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.
Some of the factors that affect shrink losses are the following: (1) Type of structure; (2) Moisture concentration at filling; (3) Chop length; (4) Rate of filling and (5) Covering the silage. Below, you will find a brief description for each category.
- Type of structure: Bunkers usually have the greatest shrink when compared to other types of storage structures.
- Moisture concentration at filling: wet silage can have high shrink losses because of excessive fermentation, whereas, dry silage can have high shrink because spoilage (molds) during storage and feedout.
- Chop length: finely chopped forages are better and lead to increase silage density. Overall, corn silage should be chopped very fine (1/4 in. to 3/8 in) to fracture kernels and improve starch utilization by animals. Chopping releases fermentable carbohydrates by rupturing cells. Desirable bacteria will appear right after chopping by using the carbohydrates as substrates. A very basic limitation of typical round bale silage is that forage is not being chopped.
- Rate of filling: slow filling will reduce the rate of fermentation so that pH stays high for longer time. As a rule of thumb, the faster you fill and pack, less shrink losses will occur. Some of the major problems with shrink losses are that the air trapped in the silage mass and air infiltration into the mass will consequently promote yeasts and mold causing serious problems to the final product and reduction of dry matter intake (DMI).
- Covering the silage: several studies have shown that covering a bunker with plastic is the best choice to reduce shrink losses. For better results, cover quickly after the bunker has been filled. From an economic stand point of view, covering a bunker with plastic will approximately save $8.00 for every single $1.00 in plastic and labor needed to cover the silage.
Silage Additives and Inoculants
Silage additives can be used to remedy some deficiencies such as lack of sufficient population of bacteria to support adequate fermentation, and low levels of fermentable carbohydrates. Most of the silage additives are applied as forages are chopped or during loading phase. Silage inoculants are inexpensive, safe, and noncorrosive. The standard silage inoculant; lactic acid bacteria (LAB), usually reduces fermentation losses but often increases losses during feeding. In most cases, if spoiling during feeding becomes a problem in a specific farm, the use of LAB may increase overall shrink losses and would not be recommended. However, if spoilage has not been a problem, then the use of LAB should be considered because reduces fermentation losses. In most cases, bacterial inoculants reduce pH, shift fermentation toward lactic acid, and reduce ammonia production. In general, inoculants are very useful on grasses, alfalfa, and clovers than in corn or small-grain silages but it also tends to be less effective with crops low in sugars. According to McDonald et al. (1991), the ideal silage inoculant should (1) grow vigorously and compete with other microorganisms; (2) tolerate pH down to a least 4.0; (3) ferment glucose, fructose, sucrose, fructans, and pentose sugars; (4) not utilize organic acids in the silage; (5) grow at temperatures up to 1200F; and (6) be able to grow in low-moisture environments.
- Stored silage can provide high quality forage needed to support livestock systems.
- Pay attention to maturity stage, leaf: stem ratio, and all the factors that might affect your overall silage production.
- Maximize nutritional value of corn silage by chopping corn when is between 30-38% DM.
- Minimize shrink losses by chopping fine enough, filling rapidly, packing and sealing well and fast with plastic.
- Feed at appropriate rate to reduce face exposure to oxygen.
- Collins M and Owens V (2002) Hay and silage preservation. In R.F. Barnes, C.J. Nelson, M. Collins, and K. Moore (eds.), Forages: The Science of Grassland Agriculture, vol. 2. Ames, Iowa: Iowa State Univ. Press. P: 443-469.
- Hinen J (2006) The big 6- Focus on the 6 keys to quality corn silage. Mid-South Ruminant Nutrition Conference. P: 1-10.
- Oelberg T, Harms C, Ohman D, Hinen J, and Defrain J (2006) Industry Presentation: Silage Density- Survey shows more packing of bunkers and piles is needed. High plains Dairy Conference. P: 47-54.
Source: Karla Hernandez