Silage is agricultural or industrial produce preserved either naturally or artificially, using lactic or acetic acids under anaerobic (no air) conditions. It is an alternative method of making hay, to prevent wastage of excessive fresh crop residue especially during cold weather seasons when precipitation is high.
The process of making silage is termed as ‘ensiling’ through fermentation. It involves the use of fresh by-products such as fodder crops (napier grass, legumes, oat or weed); banana fruits, leaves or trunks; wet pulps from fruit and vegetables; root crops and their leaves (yam, cassava, taro, potato); and, animal waste (fish and poultry). The by-product are mixed with cereals such as maize germ, sorghum or soya and refined sugars, preferably molasses. The fresh plants contain high-levels of moisture, natural sugars (carbohydrates and cellulose) and vitamins. Animal waste contains high levels of protein with amino acids. Grain cereals and molasses contain additional carbohydrates, necessary for energy during decomposition.
No additional water and air is required as this will disrupt the fermentation process of the plant and cereal sugars by the acids.
Fermentation takes place in a silo (storage structure), that can be a trench, a bag, a dug pit or a large tower depending on the capacity of the livestock farm. This process can be used to process animal feeds or bio-fuels. In this case, we look at making animal feeds for the bud-chewing animals – dairy cattle and sheep.
- Prepare a silo in form of a trench/bale, whether plastic or wooden, 5-10ft high and variable length depending on the amount of fodder available. The trench is covered on the sides with plastic tarp/sheet/film to make it airtight. The wrapper is usually bigger in size than the trench to enable top covering. It is suggested that one uses black or green sheets because they absorb heat from the atmosphere, rather than direct ultra-violet (UV) sunlight which may interfere fermentation process.
- Harvest the green vegetation at optimum height during maturity stage. That is 2m to 3m high, no pricks and twigs for naturally growing leafy herbs or tree legumes. The second harvest should be within 30 days during the wet tropical seasons, when the fresh plants are about 1.5m long to prevent loss of moisture. Transport them immediately to the point of silage. Shred the plants in small pieces of about 1.5cm long. This can be done using a machine or machete. Short lengths enable easy combustion .
Layer the cut forage on racks or against the walls, to allow the sun’s heat to evaporate some moisture from the plants. For a standard size of a silo (9m by 5m by 5m), pour in bunches of 500 kilos of the shredded forage per layer. Spread and squeeze the layer to get rid of excessive moisture.
Spread a fermentation substrate as a layer in the forage, say every 10 to 15 cm. Molasses for example, ferments the silage in a better quality with sweeter smell. Do not dilute the molasses with water as the forage is already too moist. An ideal amount per layer is 3 ltrs
- Spread about 10 kilos of maize germ, rice bran or sorghum on each consequent layer of the 3ltr-molasses and 500kg-forage, then squeeze tightly to enable mixing and absorption of moisture from the forage through the molasses to the cereal. The cereals contain high level of carbohydrates that are broken down by the acids (decomposition). Cereals and molasses are additives that increase acidity level to pH 4.1.
- Once the silo is filled to a maximum amount of the available ingredients, spread the sheet thinly over the stack and wrap. Compact the silo as tightly as possible such that one cannot insert a finger or an insect cannot interfere.
- Fermentation begins after the first few days of respiration and some dry matter (DM) loss. DM loss should not be greater than 20%. A few weeks later, respiration stops and the pH drops, while the cellulose is broken down. When closely packed, the supply of oxygen is limited, while the oxygen (O2) present is consumed. Sugars present are converted to volatile fatty acids (VFAs) as a result of the decomposition of carbohydrates and cellulose by bacteria present in the fodder. The silage becomes sour. VFAs contain energy that the bacteria use. Water-soluble proteins (albuminoids) are converted into albino and ammonium compounds but if fermentation is poorly managed, excessive ammonia is produced. As a result, the sour silage acquires an unpleasant odour. Vitamin B12 is also produced by micro-organisms present in the chopped fodder. Infiltration process allows little oxygen and respiration through the pores. Some carbohydrates (CHOs) are lost through heat and gas. Fermentation lasts at least two weeks.
- Emptying the silage exposes it to additional loss. Safety measures are crucial when handling the product. Silage gas produced during fermentation contains nitric oxide (NO), that will react with infiltrated oxygen (O2) from the air to form nitrogen oxide (NO2), which is toxic. Liquid (silo effluent) released is corrosive. This is because the airtight process contains high nutrient that result to growth of bacteria and algae.
- Disposal of the plastic sheet by burning is not commendable because of high levels of carbon emits from the smoke and bad odour from the ammonium compounds. There are recycling methods. To ensure this, Silage can be fed into anaerobic digesters to produce biogas, an environmentally-friendly fuel that can generate electricity and heat.
- Silage can then be stored in bulk and feed cattle, sheep and horses for a lengthy time, while still:- the resource remain nutritious for milk products; continuous feeding when there’s not enough yield of fodder; constituting a variety of diets; reducing toxicity of vegetables and grass to safe levels; destroying harmful bacteria from other animal waste; maintains high quality of forage into the dry season.
The outcome is 4.5 tonnes per stack/trench/box. A cow that produces 20ltrs of milk daily consumes 20kg of silage, 16kg of dairy and some fresh lusan grass. The quantity of silage required depends on the number of animals to be fed, storage space available, dry matter content available and other operation factors such as labour and size of the farm.
For more information on Dairy production, visit our model farm at Latia Resource Center, in Isinya-Kajiado, Kenya.