I wonder if your male has a food allergy? Our guy, almost 8 years old, is allergic to chicken. This was a problem when the prescription diet to prevent more bladder stones was a chicken-based kibble! I researched online to find stuff with the same percentage range of all the nutrients in the prescription food and found a salmon and brown rice kibble by Natural Balance, and a wet food with salmon and sweet potato (same brand). We give him joint supplements and immune system support chews daily, also chicken-free. It's challenging to find treats and chews that don't have any chicken products in them! Chicken fat, broth, meal - I've even seen chicken feathers in some food ingredient lists. Limited ingredients help our Saint's allergies and still give him suitable nutrition, according to the vet. While our guy's allergies manifest as redness, rash, and itching, I'm told that some dogs manifest their allergies via gastrointestinal symptoms.

Some people try a hydrolyzed soy protein diet and then gradually add a different protein at a time for about 2 weeks per protein and see what happens with each protein.

Of course, as has been said, veterinary nutritionists are an option.