Whether your switching foods because your pet is moving from one life stage to another, because he has been diagnosed with a dietary responsive illness, or just because you have found a different food that you think will suit him better, making the change gradually is usually the best way to go unless your veterinarian recommends otherwise. Dogs and cats that are forced into a sudden diet change may refuse the new food or develop vomiting and diarrhea if they do eat it. Mixing old and new foods together for a while is the best way to let your pet’s sense of smell, taste buds, and gastrointestinal tract get used to the new diet.
If your pet has handled previous dietary changes with no problems, mixing increasing amounts of the new in with decreasing amounts of the old food over just two or three days should be all that is needed. But, if your dog or cat is finicky or has a sensitive stomach, more transition time may be necessary. Start by just mixing in just 10% of the new food and take seven days or so to gradually move him over completely to the new food. Giving your pet a probiotic supplement like FortiFlora during the transition may also reduce the chances that a dog or cat develops diarrhea.
If at any point your pet stops eating or has vomiting or diarrhea, go back to his old food. If his symptoms do not improve, call your veterinarian.