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Maize silage in a silo

Silage , also called silage, fermented fodder or, rarely, ensilage , is a feed for farm animals preserved by lactic acid fermentation , especially for ruminants (especially domestic cattle ), as they are also able to digest structural carbohydrates through the fermentation of the food in the rumen . However, renewable raw materials that serve as an energy source in biogas plants are also made durable by ensiling. Basically all green forage can be ensiled, including grass ( grass silage ), maize ( maize silage ), clover , alfalfa , broad beans or grain (as whole plant silage ). Furthermore, cereal grains, beet leaves or by-products such as spent grains that have been ground and mixed with water to form a pulp can be ensiled.


Composition of a silage for dairy cattle:

Grass silage Corn silage
Dry matter (TS) 30-40% 28-35%
Raw ash <10% <4.5%
Crude fiber 22-25% 17-20%
Strength no > 30%
MJ net energy lactation (NEL) / kg DM > 6.2 (1st cut),> 5.8 (subsequent cuts) > 6.4
Crude protein > 135 g / kg DM <100 g / kg DM

Maize silage has the highest energy content due to the starch content , followed by pure grass silage. Alfalfa or clover silage is rich in protein and contains less energy. The crude protein and crude fiber content of the silage depends on the growth stage of the forage plants at the time of harvest. The crude fiber content increases with age, while the crude protein content decreases. The crude ash content depends on how dirty the silage is with sand or dirt particles and thus allows conclusions to be drawn about the cleanliness of the harvest. The dry matter content of the harvest varies between 30% and 45% and influences ensiling. In the case of grass silage, it depends on the wilting time (drying time) of the cuttings on the grassland ; in the case of maize silage, it depends on the harvest date.

Use as cattle feed and substrate for biogas plants

Cattle feeding with corn silage in winter
Hay bales in Tyrol

In dairy cattle feeding, maize silage is the most frequently used animal feed alongside grass silage. The advantage over hay is its greater independence from the weather. In addition, the efficiency is higher, which means that fewer machines are required for each tonne of harvested material. The harvest can thus be ended quickly without major losses due to the inhalation of nutrients by yeast or fungi. In addition, silage is less mechanically processed. The crumbling losses decrease, which means that the crop is not chopped as much. In the case of hay, there are losses when the grassland is picked up because the machines can no longer grasp the small particles. In order to ensure that the feed ration has a sufficient protein content, imported soy meal is usually added to feed rations with a high emphasis on corn . In organic farming , grass clover silage is predominantly used, since the cultivation of clover as a nitrogen- supplying legume is advantageous in organic farming systems.

Silage with high crude fiber and protein content is only partially suitable for use in horse feeding, which is why normal hay must be fed. The haylage harvested later is therefore more suitable for horse feeding . In areas where the production of raw milk cheese is very important , the feeding of silage is dispensed with, since the production of hard cheese is made more difficult by clostridia transferred from the silage into the milk .

Silages serve as an energy-rich substrate in biogas plants . Corn silage is often used because corn enables a high yield of dry matter per area. In addition, corn silage yields in the fermentation a high gas yield. But other whole plant silages are also gaining in importance. An attempt is made to increase the yields per area and year through two-crop systems from a winter and a summer crop. Rye , for example , is used as the winter fruit ; as green rye , it is harvested well before it is ripened in order to achieve higher yields from the summer crops grown afterwards, such as maize. Combinations with sunflower , millet and other fruits are also conceivable, but so far hardly widespread in practice. Advantages of the alternatives to maize include the possibility of crop rotation, the more balanced nutrient supply of the microorganisms in the fermenter of the biogas plant and a higher acceptance of the cultivation of energy crops in the population due to the greater variety of arable crops. These arable crops are also preserved by ensiling.

The ensiling process

Forage harvester bringing in withered grass
Fresh maize chaff before ensiling

The plant material to be ensiled is generally shredded by means of a forage harvester or loader wagon before it is placed in the silo used for ensiling and subsequent storage , since frayed or torn crops are better due to the better availability of the carbohydrates due to partially destroyed cell walls and the easier compression, thus lower oxygen content fermented. After the harvested material has been brought into the silo, it is compressed and sealed airtight. This suppresses the plant's own enzymes as well as aerobic and facultative anaerobic microorganisms (bacteria, yeasts, molds). The lactic acid bacteria convert the sugar into acids (especially lactic acid ) and the pH value typically drops to 4.0–4.5. This prevents other bacteria that are harmful to fermentation from growing: Coli Aeorogenes group, Listeria and Clostridia .

Inhibiting factors

Too high a buffer capacity (too high a content of protein, ammonia and basic ash components) can hinder the lowering of the pH value. If the dry matter content is too low (<30%), the nutrient concentration is too low and too few carbohydrates are available to the lactic acid bacteria. Long parts of the plant (> 5 cm) and a long filling time (> 2 days) increase the air supply and thus facilitate the breathing of the material. This further reduces the carbohydrate content.

Silage aids

Silage additives can improve the quality of a silage, but they cannot compensate for errors. In Germany, the German Agricultural Society (DLG) has silage additives tested for effectiveness in ensiling and feeding trials. It divides the silage aids into five directions of action:

  • Fermentation improvement
  • Improvement of the durability under the influence of air
  • Reduction of the fermentation juice flow
  • Improvement of feed intake, digestibility, fattening performance or milk yield
  • Prevents Clostridia from multiplying

As a rule, bacterial cultures are used in ensiling aids (so-called biological ensiling aids). There are also "chemical silage additives" based on chemical compounds and preparations that contain enzymes . Silage aids are available in liquid and solid form, whereby liquids can be mixed better into the material, are easier to dose and should only be used with dry matter contents> 45%.

Silage quality

Ready-to-feed maize silage

A sensual assessment of the quality of a silage can be made by smelling and seeing. If the silage smells of butyric acid or acetic acid or is burnt, the fermentation has failed. Mold or heavy soiling can be visually recognized and assessed. The length of the plant parts provides a rough indication of the structural effect of the silage. Errors in ensiling make the silage inedible for the cattle and harbor the risk of illnesses due to toxic excretion products of bacteria (e.g. botulism ) and fungi. The "DLG key for the evaluation of green fodder silages on the basis of the chemical analysis according to Weißbach and Honig 1997" offers concrete information for a fundamental and comprehensive assessment. Such an investigation not only provides information on feed consumption, loss of preservation, hygienic feed quality and possible risks to milk quality and animal health. In connection with the feed value analysis, it is also possible to draw conclusions about possible errors in grassland management, forage harvesting and forage conservation, as well as their causes.

Silage process, silage quality and their assessment

In agricultural practice, the wrong opinion is often held that an examination of the fermentation quality is unnecessary if the pH value is determined in addition to the feed value analysis. In this opinion, a low pH value below 4.6 guarantees a good fermentation quality.

There is indeed a relationship between pH and fermentation quality . However, the pH value is subject to considerable fluctuations within the individual fermentation quality levels. With very good fermentation quality, the pH value varies between 3.4 and 5.0, with poor and very poor fermentation quality between 4.6 and 6.9. Thus, neither a low pH value guarantees a high fermentation quality, nor does a low fermentation quality have to be present with a high pH value.

One reason for pH fluctuations is the degree of wilting. The more the silage has wilted, the less acid is formed and the less the pH value drops. Even if the probability of very good fermentation quality is greatest at 30–40% degree of wilting, there is no compelling relationship between degree of withering and fermentation quality of a silage. All degrees of wilting from wet silage to haylage occur in all fermentation quality levels. Accordingly, the pH values ​​also vary relatively strongly with overlaps in all fermentation quality levels.

In the ensiling process, sugar or starch contained in the silage is converted by bacteria mainly into lactic acid and smaller proportions of acetic acid . If the ensiling process does not go well, butyric acid is also produced . These three acids are called fermentation acids.

  • Lactic acid smells aromatic and is, among other things, the natural preservative of sauerkraut and silage. It is mainly formed by homofermentative lactic acid bacteria . Heterofermentative lactic acid bacteria also produce lactic acid, but in smaller quantities. Depending on the degree of wilting, fermentation pests such as clostridia , yeast and coliform bacteria below a pH value of around 4.2 (wet silage) to 5.1 (heavily wilted silage with 50% DM) are so much inhibited that the silages are stable with a relatively high degree of certainty are (Weißbach 1968). If the degree of wilting is around 30–40%, the pH value can drop to around 4.0–4.5. Then the lactic acid bacteria also stop working. For this reason, silages preserved with chemical agents are almost or completely free of fermentation acids.
  • Acetic acid has a pungent odor and is used, among other things, in the kitchen to preserve and refine food. It penetrates cell walls of microorganisms and denatures the cell proteins . For this reason, low acetic acid levels in silages are absolutely desirable.
  • Butyric acid smells strongly of vomit and is irritating to the eyes and respiratory tract. Butyric acid bacteria are involved in the digestion of cellulose in the rumen of ruminants or the human large intestine . Because of its smell, butyric acid is not used in the kitchen, but butyric acid esters provide flavorings for the food and perfume industries. Butyric acid is undesirable in silages.

Due to the buffering effect of the water and the low sugar content, wet silages often tend to fermentation with vinegar and butyric acid. In this case, the lowering of the pH value is not as great as with lactic acid fermentation. In addition, lactic acid can be bacterially converted into acetic and butyric acid in these silages.

Silage that has withered too much offers good possibilities for yeast to multiply, especially if it is not sufficiently compacted. These stop working as soon as there is no more oxygen in the silo. The lactic acid bacteria lower the pH value in these silages, but strong yeast growth is to be expected when the pile is opened, unless homofermentative lactic acid bacteria are used, including yeast inhibition. This is noticeable externally through reheating. Warm silage provides good living conditions for coliform germs, which convert lactic acid into butyric acid, increasing the pH value and ultimately spoiling the silage. In addition, the metabolic products, in particular of yeast and other fungi, are toxic. Feeding silages that have been damaged in this way can lead to performance depression and illness and even death in the animals.

The sum of lactic, acetic and butyric acid decreases from the very good to the fermentation quality in need of improvement and the pH value increases. However, the pH value also rises from the one in need of improvement to the poor and very poor fermentation quality, although the fermentation acid content also increases at the same time. The reason for this is that the main influence on the pH value is the lactic acid. On average, their content decreases with each fermentation quality level from the very good to the very poor fermentation quality initially strongly and finally only slightly. In contrast, the changes in the levels of acetic and butyric acid are much smaller. The acetic acid content remains relatively constant at 0.8–1.0% in the very good or in need of improvement fermentation quality and increases to 1.5% in the case of poor and very poor fermentation quality. The butyric acid content increases with decreasing fermentation quality from 0.24 to about 1%.

When looking at the fermentation acid pattern, i.e. the proportions of the individual fermentation acids in the entire fermentation acid spectrum depending on the fermentation quality, it becomes clear that the dominance of lactic acid as a carrier of fermentation quality and stability of the silage is visibly lost with decreasing fermentation quality. The fermentation acid pattern of excellent silages consists of 80–100% lactic acid. In addition, their fermentation acid sample can contain 10-20% acetic acid and a maximum of 5% butyric acid. With decreasing fermentation quality, the proportions of the individual fermentation acids within the fermentation acid pattern become more and more similar until, in the case of very poor fermentation quality, lactic, acetic and butyric acid are represented in approximately equal proportions in the fermentation acid pattern.

The investigation of the fermentation quality includes more than just measurements of the lactic, acetic and butyric acid content, the ammonia content of the total nitrogen and the pH value. It is supplemented by a sense test for any mold infestation, bacterial decomposition, etc. On the basis of all these tests, the quality evaluation is carried out according to the "DLG key for evaluating green fodder silages on the basis of the chemical test according to Weißbach and Honig 1997". Such a comprehensive investigation not only provides information on feed consumption, loss of preservation, hygienic feed quality and possible risks to milk quality and animal health. In connection with the feed value analysis, it is also possible to draw conclusions about possible errors in grassland management , forage harvest and forage preservation and their causes.


Grass silage production: Distribution of grass clippings on a driving silo

There are three basic forms of silo for the production and storage of silage: The high- rise silo, which is rarely found today, the flat silo ( free heap or mobile silo ) and the bale or hose silo.

Storage forms

The high silo is a cylindrical hollow body that is filled with the material from above. The advantage is that the material is compacted well by its own weight and can be stored airtight. The very high construction costs and the time-consuming filling and removal are disadvantageous. The prevalence is therefore only low today.

Driving silos are much more common . These are at ground level (partly with a solid surface) and can be bordered by walls at the side. The material is applied lengthways and compacted using tractors with silo distributors . It is sealed with special foils. The bottom film is a 40 µm thin underlay film, which is sucked in through residual breathing, followed by a thick black and white cover film, the black side of which is usually on the silo, while the white side faces up. The foils and a possible silo protection grid against bird damage are weighted down with old tires or sandbags. The advantages are the high impact power and the very low construction costs, depending on the design. In contrast to the bales, the disadvantage is that a complete silo has to be filled and the compression and the airtight seal can be problematic. Likewise, when the silo is opened again, silage must be continuously removed so that the feed does not spoil at the opened point. In the case of large driving silos, a film cover is sometimes dispensed with, and higher losses in the outer layers are then accepted.

Bales are available as round or square bales. They are wound up and compacted in a baler and sealed with foil using a bale wrapper . The ensiling in foil made silage a regionally tradable commodity, as it can be transported without opening the airtight casing. In the hose silo , which only became popular in Germany at the beginning of the 21st century, the material is pressed into a long hose with a special press. In contrast to the bales, the silage can then no longer be transported in simple portions, but the space and foil requirements are less. In contrast to the driving silo, the removal can be progressed more quickly due to the smaller cut surface.

Leachate and reheating

If the silage is too moist, unnecessary seepage is produced which, due to the mineral and acid content, must not get into the groundwater or running water. The seepage consumes a lot of oxygen in the water and affects the balance in the ecosystem ( eutrophication ). Trapped silage effluent can be used as manure to be used or be used in the biogas plant as a substrate.

The supply of air during storage can lead to reheating. Yeasts multiply and consume sugar and lactic acid. In extreme cases, poisonous molds develop. In order to prevent this, the cut surface of the silage is chosen to be as small as possible and the progression of removal large (in summer at least 2.5 m per week, in winter 1.5 m per week).


  • G. Briemle, M. Elsässer, T. Jilg, W. Müller, H. Nussbaum: Sustainable grassland management in Baden-Württemberg. In: Sustainable Agriculture and Forestry. Springer Verlag, Berlin / Heidelberg / New York 1996, ISBN 3-540-61090-1 , pp. 125-256

Web links

Commons : Silage  - collection of pictures, videos and audio files

Individual evidence

  1. ^ Horst Eichhorn (editor): Landtechnik . 7th edition, Ulmer, Stuttgart 1952/1999, ISBN 3-8001-1086-5 , p. 262 ff.
  2. Fachagentur Nachwachsende Rohstoffe eV: Project to investigate and optimize the cultivation of energy crops .
  3. Klaus-Ulrich Heyland (editor), Special Plant Cultivation, 7th edition, Ulmer, Stuttgart, 1952, 1996, ISBN 3-8001-1080-6 , p. 65
  4. DLG quality mark: Silage additive product list. Retrieved July 23, 2009.