Are dogs similar to cats in regards to changing foods gradually? I was taught to introduce foods slowly - sometimes just a spoonful mixed in with regular food - to help reduce any digestive upset.
Plus, the Rx food - If its the recovery food, high in fat and calories - it's prone to causing digestive issues because it's so rich. A little goes a long way. My cat would get diarrhea from it - even 2 days after her last recovery meal. Just FYI.
Wondering if he's developing food sensitivities or even allergies. Just because it's a Rx food, doesn't mean its made with the most wholesome ingredients.