Probiotics for dogs explained: strains, labels and what studies found

Owners searching for probiotic dog supplements meet two kinds of information: what a label says, and what published studies in dogs recorded. The word "probiotic" has an agreed scientific definition, and that definition sets conditions a label can be read against. This guide explains the term, sets out what an international working group recommended a label should state, and reports what the published dog studies did and found.

The short answer

• A probiotic is defined as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" [1]. The definition requires the organisms to be live and given in adequate amounts.
• Prebiotics, synbiotics and postbiotics are separate categories with their own definitions [2].
• A joint FAO/WHO working group recommended that a label name the genus, species and strain, and give the minimum viable count at the end of shelf life [3]. That guidance was written for probiotics in food and does not mention pet products.
• In a study published in 2003 of 19 commercial dog and cat diets claiming to contain probiotics, none contained all of the organisms listed on its label [5] (abstract only).
• A 2019 systematic review of 17 dog studies concluded that the data pointed to "a very limited and possibly clinically unimportant effect" in acute gastrointestinal disease; the studies were small and the risk of bias was generally moderate to high [6].

What counts as a probiotic?

A probiotic, by the agreed definition, is a live microorganism that confers a health benefit on the host when given in adequate amounts. A widely cited wording comes from a consensus statement published in 2014 by an expert panel of the International Scientific Association for Probiotics and Prebiotics (ISAPP), convened in October 2013: "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" [1]. It is a grammatically corrected version of the definition a joint FAO/WHO expert consultation produced in 2001, restated in the 2002 working-group guidelines [1][3].

The panel also said what falls outside the term. Traditional fermented foods with undefined live cultures were excluded, as were faecal microbiota transplants of undefined composition and dead microorganisms [1]. The panel recommended that the term be used only on products that deliver "live microorganisms with a suitable viable count of well-defined strains" [1].

Both documents were written chiefly with people and human food in mind, and that definition is the reference point used here.

Probiotic, prebiotic, synbiotic, postbiotic: what is the difference?

The four terms describe four different things, and each has an ISAPP consensus definition [2]:

• Probiotic: live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.
• Prebiotic: a substrate that is selectively utilised by host microorganisms conferring a health benefit.
• Synbiotic: a mixture comprising live microorganisms and substrate(s) selectively utilised by host microorganisms that confers a health benefit on the host.
• Postbiotic: a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.

Put plainly, a probiotic is alive, a synbiotic pairs live microorganisms with a substrate, and a postbiotic is not alive. Every one of these definitions includes a health benefit as a condition, so the word on a pack does not by itself show that a particular product meets the definition.

Probiotic dog supplements: why do strain and CFU count matter?

Strain matters because, in the words of the FAO/WHO working group, "the current state of evidence suggests that probiotic effects are strain specific". The group added that strain identity is important to link a strain to a specific health effect [3]. In Enterococcus faecium SF68, the organism used in two shelter trials described below, "SF68" is the strain designation [7].

CFU stands for colony forming units, the unit in which the ISAPP label article gives counts of viable microorganisms per dose or serving [4]. The definition requires "adequate amounts", so the count is part of what makes something a probiotic at all [1].

What should a probiotic label state?

The FAO/WHO working group listed six items. It recommended that a probiotic label carry [3]:

• genus, species and strain designation
• minimum viable numbers of each strain at the end of shelf life
• the suggested serving size that delivers the effective amount
• the health claim or claims
• proper storage conditions
• corporate contact details for consumer information

That list was drawn up for probiotics in food, and the report does not mention animals or pet products. In Australia, what a dog product may claim is a separate legal question, covered in our guide to how dog supplements are regulated in Australia.

How accurate are pet probiotic labels?

The published testing opened for this article is old and limited, and its results were poor. In a study published in 2003, Weese and Arroyo carried out a bacteriological evaluation of 19 commercial dog and cat diets that claimed to contain probiotics. No product contained all of the listed organisms. One or more of the listed organisms was isolated from 10 of the 19 products (53%), and 5 products (26%) showed no relevant growth. The authors concluded that the label descriptions did not accurately represent the actual contents [5]. Only the abstract was available.

That study looked at diets, not capsules or powders, and was published more than twenty years ago. It does not describe any product sold today.

Storage and viability

Viable counts can fall over time. An ISAPP article on reading labels notes that "most probiotic strains suffer cell count decline over the course of shelf-life", and that a label may state the count "at time of manufacture" instead of at the end of shelf life [4]. That article uses an imaginary human dietary supplement for sale in the United States as its example. For a dog owner the equivalent step is to check which point in time the stated count refers to and to follow the storage directions on the label, which the FAO/WHO list includes [3].

What have canine studies found?

The 2019 systematic review

Jensen and Bjørnvad searched six databases between 22 March and 1 April 2017 for studies of probiotics in gastrointestinal disease in dogs [6]. They identified 165 studies; 17 met the inclusion criteria, 12 on acute and 5 on chronic gastrointestinal disease. The review describes study groups "ranging between 6 and 399 dogs", but the 399 figure matches the total enrolment of one included shelter study, which was 217 cats plus 182 dogs [6][7]. Ten studies used a single probiotic species, six used a combination of two or more, and one did not specify the species [6].

The authors reported that evidence ranged from randomised controlled studies to uncontrolled crossover trials, that estimated risk of bias was generally moderate to high, and that sample sizes were small. Differences in design, populations, strains and indications prevented a pooled analysis, and differing faecal scoring systems also hampered comparison between studies [6].

Some of the 17 included dog trials reported statistically significant differences between probiotic and control groups on measures such as days to resolution of diarrhoea; the review judged the included studies small and generally at moderate to high risk of bias [6]. Weighing all 17 studies, the authors concluded that the data "point toward a very limited and possibly clinically unimportant effect for prevention or treatment of acute gastrointestinal disease". For chronic disease they wrote that "dietary intervention remains the major key in treatment, whereas probiotic supplement seems not to add significant improvement" [6].

Two trials of Enterococcus faecium SF68 in shelter dogs

Bybee and colleagues ran a double-blinded, placebo-controlled study in an animal shelter, with 217 cats and 182 dogs; treatment was allocated by room, with the rooms switched between study periods, and not dog by dog [7]. Of the dogs, 102 received SF68 mixed with food and 80 received placebo. At least one episode of diarrhoea was recorded in 9.8% of the SF68 dogs and 12.5% of the placebo dogs, and no statistical difference between the dog groups was detected. In the cats, diarrhoea lasting two days or more was recorded in 7.7% of the SF68 group (the paper's results text; its abstract gives 7.4%) and 20.7% of the placebo group (P = .0297); that is a feline finding and does not transfer to dogs. The authors noted that the median stay was 2 days for SF68 dogs and 3 days for placebo dogs, so the chance of detecting longer episodes in dogs was low, and that some diarrhoea samples may have been discarded unintentionally. The paper states that the work "was supported by a grant from Nestle Purina PetCare" [7].

Fenimore and colleagues studied shelter dogs with diarrhoea, all of which were given metronidazole and a standardised diet [8]. Dogs were randomised to a commercial SF68 product or a placebo for 7 days; 48 were enrolled and 32 analysed, 16 per group. By day 7, stools were normal in 68.8% of the 16 dogs given both and 37.5% of the 16 dogs given metronidazole alone, a difference that was not statistically significant (P = .1556). The percentage of days with normal stools was higher in the SF68 group of 16 shelter dogs than in the placebo group of 16 (65.6% against 46.9%, P = .0496). The abstract page states that the study was funded by a donation from Nestle Purina PetCare, which also donated the probiotic and placebo. Only the abstract was available [8].

What the research does not tell us

• Whether a given product matches a studied one. The FAO/WHO group described probiotic effects as strain specific [3]. A study of one strain in one preparation did not test any other.
• Much about ordinary pet dogs. Both SF68 trials above were run in shelters [7][8], and in the first the median stay for dogs was 2 to 3 days [7].
• A reliable average effect. The 2019 review could not pool results, and judged the studies small with a generally moderate to high risk of bias [6]. Its search closed on 1 April 2017, so later trials are not included.
• Independence. Both SF68 trials were funded by Nestle Purina PetCare, by grant or donation [7][8].
• Current label accuracy. The label testing reported here was published in 2003 and covered diets only [5].

When to see your vet

Signs of digestive system disease in dogs can include diarrhoea, vomiting or regurgitation, loss of appetite, bleeding, abdominal pain and bloating, straining to defecate, and dehydration [9]. Large fluid losses, for example from diarrhoea, can cause dehydration and electrolyte imbalance that may lead to shock, and black, tarry faeces may be a sign of bleeding in the stomach or small intestine [9]. Any of these is a reason to contact your vet promptly; a supplement is not a substitute for an examination. If your dog is on prescribed medication, ask your vet before adding anything to the bowl.

The most useful question to take to that conversation is a specific one: which strain, in what amount, was tested in dogs like mine, and what did that study find?

This article is general information, not veterinary advice. Speak to your vet before changing your dog's diet, supplements or medication.

References

1. Hill C, Guarner F, Reid G, et al. (2014). The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology, 11(8), 506–514. https://www.nature.com/articles/nrgastro.2014.66
2. Salminen et al. (2021). The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology & Hepatology. https://www.nature.com/articles/s41575-021-00440-6
3. Joint FAO/WHO Working Group (2002). Guidelines for the Evaluation of Probiotics in Food. London, Ontario, Canada. https://isappscience.org/wp-content/uploads/2019/04/probiotic_guidelines.pdf
4. Sanders, Mary Ellen (2022, updated 2025). Decoding a probiotic product label. ISAPP. https://isappscience.org/decoding-a-probiotic-product-label/
5. Weese JS, Arroyo L (2003). Bacteriological evaluation of dog and cat diets that claim to contain probiotics. Canadian Veterinary Journal. Abstract via AGRIS: https://agris.fao.org/search/en/records/65df1c744c5aef494fdfd349
6. Jensen and Bjørnvad (2019). Clinical effect of probiotics in prevention or treatment of gastrointestinal disease in dogs: A systematic review. Journal of Veterinary Internal Medicine, 33(5), 1849–1864. https://academic.oup.com/jvim/article/33/5/1849/8448032
7. Bybee, Scorza and Lappin (2011). 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, 25(4), 856–860. https://academic.oup.com/jvim/article/25/4/856/8451166
8. Fenimore, Martin and Lappin (2017). Evaluation of metronidazole with and without Enterococcus faecium SF68 in shelter dogs with diarrhea. Topics in Companion Animal Medicine, 32(3), 100–103. Abstract: https://www.sciencedirect.com/science/article/abs/pii/S193897361730106X
9. Rubin, Stanley I. Introduction to Digestive Disorders of Dogs. Merck Veterinary Manual, dog owner edition (reviewed May 2018). https://www.merckvetmanual.com/dog-owners/digestive-disorders-of-dogs/introduction-to-digestive-disorders-of-dogs