Stories from My Diary-rrhea (part III): Acute Large Intestinal Diarrhea (Acute Colitis)

by Dr. Laci, aka, Dr. Poop

Now that we've covered acute small intestinal diarrhea, let's talk about acute large intestinal diarrhea, aka, acute colitis.

Large intestinal diarrhea (both acute and chronic) is often seen in young or debilitated dogs. 

A closer look at acute large intestinal diarrhea tells us it is acute nonspecific inflammation of the colon. The inflammation causes mucosal damage which results in bleeding.

The blood seen with colitis is bright red, unlike the darker to black digested blood seen when the small bowel is the injured gut. 

The main functions of the large intestine are storage of fecal material and absorption of water.  When either of these is not working properly, the result is failure to store stool (increased urgency in defecation) and soft to watery stools.

Indicators that your dog is suffering from large bowel, not small bowel diarrhea: 
  • semi-formed to liquid feces
  • fresh blood or mucous in stool
  • increased frequency of defecation (six or more times daily)
  • straining, an urgent need to go
  • and no weight loss.
Poopy dog

Patients don't lose weight like they do with small intestinal diarrhea because the small intestine is the one responsible for more absorption of nutrients.  With large bowel diarrhea, the pet is still getting the vitamins and minerals needed for the most part and therefore, they aren't dropping pounds when they have large bowel diarrhea.

The good news about acute large intestinal diarrhea is that it is easier to break down and diagnose than other causes we have talked about so far. 

In fact, far more than 50% of the cases I have treated of acute large bowel diarrhea have parasitic or dietary causes.

Where I start as the veterinarian is with a thorough history.

Things you will be asked about include any medications your pet is on, dietary indiscretion (potential of eating spoiled food or foreign objects, dietary allergy or intolerance (less likely to be an acute cause, but possible with a food change), contact with other animals , and the pet is exposed to stressful situations which could predispose him/her to bacterial overgrowth.

If supportive treatment (withholding food then reintroduction with bland food) has failed and you find yourself at your vet's office, fecal tests are likely to be a starting point.

Unfortunately, there is more than one type of fecal test, and some parasites, like whipworms, shed infrequently, so your dog could be infected with whipworms and the test be negative if the worm wasn't shedding eggs at the time of the test.

The different types of fecal tests are direct smears, fecal floatation, tests specific for specific parasites (Giardia being an example), rectal cytology, and even fecal cultures.
Which tests are most appropriate for your dog will be determined by your veterinarian.

If your dog is otherwise clinically ill or your veterinarian finds abnormalities on the physical exam, even further diagnostics may be needed.  

If your vet requests to do these tests (such as a blood cell count and chemistry panel) they are trying to rule out causes of diarrhea that are non-GI in origin, or affecting the GI tract and causing the side effect of diarrhea when their is a more severe systemic disease occurring.

In summary, here is a list of some of causes of acute colitis:
  • whipworms (Trichuris vulpis)
  • garbage gut
  • Coccidia spp.
  • Giardia spp.
  • bacterial causes (Clostridium perfringens, E. coli, Salmonella, Campylobacter spp)
  • and food-induced allergic colitis
Like I promised, an easier list to sort from. Please keep in mind that multiple fecal tests may be needed, and some fecal tests may need to be repeated to try and catch those sneaky intermittent parasites. Try not to be frustrated with your vet; it is a frustrating place to be in when don't have the answers for you.

The good news is most cases of acute colitis will be solved and resolved within 72 hours.

Related articles:
A Tale of Many Tails—and What Came Out From Underneath Stories from My Diary-rrhea (part I)
Acute Small Intestinal Diarrhea
Acute Large Intestinal Diarrhea (Acute Colitis)
hronic Large Intestinal Diarrhea
Chronic Small Intestinal Diarrhea

Laci Schaible has always been an animal lover and wanted to be a veterinarian since the third grade. Eager to actualize her dreams, she left home and started college with a full scholarship at the age of 16. She graduated with honors at the age of 19, and then became one of the youngest U.S. trained veterinarians in history when she graduated with her D.V.M. at the age of 23 from Texas A&M University.

After practicing as an associate at an emergency / referral and general practice small animal hospital, she was anxious to lead and manage her own hospital, which she successfully did for years. Performing surgeries with her husband Jed (also a vet) is one of her favorite aspects of practice.

Together, after losing their beloved family dog Madison to terminal cancer, Laci and Jed realized the need for pet owners to have affordable unbiased guidance for their pet's health care beyond their veterinarian with office hours. 

Jed's entrepreneurial genes and Laci's creative passion motivated them to fill this need, and was born.  Check out their blog for a mix of pet health advice, funny stories from the vet perspective, and even cool video blogs from Dr. Jed!

You can also follow Dr. Laci on Twitter  or VetLive on Twitter  or Facebook.


  1. By maintaining a good healthy food for our pets we can improve the health condition of them. Since they cannot express themselves it is better to take precaution rather than Cure.


  3. It is certainly true that prevention is always ideal. If we only lived in an ideal world!

  4. My 3 year old rottweiler Precious, has been sick since the 29th of December 2010. This all started with loose stools which i thought was a bout of diarrhea after we overfed precious at the christmas lunch. however precious has been going to the vet and given different medications only to seem to improve for some time and than relapses. he has also been operated as the vet suspected he might have swollowed something which was not visible tru x rays. no foreign body was found and i was told that his intestines and colon where very inflamed. rodogyl was given to him after the operation where precious seemed fine for a while only to start straining again unproductivlely or to pass a little lose stools. whenever we go on walks.Precious has been given entroxl, metronidazole, rodogyl and most recently salazopyrin. Precious remains undiagnosed until today when he has been prescribed Prednisolone. I am extremely scared of the situation, vets are scared to get close to him which makes it more difficult for him to be checked without being sedated. can anyone tell me if they passed tru the same experience? i have just read that this could be large intestinal diarrhea. what is this and what is the treatment? all the way precious has been eating only Hills ID prescription diet. thanks and regards marthese from malta

  5. Hi Marthese,

    so sorry about your baby! (((hugs)))

    Ok, since you made it all the way to exploratory surgery, I assume you checked for parasites and infections?

    Are there any other symptoms present, e.g. vomiting, loss of appetite, lethargy, swollen abdomen ...?

    One thing that would be worth considering are food allergies. Jasmine had undiagnosed stool trouble for years, before she was finally diagnosed with Inflammatory Bowel Disease, caused by food allergies, nobody thought of until then. She was on Hills i/d also and guess what? It contains chicken, eggs and other ingredients which are the most likely food allergens.

    Jasmine was also put on antibiotics from time to time and they would also always temporarily help. The only long term solution for her was change in diet and later inclusion of TCVM (Traditional Chinese Veterinary Medicine).

    Since it sounds to me that your vet ran all the diagnostics he could think of, I would start with elimination diet trial.

    Most common bland diet to settle upset stomachs is usually chicken and rice. However, chicken (and rice also I think) is in the i/d. For elimination diet trial you want to use novel ingredients (ingredients your dog never had before). Fish, if fish wasn't fed before, emu, rabbit ... whatever you can acquire easiest. For carbohydrate you could maybe try millet, barley or oats (unless he had it before).

    If food allergy is at the bottom of this you should see the difference quite quickly.

    Did your vet do a scraping/tissue biopsy while he was in to determine the source of the inflammation?

    What tests/diagnostics had been done?

  6. Hi and thanks for yr fast reply. Apart from this problem, Precious remains his usual self. He loves his eating time, his walks and drives,His rough and tough play and gets all the cuddles and kisses he can get. He did lose a little weight but seems to be stronger than ever in his pull. I asked for a scraping tissue biopsy during surgery but i was told that the intestines were so inflamed that they wouldn't heal if a scraping was done so no biopsy was done. I also asked for stool sampling tests but was told that would not help. I have been to 2 different vets and they both say their greatest fear is getting close to him so this is a very frustrating situation for me. I don't know the specific tests but today after the vet prescribed 20mg of prednisolone on the phone I asked if further testing need to be done and he said all the necessary testing was done when he was opened up.(Precious weighs 40kilos) I have tried Hill's ZD diet but precious totally refused to eat it and preferred to starve himself. Can I cook for him? what other food dried and tinned can I buy besides zd? would any other ingredients he hadn't eaten before help? I would gladly cook for him if it helps.
    while I write to you he is sleeping soundly, snoring right here beside me. He's such a beautiful, happy dog I'm so sad he got unhealthy. Thanks, Marthese in Malta

  7. Is jasmine the lovely lady rottie on this page? I send her a hug and a big kiss from my Precious. I'm glad she got better :-)regards marthese

  8. Hi Marthese.

    Nope, you can see Jasmine's pictures here:

    Hm, it's too bad that the vets are afraid, did anybody considering using a fabric muzzle?

    Inflammation does have to have a cause, whatever the cause may be. The prednisone will help with the inflammation, but not with what's causing it.

    The causes for inflammation can be many, from parasites or bacterial infections to allergies or autoimmune disease.

    Since the antibiotics didn't help and the vets started the prednisone, I assume they ruled out infections.

    I think that home cooked trial elimination diet might help to settle things down and also help to determine whether food allergies could be behind this.

    I don't blame Precious for not wanting to touch z/d, Jasmine wouldn't come anywhere near it either.

    I'd try the home-cooked bland diet for a few days and see how it goes. Try novel ingredients, just boiled, you can even run them through a food processor a bit to make it more digestible.

    See if that makes any difference. If it helps, then you need to look for a good home-cooked balanced recipe or for a dog food that also doesn't contain any ingredients Precious had before, particularly meat and grains.

    I would also ask the vet what they think about adding some probiotic. This could also help the intestinal bacteria to balance.


  9. Hi Marthese,

    did you try the new diet? Any improvement?

  10. Hi jana, I've tried royal canine hypo allergenic diet and precious loved it. It could be because he is getting so hungry with the prednisolone.However he hasn't got any better. His stools are yellowish and turned very lose again. I'm not even going to work as I'm scared to leave him on his own.This morning the vet came to visit, he found out precious is not so scary at home after all. He wanted to start him on prifinial chien, but I'm scared to use it as am afraid if any virus or bacteria is inside precious this medicine will make it worse. Precious is now on flagyl 400mg twice a day and am tailing him off the prednisolone. I requested a fecal test and this will be done tomorrow. I talked to the vet about jasmine and her irritable bowel disease and he asked what worked for her besides the elimination diet. I am complety lost, exhausted and mostly scared that im going to lose my baby :(((
    regards marthese in malta

  11. Hi Marthese

    So sorry Precious isn't doing well :-( You'd think that the prednisone would settle the inflammation regardless of the cause.

    What worked for Jasmine WAS the elimination home-cooked diet, as her IBD (esionopholic gastroenteritis) was determined to be caused by food allergies. The other thing that improved situation was TCVM herbs.

    Did you try the bland home-cooked food at all? I still think that it is easier on the GI tract than any kibble could be.

    Good that you're going to do the fecal, it is important to rule out parasites and if bacterial to determine exactly what species that is.

    I'd figure that prednisone would have settled autoimmune, at least to some degree.


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