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My cat has diarrhea with blood after new food. Is it serious?

Updated On September 23rd, 2025

Pet's info: Cat | Domestic Shorthair | Female | spayed | 11 lbs

Cat having diarrhea. Very healthy, vet changed diet 3 weeks ago, diarrhea started last night. Some blood in stool, runny. Been 14 hours, still runny, no blood, yellowish tint. Still hungry, and still drinking water and urinating. Appears to be acting just a little less than normal, but not alarmingly different. Is it just a bug? Should I give it more time. She's an indoor cat, clean home, just had blood work done a month ago, everything came back healthy!

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4 Answers

Most Helpful Answer

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Answered By Daniel Fonza, DVM

Veterinarian

Published on December 17th, 2017

Hi there and thank you for using Petco Pet Education Center, formerly Petcoach to address your concerns. If you have been on a new diet for 3 weeks, I would recommend switching to a different diet such as a hydrolyzed protein diet or novel protein diet (a food which contains a meat protein Sweets has never had before). The hydrolyzed diet is prescription but cats with GI issues related to food respond quite well to hydrolyzed protein diets. I would also consider adding a probiotic to the food such as Purina Fortiflora to see if this helps. If there is still no improvement, I would recommend having a veterinarian examine Sweets so that the most appropriate diagnostic and treatment recommendations can be made. I hope this helps! Please let me know if you have any other questions or concerns and I would be more than happy to help you further.

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Other Answers

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    Answered By Jenna Beyer, DVM, MBA, cVMA

    Veterinarian, Certified Veterinary Acupuncturist

    Published on August 8th, 2017

    You're correct, changing food suddenly on a pet can definitely cause diarrhea. This type of diarrhea will usually resolve on its own in 24-48 hours, but it may be better if you go back to the original food and slowly transition him over 3 weeks. However, there are other possible causes for the diarrhea, including food allergies, intestinal parasites, bacterial or viral gastroenteritis. These may need treatment by a veterinarian. You can try an over the counter pet dewormer. You could also try a bland diet of boiled chicken breast and cooked white rice. If the diarrhea isn't gone, or if additional symptoms develop in 48 hours, Bear should see the vet. Kittens can get dehydrated very quickly.

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    Answered By Christina Kellogg, DVM

    Veterinarian

    Published on May 25th, 2017

    Lydia could have developed gastroenteritis (inflammation of the stomach and intestines) if you switched her to a new diet too abruptly. I usually recommend transitioning them to any new diet by mixing in the new diet with their old over at least a period of one week, or longer if they have sensitive GI tracts. If Lydia is still bright and happy, you could try offering her only a bland diet consisting of boiled chicken and boiled rice for 24 to 48 hours. If Lydia has returned to normal, you can start to very slowly mix in the new diet with the bland Diet over a period of about one week. You should do this by gradually increasing the amount of her new food while also gradually decreasing the amount of the bland diet. However, if Lydia continues to vomit or is lethargic (no energy, sleepy), I would recommend having Lydia evaluated by a veterinarian to rule out other causes of vomiting such as a foreign body/G.I. obstruction, parasites, and systemic diseases like kidney disease. Hope that Lydia feels better soon. Best of luck to you both.

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    Answered By David Darvishian

    Veterinarian

    Published on August 31st, 2017

    Hi and thanks for using Petco Pet Education Center, formerly Petcoach! Sorry to hear about Bella. Most commonly problems like this occur due to intestinal parasite infections (worms and small protozoan parasites) and dietary changes which occur too quickly. Other reasons could be a foreign object ingestion causing irritation and functional problems in the gut or a dietary indiscretion where she ate something not intended for her. There are many other reasons but these are the most common. If this continues, you will need to have her evaluated by your vet. Take all previous medical records with you. Your vet will take a detailed history and then do a physical exam. After that they may advise some tests like fecal/blood tests, and possibly x-rays to confirm a suspicion. Once a diagnosis is made, a sound treatment plan can be discussed and implemented. Your vet can also advise you on preventive health care including vaccines, deworming, flea/tick control, heartworm prevention, nutrition, etc. Good luck with Bella. Remember any problem that persists or worsens always needs to be evaluated by your vet. It's better to intervene early since the longer a problem persists, the longer and more expensive the treatment becomes and the harder to clear problems up.

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