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by J. B. Shepherd, R. E. Hodgson, N. R. Ellis, J. R. Mc Calmont
Several factors influence the type of fermentation produced, the nature and extent of the losses occurring during fermentation and storage, and the quality of the silage produced. Among them are the maturity and chemical composition of the crop, the ratio of soluble carbohydrates to the mineral base content of the crop, its percentage of moisture when stored, the rapidity and completeness with which air is excluded from the silo, and atmospherical temperatures when the crop is ensiled.
In handling the crop for silage, the farmer should cut the forage when it has a high content Or protein and carotene and when the yield of total digestible nutrients per acre is high. He should ensile it in a way that will produce a good palatable silage with the least loss of feed nutrients and the least wear and tear on the silo.
In doing so, he will need to give proper consideration to the stage of maturity at which to cut; the moisture content at which to store; the need for and use of preservatives; the length of cut to use; the distribution and packing of the crop in the silo; and the sealing out of the air when the silo is full.
To produce grass silage that meets those specifications requires first that it be cut at an immature stage while it is still reasonably high in protein and carotene and relatively low in crude fiber This stage corresponds closely with that recommended for early-cut hay from the various crops.
Most grasses should be cut after the heads have emerged but before the plan have started to bloom.
The moisture content of the crop at the time of ensiling is the most important factor in determining the character of the silage fermentation, the extent and character of the losses through seepage and fermentation, and the quality of the silage produced.
An excessively high moisture content leads to large losses of liquid. Too little (under 60 percent) results in molding and spoiling of the silage.
When crops are ensiled with a moisture content of more than 70 percent, fermentation takes place at a rapid rate, there is considerable seepage from the silo, and losses of most feed nutrients, except carotene, are large. If no treatment other than chopping is given, the type of fermentation will be desirable and the silage will be of good quality provided the crop ensiled consists principally or entirely of grasses or cereals that are cut after heading out and that contain a medium or low amount of protein. On the other hand, the type of fermentation will be undesirable and the silage will be of poor quality and have a strong offensive odor if the ensiled crop consists principally or entirely of legumes or of grasses and cereals that are cut before heading out and that have a high protein content.
When wilting is not possible because of unfavorable weather, the same results can be obtained by adding 5 to 15 percent of dry hay as the crop goes through the chopper. When the moisture content of the crop is reduced to 68 percent or below, the fermentation rate is reduced and seepage from the silo is eliminated. The best silage is made when the moisture of the material is not above 68 percent or under 60 percent. But occasional loads may contain as much as 70 percent or as little as 55 percent of moisture without materially affecting the quality.
Wilting high-moisture crops for silage, as we have indicated, not only produces a mild, palatable silage that will be consumed in normal roughage amounts; wilting also reduces the losses of nutrients (except carotene) that usually occur when the silo is filled with comparable unwilted materials.
But care should be taken not to wilt the crop too much, and the part that is wilted most should be placed in the lower part of the silo. The walls of silos used for wilted silage should be air-tight and smooth.
Salf has little effect on the fermentation process and is of little practical value in silage making.
Grasses and cereals cut after heading out or a mixture of such crops with legumes can be made into a mild, good-quality feeding silage without preservatives when ensiled in the fresh green state. The fermentation rate will be slowed down, fermentation and storage losses will be reduced, and the palatability of the silage will be increased by wilting the crop slightly before ensiling.
Immature grasses and cereals cut before heading out, or crops consisting principally or entirely of legumes, can be made into good silage by wilting them down to a moisture content of 68 percent or slightly less.
Wilted silages made without preservatives usually have an acidity within the PH range 4.0 to 5.0, depending on the crop.
The aim should be to wilt the crop slightly, to a moisture content between 65-70 percent but not below 60 percent. If the leaves become dry and curled, the wilting may have progressed too far unless the crop is heavy and the underside of the swath is in an unwilted state. The crop will have wilted sufficiently when the leaves and stems become limp. me stems can be readily twisted in two and the broken ends will have a dark, moist, but not excessively juicy, appearance. On rubbing the chopped crop between the hands, the material will feel cool and moist, but no free water will appear when a ball of the chopped crop is squeezed in the hands.
One or two hours on a good drying day may be sufficient to wilt the crop to the desired moisture level unless the crop is very heavy or very high in moisture. On a good drying day, therefore, the crop should not be cut too far ahead of loading and silo filling. During prolonged dry weather, crops cut at the usual stage will be ready to ensile within a few minutes after mowing. On very humid days, a half day to a day may be required to wilt the crop sufficiently. During rainy spells, the mowed crop may sometimes be in the field 2 or 3 days before it wilts enough to be siloed.
When rain interferes with silo filling operations, the rain-wet portion can be siloed without wilting by filling the silo at the slow rate of 3 to 4 feet a day so that some heat will be generated; or it can be siloed at a normal rate by running dry hay (10 to 20 percent), ground dry grain (5 to 12 percent), or molasses (3 to 5 percent), through the cutter with the wet crop.
Except for short and very immature crops put up under special conditions, it is necessary to chop the crop as it is siloed. The length of cut to use will depend upon the moisture content at which the crop is siloed. If the moisture contort is 72 percent or more, the cutter should be set for a 1/2 - to 5/8- inch theoretical cut. Crops with a high moisture content will pack well with this comparatively long cut.
When the moisture content of the crop is 70 percent or less as ensiled, the cutter should be set for a shorter cut of not more than one-fourth to three-eighths inch. If the crop is wilted considerably, the cut used should not exceed one-fourth inch. Here, too, many of the stems go through crosswise with an actual longer average length, and this short cut must be used in order to get the crop to park satisfactorily and exclude the air. The drier crop is not apt to clog the blower when a short cut is used. Failure to use a fine cut when the crop is wilted will prevent close packing, will cause considerable air to be trapped in the silage, and also will cause some mold.
When the silo is being filled, the crop material should not be allowed to pile up in the center of the silo. It should be kept well distributed over the entire area and well tramped near the wall. This is particularly important when the crop is wilted slightly. Good distribution and thorough packing are absolutely necessary in the top part of the silo.
Only heavy, unwilted crops should be used for the last few loads so that enough weight and pressure will be provided to force the air out and keep it out. to preservative will be needed in this wet top layer even if the crop is high in protein, because the material at the top warms up sufficiently to prevent undesirable fermentations and naturally makes a mild, palatable silage.
The rate at which the silo is filled affects the rapidity with which the air is eliminated from the silo and, consequently, the temperature which the ensiled mass attains. If the silo is tight and is properly filled and sealed, the temperature will seldom exceed 100° F., except at the top, and may sometimes not exceed 90°. If the ensiled material is high in moisture, or if the weather is cool, silo temperatures will be lower than when the crop is wilted or the weather is warm. When the silo is filled with a high-moisture crop, particularly in cool, moist weather, there may be an advantage in filling at a slow or moderate rate; that will allow the ensiled material to warm up slightly. That procedure also will help to prevent an undesirable type of fermentation.
When the silo is filled during a long dry spell or with a wilted crop, it should be filled rapidly in order to hold silo temperatures down to a desirable level. Spoilage is apt to occur on the surface of the ensiled material if more than 2 days elapse between filling periods. When such an interval occurs, the top of the material should be kept tramped thoroughly in the meantime, and any spoiled silage removed before filling is resumed. Where one crop only partially fills the silo and another crop is put in some time later, the silo should be tramped, sealed, and weighted down between fillings to keep silage temperatures and losses as low as possible.
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