Stress, illness, and age can disrupt beneficial microflora in the horse's gastrointestinal tract. To remedy these disruptions, pro and prebiotics may be used. Probiotics are substances which stimulate the growth of microorganisms in the intestinal flora, especially those with beneficial properties. The main purpose of adding such supplements to feeds is to keep the hindgut stabilised.
 
It’s important to note that a high-grain, high-concentrate, low-fiber diet is also hard on microbes in the hindgut. This type of diet has a more negative impact than anything else.
Prebiotics are a newer concept than probiotics. These are not microbes, but inert ingredients that help microbial populations in the hindgut remain stable and healthy. 
Pre and probiotics can be helpful in keeping the gut healthy.
Gastralign combines three key ingredients that can be helpful to keep the gastrointestinal system healthy: 
 
Yea Sacc, a probiotic live yeast culture based on Saccharomyces cerevisiae strain 1026 
Bio-Mos, a prebiotic derived from yeast cell walls
Allzyme SSF, a complex of naturally occurring enzymes

 
Gastralign aims to: 
 
improve the bioavailability of the diet
Support greater fibre digestion
improve absorption of phosphorus and calcium
boost natural immunity 
reduce damage to the gastrointestinal tract
Binds to negative bacteria preventing its absorption
Support normal digestive function during times of stress, worming & antibiotics
 
Dosage is 25 grams per day