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Puppy won't eat old food. Can I instantly switch to new puppy food?

Updated on September 23rd, 2025

Pet's info: Dog | Saint Bernard | Female | unspayed | 2 months and 2 days old | 13 lbs

I recently got a new dog food (Wellness CORE Grain-Free Puppy Food) for my 9 week old St. Bernard puppy because she didn't seem to like her old food (Nature's Domain Puppy Formula). I read it's good to gradually switch food with an increasing percentage of new food every couple of days. But if she is refusing to eat, is it okay to instantly switch her to her new food if she will eat all of that?

4 Answers

Most Helpful Answer

Answered By Dr. Heidi DVM, CVA, CCRT, CVTP, CVSMT, CVCH

Veterinarian, Certified Veterinary Acupuncturist, Certified Canine Rehabilitation Practitioner

Published on February 14th, 2018

The problem with changing foods too quickly is that dogs can get GI upset (especially diarrhea) with a sudden diet change. If a dog is not eating the old food anymore, sometimes we will use a bland diet (1/2 cooked white rice and 1/2 cooked white meat chicken without any skin or bones) as the other food to mix with the new food to allow for a gradual diet change to the new food to (hopefully) prevent any GI upset, so you might consider that option.
Good luck! I hope that was helpful. Thanks for using Petco Pet Education Center, formerly Petcoach.

2Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Dr. Melanie, BVSc MS
Veterinarian
Published on February 10th, 2019
Switching should be done slowly. Start by mixing 75% old food and 25% new food, and feeding that to Milo for a couple of days. Then do a 50/50 mixture, and again feed it for a couple of days. After that, a 25% old food and 75% new food mixture should be fed for a couple of days. Finally, he can have the new food only. I hope this helps!
1Pet Parents found this answer helpful
Answered By Jessica Keay, DVM
Veterinarian
Published on August 3rd, 2017
Usually it is best to do a gradual change to a new food. This is accomplished by mixing the old and new foods together at each feeding, starting with more of the old food and just a little of the new food and gradually changing the ratio until at the end of the week you have mostly the new food and just a small amount of the old food. This will help your dog get used to the new food's flavor and also hopefully help avoid stomach upset due to the change in diet.
1Pet Parents found this answer helpful
Answered By Destini R. Holloway, DVM
Veterinarian
Published on May 7th, 2020
It may upset his stomach a little, but yes I would go ahead and feed him what you have. An upset stomach may occur, but you can give him a probiotic to hopefully help him tolerate the sudden switch. Over the counter Culturelle can be given to dogs and works almost as well as the pet formulated ones (i.e. Fortiflora or Proviable).
Best of luck with your puppy and I hope that he likes and tolerates his new food ok. Take care.
1Pet Parents found this answer helpful

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