Choosing the right probiotic | BioStar US

Choosing the right probiotic for your horse or dog

With so many probiotic supplements to choose from, it can be overwhelming to figure out which one is right for your horse or dog. Compound this with confusing labeling, heavy marketing, and price inconsistency, and it’s no wonder consumers are often guessing, or just picking a product from a store shelf that says “probiotic.”

Sym-Biota K9 | BioStar US

The key to effective probiotic supplementation is understanding that the microbiomes of horses and dogs are complex systems; a one-size-fits-all approach will not work.

The gut of a healthy animal hosts a diversity of bacterial species—not just a single strain— in a highly varied gut ecosystem that also includes yeasts and fungi.

When does my horse need a probiotic?

Not so long ago, researchers and nutritionists recommended that probiotics for horses be used only as needed.

Now, as we understand better the effects of stress on the microbiome, the effects of domestication, lack of turnout, confinement, lack of equine socialization (living in groups), travel, training, competition, and exposure to environmental factors such as pesticides and herbicides, it’s clear that probiotics may be necessary on a daily basis for some horses.

Horses who live out and horses who live in groups are the least likely to need daily probiotic supplementation—except when given antibiotics, when they are wormed, if they need to gain weight, or if their immune system needs support.

Horses that are in training, horses that compete, and horses on lay-up are most likely to need daily probiotic support.

Sweating jumping horse

What are probiotics, prebiotics, and postbiotics?

Probiotics are certain bacterial and yeast strains beneficial to the GI tract. Mushrooms (fungi) are being studied for their role as probiotics in the gut, but at present, mushrooms are considered prebiotics.

Prebiotics are compounds such as the complex carbohydrates (fiber and starch) found in food that feed beneficial microorganisms in the gut.

Postbiotics are dead or parts of dead microorganisms or compounds (metabolites) that microorganisms produce. Postbiotics occur in the gut of humans and other mammals and contribute to the production of short-chain fatty acids like butyrate and propionate.

Active and inactive probiotics

Active probiotics are measured in colony forming units (CFUs). This tells you that the bacteria or yeast is alive and capable of colonization. Yogurt, for example, ranges between seven and 10 billion CFUs, while kefir provides up to 20 billion CFUs.

Inactive probiotics (no CFUs listed) act more like prebiotics: food for the microorganisms in the GI tract.

How many CFUs of active probiotics does a horse or dog need?

Recommended CFUs daily | BioStar US

At this point, the ideal CFU amounts of active probiotics for humans and other animals are still being studied. There is still so much we don’t know about the microbiome.

Currently, the recommended range for humans is 10-20 billion CFUs per day. Some conditions such as hypertension, high-LDL cholesterol, antibiotic-associated diarrhea, and Clostridium difficile-associated diarrhea can require up to 100 billion CFUs per day.

For dogs, one to 10 billion CFUs daily is the recommendation from Cornell University College of Veterinary Medicine.

The range for horses is estimated at 100 to 400 billion CFUs per day, based on the human and dog models, and taking into account the longer digestive tract of the horse.

Prominent bacteria in the gut microbiome

While gut microbes and the microbiome continue to be a field of increasing research and study, there are a few things we do know:

  • The microbiome of mammals is complex, with the total number of microbes far greater than the number of host genes.
  • The intestinal tract contains a diverse community of bacteria, fungi, parasites, protozoa, yeasts and viruses. In healthy horses and dogs there is a balance of beneficial microbes and pathogenic microbes.
  • The prominent bacteria phyla in equines are Firmicutes, Bacteroidetes and Proteobacteria.
  • The prominent bacteria phyla in dogs are: Firmicutes, Fusobacteria, Proteobacteria, Actinobacteria, and Bacteriodetes.

Prominent gut bacteria in horses

    • Firmicutes includes Lactobacillus, Bacillus, Clostridium, Enterococcus and Ruminococcus bacteria.
    • Bacteroidetes strains are commonly found in terrestrial soils and lakes.
    • Proteobacteria include a wide range of pathogens, such as Escherichia, Salmonella, and Helicobacter.(Remember, the gut microbiome contains a balance of both beneficial and pathogenic bacteria. In animals, this balance contributes to good health.)

Prominent gut bacteria in dogs

    • Firmicutes includes Lactobacillus, Bacillus, Clostridium, Enterococcus and Ruminococcus bacteria.
    • Fusobacteria includes strains of Bacteroides, Fusobacterium, Prevotella, and Megamonas among others. Research has shown that Fusobacterium abundance is increased in dogs with access to the outdoors. Interestingly, in humans Fusobacteria is associated with gastrointestinal disease. However in dogs, Fusobacterium is associated with good health.
    • Proteobacteria and Actinobacteria are colonizers of the small intestine.

For more detailed information on the microbiome of dogs, and the effects of diet and lifestyle, this article is very thorough:

“The Role of the Canine Gut Microbiome
and Metabolome in Health and Gastrointestinal Disease”
(Frontiers of Veterinary Science)

Colony diversity in the gut microbiome

Wild horses have a more diverse microbiome composition than domesticated horses. Newborn, healthy foals have a rich and diverse microbiota, while older horses show a decreased level of microbe diversity.1

Dogs also have more diverse microbiomes when their diet and lifestyle include less processed food and lots of time outside.

Increasing Microbial Diversity Wild Horses | BioStar US

Stress and imbalance of the gut microbiome

Horses have a sensitive intestinal tract. Stress from exercise, transport, changes in routine or feed—even differences from one hay load to another—can alter the composition of the gut microbiome.2

This change in the microbiome balance can contribute to stress on the immune system, dysregulation of the gut-brain barrier (meaning less serotonin production), and possible dysbiosis (microbial balance disruption) in the GI tract.

The effect of antibiotics


Penicillin, cephalosporins and fluoroquinolones will cause imbalances of the microbiota in the gut.3

According to one research article: “Changes in the equine microbiome composition induced by antibiotics seemed to be specific for each drug. It seems to take 25 days to rebuild the microbial composition back to individual baseline levels, but differences are still detectable beyond that time.” 4,5

A study of domestic horses and feral horses published in Nature found that domestic horses, as assessed via fecal, had genes conferring resistance to tetracycline, “likely reflecting the use of this antibiotic in the management of these animals. Our data showed an impoverishment of the fecal microbiome in domestic horses with diet, antibiotic exposure and hygiene being likely drivers.” 6

Focus on hygienic and antibiotic-dependent lifestyles may be contributing to the decline in microbiota abundance and diversity, which can actually lead to dysbiosis.


Antimicrobials profoundly disrupt the canine GI microbiota. A study published in the Veterinary Journal (Jan 2023) highlighted: “Early life antimicrobial exposure may increase susceptibility to disease. Antimicrobials commonly used in GI diseases of dogs seem to prolong GI dysbiosis.” 7

Using probiotics with antibiotics

We used to think that giving probiotics for the same duration as an antibiotic regimen was sufficient; for example, one week of antibiotic therapy requires one week of probiotic supplementation. But research is showing that to really re-colonize the gut, 20-30 days of probiotics after one week of antibiotic therapy is needed. Two weeks of antibiotic therapy needs 40-50 or more days of probiotic supplementation.

We are learning that re-balancing the GI tract takes time. There’s no quick fix.

Tips: Do not give probiotics at the same dosage time as antibiotics. Separate them by several hours. Make sure probiotic supplements with Lactobacillus or Bifidobacterium are enteric-coated or micro-encapsulated to ensure passage into the small intestine.

Probiotics in Eastern medicine

BioStar’s probiotics are based on Ayurveda. In Ayurvedic medicine, probiotics are classified by how they affect the body at large, and the GI tract specifically. We never combine warming yeast probiotic strains with cooling probiotic strains.

The term “digestive fire” (Agni) is the energy necessary for horses and dogs to digest and absorb nutrients from food. Too much digestive fire can be depleting and lead to acid indigestion, gastritis, diarrhea, other inflammatory issues, as well as irritability and aggressiveness. If the digestive fire is weak, it can lead to a slower metabolism, heaviness in the body, excess weight, constipation, gas, diarrhea, cracking joints, and may increase lethargy and lack of energy.

Probiotics can increase or decrease the digestive fire, depending on which probiotic strains you choose.

The classifications are:
Warming – (increases digestive fire) – Yeasts
Cooling – (lowers digestive fire) – Lactobacillus and Bifidus bacteria
Neutral – (neither lowering nor increasing) – Bacillus bacteria

One would not use a warming probiotic yeast with a cooling probiotic bacteria. The effect on the GI tract would be adding more fire, and at the same time putting the fire out.

When to use warming, cooling, and neutral strains for horses

BioYeast EQ for horses | BioStar USWarming (yeasts: S. boulardii, S. cerevisiae): especially beneficial for older horses, particularly those who need to gain or maintain weight. Can be helpful for horses in winter to increase digestive fire. Can be beneficial for horses with fecal water syndrome.
-(Bio Yeast EQ is warming)

BioFlora EQ | BioStar USCooling (Lactobacillus, Bifidus, Enterococcus): for horses with active ulcers or who are ulcer-sensitive. Horses under stress. Horses undergoing antibiotic therapies. Specific strains support the gut-brain axis and can help mood and emotion.
-(BioFlora EQ is cooling)
-(Hedgerow GI and Hedgerow Restore are cooling AND neutral)

Sym-Biota EQ | BioStar USNeutral (Bacillus, also known as SBOs (soil-based organisms): can be combined with warming or cooling probiotics. Horses who spend a lot of time outside in healthy pastures are exposed to SBOs when they eat grass, sniff the ground, or roll in grass and dirt. Bacillus forms spores that can crowd out pathogenic bacteria in the gut. Specific strains of Bacillus (like B.subtilis) have shown antiviral activity in vitro and in animal models.
-(Symbiota EQ is neutral)
-(Hedgerow GI and Hedgerow Restore are cooling AND neutral)

When to use warming, cooling, and neutral strains for dogs

Hedgerow K9 Boulardii | BioStar USWarming (yeasts: S.boulardii, S.cerevisiae) beneficial for diarrhea, inflammatory bowel disease, mild cases of colitis.
– (Hedgerow K9 Boulardii is warming)

CTerra Biota K9 | BioStar USooling (Lactobacillus, Bifidus, Enterococcus): beneficial for relieving gas, improving stool quality, and helping reduce colonies of harmful Clostridia. Supportive for dogs with IBS. Specific strains support the gut-brain axis and can benefit moods and emotions.
– (Terra Biota K9 is cooling)

Sym-Biota K9 | BioStar USNeutral (Bacillus, also known as SBOs (soil-based organisms): can be combined with warming or cooling probiotics. Dogs who spend a lot of time outside in healthy yards, farms, and forests are exposed to SBOs as they smell the ground or roll in grass and dirt. Bacillus forms spores that can crowd out pathogenic bacteria in the gut. Specific strains of Bacillus (like B.subtilis) have shown antiviral activity in vitro and in animal models.
– (Sym-Biota K9 is neutral)

Factors to consider when choosing a probiotic

Look for multi-strain bacteria formulas. Because the microbiome is diverse, probiotic supplements with only a single strain of bacteria go against the very essence of the microbiome.

In the case of yeasts, there are two prominent strains (S. boulardii, S. cerevisiae). They can be used together or singly. Probiotics supplements that contain active yeast strains that are coupled with neutral bacteria (like Bacillus, which can crowd out pathogens) are a very good choice.

The bacteria Lactobacillus and Bifidus are easily destroyed by stomach acids. Make sure your probiotic supplements with these strains are either enteric coated or micro-encapsulated to ensure their passage to the small intestine.

Bacillus bacteria and yeasts can survive the harsh environment of the stomach. They do not need enteric coating or micro-encapsulation.

Mixing yeasts (warming) with cooling bacteria strains is not recommended. It creates a kind of push-pull in the gut, in direct opposition to Eastern medicine for gut health.

Check the colony forming units (CFUs) on the label. Active probiotics are required to be labeled with the amount of CFUs per serving. For example: 10 billion CFUs for a horse is not very much. For a dog, however, it is in the high therapeutic range.

Ongoing research

There is still much we don’t know about the ecology of the GI tract. The microbiota colony balance can be very different from horse to horse, and dog to dog.

As more research results roll in, BioStar will continue to study those findings and implement them in the ways that best benefit our animals.











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