The microflora in the hindgut are responsible for fermentation. This microflora is sensitive to changes in diet. An overload of high-sugar type feeds or high levels of fructan can upset the normal population of bacteria, changing the environment within the hindgut that causes a cascade of problems. Typically, grain and concentrate rations are higher in sugar and starch than forages. When horses are on a ration or diet that has a high sugar and starch content, it can have dramatic effects on the digestive physiology.