Dog Diarrhea: What You Need to Know
Written by Ellen Barber, Holly Ganz, PhD, & Dawn Kingsbury, DVM, PhD, DACVIM
Published on August 21, 2020
Sometimes diarrhea is actually normal. In both dogs and humans, diarrhea can be an effective way for the body to purge itself of a toxin or pathogen. But sometimes, especially if it lasts for more than 48 hours, diarrhea can be a sign of an underlying health problem. How do you know whether your dog’s loose poop is a normal reaction or an emergency? What’s really going on when your dog has diarrhea? Figuring out the true cause of dog diarrhea can be tricky, even for a specialist. Fortunately, a gut health analysis can often uncover vital clues.
Why Does Your Dog Have Diarrhea?
Loose stool can be a minor event or a serious condition. Diarrhea can be acute (meaning that it begins rather suddenly and lasts more than 48 hours) or chronic (lasting more than three weeks, sometimes varying in intensity from day to day). Sometimes the reason for it is obvious, but more often, the exact cause can be surprisingly difficult to identify. Here are some of the most common causes of diarrhea in dogs.
Something Your Dog Ate
In any case of digestive upset, it makes sense to look first at what your dog has been eating. A sudden change in your dog’s diet (for example, switching to a new food without a gradual transition period) can cause diarrhea. A food sensitivity or allergy is another possibility.
Dogs also have a well-known fondness for eating things that don’t belong to their intended diet. Dogs are scavengers, so it’s not unusual for them to consume prizes (like animal carcasses, garbage, and table scraps) that can lead to digestive upset. Diarrhea is an adaptation that helps scavenging animals get rid of the toxins and pathogens such material can contain. Getting into the human snacks or snarfing down a dead squirrel—more politely called a “dietary indiscretion”—is a very common cause of acute diarrhea in dogs.
In many of these cases, the diarrhea will resolve itself in a day or two, but if you believe your dog has eaten something poisonous (including chocolate), see your veterinarian immediately.
Also go straight to the veterinarian if you think your dog has ingested a toy or any other object. Such foreign bodies are another possible cause of diarrhea. Materials that your dog’s body can’t digest have the potential to create a blockage in the gastrointestinal (GI) tract, interfering with the motility (movement) of the digestive system. As a result, the tissues near the obstruction may stretch and become inflamed, allowing liquid stool to seep around the blockage.
Stress is another common reason for dogs to develop sudden diarrhea. In both humans and dogs, the body reacts to stress by releasing hormones and other chemicals that can disrupt the gut microbiome, the community of bacteria and other microbes that live in the GI tract. The stress trigger for a dog could be fireworks or dehydration or an injury. A dog who has been hit by a car, for example, will often display signs of shock that include diarrhea.
Exercise-related diarrhea is very common in dogs, but it’s typically a short-term effect and not abnormal. The mechanisms are the same as in a human athlete: when the muscles are working hard, the body sends more blood flow to the muscles, directing it away from other areas, like the digestive system. The result can be a reduction of up to 80% in the blood flow going to the tissues of the GI tract, which changes the permeability of the intestinal walls. That redistribution of blood flow also raises the core body temperature and produces fluctuations in certain hormones. All of these changes can contribute to acute diarrhea.
Exercising in hot weather is sometimes a sufficient cause in itself, since diarrhea and nausea are common reactions to overheating.
Parasites and Pathogens
Intestinal parasites—such as Giardia, tapeworms, hookworms, roundworms, and whipworms—are well-known to cause diarrhea in dogs. So are pathogens like the bacteria Clostridium difficile (C. diff), Clostridium perfringens, some strains of Escherichia coli (E. coli), and Campylobacter. You won’t be able to see bacterial pathogens, but some parasites may show up as white specks or grains in your dog’s stool. Take a sample to your veterinarian for parasite and pathogen screening. Keeping up-to-date with your dog’s monthly antiparasitic treatments is a good practice for preventing diarrhea.
Inflammatory Bowel Disease (IBD)
If your dog’s diarrhea lasts for more than three weeks (either continuously or intermittently) and especially if it’s accompanied by vomiting and loss of appetite, the culprit could be chronic inflammation in the GI tract. In this condition, called inflammatory bowel disease (IBD)—also known as chronic enteropathy (CE)—inflammation of the lining of the digestive tract interferes with its ability to digest food and absorb nutrients. IBD is also associated with disruption of the gut microbiome, with some bacterial populations growing too large and taking resources away from other kinds of bacteria, so that the gut no longer has the proper variety of organisms to function effectively.
Though the causes of IBD in any given case can be difficult to figure out, several potential treatments are available. According to the Merck Veterinary Manual, more than 50% of dogs with IBD respond to a diet change alone. And the bacterial imbalances in the gut microbiome associated with IBD can often be corrected, either by fecal transplant or with oral Gut Restore Supplements.
Sometimes diarrhea isn’t a result of something going on in the GI tract itself. Bacterial infections as well as infections caused by viruses—such as the canine parvovirus (parvo)—can lead to diarrhea. So can hormonal imbalances and even some cancers. Diarrhea may point to acute disease of the liver, pancreas, or kidneys. That’s why veterinarians typically suggest bloodwork when trying to diagnose a case of dog diarrhea.
Small Intestine vs. Large Intestine
Large Intestine Diarrhea
Large intestine diarrhea tends to involve more frequent poops. The stool is semi-formed and may contain mucus or flecks of blood. Urgency—sometimes leading to “accidents”—is a typical characteristic of large intestine diarrhea. You might notice your dog straining, looking painful, or trying repeatedly to poop without producing much. If the individual stool piles or puddles produced are smaller than your dog’s usual poops (even if they’re more frequent), the large intestine is probably the origin of the diarrhea.
Small Intestine Diarrhea
With small intestine diarrhea, the stool piles or puddles are typically larger than normal. That’s because inflammation in the small intestine interferes with that organ’s ability to absorb nutrients. Particles that would normally be absorbed by the small intestine instead pass on into the large intestine, pulling water along with them and creating a larger volume of poop.
Small intestine diarrhea tends to be less frequent, with no urgency and usually no visible blood. But because the small intestine is where most of your dog’s nutrients get absorbed, problems here can mean the body is missing out on a lot of the nutrition in your dog’s food. Small intestine diarrhea is more likely to be accompanied by vomiting, nutrient deficiencies, and weight loss.
What Else Is Your Dog’s Poop Telling You?
Your dog’s poop can provide a lot of useful clues. What’s “normal” will depend in part on diet, age, and other factors, but in general, a healthy dog’s poop should be medium brown in color and should not be too hard or too soft.
Ideally, your dog’s stool should be firm in consistency and have a segmented appearance. (If it’s hard and dry, your dog might have constipation.) You may think of diarrhea as watery puddles, but completely liquid poop is really just one end of the scale. Diarrhea can refer to a range of consistencies, from moist but distinct piles to shapeless blobs to puddles. To determine where your dog’s poop falls on the scale, check out our Fecal Scoring Chart.
Brown. Poop’s usual brown color comes from bile that gets picked up on the way through the GI tract. Dog poop that’s not brown might indicate a blocked bile duct or a liver disease that’s reducing the production of bile.
Yellow, gray. Yellow or gray poop can point to serious health issues, such as diseases of the liver, pancreas, or gallbladder. Such diseases can affect the amount of bile being produced and how the bile is being processed in the intestines. Yellow poop may also arise from a food sensitivity; excess mucus or fat can give poop a yellow hue.
Green. Green poops may mean your dog has been eating a lot of grass, possibly as a reaction to an upset stomach. Diseases of the liver or pancreas can also cause green poop. Or your dog might have eaten something that contained green food coloring.
Shiny/greasy. Poop with a shiny or oily-looking surface may contain excess mucus, which can be caused by inflammation of the large intestine. Greasy-looking poop may also indicate a malabsorption of nutrients, especially fat, as may occur when the pancreas isn’t functioning well.
Pale, clay-colored. A diet that’s too high in calcium can cause light-colored stool. Pale or clay-colored poop may also indicate problems with the digestion of fats, usually due to a lack of bile.
Blue. Blue poop should always be treated as an emergency, because it may indicate ingestion of rat poison. If your dog’s poop is blue, take a sample along and seek urgent care immediately.
Pink, purple, “raspberry jam.” Pink, purple, or “raspberry jam” poop may indicate Hemorrhagic Gastroenteritis (HGE), which causes vomiting and bloody diarrhea. Most often occurring in smaller breeds, HGE requires prompt medical attention. However, eating beets (which are totally benign) can also cause pink poop.
Red streaks. Visible red blood in your dog’s stool usually indicates bleeding in the lower GI tract, which can result from injury or inflammation. Infectious diseases like Parvovirus, anal gland sac infections, and parasites like whipworms and hookworms are all possible causes. An ingested foreign object scraping the intestinal lining on its way out can also cause bleeding.
Black. Stool that is very dark or black may contain digested blood, possibly from ulcers in the stomach or small intestine. (Nonsteroidal anti-inflammatory drugs are the most common cause of ulcers in dogs.)
When to See a Veterinarian
Seek veterinary care immediately if your dog’s diarrhea is accompanied by any of the following factors:
- Loss of appetite
- Apparent abdominal pain
- Repeated vomiting
- Unproductive retching
- Large amounts of blood in the stool
- Ingestion of rat poison (or any other poison)
Eating a toy, glove, bag, or any other foreign object should also be treated as an emergency, since obstruction of your dog’s GI tract may require prompt surgical intervention.
In an adult dog, if diarrhea is the only symptom, you can wait a couple of days to see whether the episode will resolve on its own. But visit your veterinarian if the diarrhea persists for more than three days, since it may indicate an underlying health condition.
Take along a fresh sample of your dog’s poop so that your veterinarian can test it for parasites and pathogens. Veterinarians tell us that about 50% of the time, such tests can identify potential causes of chronic diarrhea.
If the screening is negative for parasites and pathogens, your veterinarian may suggest a dietary trial to test whether the diarrhea is related to a food sensitivity. An elimination diet is the gold standard for identifying which foods are acting as triggers. (While some pet parents also find food allergy testing to be helpful, research published in the Journal of the American Veterinary Medical Association has shown that many of these tests have a high false positive rate, and additional studies have found hair and saliva tests to be unreliable for identifying allergies.)
Puppies are a special case. Their immune systems aren’t mature yet, so they’re more susceptible to pathogens (like parvo) and parasites than adult dogs. Also, their small size puts puppies at greater risk of dehydration when they have diarrhea. Don’t wait longer than 72 hours to see your veterinarian if your puppy has diarrhea without any other symptoms. And if the diarrhea is combined with extreme tiredness, refusal to eat or drink, or signs of distress, take your puppy to a veterinarian right away.
Lactating Mother Dogs
Is your dog a new mother? Nursing puppies can actually be a cause of diarrhea in a mother dog. That’s because she has to take in a tremendous amount of calories to produce all that nutrition for her puppies, and that increased volume of food can cause changes in the mother dog’s own digestion. In fact, lactation is the single greatest energy demand experienced by a dog. In addition to encouraging breeding females to drink water, supplementation with the probiotic yeast Saccharomyces boulardii may be helpful to resolve diarrhea that arises after whelping.
Tips for Stopping Your Dog’s Diarrhea
Occasional, “normal” diarrhea often resolves itself in a day or two, but you may be able to help your dog feel better faster with one or more home remedies. If you’ve determined that your dog’s diarrhea isn’t an emergency, and it isn’t accompanied by any other symptoms, here are some tips for stopping it safely on your own.
Unless your veterinarian prescribes it, avoid using any kind of drug or medication.
Withhold Food (Briefly)
Fasting your dog for 6 to 12 hours can give the gut a chance to rest and heal. Provide plenty of fresh water, and reintroduce food very gradually, perhaps starting with broth. (Don’t withhold food for more than 24 hours, and never fast a puppy.) Diarrhea caused by material moving too quickly through the GI tract often responds well to a brief period of fasting.
Feed a Bland Diet
You can help your dog’s gut recover by feeding something that’s bland and easy to digest, such as boiled chicken mixed with cooked white rice. A simple broth is especially soothing and can be made with just a few ingredients.
Add Some Fiber
A little inulin or psyllium husk powder added to your dog’s food can help in two ways. These fiber supplements help absorb excess water in the large intestine to form more solid stools, and they act as prebiotics, meaning that they support healthy digestion by nourishing the beneficial bacteria that live in the colon. Another prebiotic, MOS (mannan-oligosaccharide) stimulates the immune system, binds pathogens and mycotoxins, and feeds beneficial bacteria in the gut.
Restore the Bacterial Community in your Dog’s Gut Microbiome
Just like humans, dogs depend on bacteria in the gastrointestinal tract to digest their food and extract its nutrients. But a diverse, well-balanced bacterial community in the gut benefits your dog in many other ways, especially by supporting the immune system. When some of these beneficial GI bacteria populations are missing, important digestive and immune functions may no longer work properly. More than 50% of all dogs will suffer from a medical condition related to a microbiome imbalance at some point in their lives. But replenishing those missing bacterial populations can often resolve diarrhea quickly by restoring a healthy balance to your dog’s microbiome.
Unless your veterinarian prescribes it, avoid using any kind of drug or medication. The antibiotics metronidazole and tylosin, for example, are important tools for treating severe chronic diarrhea, but they may not be appropriate for acute diarrhea. Giving your dog unnecessary or inappropriate antibiotics can actually cause or worsen diarrhea by disrupting the gut microbiome, since antibiotics kill off a lot of beneficial bacteria along with the disease-causing strains they target.
Also, never give human diarrhea remedies to a dog. These over-the-counter products contain ingredients that are dangerous and even potentially fatal for dogs. Certain breeds may be especially sensitive to these medications. Border Collies, Australian Shepherds, and other herding breeds, for example, have a genetic mutation that makes them more susceptible to the toxic qualities of certain drugs, including the common antidiarrheal agent loperamide (Imodium®).
Gut Health Testing
A Gut Health Test can tell you a lot about what’s going on in your dog’s digestive system and even how to correct certain problems. By identifying all the different kinds of bacteria in your dog’s gut, microbiome testing can determine whether those different bacterial populations are present in balanced amounts when compared to the gut bacteria of healthy dogs. Those correct proportions are the key to a thriving, well-balanced microbiome.
Bacteria belonging to the genus Escherichia (a group that includes E. coli), for example, are beneficial members of the community when they make up less than 5% of a dog’s gut microbiome. But an overgrowth of Escherichia can cause diarrhea and other digestive issues. Bacteriophages (viruses that infect and kill certain strains of bacteria) that specifically target pathogenic strains of E. coli (such as PreforPro) can help to bring the digestive tract into better balance. The journal Antibiotics recently reported that such bacteriophages provide an effective alternative to antibiotic use in medical practice.
The Fusobacterium genus is also present in most healthy dogs. When these bacteria are missing, digestion can suffer, but high levels of Fusobacterium are also associated with digestive issues, particularly diarrhea, so moderation is key. Bacteria in the Fusobacterium family do best in protein-rich environments, so if your dog’s Gut Health Test shows a deficiency in this kind of bacteria, increasing the protein content of their diet may help. If the test shows that Fusobacterium levels are high, the addition of a small amount of prebiotic fiber (like inulin or psyllium husk) to the diet can help bring these levels down by supporting bacteria in the gut that make molecules that help fight inflammation.
A Gut Health Test can even offer clues about the underlying reason for a dog’s diarrhea. Low levels of Coprococcus and Oscillospira bacteria in the gut, for example, are often observed in dogs with food allergies. Deficiencies in Faecalibacterium have been associated with IBD in dogs.
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