L. 't Mannetje
Department of Plant Sciences
6709 RZ, Wageningen, The Netherlands.
E-mail: [email protected]
Forage, crop residues and by-products are usually consumed fresh by domestic animals. However, it is possible to conserve them for use during future periods of feed shortages. Conservation can be achieved by sun drying (hay), artificial drying (meal), and addition of acids or fermentation (silage).
Hay making is difficult in tropical regions because at the time when the forage is of acceptable quality for conservation (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. Addition of acids may be beyond the resources of smallholders and can be dangerous. There remains fermentation by silage making, which can be done using fresh or, preferably, wilted material.
Silage is forage, crop residues or agricultural and industrial by-products preserved by acids, 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; additives may be added; and it is then stored in the absence of air so that facultative anaerobic bacteria, 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: 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 for as long as it remains in airtight storage.
There are three important considerations to take into account before embarking on a silage making programme:
(i) Is there a need for silage making?
(ii) If so, are there enough good quality forages or other products available to ensile?
(iii) If so, can the conditions for good silage making be met?
IS THERE A NEED FOR ENSILED FORAGE?
Silage making is practised widely in intensive animal production systems in temperate regions, mainly for two reasons. Firstly, because during the winter period there is no high quality feed available in the fields; and, secondly, in order to feed high quality conserved supplements (e.g. maize) at any time of the year to complement grass to improve milk production or nitrogen utilization.
Whether silage making is recommendable in the tropics depends on the type of farm system and on the climate. For a start, feed conservation is generally only an economic proposition for intensive farm systems, such as milk production for a liquid milk market. Secondly, in humid and subhumid climates with green forage available year-round, forage conservation is generally not profitable. If the quality of forage from permanent sources (pastures, road-sides) is inadequate, it is nearly always possible to grow a fodder crop (Saleem, 1985) or harvest stockpiled forage (Andrade et al., 1998) or use fodder banks (Milera et al. 1994; Peters et al., 1994).
Materials to be ensiled can be grasses, legumes, fodder crops (sorghum, maize), crop residues or by-products. The storage period, after which the silage is fed, depends on the purpose of the silage making. If silage is made from forage or a fodder crop of exceptional quality that is only available at a certain time of the year, it will most probably be used in a matter of months. It may also be used for an annual recurrence of periods of shortage or for unseasonable droughts that occur every number of years. Silage can also be a standard feed supply in feedlot systems.
Is there enough good quality forage to ensile?
Only excess forage, crop residues or by-products for which there is no other economic use should be ensiled. In other words, if rainfall is unreliable, farmers will not know until late in the growing season that there will be excess forage. This points to a conflict between availability of forage to ensile and its quality. The quality is highest early in the growing season, but the farmer cannot take the risk of preserving forage if he is not sure that there will be excess. Once he can be sure of that, the quality is too low to make it worthwhile to conserve it. To overcome this problem, it is possible to grow a fodder crop to be harvested, or reserve crop residues and by-products or other waste materials to be collected for silage making.
Can the conditions for good silage making be met?
Silage making is useful only if the ensiled product is of good quality, i.e. well preserved, with high digestibility and protein concentration. The main prerequisites for ensilable forage are that it should be harvested at a young stage of growth from a feeding value point of view, 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 (C4) 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 ensile tropical grasses. Problems with silage can also arise when it is being fed out, due to spoilage caused by moulds that grow particularly fast at the high temperatures common in the tropics. Therefore, 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.
Catchpoole and Henzell (1971) wrote an early review, which clearly sets the scene for silage making from tropical forages.
The aim of the conference is to review the potential of silage making for livestock production in the tropics, with special reference to the smallholder situation.
There are main papers and posters to cover the main issues of silage making under these conditions. The first main paper deals with the theory of silage making, the fermentation processes, and what problems could be encountered in meeting the requirements for good silage making. This is followed by other main papers and posters on silage making in large- and small-scale animal production systems; the use of grass-legume mixtures, of cereals and fodder crops, of agricultural by-products and industrial, non-agricultural residues, harvesting and ensiling techniques; and the use of additives to improve the silage making process for tropical forages.
Andrade, I.F., Atkinson, L.G., Sollenberger, L.E., Ruegsegger, G.J., Misley, P., & Kalmbacher, R.S. 1998. Stockpiling herbaceous tropical legumes for dry-season feed in Jamaica. Trop. Grassl., 32: 166-172.
Catchpoole, V.R., & Henzell, E.F. 1971. Silage and silage making from tropical herbage species. Herb. Abstr., 41: 213-221.
Milera, M., Iglesias, J., Remy, V., & Cabrera, N. 1994. Empleo del banco de proteina de Leucaena leucocephala cv Peru para la produccion de leche. [Use of a protein bank of Leucaena leucocephala cv. Peru for milk production.] Pastos y Forrajes, 17: 73-82.
Peters, M., Tarawali, S.A., & Alkamper, J. 1994. Evaluation of tropical pasture legumes for fodder banks in subhumid Nigeria. - 1. Accessions of Centrosema brasilianum, C. pascuorum, Chamaecrista rotundifolia and Stylosanthes hamata. Trop. Grassl., 28: 65-73.
Saleem, M.A.M. 1985. Effect of sowing time on the grain yield and fodder potential of sorghum undersown with stylo in the subhumid zone of Nigeria. Trop. Agric., 62: 151-153.