There are two main phases in the ensiling process. The first is the aerobic phase which occurs in the presence of oxygen air. Oxygen is present in the forage as it is placed in the silo. This oxygen is consumed by the living plant material through the process of respiration. Under aerobic conditions plant enzymes and microorganisms consume oxygen and bum up the plant watersoluble carbohydrates sugars producing carbon dioxide and heat. The length of this phase is variable depending on ensiling conditions; it could last for a few hours or for as long as several days. It is good silage making practice to limit this phase as much as possible since watersoluble carbohydrates are being consumed and other nutrients are being destroyed. The heat generated by an extended aerobic phase can raise the temperature of the ensiling forage material sufficiently to cause heat damage. Good silage making practices reduce the amount of time that aerobic microorganisms and oxidizing plant enzymes are able to function. This is accomplished by chopping the silage to a short length, packing it thoroughly, and sealing the silo effectively. The second or anaerobic phase begins when the available oxygen is used up through plant respiration and aerobic bacteria cease to function. Anaerobic bacteria bacteria that grow in the absence of oxygen then begin to multiply rapidly and the fermentation process begins. Ideally the microorganisms which grow most rapidly will be predominately lacto~ bacilli species which produce lactic acid from the fermented plant material. The lactic acid which is produced will lower the pH of the silage. Fermentation completely ceases after 3 to 4 weeks when the pH becomes so low that all microbial growth is inhibited.

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