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Ensilage or silaging is the process of preserving green food for livestock in an undried condition in airtight conditions, either in a storage silo (an airtight pit), or in plastic wrapping. The fodder which is the result of the process is called silage.
Ensilage creates a nutritious food for livestock. It can be substituted for root crops; it is easily digestible; milk produced by animals eating silage maintains its quality and taste; it can be provided irrespective of the weather; it provides grass all year round; and a larger number of livestock can be supported on a given area by the use of ensilage than is possible by the use of green crops.
Using the same technique as the process for making sauerkraut, green fodder was preserved for animals in parts of Germany since the start of the 19th century. This gained the attention of a French agriculturist, Auguste Goffart of Sologne, near Orléans, who published a book in 1877 which described the experiences of preserving green crops in silos. Goffart's experience attracted considerable attention. The conditions of dairy farming in the USA suited the ensiling of green maize fodder, and was soon adopted by New England farmers. The favourable results obtained in America led to the introduction of the system in the United Kingdom, where Thomas Kirby first introduced the process for British dairy herds.
Early silos were made of stone or concrete either above or below ground, but it is recognized that air may be sufficiently excluded in a tightly pressed stack, though in this case a few inches of the fodder round the sides is generally useless owing to mildew. In America structures were typically constructed of wooden cylinders to 35 or 40 ft. in depth.
Ideally the crop is mown when in full flower, and deposited in the silo on the day of its cutting. Maize is cut a few days before it is ripe and is shredded before being elevated into the silo. Fair, dry weather is not essential; but moisture content should not exceed 75% of the whole.
The material is spread in uniform layers over the floor of the silo, and closely packed. If possible, not more than a foot or two should be added daily, so as to allow the mass to settle down closely, and to heat uniformly throughout. When the silo is filled or the stack built, a layer of straw or some other dry porous substance may be spread over the surface. In the silo the pressure of the material, when chaffed, excludes air from all but the top layer; in the case of the stack extra pressure is applied by weights in order to prevent excessive heating.
The closeness with which the fodder is packed determines the nature of the resulting silage by regulating the chemical reactions that occur in the stack. When closely packed, the supply of oxygen is limited; and the attendant acid fermentation brings about the decomposition of the carbohydrates present into acetic, butyric and lactic acids. This product is named sour silage. If, on the other hand, the fodder is unchaffed and loosely packed, or the silo is built gradually, oxidation proceeds more rapidly and the temperature rises; if the mass is compressed when the temperature is 140 to 160 Fahrenheit, the action ceases and sweet silage results. The nitrogenous ingredients of the fodder also suffer change: in making sour silage as much as one-third of the albuminoids may be converted into amino and ammonium compounds; while in making sweet silage a smaller proportion is changed, but they become less digestible. In extreme cases, sour silage acquires an unpleasant odour although it keeps better than sweet silage when removed from the silo.