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Testing grass before cutting for silage is crucial and has a direct effect on silage quality. Farmers should target a High Sugar content and Low Nitrogen content when harvesting. As recommended, grass tested should have Nitrogen levels lower than 500mg/Kg and Sugar levels higher than 3%. A Sugar content of 3% or higher is critical to silage ensilability. This combination ensures good silage preservation, higher the intake potential and animal performance.
Early May silage has the highest dry matter digestibility (DMD) in combination with potentially the most difficult ensiling conditions. From early May:
– silage DMD drops by c.3% per week.
– as the time between fertilising and cutting increases Nitrate levels are dropping.
– As sunshine hours start to increase and grass starts to mature sugars start to increase.
A dairy farmer will typically need 65% of his silage of 70+ DMD to maximise winter performance while minimising concentrate requirement. The goal with silage is there for to cut early enough in May to max out DMD but to cut when sugars and nitrates are in the desired ranges to ensure good preservation. Testing your grass before cutting is the only way to know if you are ok on these parameters.
All silage fields containing a high proportion of perennial ryegrasses will have a sward
of 80% DMD by the middle of May. The DMD result is used to estimate energy of the silage, as well as expected live weight gains/milk yields and planning supplementation rates. Once grass silage fields go past this, they lose an average of 3% DMD units per week, with this loss increasing to 6% DMD units in poor weather or lodged crops.
Generally, the higher the dry matter the higher the potential intake of silage. It takes 17kg DM of 75DMD to put on 1kg of carcass as opposed to 46kgs DM of 60 DMD to put on 1 kg of carcass weight.
In good growing conditions grass crops utilise 2 units of Nitrogen per day but poor weather conditions have a negative impact on this, and Nitrogen uptake is slower. When Nitrogen levels are high in the grass this results in silage which doesn’t preserve as well as it needs to, and the quality of silage is also lower. Time of day when cutting also plays a huge factor in terms of Sugar content. Sugar contents in grass are highest around 4pm in the evening as the grass has received light/heat all day thus reducing water quantity in grass which will increase the concentration of Sugar content. As shown in the charts, grass samples which had high sugar and low nitrate levels when tested, proved to have better results in silage, compared to grass samples that had higher levels of nitrates and sugars.
