Food Technology Information Center

Technology of Forage and By-Products Preservation

9. Chopping

Chopping is the process of cutting the forage into small pieces. The chopper actually performs more than one task in the same run: it collects the forage from the ground, chops it, and transfers the pieces to the transporting vehicle Fig. 18 . The chopping stage provides the best opportunity to enrich the silage with any additive that is needed. Such additives (chemicals, enzymes or bacteria) are used in small amounts and must be well mixed into the forage. Usually the additives come in liquid or powder form, and can be sprayed onto the chopping location.

Two main types of factors determine the chopping length:

  1. Ensiling factors.
  2. Nutritional demands.

The requirements imposed by the two groups of factors are not always compatible.

Ensiling factors.

Ensiling factors affect the forage through achievement of the best compaction. Good compaction is essential for anaerobic fermentation, for which it is necessary to eliminate air penetration, especially from the face in the feed-out stage. Several factors are connected with chopping length. Dry material is more resistant to compaction, because of its elasticity, therefore, the shorter are the pieces of forage, the easier will be the compaction. Also, cows refuse to eat thick particles such as stems, but short chopping of such material will improve their intake. On the other hand, short chopping increases effluent, a factor that has to be taken into account with wet forages, and it demands more energy and slows down the harvesting process, which increases the total cost.

2. Nutritional demands.

In addition to proteins and energy, forage also has to supply enough long-fiber materials for rumination, a factor that may be crucial when cattle receive a large amount of feed concentrates. Thus, if silage is the only forage in the feed, the length of the fiber substances included in the silage has to be taken into account in planning the chopping. Experience has clearly shown that the silage contains many particles that are longer than the length set for the chopper, because of variations in the angle at which the forage pieces contact the chopper blades.

It is important to notice that a mass of small particles occupies less volume than the same mass of large ones, which means that the same volume in a truck or wagon can carry more forage and so reduce transportation costs, an important factor, especially for long-distance carriage.

In practice, the chopping length varies from 8 to 25 mm. In some choppers for corn, special rollers are incorporated, which crush the grains in order to increase digestibility. This process becomes more important when the grains are too dry, but it is much better to be aware of the correct harvesting stage, and so to avoid this additional process and its cost.

It is important to check the machinery periodically at every stage of the harvesting process, and to verify that the various machines are adjusted to the prevailing conditions. Delay in checking can lead to bad results or can even damage the material.