Sometimes diarrhea is actually a normal response. It 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.
What’s really going on when your dog has diarrhea? How do you know whether your dog’s loose poop is a normal reaction, an emergency, or could lead to secondary health concerns? Figuring out the true cause of dog diarrhea can be complex. That’s why your veterinarian will likely ask you many questions about your dog, their history and signs, and their poop.
Why does your dog have diarrhea?
Loose stool can be a minor event or a serious condition. Diarrhea can be acute (meaning it’s somewhat recent) or chronic (lasts for a longer time, though the intensity and frequency can vary 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 ingest material (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 eating material from animal carcasses—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, bone, 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 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 why dogs may develop sudden diarrhea. In both humans and dogs, the body reacts to stress by releasing hormones and other chemicals that can cause inflammation, increase intestinal emptying rate, and/or disrupt the gut microbiome, the community of bacteria and other microbes that live in the GI tract. The stress trigger for an individual dog can vary from fireworks to a car ride to new visitors in the home.
Exercise-related diarrhea is 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. Heatstroke can occur when exercising (or even sitting) in hot weather and is a serious, emergency medical condition.
Parasites and pathogens
Intestinal parasites—such as Giardia, hookworms, roundworms, and whipworms—are well-known to cause diarrhea in dogs. So are pathogens like the bacteria Clostridium perfringens, some strains of Escherichia coli (E. coli), Campylobacter, or Salmonella.
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. Did you know that most heartworm preventatives contain medications to treat or prevent intestinal parasites? Keeping up-to-date with your dog’s monthly antiparasitic treatments is a good practice for reducing the risk of diarrhea.
Inflammatory Bowel Disease (IBD)
If your dog’s diarrhea is chronic (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 targeted diet change alone. And the bacterial imbalances in the gut microbiome associated with IBD can often be corrected by the diet change alone or by fecal transplant.
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 be the result of acute disease of the liver, pancreas, or kidneys. That’s why veterinarians may suggest bloodwork when trying to diagnose a case of dog diarrhea.
Types of diarrhea in dogs
Clues about your dog’s poop can tell your veterinarian about what type of diarrhea your dog has and what the cause might be.
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 pained, 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 frank (red) 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.
When to see a veterinarian
Seek veterinary care immediately if your dog’s diarrhea is accompanied by any of the following:
- Lethargy, weakness, or collapse
- Loss of appetite
- Apparent abdominal pain
- Repeated vomiting
- Unproductive retching
- Large amounts of blood in the stool (red or digested, black, tarry blood)
- Ingestion of medication, poison, or toxic foods
- Pale, blue, or tacky gums
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 sign, you may choose to 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 or worsens, since it may indicate an underlying health condition.
Take along a fresh sample of your dog’s stool so that your veterinarian can test it for parasites and pathogens.
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.)
Diarrhea in puppies is a special case. Their immune systems aren’t mature yet, and they may not be fully vaccinated, so they’re more susceptible to pathogens (like parvovirus) 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 24 hours to see your veterinarian if your puppy has diarrhea without any other signs. 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.
How to stop 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 and your veterinary team have determined that your dog’s diarrhea isn’t an emergency, and it isn’t accompanied by any other signs (or known medical conditions), here are some tips for stopping it safely on your own.
1. 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 low-salt broth. (Don’t withhold food for more than 24 hours, as withholding food for an extended period of time can actually be detrimental to GI health. Never fast a puppy.) Diarrhea caused by material moving too quickly through the GI tract often responds well to a brief period of fasting.
2. 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. (Rice can also help firm up loose stool by absorbing water as it passes through the digestive tract.) A simple broth is especially soothing and can be made with just a few ingredients. Be sure to consider any known food sensitivities or other medical conditions (like diabetes) when choosing a bland diet.
3. 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.
4. Restore the bacterial community in your dog’s gut microbiome
Dogs depend on bacteria in the gastrointestinal tract to help digest their food, extract its nutrients, and complete other functions, such as processing bile acids. A diverse, well-balanced bacterial community in the gut can also support the immune system. When some of these beneficial GI bacteria populations are missing, important digestive and immune functions may no longer work properly.
For example, bacteria from the Fusobacterium genus are present in most healthy dogs. When these bacteria are missing, digestion can suffer. Bacteria in the Fusobacterium group do best in protein-rich environments, so increasing the protein content of their diet may help some dogs.
High-protein diets may not be appropriate for all dogs (such as dogs with kidney disease), so be sure to consult with your veterinarian before making any diet changes. Additionally, high levels of Fusobacterium are also associated with digestive issues, particularly diarrhea, so moderation of their number is key.
Often, time, diet change, or treating an underlying medical condition is enough to rebalance the bacterial population and increase its diversity. However, a small number of dogs may require fecal transplantation as a treatment. Speak with your veterinarian regarding unresponsive diarrhea and different fecal transplant options.
5. Use medications, supplements, or herbal treatments wisely
Unless your veterinarian prescribes or recommends it, avoid using any kind of drug, medication, supplement, or herbal remedy. The antibiotics metronidazole and tylosin, for example, are important tools for treating severe chronic diarrhea, but they may not be appropriate for all cases of 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. Many Border Collies, Australian Shepherds, and other herding breeds, for example, have a genetic variant that makes them more susceptible to the toxic qualities of certain drugs, including the common antidiarrheal agent loperamide (Imodium®).
This article was adapted from content written by our partners at AnimalBiome.