Dry matter (DM)
The first laboratory determination performed on feed samples is dry matter analysis. Upon entry, a fixed amount of sample is weighed and then dried overnight (> 4 hours) in a vacuum drying oven at 70-80°C. The weight remaining is the dry matter (dm) of the sample. In this method, the temperature is sufficiently low enough for the sugars not to burn.
When the sample contains a small amount of sugar (<4-5%), the 'normal' drying method can be used: a fixed amount of sample is dried in a drying oven at 103°C to a constant weight (> 4 hours).
The dry matter content is the basis for all other key figures and the feed valuation; these are actually given per kilogram of dry matter. In this way, they are easy to compare and independent of moisture content.
For compound feed raw materials, the dry matter content is generally between 85 and 99%. Compound feed contains around 88% dry matter. A lower content entails a greater chance of mould and limits the shelf life of the feed. When the dry matter content of a raw material is too low, drying or adding an acid should be done first.
The dry matter content determines the quality of silage. The optimum dry matter content for grass silage is 35-45%, and 34-38% for silage maize, depending on other factors such as the presence or quality of chopping, compaction, and sugar content, etc.
During the Forage analysis, dry matter is also measured.
|Product||Dry matter levels|
|Grass silage||30 - 50%|
|Maize silage||30 - 40%|
|Straw||83 - 86%|
|CCM silage||50 - 65%|
|Fresh grass||15 - 17%|
|Potato fibre||14 - 16%|
|Brewer grains||22 - 26%|
- Dry matter content too low: More likely to cause press juice and preservative loss. Use of an additive is recommended.
- Too high dry matter content: Greater chance of scalding at silage, especially at low feed rates. A feed additive is recommended.
- A dry matter content of about 36% in silage of maize gives the maximum usable feed value yield. In addition, both starch content and starch resistance will be higher. On the contrary, palatability may decrease slightly with drier silage, depending on the total ration.