The World Health Organization definition of probiotics is live organisms which, when administered in adequate amounts, confer a health benefit on the host. This usually refers to oral ingestion but they may also be used for health of the skin or the female reproductive tract.
Populating the gut begins in the birth canal.
The term microbiome describes the population of organisms that inhabit a specific location. Foals are sterile in the uterus but they begin to populate their bodies with organisms during the birth process. Everything their muzzle touches introduces more organisms that could take up residence in their intestinal tract. They have to survive stomach acid and be able to thrive in the pH and low oxygen tension in the bowel, on the type of food the animal is ingesting. However, there is no lack of diversity in the environment and this process proceeds uneventfully.
Amazingly, the precise microbiome makeup is different for every horse but they are often similar in terms of the families of organisms present and their percentages. The relative number of species shifts predictably with diet changes. This isn’t surprising since the major determinant of which organisms can thrive is whether or not they have a food source.
If the organisms are so abundant and adaptable, why would you ever have to feed probiotics? For healthy horses with normal intestinal function and holding weight as they should, you don’t have to routinely feed probiotics but there are situations where they can be helpful, including:
- After antibiotic use
- In horses performing extremes of speed or endurance exercise, or after long distance shipping
- Older horses having trouble holding weight
- Horses with suboptimal hind gut fermentation
These are all situations when we know there can be compromise of the microbiome of the intestinal tract.
Once you have identified candidates for probiotic supplementation, you need to pick products most likely to be helpful, including those with equine specific strains in the formulation. Saccharomyces cerevisiae yeast have proven their beneficial effects in multiple studies with a wide spectrum of diets. Saccharomyces boulardii yeast are helpful after antibiotic use and in imbalances involving harmful organisms.
Lactobacilli are found throughout the intestinal tract and are the dominant species in the stomach and small intestine where they help digestion of sugar and starch. Equine specific strains include L. salivarius, L. equi and L. reuteri. In addition to the Saccharomyces yeasts, the hind gut can benefit from Bacillus subtilis, Enterococcus faecium and Propionibacterium as well as Bifidobacterium species.
For routine use after antibiotics or shipping, a basic probiotic product which has a high dosage of S. cerevisiae is a good choice. Horses with weight problems will benefit from a product which also has high digestive enzyme activity documented. For horses with evidence of irritation to the lining of the intestinal tract, the addition of ingredients like Slippery Elm Bark, sodium copper chlorophyllin, Marshmallow Root, Glutamine and Aloe Vera can be soothing and support a healthy mucosa.
Digestive supplements aren’t needed for every horse but when you are stressing the GI tract or the horse has obvious signs of difficulty, probiotics and other support supplements can help.
Eleanor Kellon, VMD