Silage – Preserving Silage Quality


When corn silage harvest commences, producers must remember to preserve silage quality through the following simple steps:

  • Pack corn silage to a density of 15 lbs dry matter (DM) per cubic foot. 
  • Fill silo/bunker as quickly as possible without compromising quality. 
  • Cover to prevent aerobic respiration.

To understand the importance of these three guidelines, we will quickly review the ensiling process and how they relate. Researchers have broken the ensiling process into four phases. The first is an aerobic phase (Phase I). The duration of this phase is influenced by filling time (exposure time) and density (porosity) of the silage. The microbes associated with this phase require oxygen for respiration and water soluble carbohydrates. Prolonged exposure to the air will cause increased nutrient loss and/or 'shrink.' This is why researchers and agriculture consultants emphasize the importance of proper packing (silage density) and quick filling time.

It is very important to match packing machinery to the quantity of material produced hourly. The general rule of thumb for proper compaction is 800 lbs of tractor per ton of silage per hour. They also recommend that producers use a leading wedge shape (1:4 slope) in which a thin layer is spread and packed, thereby improving the density of the silage. Once the pile or silo has been filled, it is important to cover the bunk as soon as possible. This will sever the source of oxygen required by the obligate aerobe bacteria for respiration. Once the oxygen source has been depleted the next step is phase II.

Phase II is the fermenting or anaerobic phase of ensiling and its duration is dependent on a number factors. Homo and heterofermentative lactic acid bacteria (LAB) are the dominant organisms driving the fermentation process. They are both obligative anaerobes and produce lactic acid. However, the hetero form also produces ethanol and CO2. The production of CO2, similar to respiration, results in another source of shrink. The use of homofermative inoculants helps to reduce shrink and nutrient loss. As lactic acid accumulates, the pH will decrease, thereby eliminating the bacteria except for LAB. Once the LAB has utilized the available carbohydrates the silage will move to the third phase (Phase III).

Phase III is what most nutritionists consider cured silage. Losses are minimal when the sealed barrier is maintained. The silage temperature and pH are constant and can remain in this state for a prolonged period of time.

Phase IV represents the feed out period. Losses can be substantial if proper bunker management is not adhered to.