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changing diets

Note: any changes in diet, routine, exercise or environment should be discussed with your veterinarian to ensure they are appropriate for your pet and his/her unique health needs

In the veterinary clinic we often see sick pets due to abrupt food changes. Often, we are presented with dogs or cats with diarrhea or occasionally vomiting and the problem is not that hard to treat. Occasionally though, if a cat resists a food change and goes on hunger strike for more than 2 – 3 days, we can see life threatening liver changes. So, it is important to make food changes very carefully. So a gradual diet change will help avoid these health issues.

As with all my articles, I do suggest that you check with your veterinarian first and discuss any food changes with him/her. This is especially important if your pet is overweight or has health problems. Advice is given for general information only.

In any case, prevention sure beats a veterinary bill so here are some tips on changing diets.

Tips for dogs:

  • For the first week replace 1/8 of your regular diet with the new diet and mix it in. That is 7 parts old diet to 1 part new diet based on the calories – ask your veterinarian to calculate if you aren’t sure.
  • Watch for normal stool consistency and vomiting or any other changes in health. Discuss with your veterinarian if you notice changes.
  • For the second week, replace ¼ of your old diet with the new diet and continue monitoring the dog.
  • If all is going well, the third week do ½ of the meal as the old, ½ as the new.
  • On the fourth week, switch to the new food totally.
  • If your pet gets soft stool or diarrhea, contact your veterinarian for further advice and discontinue the new food until you are able to discuss this with them.
  • There may be situations where you need to get your dog onto a new food faster.. say you ran out of the old food on a weekend for example. In this case, I’d recommend the following:
    • Follow the above using 1/8 of the calories as the new food and the rest of the diet as long grain cooked rice (small dog maybe about ¼ of a cup/day of rice; medium dog 1 cup/day and large dog 2 cups/day).
    • Keep increasing the new food and reduce the rice slowly.
    • Watch carefully for changes in stool as you are more likely to get diarrhea on this method vs. the above method. Contact your veterinarian if you have questions.
  • Consider asking your veterinarian for a probiotic which can help prevent diarrhea by providing good bacteria for the gut.

Troubleshooting for dogs:

Questions: My dog is very picky and he won’t eat the new food. What do I do?

Answer: Sometimes in dogs we need to encourage them to eat by making them hungry. If your dog doesn’t eat a meal within 5 minutes, then pick up the bowl and don’t give any food until the next meal time. At that meal, reduce the food by half. Continue this process of timed feedings and halved meals until the dog is eating well, then gradually increase up to the normal food. If after 2 – 3 days your dog still refuses to eat any of the new food then ask your veterinarian whether it is safe to continue this method or whether you should try a different food. This information is different for cats, please see below.


Question: My dog loves the new food and won’t eat the old food? What do I do?

Answer: Continue feeding the recommended mix and regular amounts even if the dog isn’t eating the whole meal. (Unless the dog is thin or underweight, then talk to your veterinarian).

Tips for Cats:

Cats can be notoriously picky and it can take months to get them to switch to a new food. Just like children, sometimes they have to see it over and over again before they will even consider tasting it. We can also run into health issues such as liver problems if an overweight cat fasts for too long (more than 2 – 3 days). So food changes and diets have to be managed carefully. For starters I’d suggest asking your veterinarian for 2 – 3 different diets that he/she would recommend for your cat. You may be abe to get small samples of each diet to try out. That way you can choose the one the cat likes best. To determine this, withhold food from your cat for 8 – 12 hours (unless your veterinarian doesn’t feel this is safe for your cat). Then give 1 tsp. of each of the new foods on three different plates. If the cat chooses one then that is the one that you would want to change too. Then follow the method below:

  • Give 1/8 of the recommended food and 7/8 of the old food (on a calorie basis) as a meal three times/day.
  • Continue doing this until the cat is at least trying the new food.
  • Then start increasing every week or two until the cat is on the new food.
  • Short fasts of 6-12 hours can be used to induce hunger. Meal feeding are suggested for this reason. Consider 2 – 3 feedings/day.
  • You can try offering the new food separately first and only feeding the old food after the new food is gone but don’t let the cat fast too long.
  • Be patient and don’t give up. Like I said, it can take months.
  • If your cat likes being handled and petted you can rub a bit of a new wet food onto his/her paw for the cat to groom off. Sometimes once they actually taste it they quite like it. Note, if this stresses your cat then don’t do it or it will cause a food aversion.
  • If the above is not working after a few weeks then try putting a bit of tuna juice over the old food. If the cat likes that then try some over the new food. Once the cat is eating the new food with a bit of tuna juice then slowly phase out the old food. Then phase out the tuna juice slowly. Note: tuna is not a good choice for cats with food allergies, inflammatory bowel disease or in general for long term use. Check with your veterinarian.
  • If your cat(s) are not used to meal feedings they might bug you for food between meals. Don’t give in. Time your feedings to when you will be home most (i.e. if you work all day consider a small meal in the am and then two larger meals when you are home in the evening). Have a plan for what you will do if they are bugging you too much… Some ideas:
    • Pet them, groom them or play with them instead!
    • Play can be especially good for giving them an appetite for the new food.
    • Go to another room and close the door or if it is really getting to you leave the house for a while. This will send a strong message that begging no longer works!
    • Be strong! I know it is tough!
  • Some sources recommend putting the old food in the fridge as the cat will smell it in the cupboard and be more inclined to hold out for it.
  • Canned foods can be warmed carefully to mouse temperature. Be careful to stir and check for hot spots. Warm food gives off more aromas. Only warm the new food!
  • A probiotic for cats can be sprinkled on foods as with the tuna.. first the old food and if the cat likes it then on the new food. As well as the health benefits of the probiotics it seems to be quite tasty to them.
  • Check your pet’s weight at the veterinary clinic once/week during the transition. This will help be sure that your pet isn’t losing weight. Or, if the transition is to a diet food, it will help ensure that your pet isn’t loosing weight too quickly.
  • If switching from dry food left out in a bowl, to canned food in meals, the cat may end up with a dish that's not as full as usual. Some cats don't like their whiskers to touch the edges of their bowl, so try feeding on a plate instead. This tip is supplied with thanks to Dr. Angie Robinson!

Hang in there and you’ll have a healthier pet on a better diet!

Dr. Liana Mawer