Yesterday we started to change Toby over to Nutram from Iams dog food. He's never eaten Iams without incentive - cheese, broth, peanut butter, etc. Funny thing - we combined it 3/4 old food, 1/4 new food, and put nothing on it. He picked out all the new food pieces, and spit the Iams on the floor! So I'm thinking - what's the point of combining them? He did the same thing this morning too. He just does not like the Iams, and loves the Nutram! I know he may get the runs a little from an abrupt switchover, but I don't think that can be helped.
Our puppy had diarrhea when we put just a little bit of new grain free food in with her old. We talked with the lady at the dog food store and she recommended just switching her to the new food completely since she had a sensitive stomach. Lucy had diarrhea for about a day and then normal stools from then on out - except for her last BM each night - it was always pudding-like for about a week. I say just switch him right over. Good luck!
We have just switched completely. Ours often do the same thing and pick out all of the new to eat. Any adverse reactions we had passed pretty quickly. Additionally we have used digestive enzymes to aid in this transition and had no issue what so ever. Wholistic Pet makes a good on, but there are many other similar ones available. Good luck!
Thanks - we did end up switching abruptly, and he was fine. No adverse reactions at all. He is the picture of health - a rapidly growing picture of health!