Considered here are all impurities which may be present in the forage: e.g. foreign bodies, soil, ensiled manure and plant residues, carcasses and mineral oil. All of these will have negative effects on the forage quality and therefore the farm´s profitability. The level of impurities must be kept to an absolute minimum. In practice, the discussion is dominated by the presence of soil in the forage.
Effects of soil on the forage
Crop contamination from soil is one of the most eminent problems for the quality of grass silages. In order to avoid poor fermentation and reduced feed values, producing forage with as little incorporated soil as possible is crucial.
High soil content:
- Deteriorates the ensilability due to an increased buffering capacity
Soil contamination and energy content
The content of crude ash in the forage provides a good indication as to the level which the forage is contaminated with soil. Rising crude ash levels leads are synonymous with decreasing energy content. The figure below, depicting data of a grass silage after the first cut, shows this link very clearly. The strong decline of the energy concentration of the forage can be traced back to dilution effects as well as to energy-reducing faulty fermentation.
It is important to remember that minimizing the soil content in forage is essential to achieving high feed values, and also pays off economically. The financial losses due to forage contamination may be considerable: the table below compares two grass silages, one with an acceptable soil content of approximately 2% and one with an increased soil content of approximately 4 % (see table).
- Increases the danger of undesirable butyric acid fermentation because of elevated clostridia content
- Reduces the energy content of the forage, because it is “diluted” with soil
- Affects animal health and performance, as they can less easily digest the forage and will absorb fewer nutrients from it.
Effects of crop contamination in the case of grass silage
(1) Compensated by concentrates, (2) stocking rate, 1.5 cows/ha
Assuming a yield of 10 t DM/ha per year and a lower energy content of 0.2 MJ NEL/kg DM, the energy loss per ha per year add up to 2 000 MJ NEL for the silage with greater contamination. This represents approximately 48 €/ha per year, if compensated for with concentrates. Additional costs must also be considered as a lower energy content reduces the feed quality and therefore energy uptake. Summarizing the effects, losses of approximately 89 €/ha per year have to be budgeted.
Source: Landwirtschaftskammer Niedersachsen 2014