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My dog has diarrhea after switching food. Is a grain allergy possible?

Updated On September 23rd, 2025

Pet's info: Dog | Boxer | Male | unneutered | 3 months and 23 days old | 87 lbs

We switched our dogs from the Merrick grain free dry dog food to the canidae all breeds all life stages dry dog food and Declan has the runs pretty bad we did the transition it's been about two and a half weeks is it possible he could have a grain allergy

3 Answers

Most Helpful Answer

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Answered By Makenzie Kurth, DVM

Veterinarian

Published on March 30th, 2018

Thanks for using Petco Pet Education Center, formerly Petcoach! I’m sorry to hear about little Declan! Just to be clear, if you did the transition to the new food slowly over a few days and he was fine for say, 10-14 days, then suddenly got diarrhea, it is unlikely to be related to the food. (PS, few dogs actually are allergic to grain, it’s more likely to be the beef or chicken.) If you switched all of a sudden (one day merrick, next day candidae) two weeks ago and he’s still having diarrhea that could be the cause. Other things that cause diarrhea: eating something naughty (garbage, a toy, underwear, etc), eating a new treat or people food, intestinal worms, stress, excitement, others. Try a bland diet (half plain boiled/canned chicken half plain cooked white rice) for a few days and I expect the diarrhea to improve after 1-3 days. (Then transition back to her regular diet slowly over 3-5 days.) If at ANY time Declan is lethargic, vomiting, not wanting to eat, or you have other concerns, you need to go to the vet clinic right away to make sure it’s nothing more serious. Best of luck to you and Declan!

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Other Answers

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    Answered By Jessica Keay, DVM

    Veterinarian

    Published on August 23rd, 2017

    Some dogs have very sensitive digestive tracts and any change in diet can cause some diarrhea. If you didn't do the diet change gradually over several weeks time then it is possible the diarrhea was caused by the abrupt change in diet. If you would like to try changing Chloe's diet again I would recommend doing it very gradually by mixing in small amounts of the new food in with her old food at first, then gradually increasing the amount of new food and decreasing the amount of old food over several weeks. It is possible she could have GI upset from grains but it is also possible there was a different protein source or preservative that disagreed with her. You can compare the ingredients on the food labels to look for the differences if she has diarrhea again.

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    Answered By Daniel Fonza, DVM

    Veterinarian

    Published on August 5th, 2017

    Thank you for your post! Switching from a different food without transitioning over a 5-7 day period can certainly cause dietary indiscretion / GI upset. I wouldn't necessarily say that grains are what caused the diarrhea at this point in time. I would give it some time for a smooth transition before concluding that the grains are the cause. It may also be the type of food (brand) and maybe Chloe is having a sensitivity to that particular brand? You could always switch to a different brand and see if that helps as well. I like Science Diet, Royal Canin, Natural Balance and Eukanuba. Let me know if you have any further questions / concerns

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