I would say if your dog has been eating that brand of food for years then he is just not capable of digesting the Instinct. He has only been exposed to and digesting the certain set of ingredients in Muenster so his body is not use to the ingredients in Instinct. Not to mention the high protein and fat in Instinct is probably quite different than the Muenster. I would suggest going back to his old food until his bowels are back to normal. Then do a very slow transition. Also give him probiotics to help strengthen his gut and give him a more variety of beneficial organisms that help with digestion. He might even need a digestive enzyme. When I say slow transition, I mean real slow. Go with 75% old food with 25% new food until you know for sure he is digesting well and having normal stools. That could be a few days to over a week, maybe two. Then go to 50/50, then 25/75 but only increase the Instinct food when he has normal bowels for several days or longer. I would call going from Muenster to Instinct a drastic food change. I might have gone with a food in between Muenster and Instinct. Maybe Nutrisource grain free Heartland Select or Grain Free Lamb. My fosters do well with those and I get fosters of every age and have no idea what they have been eating in their previous home.
