How can we define Silage? We can define silage as forage preserved by anaerobic stage, under conditions that encourage fermentation of sugars to organic acids (lactic acid, acetic acid, and propionic acids). Silages are classified according to their moisture levels. For example, high moisture silage has more than 70% moisture; haylage (low moisture silage) has 40-60%; whereas, wilted silage has usually between 60-70% moisture. Once we understand what silage means, we can jump ahead and think about the phases of silage preservation. Interestingly, silage preservation has four phases: (1) aerobic, (2) fermentation, (3) stable phase, and (4) feedout. Why is this important? Well-fermented silage tends to have a long stable phase but excessively wet or poorly fermented silage is less stable and could develop undesirable bacteria growth.
Phases of Silage Preservation
- Aerobic: Oxygen is excluded through respiration generating heat, carbon dioxide, and water. Generally it should last a few hours if forage was harvested at proper moisture, adequately packed and covered.
- Anaerobic: The pH is reduced from 6.0-7.0 to approximately 3.8-5.2. It lasts from 2 to 3 weeks when successful.
- Storage: Lactic acid bacteria die at low pH levels. Any entry of air (oxygen) will lead to aerobic microbial activity, which could be a problem during the feedout phase.
- Feedout phase: Silage should be used as quickly as possible. Aerobic microorganisms begin to grow rapidly when silage is exposed to air. A general trend is that removing around 6 inches per day from the bunker reduces losses during feedout.
Minimizing Corn Silage Shrink Losses
This is the time of the year that we need to be thinking about how to manage and minimize corn silage shrink losses. Stored silage can provide the quality needed to support many different livestock systems. Corn silage is a major ingredient in most dairy rations in United States. It should typically be harvested for silage between 60-70% moisture content to ensure good storage and fermentation. One of the main characteristics of corn silage is that is well-suited to forage preservation with an optimum harvest stage for maximum energy yields that corresponds well with the ideal moisture range. This will help to produce a rapid pH drop near 4.0 which will be characteristic of well-preserved corn silage.
A very basic estimate of whole plant moisture for harvest can be made using the kernel milk line. The kernel milk line is what divides between sugars in the maturing kernel and the starch. Most producers in South Dakota will use the 1/3 milk line as the point to start checking whole plant moistures to determine the optimum timing for silage harvest. On the other hand, maximizing the nutritional quality of corn silage and minimizing shrink losses are two main factors to take in consideration when feeding your livestock. Therefore, harvesting corn silage too early with less than 30% dry matter (DM) will result in lower starch concentration in the silage. However, mature corn silage (silage with more than 38% DM) also could have less nutritional value because of lower fiber and starch digestibility.