Basic Principles of Silage

24 February 2014
2 minutes

Silage is one of the most important nutritional sources for the modern dairy industry. It provides high energy roughage at a relatively low cost. Good management is vital for the maximum utilization of the resource. This is, however, one of the many areas for which the dairyman has to take responsibility, as he determines the quality of his own fodder production.

Ideal maize roughage quality is dependent on the decisions and management practices implemented before, during and after the ensiling process. Making and using maize silage is a process that is divided into two main phases:

  • the ensiling process
  • the removal and feeding process
Both of these processes are accompanied by their own set of potential problems and management issues.

The ensiling process

The main management factors that determine silage quality during the ensiling process are:

  • age of the crop when harvested
  • the type of fermentation that takes place in the silo or bunker
  • the storage structure (bunker layout and design)

Age when harvested

The age of the crop when it is harvested can influence the quality; of the maize silage because it will effect the maize kernels, the moisture content and the digestibility of the silage. The best way to determine the correct age is by using the milk line on the kernel. The milk line is the transitional phase between the liquid and the solid part of the kernel. The optimum age is when the milk line has moved one half to two thirds away from kernel. Harvesting at the correct age ensures adequate sugar fermentation and adequate moisture for compaction.

The type of fermentation that occurs in the silo or bunker

The type of fermentation that occurs is determined by several factors such as chopping length, the speed of filling, compaction and sealing. Optimum fermentation takes place in an anaerobic environment, that is in the absence of oxygen. Thus, the faster oxygen is excluded out of the system, the better the quality silage that can be produced.

Chopping length

The ideal chopping length for silage is approximately 6 mm to 12 mm. The length of the chopped pieces is important for two reasons:
  • a long chopping length makes compaction difficult and oxygen will be trapped in the silage which results in a weak final product 
  • a chopping length that is too long also makes it difficult to remove the roughage from the bunker without too much wastage

Filling, compacting and sealing

A silo must be filled and compacted as quickly as possible. The faster the process is completed the faster aerobic respiration and anaerobic fermentation stops taking place and thus wastage is reduced. Compacting is the most important aspect and should be given the most attention. Attention should be given to compacting the silage sufficiently before the next load is dispatched at the silo. The affectivity of the compaction process ensures the quality of the final product.

The silo should be sealed as soon as possible after compaction. Strong, UV-resistant canvas tarpaulins should be used. It is also advisable to use white tarpaulins in areas with very hot weather as the white cover reflects the heat away from the contents of the silo. Tarpaulins must be held down with old tires or even a thin layer of soil to provide additional compaction and reduce wastage.

Design of storage area

A long narrow bunker will ensure better quality silage. The reason for this is that one can move through the bunker quickly when roughage is removed from it and therefore the contents are not exposed to lengthy periods of aerobic respiration. The bunker should be emptied at a minimum rate of approximately 1,5 m per week.


Generally additives are bacterial inoculants, organic acids, NPN sources, salt and enzymes. Most silage inoculants supply benign bacteria, enzymes or fermentation substrates. These are useful for the improvement of the quality of the silage. However, they are, not substitutes for ineffective silage management.

The removal and feeding process

Although the process of removing a short section of silage is often seen as the latest step in a long process, it can destroy all the good, hard work of the previous season in a relatively short time. Most farmers repeatedly fall into the trap of bad fetching and feeding practice and then they do not understand why the quality of their silage is not adequate.

Bunker management

Ideally a new load of silage should be removed from the bunker just before each feeding. General, but poor, practice is to remove silage once a day or even once every two days in order to feed animals. In such a case, the silage is exposed to aerobic respiration which results in negative fermentation and a lower quality silage being fed to the animal.

During the removal of the silage attention should be given to cutting the face of the bunker as neatly as possible. If the silage in the bunker is cut neatly, there is less exposure of oxygen to the face of the bunker, which prevents unnecessary aerobic respiration and poor quality silage. Care should also be taken not to leave loose silage on the face of the bunker. After the removal of silage, the tarpaulin and the tyres should be neatly replaced. It is of the utmost importance that the management aspects are carefully followed; otherwise it can destroy all the hard work of previous months.

Any silage which shows indications of weak fermentation must be removed and not fed to animals with the rest of the silage. There is often a thin brown layer on top of the silage. The brown layer is a good example of silage that should be removed rather than being fed to the animals. The brown layers are a breeding ground for the production of mycotoxins and can lead to major financial losses if they are mixed into animal fodder.

Nutritional value of maize silage

Maize silage is a good source of energy but also acts as roughage. There are several factors that need to be considered when it is used as an ingredient.

Energy content can vary depending on the quality of fermentation, the age of crop at harvest, and also on general management practices. The variations must be taken into consideration when formulating.

Starch content of the silage is also an important aspect that can affect energy. Starch is not only determined by the amount of grain on the plant, but also by the ratio of grain to plant. Current general trends are to have a plant which has high dry matter yields and this often results in a reduction of starch content.

A third factor that plays an important role during formulation is the moisture content of the silage. Small differences in moisture content can cause large differences in dry mass intake and general ration balancing. It is important to take regular samples of silage because moisture can vary as one gradually moves through the bunker.

The final factor that may indirectly influence nutrition is the formation of moulds and mycotoxins in silage. It can generally be accepted that almost all mycotoxins are present in silage. Poor management will, however, increase the problem. Mycotoxin binders can be used to minimize the effect of mycotoxins in silage to a large extent. This is not a solution for the problem and the solution should rather be the overall management practices used for silage on the farm.


Silage is a resource that is totally under the control of the farmer, who decides whether it will be successfully or unsuccessfully utilised. The ensiling period is rarely more than two 2 weeks of the year, and if properly managed, it will be an advantage to the farmer for the rest of the year. Would it not be wise to give substantial attention to the ensiling period? A farmer once said: "The cows do not eat my excuses" and in the case of silage this is very true.