Arabinogalactan, a form of fiber usually isolated from the bark of the Larch tree, has well documented prebiotic effects on probiotic organisms within the digestive tract.
Arabinogalactan also has a stimulatory effect on GALT (gut associated lymphoid tissue). Read more on GALT in Dr. Eleanor Kellon’s article The Gut & Immunity.
We typically think of the intestinal tract as a digestive organ, but it has a very important role in the immune system as well. We all know, with horses especially, proper digestive function is key to overall health and survival.