Silage is a product obtained by packing fresh fodder in a suitable container (Silo) and allowing it to ferment under anaerobic conditions with out undergoing much loss of nutrients. Fermentation under anaerobic condition preserves the nutritive value and enhances the keeping quality of the fodder. The process of conserving the green fodder in this way is termed as ‘Ensiling’.
Qualities of good silage
• A good silage should be greenish or yellowish brown, with pleasant odour, possess high acid content (pH ranges from 3.5–4.2).
• Silage having acidic taste and odour, being free from butyric acid, moulds with ammonical “N” (less than 10% of the total nitrogen).
Crops suited for silage making
Generally, the fodder crops rich in soluble carbohydrates and low to medium in protein content are ideally suited for silage making. High content of soluble carbohydrates provides excellent growth medium for the anaerobic bacteria to form abundant acids, which increases the keeping quality of the silage. Maize, Jowar, Bajra, Guinea grass, Para grass and Napier grass are highly suitable for making good quality silage. On the other hand, leguminous fodders, which normally have high moisture and high crude protein and low soluble carbohydrates, are not considered fit for silage making.
Types of silos
(i) Tower silos: They are permanent type and are costly. They are constructed above the ground level in the form of cylindrical towers. The diameter and height vary according to the needs. The loss of dry matter in such silos is 5–10% only.
(ii) Bunker silos: These silos are constructed on the surface of the ground. They should always built on firm soils having good surface and subsurface drainage.
(iii) Pit or Trench silos: Pit silos are less costly than tower silos and are widely adopted for silage making. Pits of desired sizes are dug according to the availability of green fodder. Pits silos are not suited to the areas where there is higher water table.
A pit size of 20′ × 20′ × 20′ is sufficient for 50–55 t green fodder. The fodder crops should be harvested and chaffed at proper stage of growth. The early harvesting of crops affects the production of different acids. Thus the green fodder should have about 30–35% dry matter. In silo pits, the bottom and sides should be carpeted with dry grass or long straw of grasses or cereal crops etc., so as to make 5–6 cm thick carpet all around. This carpeting helps to prevent the direct contact between fresh-chaffed material and soil.
The fodder to be ensiled should be chaffed in the small pieces (1–2 cm) by using the chaff cutter. The silo pits must be filled very quickly (within 3–4 days) and the materials must be compacted in such a way as to remove as much air as possible through constant pressing either by manual labourers or bullocks or using tractor. The exclusion of air causes fermentation under anaerobic condition. The level of chaffed material should be about 1–2 m above the ground level. During the course of fermentation, the material will gradually settle down. Urea at the rate of 3–4 kg per t of chaffed material is mixed with or sprinkled evenly on different layers, if the chaffed material happens to be very low in protein content in the case of cereal fodder. The silo pits after filling and compacting the material carefully, should be given a doom–like shape for drainage of rainwater. Then thick layer of straw is put on the chaffed material from all sides and over the straw a thick layer of moist soil (10–12 cm) is spread.
The surface is covered either by mud plaster or polythene or alkathene sheets. This avoids contact of atmospheric ‘N’ with ensiled material, which prevent the anaerobic fermentation. The silage is ready after 2–3 months. A silo pit is opened and the material is removed daily by exposing little surface area to prevent sunlight. The feeding of the silage should be regulated in such a way that the silage is used within a reasonable period. Otherwise long exposure causes drying and deterioration in keeping quality. Silage may be fed in small quantities (4–5 kg per cow) to start with and later quantity may be increased to 15–20 kg. Under ideal condition, it can be stored easily for 1 year.
It is more suited in lean seasons when weather is not conducive for haymaking. Thick stemmed crops like sorghum and maize are better utilized. Weeds are used as fodder, consequently the weed seeds are destroyed. The final product is highly palatable and nutritious. Organic acids produced during ensiling are similar to those organic acid produced in the digestive tract of the animals (ruminants) and used in the same manner (Lactic acid 3–13% and Butyric acid 0.2–0.5 %).
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