Submitted to: Sixth Edition of Forages, Volume II The Science of Grassland Agriculture
Publication Type: Book / chapter
Publication Acceptance Date: 3/14/2006
Publication Date: 2/1/2007
Citation: Muck, R.E., Kung, L. 2007. Silage production. In: Barnes, R.F., Nelson,C.J., Moore, K.J., and Collins, M., editors. Forages: The Science of Grassland Agriculture, Volume II. 6th edition. Ames, IA:Blackwell Publishing. p. 617-633. Interpretive Summary:
Technical Abstract: Ensiling is a growing practice worldwide, allowing a moist forage to be preserved until fed to livestock. Preservation is due to a combination of three factors: an oxygen-free environment, a low pH and fermentation products (lactic and acetic acids). The low pH and acids are the results of the fermentation of sugars by lactic acid bacteria naturally present on the crop. The easiest forages to ensile are whole-crop cereals because of high sugar concentrations and low buffering capacity. Of the perennial forages, cool-season grasses are easiest to ensile and legumes are the most difficult. At harvest, the most important consideration is the moisture content of the crop. Ensiling too wet may result in effluent losses and a clostridial fermentation, both reducing the feeding value of the silage. Ensiling too dry predisposes a silage to aerobic microbial spoilage and heating when the silage is exposed to oxygen. Crops may be ensiled in a wide variety of silo types: covered piles, horizontal walled silos (bunkers), tower silos, pressed bag silos and wrapped bales. Keeping out oxygen is the key to low losses. All but tower silos rely on a polyethylene plastic film to seal out oxygen during storage. As a consequence the smallest silos (wrapped bales and bag silos) are the most susceptible to large losses if the plastic seal is not maintained. During emptying, feed out rate determines the exposure time to oxygen prior to feeding. At recommended feed out rates, a silage is exposed to oxygen for approximately seven days, providing substantial time for spoilage to occur. Various additives are used to improve silage quality: inoculants, enzymes, nonprotein nitrogen, and acids. Intake and animal performance problems with silages are most frequently associated with either clostridial fermentation or aerobic spoilage microorganisms. Clostridial fermentation reduces intake, and the butyric acid produced increases the risk for ketosis. Aerobic spoilage not only reduces the digestible dry matter but may heat the silage, reducing intake. Also molds may produce mycotoxins that may adversely affect animal health.