Silage is the material produced by controlled fermentation of crops under anaerobic conditions. It prevents fresh fodder from decaying and allows it to maintain its nutrient quality. This process is known as ensilage and the container used for the purpose is known as a silo.
The fermentation process is governed by microorganisms present in fresh herbage or by additives to maintain anaerobic conditions. When herbage is placed in an airtight container, naturally occurring bacteria ferment the carbohydrates (sugar) present in the herbage to produce mainly the lactic acid.
Green fodder can be preserved as silage stored for a long period (up to 6months). During the monsoon, plenty of green grass is available. Most commonly, it is cut as dry grass and stored for feeding livestock in summer. If it is cut at the early flowering stage can be preserved as silage, then the grass will be more nutritious.
The aim is to achieve a sufficient concentration of lactic acid to prevent other types of bacterial activity, i.e. clostridia activity. The main requirements are the exclusion of air to maintain anaerobic conditions and to discourage clostridial fermentation which leads to the production of carbon dioxide, ammonia, amines, butyric acid, etc.
The silage is palatable, laxative and highly digestible for the dairy cattle. If you feed your dairy cattle with silage it will ensure high milk production and stay healthy. Especially during dry seasons, silage is a great relief for the dairy farmers. Unlike haymaking, which has seasonal constraints and heavy nutrient losses, silage, on the other hand, is superior and has better acceptability, digestibility and nutritive value.
Table of Contents
- 1 What crops can be used to make silage?
- 2 Methods of Controlling Fermentation
- 3 Different types of Silos
- 4 Techniques of Silage making
- 5 Silage quality parameters
- 6 Silage pit size and capacity
- 7 When and how much can Silage be fed?
- 8 Nutritional Quality Improvement in Silage
- 9 What are the advantages of Silage?
- 10 Drawbacks of Silage making
What crops can be used to make silage?
Below are the crops used to make silage:
- Napier grass
- Sugarcane tops
The quality of the silage you get from the above crops can be enhanced by adding molasses, urea or forming acids.
Methods of Controlling Fermentation
There are several ways in which the clostridial type fermentation can be checked. One of the commonly used practices is to increase the dry matter of the herbage. In ensiled crops containing 30% or more dry matter, crop ensile satisfactorily. The promotion of lactic acid fermentation is an important pathway for controlling clostridial growth.
Another method of controlling fermentation is by addition of preservatives and additives. Carbohydrates in the forages may be naturally occurring or may be added as a separate ingredient such as molasses obtained as sugar industry byproducts, which acts as a fermentable substrate.
Additives for effective ensiling of nutrients
Various types of additives can be used to improve or inhibit the fermentation or supplement nutrients needed by ruminants to be fed as silage. Propionic acid, formaldehyde, etc. have been used to increase the rate of lactic acid fermentation and produce stable silage. Carbohydrate sources such as molasses, whey, yeast, and other energy-rich ingredients have also been used as additives to increase the fermentation and feeding value of silage. Urea @ 0.5-1.0% has been found to increase crude protein content and also the lactic acid content of silage made from cereal fodders.
As anaerobic conditions are achieved in a silo, the species of Escherichia, Bacillus, Clostridium, Leuconostoc, Lactobacillus, and Pediococcus develop. Lactic acid bacteria (Streptococcus, Leuconostoc, Lactobacillus, and Pediococcus) are the important organisms for the preservation of silage of good quality.
Different types of Silos
The different types of silos generally used are (i) pit silo, (ii) tower silo, (iii) trench cum bunker, (iv) trenches, and (v) drum and PVC silo. The silo must provide a solid surface to permit the consolidation of the ensiled material and elimination of air. It must protect the silage from water. In India, pit silo is the most common.
1. Tower silo
Tower silos are constructed from brick and are several meters in diameter and 10-20 m in height. The advantages of this type of silo include:
- long life
- small space required
- low storage losses
- possibility for mechanization.
Both the filling operation and daily extraction can be mechanized. However, tower silos are expensive, and therefore not widely used.
2. Cellar silo
The cellar type is the most common silo on individual farms. Round or square concrete silos are usually built inside houses for protection from the weather. The advantages are lower cost and easy management. Size can be adjusted according to scale of production. A disadvantage is high effluent loss, especially with clay walls.
3. Trench silo
This type is generally built underground or semi-underground, with two solid walls of 1.5-2 m in height. The advantages are similar to the cellar silo, but the trench silo is more suitable for mechanization. The tractor can be driven on top from one side to the other for compaction purposes. After compaction, it is covered with a plastic sheet pressed down with soil, sandbags or straw bales to maintain anaerobic conditions.
On many dairy farms, trench silos are built on the surface of the ground. This type of trench silo resembles a bunker silo but has vertical walls of 0.4-0.5 m in thickness and 3-4 m in height. This design makes mechanization more convenient, and may also prevent bottom leakage.
4. Stack silo
This type of silo implies a pile of material on the ground surface. On flat and dry ground, the plastic sheet is placed underneath and the material is laid in a stack. The top is covered with plastic and sealed all round with soil. Sandbags or old tires, or any other suitable objects, are placed on top to prevent the top cover from being blown away by the wind. The advantages of the stack silo are low cost and flexibility of placement.
5. Plastic silo
The plastic silo is similar to the stack silo but it is covered with plastic sheets of polyvinyl chloride (PVC) or polyethylene. Alternately, the silo can be made in bags with sealed tops. The stack silo is also inexpensive and can be placed anywhere. However, labor requirements are high due to manual filling and handling.
Techniques of Silage making
1. Dry matter
The dry matter should be above 30%. Crops of high moisture should be ensiled with the addition of preservatives and additives. In poor weather, wilting should be avoided and additive should be used for good fermentation.
2. Stage of growth
Crops should be cut at a proper stage of maturity as it is the most important factor for controlling the silage quality. The appropriate stage of growth for cutting different fodder crops for silage making is given below:
Sorghum – Flowering to dough stage
Maize – Milk to dough stage
Oat – 50% flowering to dough stage
Grasses – Early flowering stage
The crop should be chopped before ensiling. For good silage, the shorter the chop length, the better is the quality. Chopped silage is more palatable to livestock and has little chance of secondary fermentation.
4. Filling of Silo
The silo should be filled rapidly and should not be left open. It should be sealed as soon as possible. Packing is important to create anaerobic conditions. It should be thoroughly pressed so that no air pocket is left in the silo otherwise chances of mold formation will be there which will spoil the silage. After filling, silo should be covered with the polythene sheet followed by that of a layer of soil, etc.
5. Removal of Silage
After 45 days of ensilage, the silage can be removed for feeding to animals. A pit size of 20 x 20 x 20 feet is sufficient for 50-55 t of green fodder. One cubic foot of settled silage will weigh about 15 kg.
Care should be taken in removing the silage from the silo. It should not be allowed to deteriorate after the silo is opened for feeding. Covers should be kept firmly in place as long as possible and the minimum face should be exposed at one time. The sugars, proteins and lactic acid present in the silage are subject to attack by mold growth and oxidation as some air is allowed to fermentation and causes loss of feeding value and intake by the animals.
6. Silage quality
Silage quality is determined mainly by the odor, physical state, pH, ammonical nitrogen, volatile acids, and lactic acid. For desirable fermentation, the forage should be rich in water-soluble sugar (more than 5% on a dry-matter basis).
Silage quality parameters
Good-Quality silage should have the following characteristics
- pH 4.0-5.0 (below 4.5 for wet crops and below 5.0 for wilted silage)
- ammonical nitrogen of total N – less than 10% of total N
- The moisture content of 60-70%.
- butyric acid- less than 0.2%
- lactic acid -3 to 12%
- volatile acids, alcohol should below
- No mold growth
- Pleasant fruity odor/ an acceptable aroma.
- Free-flowing and non-sticky texture.
1. pH value
The pH is the simplest and quickest way of evaluating silage quality and may be determined on-farm using wide-range pH test papers such as bromophenol blue (range 2.8-4.4), bromocresol green (range 4.2-5.6) and methyl red (range 5.4-7.0).
The classification of silage based on pH value is:
|pH below 4.0||excellent|
|pH between 4.1 and 4.3||good|
|pH between 4.4 and 5.0||average|
|pH above 5.0||bad|
Good silage usually preserves well the original color of the standing plant. When green raw material produces silage with green or yellow color, it can be considered of good quality. Temperature is one of the important factors affecting silage color. The lower the temperature during ensilage, the less color change. Above 30°C, grass silage becomes dark yellow. Above 45 to 60°C, the color becomes closer to brown. Beyond 60°C, the color darkens towards black due to the caramelization of sugars in the forage.
However, silage quality can be misjudged by on a color basis. A more useful indicator is the color of the silage juices. It can generally be said that the lighter the color of the juice, the greater the success.
Good silage usually has a mild, slightly acidic and fruity smell, resembling that of cut bread and of tobacco (due to the lactic acid). A rancid and nauseous smell denotes the presence of butyric acid and signifies a failed silage. A musty smell is a sign of deficient compaction and the presence of oxygen.
Plant structures (stems and leaves) should be completely recognizable in the silage. A destroyed structure is a sign of severe putrefaction. A vicious, slimy appearance reveals the activity of pectolytic (sporulating) micro-organisms.
Silage pit size and capacity
|Length (ft)||Width (ft)||Depth (ft)||Capacity (q)|
When and how much can Silage be fed?
Silage can be fed to all kinds of animals: replacement cattle, fattening cattle, dairy cows, sheep, goats, and even pigs. The amount of silage offered depends on the animal and its age, as well as on the type and quality of silage. Silage should not be given before milking. The effect on milk taste is more marked when the silage is fed 2 hours before milking, and least when given 6 hours after.
Taking cattle as an example, the recommended amount to be fed daily is:
|Grass silage||4 kg per 100 kg live weight,|
|Legume silage||3 kg per 100 kg live weight,|
|Maize stove silage||4 kg per 100 kg live weight,|
|Starch-rich forage (whole-maize silage)||5 kg per 100 kg live weight,|
Nutritional Quality Improvement in Silage
- Nutritional quality of grass and cereal silage can be improved by mixing with legumes like cowpea (4:1) or by spraying urea solution at the time of ensiling (1% on a fresh weight basis, sprayed with l:l matter).
- Often the green fodder is mixed with molasses and salt to improve the quality of the silage.
- Commonly 20 kg molasses plus 8 kg salt per ton of green fodder is recommended.
- The other additives used include the addition of limestone (0.5-1.0%), sodium metabisulphite, organic acids like propionic and formic acids at 1% level and bacterial cultures like lactobacillus, etc.
What are the advantages of Silage?
- It helps ease feed shortages during dry seasons.
- The adequate feed is available all year round; hence animals remain in good health. Silage can be made using fresh or better-wilted mater
- Stable composition of the feed for a longer period.
- Efficiently used by livestock
- Reduction of nutrient loses which in hay may amount to 30% of the dry matter.
- It requires 10 times less storage space compared to the storage of hay.
- Maize silage has 30-50% higher nutritive value compared to maize grain and maize straw.
Drawbacks of Silage making
Here are a few limitations on Silage making:
- High capital investment is required for making silage. From chopping of forage, packing of silage and other expensive equipment for removing/packing silage are required, which for small farmers be expensive.
- The management of Silo is difficult. Once Silo is opened, silage should be consumed on a daily basis. It will be more prone to spoilage due to exposure to oxygen and warm weather conditions.
- Silage cannot be transported to long distances.