Do dogs and cats need probiotics for gut health?

A healthy dog or cat eating a complete diet does not need a probiotic. Veterinary nutritionists at Tufts put it plainly: there is not yet evidence that probiotic supplements improve overall wellness in otherwise healthy animals. The better case for them is narrower, in cats given antibiotics or living in shelters, and even there the effect is modest and depends on the exact strain.

The gut microbiome in brief

The intestines of dogs and cats carry very large numbers of bacteria and other microorganisms, known together as the gut microbiome. These microbes ferment fiber the animal cannot digest, producing short-chain fatty acids that feed the cells lining the colon, and they interact constantly with the immune tissue in the gut wall. Diet, age, medication and illness all change which microbes thrive.

Research has found differences in gut bacteria between lean and overweight animals, and between healthy and sick ones. The Tufts Petfoodology team notes that many of the striking benefits of changing the microbiome come from studies in mice and rats, and that trials in people and pets have usually shown much less. Finding a difference is not the same as knowing which bacteria to add, or how many.

Digestive signs that need a vet

Probiotics are often sold for symptoms that have many possible causes, including parasites, dietary indiscretion, food intolerance, infection, pancreatitis and chronic enteropathy. Settle the cause before reaching for a supplement. See a vet promptly for:

• Diarrhea lasting more than a day or two, or coming back repeatedly
• Blood in the stool, or black, tarry stool
• Repeated vomiting, or vomiting with diarrhea
• Weight loss, poor appetite or lethargy alongside digestive signs
• Any diarrhea in a young puppy or kitten, an elderly animal or one with other illness

A single soft stool after a new treat, with a bright animal that is eating normally, can usually be watched for a day.

What probiotics are, and why the strain matters

A probiotic is a live microorganism that, given in adequate amounts, benefits the animal taking it. The label gives the genus and species, and ideally a strain code, plus a count in colony-forming units (CFU).

That strain code carries more weight than it seems. Tufts points out that results in animal studies are often strain-specific, so a benefit found with one product at one dose in one species may not appear with a different product, even one listing the same species. Many products on the shelf have no published trial of their own.

Quality control is a second problem. When a Canadian veterinary team tested 25 commercial probiotics sold for animals, only 4 of the 15 products that claimed a specific count of live organisms met or exceeded it, and only 2 of those had labels that described the contents properly. Some had misspelled organism names. An older study by the same group found that none of 19 dry pet foods advertising probiotics contained all the organisms listed. Tufts adds that there is no evidence foods with added probiotics benefit pets compared with foods without them, and recommends a concentrated supplement with independent quality testing, chosen with a vet.

Where the evidence is

Sudden diarrhea in dogs

Diarrhea is the most studied use of probiotics in pets, Tufts notes, yet for sudden diarrhea in dogs the evidence is weaker than marketing suggests. A 2024 systematic review, carried out to build European treatment guidelines, pooled randomized trials of probiotics, prebiotics and synbiotics in dogs with acute diarrhea. These products did not shorten diarrhea by a clinically meaningful amount, though the certainty of the evidence was very low to moderate. No adverse effects were reported. The same review found, with high certainty, that antibiotics made no clinically relevant difference in dogs with mild or moderate acute diarrhea.

Cats in shelters

In a blinded, placebo-controlled trial in an animal shelter, cats given Enterococcus faecium SF68 were less likely to have diarrhea lasting two days or more: 7.4% compared with 20.7% on placebo. No difference was found in the shelter's dogs, but diarrhea was uncommon in both dog groups, so the study says little either way about dogs.

Cats on antibiotics

Amoxicillin-clavulanate can cause vomiting or diarrhea in cats. In a small trial in laboratory cats given the drug for a week, those also fed SF68 had lower total diarrhea scores than cats on placebo, and the most severe stool scores appeared only in the placebo group. Most cats in both groups still had some loose stools. The probiotic softened the problem rather than preventing it.

Chronic gut disease

For inflammatory bowel disease and other chronic enteropathies, Tufts describes probiotics as a potential use rather than an established one. A probiotic can be part of a plan a vet builds around diet and, where needed, medication. It does not replace a diagnosis.

Saccharomyces boulardii, a yeast rather than a bacterium, is sometimes chosen alongside antibiotics because antibacterial drugs do not act on yeasts, although published evidence for it in dogs and cats is limited.

Prebiotics and fiber

Prebiotics are ingredients the animal cannot digest but gut bacteria can ferment. Pet food labels commonly list fructooligosaccharides (FOS), inulin from chicory root, mannanoligosaccharides (MOS) from yeast cell walls, and beet pulp, a mixed fiber. A synbiotic is a product that combines a probiotic with a prebiotic.

Dogs and cats have no dietary requirement for fiber, but the right type and amount can help with diarrhea, constipation and weight control. The difficulty is getting the type right. As a Tufts nutritionist explains, the crude fiber figure on a pet food label measures only insoluble fiber, so two foods listing the same number can differ a lot in total and soluble fiber. For a pet that needs more fiber, a vet can prescribe a therapeutic diet or a measured supplement such as psyllium, a mix of soluble and insoluble fiber.

Home remedies

Canned pumpkin is the classic one, and it does less than people think. Owners usually give between a quarter teaspoon and 2 tablespoons per meal. To match the fiber in one high-fiber therapeutic diet, Tufts calculated, a cat would need more than 2.5 cups of pumpkin a day and a medium-sized dog nearly 12 cups. Pumpkin pie mix adds sugar and calories, and salted brands carry a lot of sodium, a concern for pets with heart or kidney disease.

Yogurt and kefir contain live cultures, but the strains and numbers are not those tested in pets. The ASPCA notes that pets make little lactase, the enzyme that digests milk sugar, so dairy can itself cause diarrhea. Any sweetened product is a risk, since xylitol can cause low blood sugar and liver damage in dogs.

Bone broth and fermented vegetables are popular too, with no published evidence of a gut benefit in pets. Store-bought broths may contain onion or garlic, which can damage red blood cells in dogs and cats.

For a healthy animal, the gut is best served by a complete diet it tolerates well, changed gradually over about a week when a change is needed, and without frequent swaps between foods and treats.

Sources

1. Good bugs/bad bugs: the confusing world of probiotic supplements. Petfoodology, Cummings School of Veterinary Medicine at Tufts University, 2017.
2. Assessment of commercial probiotic bacterial contents and label accuracy. Canadian Veterinary Journal, 2011.
3. Efficacy of antimicrobial and nutraceutical treatment for canine acute diarrhoea: a systematic review and meta-analysis for European Network for Optimization of Antimicrobial Therapy (ENOVAT) guidelines. The Veterinary Journal, 2024.
4. Effect of the probiotic Enterococcus faecium SF68 on presence of diarrhea in cats and dogs housed in an animal shelter. Journal of Veterinary Internal Medicine, 2011.
5. Effect of Enterococcus faecium strain SF68 on gastrointestinal signs and fecal microbiome in cats administered amoxicillin-clavulanate. Topics in Companion Animal Medicine, 2017.
6. The problem with pumpkin. Petfoodology, Cummings School of Veterinary Medicine at Tufts University, 2017.
7. People foods to avoid feeding your pets. ASPCA.