ARS | Publication request: MICROBIOLOGY OF ENSILING

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 1, 2001
Publication Date: November 1, 2003
Citation: Pahlow, G., Muck, R.E., Driehuis, F., Oude Elferink, S.J., Spoelstra, S.F. 2003. Microbiology of ensiling. In: Buxton, D.R., Muck, R.E., Harrison, J.H., editors. Silage Science and Technology. Madison, WI:American Society of Agronomy, Crop Science Society of America, Soil Science Society of America. p. 31-93.

Technical Abstract: In ensiling, crops are stored at a biologically active moisture content. As a consequence microorganisms are implicated in both the preservation and spoilage of silages. The most important microorganisms are the lactic acid bacteria (LAB). This group of facultative anaerobes ferment primarily sugars to lactic acid, acetic acid, ethanol, carbon dioxide and other minor rproducts. Their activity reduces crop pH so that other anaerobic microorganisms are inhibited. They are divided into three groups (obligate homofermenters, facultative heterofermenters, obligate heterofermenters) based on the products of hexose fermentation and on their ability to ferment pentoses. Enterobacteria are important at the start of ensiling. They compete with the LAB for sugars, fermenting them mostly to acetic acid. Another role is in reducing nitrate to nitrite, nitrogen oxides and ammonia. The nitrogen oxide gases are commonly called "silo gas" and are a safety hazard. Clostridia are the other major group of anaerobic bacteria that are detrimental to silage quality, fermenting sugars and lactic acid to butyric acid and amino acids to amines, organic acid and ammonia. These fermentations cause substantial dry matter loss and reduce silage palatability. Other minor fermenters are propionic acid bacteria, yeasts and bacilli. When silage is exposed to air through inadequate sealing or during feed out, aerobic microorganisms may develop and cause substantial dry matter losses. Yeasts are normally the first group to develop with the exception of acetic acid bacteria in corn silage. These microorganisms utilize fermentation products and raise pH so that other microorganisms such as bacilli, molds, listeria and other bacteria may proliferate.