Probiotics and Prebiotics

We recently had a question about prebiotics vs probiotics. I’ll answer that here.

The intestinal tract of a horse is very complex. In addition to digestive actions of stomach acid, pancreatic enzymes and bile, teeming populations of microbes assist in the breakdown of all forms of carbohydrates, including fiber and complex plant carbohydrates that cannot be digested by the horse’s own enzymes.

These microbes also have an important function in the immune system.  They secrete compounds which keep potentially dangerous bacteria and viruses in check. They also gently stimulate the immune tissue lining the intestinal tract.


Prebiotics are substances that support the growth of beneficial bacteria. Food is the major prebiotic and the types of bacteria in the intestinal tract will reflect the type of diet. In addition, adding very easily fermented forms of fiber to the diet can improve the numbers of fiber fermenting bacteria. This includes soy hulls, beet pulp, psyllium husk fiber and oligosaccharides.

Also in the prebiotic category is bacterial or yeast fermentation products. These are compounds secreted when the organisms are growing rapidly in cultures.  Growth factors and other substances help support the growth of the same type of organism inside the intestines.

Probiotics are actual live organisms fed to the horse on a daily basis. When the foal is born, the intestinal tract is sterile.  The foal begins to pick up bacteria with everything its mouth touches. Some survive the stomach acid to take up residence inside the intestines.

The rationale behind probiotics is that by feeding large numbers (tens of billions) of beneficial bacteria or yeast you can build strong populations inside the horse. Ongoing current research is beginning to provide detailed information about the types of organisms in horses, using advanced genetic techniques. One day this will allow manufacturers to formulate mixtures specific for the horse.

In the meantime, Lactobacillus bacterial strains and Saccharomyces yeast have been shown to  benefit horses.  If your horse is already utilizing his diet well with no GI issues or abnormal manure, probiotics are not likely to be beneficial. Otherwise they are worth a try with digestive issues.

Eleanor Kellon, VMD

About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions,, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition.
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