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We are always expressing the need to ‘condition or train-up the digestive system of the pets,’ to their custodians, with the aim to optimize their natural abilities to defend and repair their own bodies.

Creating a healthy and balanced microbiome in the digestive system is the first imperative step.

One of the definitions by the World Health Organization for “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” is Probiotics (1) (2)


Lactobacillus and Bifidobacterium are significant genera in this context because they are unaffected by the gastrointestinal acidic environment and readily form colonies by attaching to the intestinal tract (3) when fed orally. 


There are only limited published, peer-reviewed, controlled clinical trials or reports on probiotic uses on either diseased or healthy pet cats and pet dogs (4).


The studies done in humans and other mammals have amassed evidence to link a balanced and stable gut microbiome to a range of physiologic processes that are vital to host health, including energy homeostasis, metabolism, gut epithelial health, immunologic activity, and neurobehavioral development (4).

Any changes or dysbiosis to these gut microbiomes can result in diseases or medical conditions like inflammatory bowel disease, asthma, obesity, metabolic syndrome, cardiovascular disease, immune‐mediated conditions, and neuro-developmental issues (4).


Most discussed benefits and narratives about probiotic uses are extrapolated from these studies on human health, laboratory animals, and production animals. It is essential to understand that the effects of all mentioned probiotics can vary from animal to animal (1).


To expound on this point, we can consider the domestic short hair pet cats. Being obligate carnivores that need a protein-rich diet, their gut microbiota, logically, should constitute a very different composition of microorganisms, compared with those of omnivorous humans and many other mammals (4).


Therefore, the true impact and benefits on the immune system after and during probiotic therapy are dependent on an individual's overall health condition, the specific strain of probiotics, and the dosage or concentration used (1).


Lactobacillus is a well-known beneficial bacterium genus that can be found in various parts of the body, especially in the digestive system.


Many Lactobacillus species contribute to the overall health of the host by maintaining a healthy and slightly acidic pH level, consequently, a balanced yet diverse, beneficial gut microbiome in the digestive system when fed correctly. It can help to prevent the overgrowth of harmful bacteria or alleviate certain digestive issues, such as bloating, flatulence, and diarrhea (5, 22).


They can assist in the digestion of food by breaking down complex carbohydrates (a common ingredient in pet food) and producing enzymes that aid in nutrient absorption (21).


Some strains, like Lacticaseibacillus rhamnosus and Lacticaseibacillus paracasei (formerly known as Lactobacillus rhamnosus and Lactobacillus paracasei respectively)  (2), are believed to support the immune system and help prevent infections (5, 6). They can enhance the body's immune responses and modulate inflammation, making it more effective in defending against common gastrointestinal infections and even respiratory infections. Other studies picked up potential antiviral properties in Lacticaseibacillus casei (formerly known as Lactobacillus casei) as well (2,7,6,22).

One of the most familiar strains is none other than Lactobacillus acidophilus. It potentially inhibits the growth of pathogenic microorganisms and reduces the production of enzymes by them, it may also inhibit the catalysing of the conversion of carcinogenic precursors to carcinogens like reductase, nitro reductase, and β-glucosidase (8).


Bifidobacterium is another genus of beneficial microorganisms with 48 recognized species (9,10) that inhabit the intestinal tract of a wide range of animals (9), primarily residing in the colon (5, (10).


It has also been shown in studies that bifidobacterium and other butyrate-producing colon bacteria are negatively correlated with disorders such as inflammatory bowel disease and colorectal cancer (11).


Species, like Bifidobacterium longum, Bifidobacterium adolescentis, mainly aid in the fermentation and breakdown of dietary fibre (which are also found in pet food) and other complex carbohydrates (12), producing short-chain fatty acids (SCFAs) and helps to extract energy from otherwise indigestible compounds (9,10) in the food.

Others, like Bifidobacterium bifidum adhere to the intestinal lining, directly competing with harmful bacteria for resources, helping to keep the microbiota in balance and preventing the overgrowth of pathogenic microorganisms physically through colonisation of the intestinal linings (9). They also help maintain the integrity of the intestinal barrier, which is crucial in preventing and defending the entry of harmful substances produced by these pathogenic microorganisms into the bloodstream (13,22).


While others, like Bifidobacterium animalis subsp. Lactis, are known for their role in promoting regular bowel movements and preventing constipation by softening the stool (10,13).


There are even species, like Bifidobacterium breve, that research has found may possibly trigger tumour apoptosis and inhibit tumour growth in mice by the recruitment of intestinal defense cells, like Interleukin 12 and T cells that can enhance antitumor effect (14, 21).


Saccharomyces boulardii, a non-pathogenic yeast, has been used worldwide for several decades to modulate against intestinal injury and inflammation (15).


This yeast was seen to alleviate the clinical signs of several diarrhea diseases, including pediatric diarrhea, antibiotic-associated diarrhea, acute diarrhea, traveler’s diarrhea caused by bacterial, viral or parasites, and enteral nutrition-related diarrhea (16, 17, 18).


Current data indicate that the benefits of Saccharomyces boulardii are not reliant on colonization of the digestive system, differentiating its mode of action from other widely used bacterial probiotics such as Lactobacillus and Bifidobacterium (15). It grows well at normal human body temperature (37°C) and is resistant to some antibiotics (16). However, these benefits also appear to be transient, lasting not more than 5 days after discontinuation (19).


Studies on non-diseased laboratory mice have shown that the administration of Saccharomyces boulardii during antibiotic treatment (Amoxicillin-clavulanate, 150 mg/kg) and another 1 to 2 weeks beyond the end of antibiotic treatment was able to maintain a high level of beneficial, commensal bacteria, promoting an efficient return to eubiosis for the gut system (19).

However, there is currently not enough scientific research done on the use of yeast-based probiotics on cats (obligate carnivores) and any other carnivorous animals’ digestive systems. A small number of studies and anecdotal reports on its pet use and carnivore-related digestive condition can be found but scientific literature and evidence is still lacking (20, 21).


Before you dash out to the shop to grab a probiotic for your pets, be aware that there are many, many products in the market carrying the label ‘probiotic’. 

The misuse of the term ‘probiotic’ (in the pet and human industries) has also become a major issue, with many products exploiting the term without meeting the established requisite criteria (1,2)

For example, some manufacturers of products containing some level of live microbes, that is not well-defined in terms of strain composition, stability, and ability to provide substantiable host benefits, will misleadingly label their products as ‘probiotics’. (1,2)

On the contrary, they are at best ‘items that contain live and active cultures’, without established true probiotic activities or benefits. (1)

The International Scientific Association for Probiotics and Prebiotics (ISAPP) gathered an expert panel in October 2013 to clarify and deliberate about a more precise definition of the term ‘probiotic’ to help steer clinicians and consumers to differentiate the diverse products on the market. (1)

World Gastroenterology Organisation (WGO) and (ISAPP) unequivocally recommend that the term ‘probiotic’ be used only on products that deliver live microorganisms with a suitable viable count of well-defined strains with a reasonable expectation of delivering stated benefits for the wellbeing of the host, backed by peer-reviewed studies. (1,2)

The goal to standardised and create accountability is difficult to achieve because of the vast differences in restrictions and requirements on product labels according to regulatory agencies of different countries(1)

The development of an internationally accepted and endorsed product-labeling guideline that communicates the information known about the probiotics being sold would be most useful for consumers (including pet custodians) and health-care providers (including veterinarians). 

For example, from a scientific perspective, WGO recommends that the labels for probiotics should include the following (2):


  1. Name of probiotic including Genus, species, subspecies, identification, with nomenclature consistent with current scientifically recognized names

  2. Strain designation

  3. Viable count of each strain at the end of shelf-lif

  4. Recommended storage conditions

  5. Recommended dose

  6. An accurate description of the physiological effect/ benefits

  7. Contact information of manufacturers


This narrative should be seriously deliberated and considered for future use in all probiotic products in Singapore (whether for human or animal consumption) to encourage better accountability to consumers at large. 


The strains of probiotics discussed represent a core group of well-studied and safe species likely to impart some general benefits for the host as extrapolated from human studies (2)

However, there are some reports of sepsis from bacterial probiotics and fungemia in human patients. 

Although these reports are uncommon and usually associated with human patients with central access catheters in intensive care (15,16) , we caution you to consult your appointed veterinarian before embarking your pet on probiotic therapy, whether the intention is to condition the digestive system during the healthy phase of life, or for recuperation from a diseased phase of life.

Author Contributions

Dr. Denise Ng BSC BVMS


Conflict of interest

The author declares that there is no conflict of interest.



The author received no specific grant from any funding agency in the public, commercial or not-for-profit sectors for the preparation of this review article.


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