Silage is high-moisture fodder preserved through fermentation in the absence of air. These are fodders that would deteriorate in quality if allowed to dry. Silage can be made from grasses, fodder sorghum, green oats, green maize or Napier grass. An ideal crop for silage making should; i) contain an adequate level of fermentable sugars in the form of water-soluble carbohydrates ii) have dry matter content in the fresh crop above 20% iii) possess a physical structure that will allow it to compact readily in the silo after harvesting Crops not fulfilling these requirements may require pre-treatment such as: i) field wilting, to reduce moisture ii) fine chopping, generally 20–25 mm preferred to allow compaction iii) use of additives, to increase soluble carbohydrates
Napier grass should be harvested at about 1 metre when protein content is about 10%. Maize and sorghum should be harvested at dough stage, that is when the grain is milky. The grains will provide water-soluble sugars and molasses is not necessary when ensiling. When ensiling napier grass, molasses should be added to increase the sugar content. To improve silage quality, poultry waste and legumes like lucerne and desmodium may be mixed with the material being ensiled to increase the level of crude protein.
Types of silos
A silo is an airtight place or receptacle for preserving green feed for future feeding on the farm. Silos can be either underground or above ground, the qualification being that the silo must allow compaction and be air tight. Five types are described here: tube, pit, above-ground, trench and tower. Silage can be made in large plastic sacks or tubes. The plastic must have no holes to ensure no air enters. This is popularly referred to as tube silage. Silage can also be made in pits that are dug vertically into the ground and then filled and compacted with the silage material. An above-ground silo is made on slightly slanted ground. The material is compacted and covered with a polythene sheet and a layer of soil is added at the top. When finished, it should be dome-shaped so that it does not allow water to settle at the top but rather collect at the sides and drain away down the slope. The trench silo is an adaptation of the pit silo, which has long been in use. It is much cheaper to construct than a pit silo. Construction is done on sloping land. A trench is dug and then filled with silage material. This method is ideal for large-scale farms where the tractor is used. Drainage from rain is also controlled to avoid spoiling the silage. Tower silos are cylindrical and made above-ground. They are 10 m or more in height and 3 m or more in diameter. Tower silos containing silage are usually unloaded from the top of the pile. An advantage of tower silos is that the silage tends to pack well due to its own weight, except for the top few feet.
Qualities of good silage
Well-prepared silage is bright or light yellow-green, has a smell similar to vinegar and has a firm texture. Bad silage tends to smell similar to rancid butter or ammonia. Natural microorganisms turn the sugars in the plant material or any added as molasses into weak acids, which then act as a preservative. The result is a sweet- smelling, moist feed that cattle like to eat once they get used to it.
Storage and feeding
Tube silage should be stored under shade, for example in a store. Rodents like rats that could tear the tube need to be controlled. When feeding, open the tube and scoop a layer and remember to re-tie without trapping air inside. When feeding from the pit, scoop in layers and cover after removing the day’s ration, making sure the pit is air tight. Drainage from the top should be guided to avoid rainwater draining into the pit.
Nutrient losses may occur during silage making. In the field during cutting, losses due to respiration during wilting will be about 2% per day. If it rains, leaching may cause some loss. Overheating due to poor sealing gives a brown product, which may smell like tobacco and result in severe damage to nutrients e.g. proteins. Effluent losses of 2–10% that occur from moisture seepage contain soluble and highly digestible nutrients; seepage should be avoided by wilting the herbage.
During silage preparation, different types of additives can be added to improve the quality. These include fermentation stimulants. Some crops may not contain the right type or the right number of lactic acid bacteria. Bacterial inoculants and enzymes can hasten and improve fermentation by converting carbohydrates to lactic acid. Most inoculants contain Lactobacillus plantarum. Fermentation inhibitors include acids such as propionic, formic and sulphuric. Inorganic acids are more effective but are strongly corrosive thus not recommended. Of the organic acids, formic is more effective than propionic, lactic or acetic. Substrate or nutrient sources (grains, molasses, urea or ammonia) are used when there are insufficient soluble carbohydrates in the material to be ensiled (e.g. legumes, Napier grass, crop residues). They are also used to increase the nutritive value of the silage. Molasses can be added at about 9 kg/t of silage. Note: Use of additives is not a prerequisite for making good silage, but it is good for problem crops.