If your cat’s diarrhea gets worse please stop the supplement. Just like anything else, it does not work for every kitty and this can sometimes happen. 

Probiotics by Laurie Goldstein

PLEASE NOTE when S boulardii will NOT work:

–  If your cat’s B12 levels are low (31) (common when there is intestinal lymphoma or inflammatory bowel disease), S. boulardii will not resolve the diarrhea. B12 must be supplemented to bring blood serum levels back to normal.

– If your cat has exocrine pancreatic insufficiency (32) (“EPI”), S. boulardii will not resolve the diarrhea. Pancreatic enzymes must be used to treat EPI.

– If your cat has diarrhea as a result of hyperthyroidism, (33), S. boulardii will not resolve the diarrhea, kitty needs methimazole or radioactive iodine-131 treatment.

NOTE ON FORTIFLORA:  Regarding FortiFlora, the “probiotic” many vets recommend. Marketed as a nutritional supplement, please take a look at the ingredients: “Animal digest, Enterococcus faecium, brewers dried yeast, L-ascorbyl-2-polyphosphate (source of Vitamin C), Vitamin E supplement, beta-Carotene, zinc proteinate, taurine, salt, manganese proteinate, ferrous sulfate, copper proteinate, calcium iodate, sodium selenite.” The first ingredient is animal digest. The supplement contains one strain of probiotic, E faecium, with just 100 million colony forming units – the very lowest end of the range of probiotic doses discussed by Dr. Suchodolski. If you are using FortiFlora and it hasn’t worked, that does not mean that “probiotics” do not help your cat. You have not been using the right probiotic for your cat.

There is plenty of research supporting the benefits of E faecium SF68 in cats and dogs, but in the combined experience of cats with IBD in the Facebook group(s), this supplement rarely contributes to the resolution of IBD-related diarrhea. We don’t know, but suspect it is due to two potential factors: the inclusion of the animal digest, and the fact that it is ONE strain, and not very much of it.

What’s the problem with animal digest? It is beyond the scope of this discussion to cover the ingredient in any detail – but animal digest causes diarrhea in some cats. Please refer to the discussion of animal digest by Truth about Pet Food:

How to Use Probiotics

Probiotics & Antibiotics: Most probiotics should be given separately from antibiotics, at least 2 hours before or after antibiotic administration. The exception is the yeast-based probiotic, Saccharomyces boulardii, which can be used as adjunct therapy with antibiotics (though the use of S. boulardii can, in some instances, replace the need for antibiotics as noted above).

Introducing Probiotics: Remember when working with cats with impaired GI systems (IBD, pancreatitis, chronic kidney disease, etc.), ANYTHING new should be discussed with your vet, and if you decided to use a probiotic, it should be introduced slowly. Start with an amount lower than the recommended dose and work up to it. The slow-introduction exception is if your kitty is in crisis, and you’re adding S. boulardii to stop diarrhea. For emergency use, see instructions below. That said, if the addition of S boulardii makes diarrhea worse, obviously stop, start over, and introduce it slowly.

The Benefits of Kefir:
Kefir is the best probiotic you could give as it’s completely natural and contains the most available live cultures. For more on Kefir and instructions see:
Kefir – The “Feel Good” Probiotic You Make Right at Home

Regarding Recommended Doses: If the suggested dose does not provide benefit and does not create a gassy tummy or has no impact on incidence of vomiting, diarrhea, or constipation, you can safely double (or more) the suggested therapeutic dose before considering trying a new probiotic. This is a combination of art and science at this point, and you need to see how your cat reacts to determine how much is truly needed. If you see improvement, but not resolution of symptoms, try a higher dose. Of course, we again note, please consult with your vet prior to probiotic administration.

Regarding Brands: There is no need to use these particular brands and this is list is by no means exhaustive. As mentioned, any quality L. acidophilus supplement can provide benefit, as can any S. boulardii supplement. We recommend human probiotics specifically because they tend to be of higher quality (with claims of active colony forming units matching label claims, for instance) than many pet probiotics. The important things to consider are the number of colony forming units (CFU) (an adult cat dose of a human probiotic is between 2.5 billion CFU and 20–40 billion CFU daily, depending on whether use is maintenance or therapeutic. For kittens, use half the adult dose). The most proven bacterial probiotic strains in humans are L. acidophilus, L. rhamnosus (which colonize the intestines), and several strains of Bifidobacterium (which colonizes the colon). L. acidophilus is one of the few strains also studied in cats, and it did show significant benefit (35). So consider the mix of strains, bearing in mind that more isn’t always better, and be mindful of the “other” ingredients.

For S. boulardii, the therapeutic (treating diarrhea) adult cat dose is typically 5 billion CFU split into two daily doses of 2.5 billion CFU each and can be doubled, though even this can be adjusted up (or down) as needed. Again, this is not an exact science, it is guidelines that work for many cats. You may need to experiment to find what works best for yours.

Saccharomyces boulardii
This yeast-based probiotic is often used in conjunction with an L. acidophilus-based probiotic and is a very important tool in resolving diarrhea and healing inflammation in IBD cats.

“A probiotic, non-colonizing yeast species closely related to Brewer’s yeast and not related to the yeast group to which Candida belongs, Saccharomyces boulardii taken orally supports the production of secretory IgA, and helps friendly probiotic bacteria to colonize the GI tract. It is a transitory microorganism and is eliminated after supplementation is stopped.”  This probiotic has been studied extensively, and has been shown to be effective in resolving clostridium and coccidia infections, even without the use of antibiotics – the time for efficacy is one month, and then the cats should be kept on a maintenance dose. Please do not attempt to treat known bacterial/parasitic infections without vet knowledge. Finally, as a non-colonizing probiotic, S. boulardii can be used as adjunct therapy to improve efficacy of probiotics without worry about the timing of probiotic administration in relation to delivery of antibiotic.  Please see Further Information at the end of the document for links on the benefits of S boulardii in managing and treating GI disease.


Jarrow Brand S. Boulardii is the most commonly locally available S. Boulardii supplement (in the U.S.). It is usually sold as S. Boulardii + MOS. “MOS” are mannan-oligosaccharides, a medium that promotes utilization of the probiotic in the intestines. Jarrow does have a product available in premeasured packets rather than capsules. If available, these packets will make it a little easier to use for emergency treatment if you have or can purchase small (size 3) empty capsules. Some cats eat the Jarrow S boulardii mixed into a bit of Beechnut baby food and fed as a “treat.”

For emergency “stop diarrhea” use, it is recommended to purchase size 3 empty capsules. Fill 10 or so of these, and administer them to your cat every 2 hours. This often stops diarrhea within 24 – 48 hours, other than when diarrhea is caused by another disease that requires treatment (low B12, exocrine pancreatic insufficiency, hyperthyroidism, as examples). This “loading dose” can be continued for three to four days if necessary. It is NOT necessary to use this approach, it can be given at “therapeutic” doses twice a day (and doubled if you see improvement in stool but diarrhea or soft cow patty stools have not resolved).

NOTE: IF USE OF S BOULARDII MAKES DIARRHEA WORSE, STOP. Give kitty a break for 3 days, and start over at a MUCH smaller amount, and very slowly work up to the therapeutic dose. If even the small amount makes diarrhea worse, your cat is likely sensitive to yeasts and this cannot be given. When the diarrhea has resolved with use of the emergency stop treatment protocol, begin use of S. boulardii at the therapeutic dose level (2.5 billion CFU twice daily) and continue for at least one week and up to one month; then adjust dose to the maintenance level (half that. If stools soften, resume use of S. boulardii at the therapeutic dose as needed. Given its role in improving performance of bacterial probiotics and its anti-inflammatory properties, the use of S boulardii at maintenance levels can be continued indefinitely along with a bacterial probiotic.

Probiotic Dosing Instructions

Especially for IBD cats, please remember to start very small and work up to the dose you want to use. The exception is the “emergency stop diarrhea” instructions for S boulardii.

Adult Cat Therapeutic doses
For probitiocs with lactobacillus and bifidobacterium: therapeutic benefit is at higher doses, and should be a minimum of 10 billion CFU (colony forming units) twice a day. If you buy a 15 billion CFU probiotic, you can use just half a capsule 2x a day. These are not drugs with toxicity limits, and actual proper dosing is very cat-dependent. Some cats do better with 20 or 30 billion twice a day.

For S boulardii: this is usually sold in capsules of 5 billion CFU (250mg). Target ½ capsule 2x a day, for a total of 5 billion CFU. If you see improvement at this dose, but not resolution of diarrhea, you can go as high as three capsules daily (15 billion CFU). This should be used for at least a few weeks if not a month before starting to slowly scale it back to a maintenance dose.

Adult Cat Maintenance dose
For probiotics with lactobacillus and Bifidobacterium: the ongoing maintenance dose is half the therapeutic dose, or as low as 5 billion CFU total split into half, given 2x daily (2.5 bn CFU 2x a day).

For S boulardii: the ongoing maintenance dose is ¼ of the 5 billion capsule 2x a day, unless this doesn’t control your cat’s stool. Whatever is needed to maintain formed stool is fine to use long term.

Kitten Doses: half the adult doses.



Further Information
Beasley DE, Koltz AM, Lambert JE, Fierer N, Dunn RR (2015). The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome. PLoS ONE 10(7): e0134116.

Janet Chow, Sarkis K. Mazmanian (2010). A Pathobiont of the Microbiota Balances Host Colonization and Intestinal Inflammation. Cell Host & Microbe, 2010; 7 (4): 265.

Studies of the feline microbiome:
LE Ritchie 2008. Molecular characterization of intestinal bacteria in healthy cats and a comparison of the fecal bacterial flora between healthy cats and cats with inflammatory bowel disease (IBD), MS Thesis, Texas A&M, Veterinary Medical Sciences.

Janeczko et al. 2008. The relationship of mucosal bacteria to duodenal histopathology, cytokine mRNA, and clinical disease activity in cats with inflammatory bowel disease, Vet Microbiol 128 (2008) 178-193.

Desai et al 2009. Characterization and quantification of feline fecal microbiota using cpn60 sequence-based methods and investigation of animal-to-animal variation in microbial population structure, Vet Microbiol 2009 May 28;137(1-2):120-8.

JF Garcia-Mazcorro and Y Minamoto 2013. Gastrointestinal microorganisms in cats and dogs: a brief review, Arch Med Vet 45, 111-124 (2013).

Honnafer, Minamoto, Suchodolski 2014. Microbiota alterations in acute and chronic gastrointestinal inflammation of cats and dogs, World J Gastroenterol. 2014 Nov 28; 20(44): 16489–16497.

Suchodolski et al. 2015.  The Fecal Microbiome in Cats with Diarrhea, PLoS ONE 10(5): e0127378. doi:10.1371/journal.pone.0127378.

S. boulardii
Simply explained in the Biocodex FDA submission (last link), S boulardii is not digested and absorbed in the gut and does not exert its effect systemically. Instead, S boulardii acts locally in the lumen of the gut. During its passage through the intestine, S boulardii mimics the physiological effects of the digestive flora, stimulating healthy immune response and reducing inflammation.

Saccharomyces boulardii prevents enteritis from Clostridium difficile infection

“Saccharomyces boulardii in Gastrointestinal Related Disorders,” Point Institute Technical Report (2008)

Saccharomyces boulardii effects on gastrointestinal diseases, (Zanello et al. 2009)

Review article: anti-inflammatory mechanisms of action of Saccharomyces boulardii, (Pothoulakis 2009)

“Systematic review and meta-analysis of Saccharomyces boulardii in adult patients,” (McFarland 2010)

Anti-inflammatory effects of Saccharomyces boulardii mediated by myeloid dendritic cells from patients with Crohn’s disease and ulcerative colitis, (Thomas et al. 2011)

Efficacy and safety of the probiotic Saccharomyces boulardii for the prevention and therapy of gastrointestinal disorders, (Kelesidis & Pothoulakis 2012)

New Dietary Ingredient Notification for S boulardii (FDA submission) by Biocodex (Florastor) (includes summary table and references)

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