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13/04/2010
From field to feed
In order to make the best quality silage there are five key rules that must be observed: cut grass early, cut grass dry, ensure speed of ensiling, ensure pressure in silage clamp, and ensure airtightness of the silage clamp.
Cut early
Early cutting means that you get the best quality of grass, with the highest digestibility and many tests have shown that with later cutting the overall bulk of material may increase but the resulting digestibility of the crop decreases.
Therefore, the use of your own machinery, or getting a contractor when you require one, is very important as this will enable you to cut the crop at the ideal time, giving you the chance to maximise the quality of the silage made.
Cutting dry grass can be sometimes easier said than done. Normally grass contains approximately 85% water when it is cut, or 15% dry matter. This, if possible, should then be dried by a combination of wind and sun to a dry matter content of approximately 30% as soon as possible, in order to avoid loss of nutrients from the grass. Conditioning, wide spreading or tedding can be used to assist this rapid drying pocess.
Speed of ensiling
The goal of silage making is to convert sugar into lactic acid and to preserve the grass for the animals. Speed is important, as once the grass is cut it start’s to deterioate, and with the risk of wet weather, speed of ensiling can ensure that all the grass is ensiled before the rain arrives. Tests have shown that 10mm of rain can wash 10% of the sugars out of the grass, which then reduces the amount of lactic acid produced when ensiled. This, in turn, will have an effect on the frementation process. Speed is also important as grass can start to heat when mowed as the energy used to produce the heat comes from the grass sugars. This again reduces the amount left to produce lactic acid.
Pressure
Pressure is required to expell any air from the grass as it is ensiled to avoid any air pockets. This is achieved by compression from the buckraking machine and skillfull filling of the silo in layers to avoid air pockets. Pressure is easier to apply to shorter cut material as the compaction will travel deeper into the clamp, compressing the material more. Expelling more air will enable the silo to hold an increased volume of material into a given space.
Airtightness
Airtightness is required to ensure that no air can enter the silo. When air enters the silo, a process will begin the production of butyric acid. This is produced by butyric acid bacteria (chlostridium), which can live on almost anything. Their waste product is not wanted as it has a strong odour and grass in a silo will be decomposed into compost if the air is changed 55 times. This often happens with a loose silo top acting like a lung, pumping oxygen down into the silage. Wilting, and the avoidance of soil and manure in the grass, will also assist with the reduction of butyric acid production.
Stationary Knives or Precision cut
It used to be said that chopping should only be done out of consideration for the mechanization of the feeding process and not out of consideration of the cow. This attitude has now changed, partly because it is important for the compression of the silo and thus the silage quality, and partly because it is necessary in order to manufacture quality feed in connection with complete diet mixers.
Therefore, today, it is important how the grass is cut or chopped. A slow moving cut against stationary knives can result in there not being any sap at the outer surfaces of the grass and it will take longer before the lactic acid bacteria get into contact with the sugar in the grass and starts the ensiling process.
It is different with any high speed rotating chopper which crushes the grass when chopping it and smears the sap out on to the grass surface. A test carried out at the Royal Veterinary and Agricultural University of Denmark comparing these two Cutting/Chopping methods confirms that these assumptions are correct.
Why Precision Chop?
The grass sap and possible additives will be evenly distributed on all surfaces. The process of ensiling starts earlier and the quality is better. Often the surface of the grass is dry and the bottom wet. The precision chop forage harvester will mix top and bottom so that ensiling material will be completely mixed up. In this way you avoid mildew spots in the silage, thus achicving less bad quality and less wastage. Precision chop silage is more uniform in chop lenght than cut grass, as the precentage of grass cut within a small tolerance of the set theoretical chop lenght is much greater than with cut grass. This helps to avoid mildew spots and bad quality silage in the silage clamp.
When the crop has been precision chopped it is easier to compress to a higher density. Furthermore the cubic content of the silo will be better utilised. The feeding out of the silage is easier to mechanise so that total mixed ration can easily be carried out.
Written by Frank Ward, JF-STOLL Ireland
