Enterococcus faecium is a lactic acid bacterium that lives naturally in the canine gut, and specific strains of it are the single most common probiotic ingredient in dog supplements sold today. It is the organism behind the best-known veterinary probiotic powders, and it is one of the few probiotic strains formally approved for dogs in the European Union. What almost no product page tells you is that the canine trial record for it is far more mixed than the marketing suggests — including one large placebo-controlled shelter study where the benefit showed up in cats and not in dogs.
This guide walks through every canine study we could verify, names the strains that actually have data behind them, covers the safety question that rarely appears on a label, and explains how to read a probiotic panel in about three minutes.
What Enterococcus faecium is, and why it ended up in your dog's supplement
Enterococcus faecium is a Gram-positive, lactic-acid-producing bacterium that is a normal resident of the intestinal tract of dogs, cats, and people. It survives stomach acid and bile better than many fragile species, it grows easily in industrial fermentation, and it tolerates drying — three unglamorous manufacturing traits that explain much of its popularity in pet products.
Critically, "E. faecium" on a label means almost nothing on its own. Probiotic effects are strain-specific, not species-specific. The strains with published canine work are:
- SF68 (NCIMB 10415) — the strain in the most widely veterinary-recommended probiotic powder, and the subject of most canine research.
- NCIMB 10415 as a complete-diet additive — one of the few probiotic strains authorised for dogs in the European Union.
- Kimate-X — a newer strain with a 2025 transport-stress paper, published by authors employed by the manufacturer.
A label that says only "Enterococcus faecium" with no strain designation is telling you the genus and species of an organism whose behaviour changes completely from one strain to the next. That is the first thing to check.
What the canine studies actually found
Here is the published record, reported as the abstracts report it — including the results that do not flatter the ingredient.
| Study | Design | What it found in dogs |
|---|---|---|
| Bybee, Scorza & Lappin, J Vet Intern Med 2011 (SF68, shelter) | Double-blinded, placebo-controlled; 217 cats and 182 dogs | No significant difference in dogs. The significant reduction in diarrhoea (7.4% vs 20.7%, P = .0297) was in the cats. The authors note diarrhoea was uncommon in both dog groups. |
| Fenimore, Martin & Lappin, Top Companion Anim Med 2017 (SF68 + metronidazole) | Randomised, placebo, 7 days, masked faecal scoring | Normal stool by day 7: 68.8% with dual therapy vs 37.5% with metronidazole alone — not significant (P = .1556). Percentage of days with normal stools was significantly higher (65.6% vs 46.9%, P = .0496). |
| Simpson et al., J Vet Intern Med 2009 (SF68, giardiasis) | 20 adult dogs, randomised crossover vs placebo, 6 weeks per arm | Fully negative. No difference in giardial cyst shedding, faecal antigen, faecal IgA, or leukocyte phagocytic activity. |
| Benyacoub et al., J Nutr 2003 (SF68, puppies) | Feeding study, weaning to 1 year, 5 × 10⁸ CFU/day; not described as randomised or placebo-controlled | Higher faecal IgA and higher distemper-vaccine-specific circulating IgG and IgA vs controls; greater proportion of mature B cells. No p-values reported in the abstract. |
| Nybroe et al., Animals 2022 (NCIMB 10415 in a complete diet) | 11 healthy dogs, randomised, double-blinded crossover, 16 days per diet | Owners reported 0.6 ± 0.3 fewer days of loose stools. Both diets raised faecal acetate and butyrate and microbial diversity — "effects were observed regardless of the addition of E. faecium." |
| Lucena et al., J Vet Intern Med 2019 (SF68, liver function) | 36 healthy dogs, blinded, controlled, 14 days | Safety study. No significant change in ALT or ALP. Cholesterol fell by day 28 (P < .01); triglycerides rose by day 28 (P < .05), with one dog developing hypertriglyceridaemia. |
Read together, the honest summary is this: E. faecium SF68 has a real safety record in dogs and some signal as an add-on during an antibiotic course, but no canine study has shown it resolves diarrhoea on its own, and the one large placebo-controlled shelter trial found no benefit in dogs at all. The immune and vaccine findings rest on a single non-randomised feeding study from 2003.
None of this makes the ingredient useless. It makes single-strain claims about it far weaker than most product pages imply — which is exactly the sort of gap worth knowing before you spend money. For a wider view of how the formats compare, our breakdown of liquid, powder and chew probiotics sets the same evidence standard across delivery types.
The safety question that rarely reaches the label
Enterococci occupy an awkward position in microbiology: they are commensals, they are used as probiotics, and they are also recognised opportunistic pathogens with a well-documented talent for acquiring and transferring antimicrobial resistance genes.
In a 2023 survey of enterococci isolated from dogs and cats in Northeast China, researchers recovered 469 strains from 610 samples — 238 of them E. faecium — and reported that 68.92% of isolates were multidrug resistant, concluding that pets represent a reservoir of resistant enterococci relevant to public health. A broader review of antimicrobial resistance in animal-origin Enterococcus notes the genus carries both intrinsic resistance mechanisms and the capacity to acquire new ones, including the transferable optrA and cfr genes.
To be precise about what this does and does not mean: none of the records we retrieved showed that the probiotic strain SF68 itself is resistant or virulent, and regulators in the EU authorised NCIMB 10415 for dogs after safety assessment. Commercial probiotic strains are screened for resistance genes before approval precisely because of this concern. But it is a reasonable question to ask a manufacturer, and one more argument for buying from a company that publishes a certificate of analysis for every batch rather than one that names no strain at all.
Why one strain rarely carries a whole gut
The canine dysbiosis literature describes a consistent pattern: dogs with chronic enteropathy show reduced overall bacterial diversity and depletion of several unrelated functional groups at once — particularly the short-chain-fatty-acid producers. A single organism, however well characterised, does not repopulate a depleted community by itself. The Nybroe 2022 finding is the cleanest illustration available: faecal butyrate and diversity rose on both diets, with or without the added E. faecium, which points to the substrate as much as the organism.
That is the reasoning behind the way Pure Majesty Pets 3B Liquid Probiotic is built. Rather than a single strain in a carrier, it combines multiple live strains with prebiotic fibres to feed them and digestive enzymes to help break down the meal they arrive with — a three-part approach to a three-part problem. It is manufactured in North America under GMP conditions with a certificate of analysis on every batch, and it ships free worldwide.
The liquid format matters for a specific, practical reason rather than a marketing one: a liquid is dosed by drops against body weight and mixes into food, water or a syringe, so it works for a small dog on a quarter dose and a large dog on a full one from the same bottle, and it does not require the dog to chew and swallow a flavoured treat. Soft chews are genuinely convenient and many dogs take them enthusiastically — that is a real advantage, and for a dog who eats normally and likes them, a good chew is a perfectly sensible choice. The liquid simply removes the appetite requirement, which matters most on exactly the days a gut supplement is most wanted.
Comparing what you are actually buying
| Typical single-strain E. faecium powder | Pure Majesty Pets 3B Liquid Probiotic | |
|---|---|---|
| Live organisms | One strain | Multiple strains |
| Prebiotic substrate | Usually none | Included |
| Digestive enzymes | No | Included |
| Dosing | Fixed sachet | Drops, scaled to body weight |
| Requires appetite | Mixed into food | Food, water, or direct |
| Batch COA | Varies by brand | Every batch |
| Shipping | Varies | Free worldwide |
How to read a dog probiotic label in three minutes
- Look for a strain designation, not just a species. "Enterococcus faecium SF68" or "NCIMB 10415" tells you something. "Enterococcus faecium" alone does not.
- Check whether anything feeds the bacteria. Inulin, FOS, GOS or beta-glucans on the panel mean the product brought substrate as well as organisms.
- Ask for the certificate of analysis. A 2003 Canadian Veterinary Journal audit of 19 commercial pet diets claiming to contain probiotics found that no product contained all of the listed organisms, and five (26%) showed no relevant growth at all. Batch testing is not a luxury in this category.
- Check the dosing method against your dog. A fixed sachet is fine for a 30 kg dog and clumsy for a 4 kg one.
- Ignore any claim to treat, cure or prevent disease. A supplement that makes one is telling you something about the company, not the product.
What we will not claim
Because the temptation in this category is to overstate, here is the explicit list:
- We do not claim E. faecium resolves diarrhoea in dogs. The largest placebo-controlled canine dataset found no significant effect in dogs.
- We do not claim it helps with Giardia. The dedicated crossover trial in dogs was negative on every endpoint.
- We do not claim it improves vaccine response in dogs. That rests on one 2003 non-randomised feeding study with no p-values in the abstract.
- We do not claim any probiotic treats, cures or prevents inflammatory bowel disease, pancreatitis, atopic dermatitis or any other diagnosed condition in dogs. No canine trial supports that for this organism.
- We do not publish CFU or milligram figures we cannot stand behind on a batch certificate.
When to call your vet instead of reaching for a supplement
A gut supplement is for daily support in an otherwise well dog. Contact your veterinarian promptly if your dog has diarrhoea lasting more than 48 hours; blood or black tarry material in the stool; repeated vomiting; lethargy, collapse or a painful abdomen; signs of dehydration; or any of these in a puppy, a senior, a toy-breed dog, or a dog with a known chronic condition. Unexplained weight loss alongside loose stools warrants a proper work-up, not a supplement.
Frequently asked questions
Is Enterococcus faecium safe for dogs?
Probiotic strains such as SF68 have been fed to healthy dogs in controlled studies without significant changes in liver enzymes, and NCIMB 10415 is authorised for dogs in the European Union. Lucena et al. did record a rise in triglycerides by day 28 in one blinded study, with one dog developing hypertriglyceridaemia, so dogs with a history of pancreatitis or lipid disorders should start any probiotic only under veterinary guidance.
Does Enterococcus faecium stop diarrhoea in dogs?
Current research does not strongly prove this. The large blinded shelter study by Bybee and colleagues found a significant benefit in cats but not in dogs, and the Fenimore study found a benefit only on a secondary measure, as an add-on to metronidazole rather than on its own.
What is the difference between SF68 and NCIMB 10415?
They refer to the same deposited strain under different naming conventions — SF68 is the commercial designation, NCIMB 10415 the culture-collection accession. Any other E. faecium on a label is a different organism with its own, usually thinner, evidence base.
Can I give my dog a human Enterococcus faecium probiotic?
Human products are formulated for a human gut, a human body weight and a human diet, and many contain sweeteners or excipients that are unhelpful or unsafe for dogs. A canine-formulated product with weight-based dosing is the sensible default. Speak to your veterinarian before using anything from your own medicine cabinet.
How long before I might notice anything?
Stool consistency is usually the first thing owners report changing, typically over the first one to two weeks of consistent daily dosing. Coat and appetite observations, where they occur, tend to be described later. These are owner observations, not clinical endpoints, and individual dogs vary widely. Our guide to how long probiotics take to work in dogs sets out a realistic timeline.
Where to go next
If you are choosing a product rather than researching an ingredient, start with our main guide to the best probiotic for dogs. If you arrived here because of a specific brand, our review of FortiFlora for dogs covers the best-known SF68 product in detail. For other single organisms with their own evidence bases, see Saccharomyces boulardii for dogs and soil-based probiotics for dogs. If your dog has just finished a course of antibiotics, probiotics for dogs after antibiotics is the relevant read. You can browse everything we make at Pure Majesty Pets.
Scientific References
- Bybee SN, Scorza AV, Lappin MR. Effect of the probiotic Enterococcus faecium SF68 on presence of diarrhea in cats and dogs housed in an animal shelter. J Vet Intern Med. 2011;25(4):856-60. PMID: 21689152
- Fenimore A, Martin L, Lappin MR. Evaluation of metronidazole with and without Enterococcus faecium SF68 in shelter dogs with diarrhea. Top Companion Anim Med. 2017;32(3):100-103. PMID: 29291770
- Simpson KW, Rishniw M, Bellosa M, et al. Influence of Enterococcus faecium SF68 probiotic on giardiasis in dogs. J Vet Intern Med. 2009;23(3):476-81. PMID: 19298607
- Benyacoub J, Czarnecki-Maulden GL, Cavadini C, et al. Supplementation of food with Enterococcus faecium (SF68) stimulates immune functions in young dogs. J Nutr. 2003;133(4):1158-62. PMID: 12672936
- Nybroe S, Horsman PB, Krag K, et al. Alterations in healthy adult canine faecal microbiome and selected metabolites as a result of feeding a commercial complete synbiotic diet with Enterococcus faecium NCIMB 10415. Animals (Basel). 2022;13(1):144. PMID: 36611752
- Lucena R, Olmedilla AB, Blanco B, et al. Effect of probiotic Enterococcus faecium SF68 on liver function in healthy dogs. J Vet Intern Med. 2019;33(6):2628-2634. PMID: 31578761
- Zhang R, Hu W, Zhong S, et al. Impact of Enterococcus faecium Kimate-X on reducing stress in dogs through gut microbiota modulation. Vet Sci. 2025;12(5):412. (Authors employed by the strain's manufacturer.) PMID: 40431505
- Yuan TY, Chen HY, Sun YH, et al. Virulence genes and antimicrobial resistance in Enterococcus strains isolated from dogs and cats in Northeast China. J Vet Med Sci. 2023;85(3):371-378. PMID: 36724969
- Torres C, Alonso CA, Ruiz-Ripa L, et al. Antimicrobial resistance in Enterococcus spp. of animal origin. Microbiol Spectr. 2018;6(4). PMID: 30051804
- Weese JS, Arroyo L. Bacteriological evaluation of dog and cat diets that claim to contain probiotics. Can Vet J. 2003;44(3):212-6. PMID: 12677689
- Suchodolski JS. Diagnosis and interpretation of intestinal dysbiosis in dogs and cats. Vet J. 2016;215:30-7. PMID: 27160005
Veterinary disclaimer. This article is for general education and is not veterinary advice, diagnosis or treatment. Pure Majesty Pets products are supplements, not medicines; they are not intended to diagnose, treat, cure or prevent any disease, and they have not been evaluated by the FDA or Health Canada for such purposes. Always consult your veterinarian before starting a supplement, particularly if your dog is unwell, pregnant, a puppy, or taking medication.