Current Perspective on Probiotics
- Jan 11, 2023
- Eleanor Kellon, VMD
The microbiome is the microorganisms inhabiting a specific environment, like the gut or skin.
The number, complexity, and diversity of organisms in the intestinal tract have captured everyone's imagination. The idea that they may influence health outside the gut is both exciting and a little frightening. It's also the most controversial, but everyone can agree that the intestinal microbiome is critical to the normal function of the horse's digestive tract.
Upper Intestinal Tract
The upper intestinal tract [stomach and small intestine] is populated primarily by organisms that break down and ferment starch and other simple carbohydrates. This benefits the horse by reducing the amount of glucose that will be absorbed and help protect the large intestine [cecum and colon] from too many simple carbohydrates.
Once the large intestine starts, in the cecum, there is known to be an abrupt change in the number and types of organisms. There are two major phyla (Firmicutes and Bacteroides) but many smaller populations as well. The density and diversity of organisms are much greater and while some generalizations can be made it's also true that every horse has a microbiome that is unique to them. like a human fingerprint.
The hind gut population is capable of breaking down sugars, starch, complex plant carbohydrates, fiber, and protein. The organisms often work together. For example, some may ferment sugar and start to lactate while others use the lactate themselves thus buffering the intestine.
How are Probiotic Organisms Chosen?
Probiotics have been appearing in basic feeds and all sorts of supplements for about a quarter of a century now. Supporting normal intestinal function is something everyone can get behind but how are the organisms chosen? Does it matter?
It certainly does matter. While the safety profile of probiotics is quite good, it has been shown that using the wrong strain can have negative GI effects, especially in the fragile gut environment of foals. For many years the strains used in equine products were largely based on what was beneficial in people and to a lesser extent in other farm animals. We can now do better.
Recent improvements in gentic techniques has led to a mini explosion of studies on the makeup of the equine intestinal microbiome. We can now at least identify the common equine specific species and focus on supplying a blend of organisms that is more approptiate for the horse.
For example, Lactobacilli are in the larger family Firmicutes. They are found throughout the equine intestinal tract but different species are present in the stomach/small intestine than in the hind gut. Lactobacillus acidophilus is one of the most well-known probiotic species but we have found many other strains that are specific to horses such as L. reuteri and L. salivarius for the upper part of the digestive tract and L. equi, a horse-specific strain in the hind gut.
Other important bacterial strains include Bacilus subitilis which favors the growth of beneficial bacteria over pathogens and Propionibacterium freudenreichii which metabolizes lactate and helps control pH. The yeast Saccharomyces cerevisiae is perhaps the best-researched equine probiotic of all assists fermentation with any type of diet and should be a prominent ingredient in all equine probiotic products.
Look for these specific organisms and counts in the billions (BCFU = billion colony forming units = billion organisms) to give your horse the most state of the art support possible.
- Eleanor Kellon, VMD