Silage

Hay making is difficult in many tropical regions because at the time when the forage is of acceptable quality for forage conservation to be worthwhile, which is normally early in the wet season, the weather is likely to be too unreliable for sun drying. Artificial drying is expensive and facilities are not widely available. Silage on the other hand can be made using fresh or, preferably, wilted material.

Silage consists of forage, crop residues or agricultural and industrial by-products preserved that are by acids. These acids are either added or produced by natural fermentation.

Fresh forage is harvested, or crop residues and by-products are collected. The material may be chopped or conditioned, and additives may be included. It is then stored in the absence of air so that facultative anaerobic bacteria, naturally present on the forage, or added as inoculants, can rapidly convert soluble carbohydrates into acids.

The quality of the ensiled product depends on the feeding value of the material ensiled and on the fermentation products present, as well as on the types of acids and the amount of ammonia. The resulting pH of a well-ensiled product becomes so low that all life processes come to a halt and the material will be preserved so long as it remains in airtight storage.

There are four main roles played by ensilaging and silage. There are:

• to build up feed reserve for utilization during periods of feed deficiency, e.g. dry season or winter
• as a routine feed supplement to increase productivity of animals
• to utilize excess growth of pasture for better management and utilization
• to store and enable extended use of potentially unstable material.

There are a number of factors to take into account before considering a silage making program:

Is there a need for silage?

Silage making is practised widely in intensive animal production systems in temperate regions for two main reasons. During the winter period there is no high quality feed available, and there is a need to feed high quality feed supplements to complement available grass in order to improve production, e.g. milk, or to ensure good condition, e.g. for breeding.

Under tropical conditions, decisions depend on a number of factors, including the type of farm system and the climate. Feed conservation is may only be economic for the more intensive farm systems, with products such as milk. In humid and sub-humid climates with green forage available year-round, forage conservation is generally not profitable and in many cases there is no need. If the quality of available forage from permanent sources such as pastures and road verges is inadequate, it is nearly always possible to grow a fodder crop or
or use fodder banks.

Crops suitable for silage

Non-leguminous fodder crops rich in soluble carbohydrates, such as maize, oats, sorghum, pearl millet, and cultivated grasses are most suitable for ensiling. Materials can be grasses, legumes, fodder crops (e.g. sorghum, maize), crop residues or by-products.

• Only excess forage, crop residues or by-products for which there is no other economic use should be ensiled.
• Can fodder crops be grown specifically for production of silage?
• One should not rely on crop failures, since by the time it is known that crop failure is likely, the quality is normally too low to make it worthwhile to conserve it by making silage.

Silage making is useful only if the ensiled product is of good quality, i.e. well preserved and of high digestibility and protein content. The main requirements are that it should be harvested at a young stage of growth and that it should contain enough sugars for fermentation. The material to be ensiled should be easily compactable and covered to exclude air. If the material is of adequate quality, but lacking in sugars, molasses or another source of sugar may be added. Chopping before ensiling will also help to compact the material.

Tropical grasses are inherently low in soluble carbohydrates, with the exception of maize and Sorghum species. To ensure good quality silage it may be better to grow a crop of maize or sorghum for silage than to rely on a tropical grass.

Problems with silage can also arise when it is being fed out due to spoilage caused by moulds that grow particularly fast at high temperatures. Silage pits or heaps for smallholders should be small, so that they can be fed out in a very short time (1 or 2 days). Poorly made silage can cause health problems in animals and man.

Basic Method of Silage Making

The reference by Moore (1943) includes information on methods of making silage that is still relevant today, and is well worth reading.

The two references by Coblentz present a North American, mechanized perspective and also includes useful information on the microbial processes that enable forage to be preserved as silage. An basic understanding of these processes is essential if good quality silage is to be produced. The paper by Ba presents information on the use of mulberry leaves for silage in Vietnam.

The Forage Production and Conservation Manual by Mhere et al. provides valuable information on production of silage and growing and ensiling annual and perennial forage crops in marginal and semi-arid areas of Southern Africa.

Silage can equally well be produced in small quantities and stored in small bags. The work by Lane on Little Bag Silage illustrates a system for producing small quantities of silage, sealed in plastic shopping bags, and used by livestock keepers in northern Pakistan and in Nepal.

The production process of silage may be divided in four stages:  

• Forage harvesting
• Transport to the silo. In the case of Little Bag Silage, the containers can be transported to the forage.
• Compaction (exclusion of air)
• Sealing (make sure the container is air-tight).  

The success of these stages has a big impact on the success or failure of the fermentation and the quality of the silage. The first decision to take when planning to make silage is on the amount of silage required, which depends on the following factors:  

• Number and type of livestock receiving silage.
• Length of the feeding period
• Percentage silage of the full ration
• Material resources available (equipment, labour, financial means, technical assistance, etc.).  

For example: An adult bovine, consuming 50% of the ration in the form of silage would receive 5 kg of dry matter (DM) per day. For a feeding period of 180 days, 900 kg of DM/animal would be required, that is, 3.6 t of fresh forage, containing 25% DM. Considering 15% silage loss 540 kg of fresh forage should be added, to arrive at a total of 4.14 t per head. This is equivalent to 2.3 cubic metres of silage capacity per animal, assuming a density of 0.6 t/m3.  

Using the same assumptions for a goat, the requirement would be 108 kg of DM silage at a rate of 0.6 kg per day, an amount of 497 kg fresh forage per animal would need to be ensiled, equivalent to a volume of 0.83 cubic metres of silo capacity per animal.   This calculation can also be carried out in reverse, taking into account the resources available on the farm and the potential area or amount of forage resources that can be conserved.  

Irrespective of the amount of silage to be made the following principles for good silage apply:  

• The material to be conserved must have a high nutritive value.  
• The forage must not be contaminated with soil.  
• The forage should be chopped into pieces no longer than about 2 cm in length to facilitate good compaction and reduce the amount of air in the silage.  
• It is necessary to expel the maximum amount of air within the forage before closing the silo, or sealing the bag, to avoid its re-entry and prevent water penetration.  
• Collection and processing of the forage and sealing the silage in containers should be done in the shortest possible time.  
• During the feeding of the silage, the area exposed to air should be as small as possible and the time between opening and finishing the silo as short as possible.

Although the total silo capacity on a farm depends on the number and type of animals and the period of silage feeding, it is recommended not to have all the silage required in only one silo, to keep losses at a minimum. The best system is to create silos that can be emptied over short periods, so the actual silo size depends on the amount of silage per animal and the number of animals to be fed. The best strategy is to make silage at different times of the year and to feed it after approximately 60 to 70 days of conservation. This way the silage would have optimum fermentation and least chance of aerobic deterioration. However, the time of silage making also depends on the growing conditions and the availability of forage to be ensiled.

Wilting of the forage before ensiling has many advantages. When DM levels are 30- 35%, effluents will not be produced, the development of undesirable micro organisms will be reduced, better fermentation will be promoted and intake increased. Anti-nutritional metabolites (e.g. tannins and alkaloids) in certain forages (e.g. herbaceous and woody legumes and cassava leaves) will be eliminated or reduced. However, these species tend to loose their leaves during handling when dehydrated. The field-drying time required to reach an optimum dry matter content depends on the individual species as well as on the weather conditions. The time may also vary between 4 and 24 hours depending on the thickness of the stems.

It is important to estimate the total man-hours required to cut, carry and chop a certain amount of forage. This will will determine the size and quantity of the containers or silos and the number of people necessary to do the work in order to start and finish a silo within one day. The simplest cutting system is to cut forage with machetes, scythes or similar equipment. Manual cutting has a low productivity. Erect forage can be cut at a rate varying between 0.5 to 0.8 t/person/hr. With prostrate species the rate of cutting is lower. It is not possible to give a general estimate of time required to prune shrubs and trees because it depends on the density of the edible material and the density of the plants. However, one could accept an estimate of 0.8 t/person/hour.

In addition to the time required to cut the material there is also the time needed to carry it to the silo and to chop it before entering it into the silo.

 

Silage Effluent: prevention of environmental pollution

Silage effluent is produced from any forage crop which is being made, or has been made, into silage. It is also defined as a mixture consisting wholly of or containing such effluent, rain or groundwater emanating from a silo, silage effluent collection system or drain. In some intensive agricultural areas, silage effluent may be one of the commonest forms of agricultural pollution.

For more on silage effluent and pollution