Crude fibre
Definition
A plant cell consists of cell contents and a cell wall.
- The cell content contains substances such as starch, sugars and proteins, which are important for milk production.
- The cell wall consists of structural carbohydrates; these give structure and firmness to the plant.
The main cell wall components are cellulose, hemicellulose, pectin and lignin.
Determination and composition
The crude fibre content gives an indication of the amount of cell walls in the feed material. The fraction is determined by the Weende analysis and is the non-acid and non-base soluble residue of a feed material, free from fat, nitrogen and crude ash.
However:
- The crude fibre fraction mostly contains cellulose and only a (varying) part of hemicellulose and lignin.
- In addition, the crude fibre content is the most difficult component to determine within the Weende analysis.
For these reasons the crude fibre fraction as an indication of the number of cell walls has meanwhile been superseded by ADF, ADL and NDF (determined according to the Van Soest method).
Role of crude fibre in feed evaluation
However, crude fibre is still used as a parameter in a number of important feed value formulas, such as:
Structure value
- The higher the crude fibre content, the higher the structural value of a feedstuff.
- A sufficiently high structural value is essential for good rumen function and prevents rumen acidification.
Satiety value
- The satiety value increases as the crude fibre content in a feedstuff or ration increases.
Feed Unit Milk calculation
- Since the crude fibre fraction also makes a certain contribution to the amount of energy; this fraction is included in the Feed Unit Milk calculation.
Crude fibre content in common forages
Roughage contains the highest crude fibre content of all forages:
- Grass silage has about 21-28%
- Maize silage 18-23%
- Hay 30-35%
- Straw up to more than 40%
The longer a crop is on the land, the higher crude fibre content and thus higher structural and saturation value it will have. Intensive fertilisation, on the other hand, usually leads to a lower crude fiber content.
