 days only.
-- If there is no improvement after 7-10 days or if he gets worse, please take him to your vet for examination and discuss the information above.
Hope this helps! Please let me know if you have ANY other questions and good luck!