Prebiotics, such as short-chain fructo-oligosaccharides, are specially fermented compounds that alter the composition and/or activity of gastrointestinal bacteria and microflora to ameliorate the health of the host. Until now, only a limited amount of research on the effect of prebiotics in horses has been performed, despite the fact that horses are particularly sensitive to changes in the microflora in the hindgut (including the colon and cecum).
In a study performed by French researchers, the short-chain fructo-oligosaccharide supplementation was evaluated in four horses subjected to a sudden diet change designed to mimic a feeding error.
The study found that daily supplementation with 0.05 to 0.07 grams of short-chain fructo-oligosaccharides per kilogram of body weight should be beneficial in preventing digestive disorders caused by stressful situations, such as acute starch overloads.

Horses are exceedingly sensitive to environmental stress and rapid alterations in diet. According to Equine Extension Specialist Carey Williams, PhD, from the Equine Science Center at Rutgers, The State University of New Jersey, "These changes can result in the development of colic or laminitis, potentially due to alterations in the microbial population or lack of the proper microbes in the hindgut."

"Based on the positive results reported in this study, prebiotics may also be beneficial for horses subjected to a variety of stressful situations, such as transport, competition, or weaning," explained Williams. "However, further research is certainly warranted."

The study "Effects of dietary short-chain fructo-oligosaccharides on the intestinal microflora of horses subjected to a sudden change in diet" will be published in an upcoming edition of the Journal of Animal Science. The abstract is currently available on PubMed. Contributing authors were Respondek, Goachet, and Julliand.

Prebiotics are a category of functional food, defined as:
Non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improve host health.[1]
This was updated by Roberfroid in 2007 J. Nutr.; 137:830S to: "A prebiotic is ‘‘a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health.’’ Today, only 2 dietary nondigestible oligosaccharides fulfill all the criteria for prebiotic classification." Those 2 being fructooligosaccharides and galactooligosaccharides. Use of the term other than in that manner is incorrect, since all oligosaccharides do not fit this definition, i.e. mannanoligosaccharides (MOS). They may confer other positive benefits, but are minimally utilized by the comensural bacteria.
Typically, prebiotics are carbohydrates (such as oligosaccharides), but the definition does not preclude non-carbohydrates. The most prevalent forms of prebiotics are nutritionally classed as soluble fibre. To some extent, many forms of dietary fibre exhibit some level of prebiotic effect.

The prebiotic definition does not emphasize a specific bacterial group. Generally, however, it is assumed that a prebiotic should increase the number and/or activity of bifidobacteria and lactic acid bacteria. The importance of the bifidobacteria and the lactic acid bacteria (LABs) is that these groups of bacteria have several beneficial effects on the host, especially in terms of improving digestion (including enhancing mineral absorption) and the effectiveness and intrinsic strength of the immune system. A product that stimulates (or claims to stimulate) bifidobacteria is considered a bifidogenic factor. Some prebiotics may thus also act as a bifidogenic factor and vice versa, but the two concepts are not identical.

Traditional dietary sources of prebiotics include soybeans, inulin sources (such as Jerusalem artichoke, jicama, and chicory root), raw oats, unrefined wheat, unrefined barley and yacon. Some of the oligosaccharides that naturally occur in breast milk are believed to play an important role in the development of a healthy immune system in infants, but these are not considered prebiotics, as they do not act through the intestinal microflora.
Prebiotic oligosaccharides are increasingly added to foods for their health benefits. Some oligosaccharides that are used in this manner are fructooligosaccharides (FOS), xylooligosaccharides (XOS), polydextrose and galactooligosaccharides (GOS). Some monosaccharides such as tagatose are also used sometimes as prebiotics.[citation needed]
In petfood also mannooligosaccharides are being used for prebiotic purposes.

Studies have demonstrated positive effects on calcium and other mineral absorption, immune system effectiveness, bowel pH, and intestinal regularity. Correlations have also been made with other positive health factors, but more research is required.
The immediate addition of substantial quantities of prebiotics to the diet may result in a temporary increase in gas, bloating or bowel movement. It has been argued that chronically low consumption of prebiotic-containing foods in the typical Western diet may exaggerate this effect.