The role of microorganism in silage making is directly related to the production of the following acids - lactic acid, acetic acid, propionic acid and butyric acid. Lactic acid is the most important of the four. If formed rapidly and sufficient quantity preserves the ensiled plant material therefore no decay. Lactobacilli occur in large amounts in green plants. Their development in the ensiled material depends on the presence of large quantities of sugar in the plant material. Crop plants like maize which have large carbohydrate content are easier to ensile than legume plants with low carbohydrate content because of the presence of high levels of lactobacilli..
Other acids are formed during the ensiling process but are not desirable. If green fodder used as ensiling material have very high moisture content the silage formed have high acetic acid and therefore unpalatable. If butyric acid forms in silage the result is unpleasant smell and silage in unpalatable. Presence of butyric acid is an indication that silage has undergone undesirable fermentation.