Prior to the 1980’s most people would have balked at the idea of putting “bugs” into our bodies on purpose. Indeed, the realization that some microorganisms are beneficial, even imperative, to our gut health is fairly recent. We have much to learn about which are the most helpful, though preliminary evidence points to the efficacy of several particularly friendly groups, including Lactobacilli, Enterococci, Bifidobacteria, and the yeast, Saccharomyces bouldardii.

Probiotics are generally very safe and well-tolerated by both cats and dogs, though one should take extra care before administering them to an immunocompromised animal. Regardless of the health of your pet, it is always a good idea to consult your veterinarian before adding any supplements to your furry friend’s diet.

Increasing the Lactobacillus levels with the use of a probiotic has been shown to alleviate symptoms of gastrointestinal distress, including abdominal pain due to inflammation of the internal organs. These benefits are thought to be due to Lactobacillus’ production of anti-inflammatory byproducts (Park et al, 2017). In a study of sixty dogs suffering from acute diarrhea, treatment with a Lactobacillus-based probiotic reduced vomiting, maintained appetite, and normalized stool consistency. In addition, when the feces of the probiotic-treated dogs were analyzed, they contained lower numbers of potential pathogens when compared to the control group (Gomez-Gallago et al, 2016).

Most mammals, dogs and cats included, have at least some degree of lactose-intolerance. However, this does not mean that Lactobacilli are unsafe for mammalian consumption, as Lactobacillus is merely a group of bacteria that is capable of digesting lactose. They do not themselves contain lactose.

For pets with suspected or confirmed IBD, Lactobacillus-based probiotics may be especially helpful during an IBD-associated “flare.” However, there is also a case to be made for longer-term administration. We know that many IBD patients have trouble maintaining a healthy gut microbiome, including the presence of biologically-appropriate levels of Lactobacillus. Studies have shown that when probiotics are administered to these individuals and subsequently stopped, the gut microbiome can begin to revert to its pre-probiotic composition in as little as 48 hours.

Even for pets without chronic GI issues, a Lactobacillus supplement may be a good short-term remedy to keep on hand for managing acute diarrhea and/or vomiting caused by stress or infection. For these individuals, probiotics can decrease the time it takes for the individual to re-establish healthy colonies of bacteria following an illness.

Enterococci are a particularly hardy group of bacteria that are normally present in a healthy mammalian gut. They are extremely adaptable, and this quality affords them the ability to survive potentially lethal acid (Belli et al, 1991). Their robust nature makes them a potentially promising option as an oral probiotic supplement. Indeed, one of the major barriers to oral probiotics’ effectiveness is that the bacteria need to survive the highly acidic stomach contents before they can make it to their intended destination, the intestines. Many strains of Enterococci have no trouble with this journey.

Studies show that for healthy cats subjected to prolonged stress, administration of an Enterococcus-based probiotic decreases their likelihood of having diarrhea by threefold. This suggests that long-term Enterococcus supplementation could reduce the incidence of diarrhea, regardless of whether the animal has a history of gastrointestinal issues. In addition, it has been shown that administering an Enterococcus-based probiotic significantly reduces populations of Pseudomonas bacteria, which are present in elevated levels in dogs with IBD (Macinakova et al, 2006; Suchodolski et al, 2010). This sort of supplementation could be helpful to bring an IBD patient’s Pseudomonas populations back down to acceptable levels. Healthy animals can seemingly benefit too, though: even if your animal has no symptoms of IBD or general GI distress, many species of Pseudomonas have the potential to be pathogenic and cause serious illness. Decreasing their abundance within the gut decreases the odds of infection.

Unfortunately, the hardiness and efficacy of Enterococcus comes at a cost: members of this genus have a relatively high likelihood of developing antibiotic resistance, so in the unlikely event that a strain causes an infection, it could be very difficult to treat. One researcher described the danger of antibiotic-resistant strains of Enterococcus as a “great public health hazard for pet owners” (Abdel-Moein et al, 2017).

Bifidobacteria are another group of bacteria which are typically present in a healthy mammalian gut; they are known for their ability to carry out the fermentation of carbohydrates. The fermentation process yields lactic acid as one of its end products. Lactic acid, in turn, feeds such beneficial strains of bacteria as the aforementioned Lactobacilli. Thus, an insufficient population of bifidobacteria in the gut can trigger a cascade of gastrointestinal issues, because the waste products of bifidobacteria help sustain a number of other beneficial microorganisms.

The biochemical processes of bifidobacteria have proven clinical significance: for example, in people experiencing gastrointestinal symptoms, supplementation with an oral Bifidobacterium probiotic was shown to significantly decrease the incidence and severity of their symptoms (Gomi et al, 2015). In dogs suffering from acute hemorrhagic diarrhea, gut populations of bifidobacteria have been shown to be significantly decreased compared to healthy individuals (Heilmann et al, 2017).

Many of the benefits associated with Bifidobacteria are likely due to their favorable effects on the immune system. Bifidobacteria have been linked to increased activity of neutrophils, which are cells associated with the immune system that engulf and destroy disease-causing pathogens (Strompfova et al, 2014). In addition to bolstering defense against harmful organisms, they also are thought to prevent inappropriate activation of the inflammatory response. CD4+ T cells are one of the most important players in the mammalian immune system; in many cases of Inflammatory Bowel Disease, CD4+ T cells are activated when they should not be, which leads to excessive inflammation and subsequent gastrointestinal distress. One study has linked supplementation with Bifidobacterium to the “inhibition of disordered [CD4+] T cell activation,” decreasing the likelihood of excessive inflammation (Kim et al, 2007).

Bifidobacteria supplementation may be a good choice for your pet if diarrhea is a frequent concern. Though there needs to be more investigation into the long-term effects of Bifidobacteria supplementation, preliminary studies have found it to be very safe, with little evidence of any harmful side effects. In addition, it could be a viable option for immunocompromised pets, given the way that Bifidobacteria support the immune system. However, they are not just for sick or immunocompromised animals: even for healthy individuals, they help protect against harmful pathogens.

Unlike the probiotic strains mentioned thus far, which are of bacterial origin, S. boulardii is a type of yeast normally found growing on the skins of tropical fruits like mango and lychee. This strain of yeast has been shown to possess both anti-microbial and anti-inflammatory effects; as a result, it has been advanced as a viable probiotic treatment for both the prevention and the treatment of a wide range of gastrointestinal issues.

Researchers believe that S. boulardii’s anti-inflammatory effects are due to the influence it has on the CD4+ T cells (those immune cells mentioned earlier which, in IBD, are sometimes activated when they shouldn’t be). CD4+ T cells can migrate, and when too many of them migrate to the colon, it leads to excessive inflammation. S. boulardii yeast cells help trap some of the CD4+ T cells before they get to the colon, keeping them inside the lymph nodes where they can’t cause any harm (Dalmasso et al, 2006).

In addition to its anti-inflammatory effects, S. boulardii helps protect against disease-causing pathogens by preventing them from taking up residence inside the gut. Harmful microorganisms like Salmonella bind to the surface of S. boulardii cells, and once this binding takes place, the pathogen can no longer bind to the surface of the intestine (Gedek et al, 1999). The pathogenic cells and S boulardii cells are together eliminated during the next bowel movement. S. boulardii has been shown to be particularly effective to treat diarrhea arising as a result of systemic antibiotics, so this therapy is definitely something to consider in these cases (McFarland, 2010). However, it has also been shown to be effective in preventing relapses in IBD patients, so even if your pet’s GI symptoms are well-controlled, you might consider supplementing (Guslandi et al, 2000). S. boulardii’s anti-microbial effects are not limited to animals with GI issues; it has been shown to decrease the incidence of diarrhea even in healthy individuals, and is very unlikely to cause any harm (Can et al, 2006).

Most beneficial bacteria found in healthy cats and dogs have yet to be isolated and developed into probiotics.Lactobacillus, Enterococcus, and Bifidobacteria are important and useful probiotics, but they are not the dominant taxa found in the healthy cats. In the ranking of those bacterial taxa found in the digestive tract of healthy cats, Lactobacillus ranks 49th and occurs in only 27% of healthy cats.  Bifidobacteria ranks 35th and occurs in 49% of healthy cats and Enterococcus ranks 36th and occurs in 48% of healthy cats (AnimalBiome data). The most abundant taxa found in the digestive tract of healthy cats are Prevotella, Bacteroides, Blautia, and Fusobacterium (AnimalBiome data). Due to the clear success of fecal transplants in people with Clostridium difficile infections, a growing number of veterinarians are starting offer fecal microbiota transplants (FMT) as a way to provide microbial supplementation from a healthy, live donor of the same species. Recognizing that many pets could benefit from FMTs, AnimalBiome has created dog- and cat-specific oral FMT capsules (also known as “poo pills” or “poobiotics”) using material from carefully screened donors and made them readily available to pet owners.