The American Kennel Club (AKC) warns that “switching your dog’s food abruptly can cause gastrointestinal upset such as vomiting, diarrhea, and a decreased appetite.” Many of you shared firsthand experience with that fact.
“I didn’t know that dogs got sick if you change their food when I first got my dog. So I was just switching between what was on sale and she was getting sick and then I figured it out. Could have saved myself some horrible crate clean ups.” –Paulette
Then again, commenter panthercougar contends that “this is true of some dogs, but definitely not all dogs. Mine can seemingly eat anything and everything and be just fine.”
Apparently, the same issues can be said for cats, too:
“The same goes for some cats, particularly if you switch your cat from dry food to wet food. Oh. My. God. So much poo. So smelly.”
“And what you feed them tends to affect the smell of their poop. I fed my cats grain free food. Once one of them developed chronic kidney disease (CKD), I had to switch some of their food to the special diet food, which does not (yet) come in grain free formulations. My cats’ poop has definitely gotten much stinkier, and they are also both now more prone to gassiness, which has been… fun.” –HeathMaiden
If you’re about to switch pet foods, here’s the official advice from the AKC: “Any time you decide to change your dog’s food, you should transition to the new diet gradually in order to give your dog’s system time to adjust to the change.”