I switch Brew between Dog Chow flavors cold turkey BUT! He never has any issues. It can take up to 12 weeks for some dogs to fully adjust to new foods. Probably less within the same brand but still. Some dogs you have to go VERY slow. Also any people food or treats could cause it too. Also lately I’ve been sticking to just Beef the last few bags and haven’t switched him to Lamb for a while. LOL he doesn’t really like Chicken although I did buy the 4.4 bag a couple weeks ago when I didn’t buy the big Beef bag in time and ran out of food LOL

but besides that, he’s been on exclusively Beef lately. But he loves Beef and Lamb best. I’ve also tried Little Bites (Chicken and Beef) briefly and Tender & Crunchy (Turkey and Lamb). He loved both of those. I have not tried the High Protein. I also fed the Purina One for a while but it got really expensive.