Changing your dog's diet should occur over a period of time to prevent your dog from developing gastrointestinal upset and vomiting. Sometimes a change in his diet is necessary to transition him to a more age-appropriate food, such as a change to a senior food for an adult dog and an adult food for a puppy. Your veterinarian may also recommend a change to a prescription brand of dog food from your current one to treat a food allergy or other type of chronic illness. Whatever the reason, the change must be gradual.
Mix in one-quarter of the daily recommended portion of the new brand of dog food into three-quarters of the portion of your dog's current brand of food. Serve this mixture to your dog for three to four days, depending on how receptive your dog is to the food.
Add a teaspoon or two of low-sodium beef or chicken broth to the food if your dog shows resistance to try the new food. The broth makes the food more appetizing without adding any calories to the food or potentially stomach-upsetting ingredients. If transitioning from a canned food to a dry one, the broth will soften the harder kibble during the change
Change the mixture of the old brand of dog food and the new one to equal amounts, with each making up one-half of the daily recommended portion by the manufacturer of each food. Feed this mix of food for four days. If you notice that your dog's stool becomes loose or he begins to vomit or refuse to eat, go back to the previous mix of one-quarter to three-quarters for four days and start the change again.
Increase the amount of the new brand of food in your dog's daily feeding to three-quarters of the daily recommended amount, reducing the old food to one-quarter of the portion. Feed this amount for four to five days.
Monitor your dog's stool and behavior. Eating a majority of the new food may cause diarrhea, constipation or vomiting. Other symptoms, such as itchy skin or lethargy, may indicate an allergy to the new food or one of the ingredients in it; seek the advice of a veterinarian if this occurs.
Feed only the new food according to the manufacturer's directions to complete the transition. If you have been adding low-sodium broth to the food, reduce the amount over the course of three to four days until you are only feeding the new food with nothing added to it.