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Paper 5.0: The potential use of tropical silage for livestock production, with special reference to smallholders - David H. Machin

David H. Machin

CAMBAC Associates
Manor Farm
Draycott Cerne

Chippenham, Wiltshire, England

E-mail: [email protected]


Forages have been preserved using acids for many years, and the process is referred to as ensilation. This term has also been adopted to describe the preservation and storage of protein-rich materials such as fish and animal products to be used as animal feeds. More recently, this process has been used to preserve carbohydrate rich materials, either alone or through fermentation with other materials.

The essential feature of this means of preserving organic materials is the use of acids. These can either be mineral or organic, which can be provided by direct addition or produced by fermentation. Clearly, the choice of acid will affect the composition and use of the ensiled product, as well as having financial implications for the economic viability of its use.

For such a system to be suitable for smallholders in the tropics it must: -

- have low investment costs;
- be reliable and repeatable;
- use uncomplicated technology;
- use locally sourced equipment and consumables;
- be safe; and
- give rapid and significant returns on investments.

This paper will therefore consider the various alternative silage production systems in the context of the above requirements. Furthermore, this paper will focus on the use of wastes and by-products that otherwise would be under- or not utilized, as well as the non-conventional use of forage silage by species other than ruminants.


Traditionally, most wastes used as animal feeds are heat-treated to sterilize the materials and if the heat-treated product cannot be utilized locally or in a short time, the product would then be dehydrated to facilitate storage and transport. Such processing is generally carried out where waste materials are available in large quantities on a regular basis and where the final product is of medium to high value. Such circumstances are unlikely to apply to the smallholder situation.

Whilst cooking of perishable materials is commonly and successfully carried out by smallholders for materials that are to be used within a short time, the dehydration process is less commonly and successfully practised. The exception to this is where local fish products are manufactured using solar drying. This type of processing is generally carried out in unhygienic conditions, with the product frequently becoming contaminated with bacteria.

Smallholders are likely to have only small to medium quantities of materials available for processing, which are likely to be used for local consumption.

In such circumstances, and where materials cannot be used immediately, the use of ensilation for the processing and storage of small to medium quantities of organic material could be a useful system.


Almost all organic materials could be suitable substrates for ensilation in one form or another. The decision on the approach and technique to apply will depend upon:

- the composition of the material, including DM content;

- the type and degree of pathogenic and fermentative bacteria contamination;

- the buffering capacity of components of the material;

- the presence of potential autolysing enzymes in the main substrate, or of naturally present bacteria;

- the availability of other materials, such as acids, fermentable substrates and fermentative bacteria, to assist in ensilation; and

- the cost of preservation using the technique in the prevailing circumstances.

Considering these criteria, it is clear that the range of possible ensilation processes consist of the following:

- ensilation using acids produced by the fermentation of carbohydrates within the material by naturally present bacteria or cultures of added bacteria;

- ensilation using acids produced by the fermentation of carbohydrate-rich materials added to the substrate to be preserved using naturally present or added fermentative bacteria;

- ensilation using added inorganic acids such as hydrochloric or sulphuric acids, or mixtures of such acids; or

- ensilation using organic acids such as formic, propionic or acetic acids, or mixtures of such acids.


This type of ensilage is typical of that carried out with plant materials having a low buffering capacity, a DM content higher than 20%, a fermentable carbohydrate concentration of between 5 and 20% and with naturally occurring lactic acid fermentative micro-organisms present.

This traditional silage making process has been extensively reviewed and the present paper will only consider the possible use of this type of material for animal species not traditionally fed such materials.

Use of ensiled forages for non-ruminant animals

Whilst ensiled forages have commonly been fed to ruminants in all parts of the world, such materials have rarely been fed to monogastric animals, such as pigs, in commercial situations.

Currently, there is considerable interest in the possibility of feeding forages, including those preserved by ensilation, to pregnant sows in order to improve their reproductive performance through improved welfare (Lee and Close, 1987). In this situation it is agreed that most pregnant sows suffer stress through being fed relatively small quantities of compound feeds (approx. 2.2 kg) when their appetite would be for two or three times that amount. The main objective is to prevent such animals becoming over-fat, which is associated with breeding problems. It is proposed that by feeding such animals on low nutrient dense feeds to appetite, they would be less stressed, stay within targeted weights, which could result in improved reproductive performance, longer reproductive life and lower feed costs.

Ensiled forages would be ideal materials for use in such circumstances, since pigs would be able to digest all enzymically digestible components in the upper gut and then through fermentation in their lower gut digest fibrous materials and absorb the associated products.

Similarly, work with such materials has been carried out with growing pigs. It has been demonstrated that the guts of commercial-type pigs (Large White, Landrace, etc.) are able to use such materials from about 50 kg liveweight (Machin, 1990). However, where such a feeding system is practised, the rate of gain has been correspondingly less than where commercial feeds were used. Nevertheless, such low-cost feeds might well be financially attractive in circumstances where compound feeds are expensive and where through lower labour and housing costs a better margin can be obtained using such an approach.

The use of ensiled forages could offer considerable benefit for smallholder pig farmers in the feeding of gestating sows and growing/fattening pigs. However, due to the high nutrient demands of lactating animals this system would not be recommended for lactating sows.

The remainder of this paper will concentrate on the application of the ensilation process to store and preserve non-forage, nutrient-rich, perishable materials.


The materials that have been preserved by ensiling can be divided into those that produce acids through anaerobic fermentation, which preserve the unfermented remainder of the substrate, and those that are preserved by acids added directly or produced by the fermentation of materials mixed with them. Many of these materials also undergo autolysis of the substrate, using naturally containing autolytic enzymes as a secondary phase of preservation.

Fermentable substrates

These materials contain carbohydrates that can be fermented to produce acids such as lactic or acetic acid. Clearly, such a process requires the presence and action of micro-organisms. These may be naturally occurring or may be added as a separate culture (Martin and Bozoglu, 1996). Similarly, some substrates may contain insoluble carbohydrates that are not readily fermentable and require enzymes to break them down into simple soluble carbohydrates that can be fermented. These can then generate acids to preserve the remainder of the material or mixture.

Table 1. Examples of materials that have been used as fermentable substrates



Sugar Industry By-products

Molasses - sugar cane

Evers and Carroll, 1998

Molasses - beet

Fagbenro and Jauncey, 1998

Sugar cane wastes

Alimon et al., 1994

Fruit Wastes


Ash and Elliott, 1991


Bello and Fernandez, 1995


Bello and Fernandez, 1995


Megias et al., 1998

Apple pomace

Nikolic and Jovanovic, 1986

Kiwi fruit

Ciruzzi et al., 1996

Grape waste

Nour et al., 1981

Other Agro-industrial Wastes

Brewery and distillery wastes

Pelz and Hoffman, 1997

Vegetable processing wastes

Ashbell et al., 1995

Milk by-products

Sander et al., 1995

Flower wastes (carnations)

Ceron et al., 1996

Taro roots

Ash and Elliott, 1991

Cassava root wastes

Fagbenro and Bello, 1997

Bakery by-products

Bastian, 1990

Olive waste

Hadjipanayiotou and Koumas, 1996

Tofu cake

Niwa and Nakanisi, 1995

Sisal waste

Rodriguez et al., 1985

Oil palm fronds

Abu Hassan et al., 1996

In contrast, materials rich in soluble carbohydrates, such as fruits, sugar cane or beet products, are capable of preserving materials at relatively low DM levels through osmotic effects alone, without the need for acid fermentation. The list of materials that have been successfully ensiled (see Table 1) demonstrates the broad range of products that can be preserved in this way. However, only those with high levels of soluble carbohydrate, such as sugar and fruit products are likely to be able to produce sufficiently high levels of acid by fermentation to assist in the storage of non-fermentable materials.

Clearly, ensilation could be a useful means of preserving a wide range of perishable materials that would otherwise be unused as animal feeds.

Table 2. Examples of non-fermentable materials that have been preserved by ensilation



Slaughterhouse Wastes

Poultry carcass waste

Machin et al., 1984

Poultry viscera

Fagbenro and Fasakin, 1996

Hatchery waste

Deshmukh and Patterson, 1997

Feather meal

England et al., 1991

Large animal carcass waste

Machin, 1986


Le-Van-Lien et al., 1996

Fishery Wastes

Waste whole fish

Machin et al., 1990

Shrimp by-catch

Ames and Ward, 1995

Salmon viscera

Dong et al., 1993

Scallop viscera

Myer et al., 1990

Prawn and shrimp heads

Le-Van-Lien et al., 1996

Evers and Carroll, 1998

Crab waste

Evers and Carroll, 1996

Fish viscera

Ahmed et al., 1996

Many of these materials (see Table 2) are available to smallholders in small to medium quantities in a variety of locations around the world. A simple, low-capital process such as ensilation could be an attractive way of preserving such materials. Quite clearly, matching the availability of suitable supplies of fermentable materials to mix with these types of materials could cause logistical difficulties. In such circumstances, the use of low cost by-products such as fruit wastes would be the first choice, with more expensive sugar by-products used as back up materials.

However, the main problem with such an approach for smallholders would be the higher degree of technical knowledge required to be able to change systems to meet variations in raw material availability. Unless fermentable and non-fermentable proteinaceous material supplies are available at the same time, it might be best to place most emphasis on the use of storable fermentable materials, such as molasses, for this type of processing for smallholders.


Considerable research has been carried out on the preservation of perishable proteinaceous wastes using added acids (Machin, 1986; Perez, 1995). Initial studies focused on the use of mineral acids such as hydrochloric, sulphuric or phosphoric acids, but these alone were shown to be poor preservers of silages (Disney et al., 1977). Silages have, however, successfully been made using mixtures of organic (formic, propionic, citric, etc.) acids and mineral acids, or organic acids alone (Perez, 1995). Nevertheless, the use of direct addition of organic and/or mineral acids is very unlikely to be a means by which smallholders could process feed materials due to the cost and danger of handling strong acids in low-technology situations. For this reason it would appear that the most appropriate way that smallholders will be able to use the acid ensilage process will be through a natural fermentation system.


In recent years, most researchers in this field have focused on this approach to processing small to medium quantities of perishable organic materials. Although some researchers have been able to get successful fermentation using sources of fermentable carbohydrates alone mixed with non fermentable materials (Raa and Gildberg 1982) most have used lactic acid bacterial cultures to stimulate fermentation. Some of the most successful bacteria have been Lactobacillus plantarum, Streptococcus faecium and Pediococcus acidilactici (Deshmukh and Patterson, 1997).

However, the use of bacterial cultures would obviously be a deterrent for low-technology processing by smallholders. It is therefore interesting to note that, although raw materials low in LAB content generally benefit from the use of suitable inoculants, it is not always essential that they be included (Martin and Bozoglu, 1996).

There are also reports that if the raw material already has a high concentration of LAB, inoculants do not improve the process (Desmukh and Patterson, 1997). It would therefore appear that smallholders could well be able to produce fermented silages without the need to produce or purchase starter cultures, provided that appropriate mixtures of fermentable and non-fermentable materials are selected. In contrast, where mixtures not capable of generating a rapid fermentation and sufficiently low pH have been tried, successful silage production has not been achieved (Urlings et al., 1993).

In this context it is interesting to note that non-fermentable materials have been preserved by mixing them with fermentable carbohydrates, include poultry slaughterhouse wastes, hatchery waste, large animal slaughterhouse waste, whole waste fish (fish viscera, shrimp by-catch), shrimp and prawn heads and crab waste.


There is considerable concern about the presence of pathogenic bacteria in food materials fed to farm animals. Unfortunately, many of the materials listed above as possible substrates for preservation through ensilage could well be contaminated with such bacteria. The acid ensilage process has been shown to be an effective means of reducing or eliminating pathogens and indicator organisms in materials such as poultry slaughter house wastes, hatchery waste and fishery waste. Many other researchers reviewed in Machin (1986) showed a range of silages to be free from coliformes, Salmonella spp., Clostridium spp., Staphylococcus spp. and faecal Streptococcus, and to have a very low bacteria count or to be bacteria free. This conclusion is supported by Frazier and Westhoff (1978), who showed that all common bacteria that cause food-borne infections are inhibited at pH values below 4, and in the case of Clostridium botulinum, toxication is prevented below pH 4.5.

In particular, fermentation of such inedible wastes has been shown to decrease the numbers of Gram-negative pathogens (Talkington et al., 1981) and viruses (Wooley et al., 1981).

The means by which this occurs relates to the effect of low pH, the presence of antibiotic substances produced by LAB and the ability of organic acids to pass over the cell membranes of micro-organisms by dissociation and lower the organisms internal pH to destructive levels (Raa and Gildberg, 1982). LAB also produce antibiotics and bacteriocins which are often bacteriostatic against other bacterial species (Urlings et al., 1993). Mineral acids do not have the same dissociating ability as organic acids and so are much less effective in silage production.

Many wastes of animal and fish origin contain autolytic enzymes, which at low pH are able to break down large organic molecules, so exposing any micro-organisms present in the waste to anti-microbial action (Backhoff, 1976).


Following ensilation, most animal wastes have been successfully processed and fed to a wide range of domestic animals without problem. Perez (1995) noted that fish silages were suitable for feeding to pigs, poultry, ducks, ruminants and camels. Other researchers have successfully fed fish silages to farmed fish. Many others have shown that materials such as poultry slaughter house and hatchery waste as well as ruminant offal silage could be successfully fed to pigs, poultry, mink, fish (catfish - Clarias gariepinus; common carp - Cyprinus carpio) compared with control feeds.


It is clear that the ensilation of waste materials could offer a simple and inexpensive means by which smallholders in certain circumstances might be able to process and preserve a wide range of materials for use in animal feeding. However, there are likely to be many situations where the correct balance of materials and knowledge are not in place and so this approach should not be applied without due care. In particular, most benefit is likely to occur using fermentation not requiring the use of prepared bacterial inoculants.


Abu Hassan, O., Ishida, M., Dukri, I. Mohd. S., & Tajuddin, Z. Ahmad. 1996. Oil palm fronds as a roughage feed source for ruminants in Malaysia. Extension Bulletin 420. Food & Fertilizer Technology Center for ASPAC Region, Taipei, Taiwan.

Ahmed, J., Ramesh, B.S., & Mahendrakar, N.S. 1996. Changes in microbial population during fermentation of tropical freshwater fish viscera. J. Appl. Bacteriol., 80: 153-156.

Alimon., A.R., Lim, S.Y., Dahlan, I., Halin, I., Djajanegara, A., & Sukmwati, A. 1994. Effect of urea treatment on intake and digestibility of sugar cane waste by goats. Proc. 7th AAAP Animal Science Congress, Bali, Indonesia, vol. 2: 109-110.

Ames, G.R., & Ward, A.R. 1995. Problems of utilising shrimp by-catch in the tropics. Trop. Sc., 35: 411-417.

Ash, A.J., & Elliott, R. 1991. Tropical crop and crop by-product additives can improve the quality of taro leaf (Colocasia esculenta) silage. J. Agric. Sc., 117: 233-240.

Ashbell, G., Weinberg, Z.G., & Hen, Y. 1995. Studies of quality parameters of a variety of ensiled broiler litter. An. Feed Sc. Techn., 52: 271-278.

Backhoff, H.P. 1976. Some chemical changes in fish silage. J. Fd. Techn., 11: 353-363.

Bastian, R.W. 1990. The use of enzymes and bacteria to successfully upgrade animal offal. p. 405-418, in: T.P. Lyons (ed) Biotechnology in the feed industry. Proceedings of Alltech’s Sixth Annual Symposium.

Bello, R.A., & Fernandez, Y. 1995. Evaluation of biological fish silage in broiler chicken. Arch. Latinoam. Nutr., 45: 134-139.

Ceron, J.J., Hernandez, F., Madrid, J., & Gutierrez, C. 1996. Chemical composition and nutritive value of fresh and ensiled carnation (Dianthus caryophyllus) by-product. Small Rum. Res., 20: 109-112.

Ciruzzi, B., Laudadio, V., Vincenti, A., & Marisco, G. 1996. Ensiling of refuse kiwifruit and utilisation in ruminant nutrition. Agric. Mediter., 126: 5-12.

Deshmukh, A.C., & Patterson, P.H. 1997. Preservation of hatchery waste by lactic acid fermentation. 1. Laboratory-scale fermentation. Poultry Sc., 76: 1212-1219.

Disney, J.G., Tatterson, I.N., & Olley, J. 1977. Recent development in fish silage. Proc. Conference on Handling, Processing and Marketing of Tropical Fish. London. Tropical Products Institute.

Dong, F.M., Fairgrieve, W.T., Skonberg, D.I., & Rasco, B.A. 1993. Preparation and nutrient analyses of lactic acid bacterial ensiled salmon viscera. Aquaculture, 109: 351-366.

England, M.L., Combs, D.K., & Shaver, R.D. 1991. Animal protein by-products and level of undegraded protein intake in diets for early lactating dairy cows. J. Dairy Sc., 74: 215.

Evers, D.J., & Carroll, D.J. 1996. Preservation of crab or shrimp waste as silage for cattle. An. Fd. Sc. Techn., 59: 233-244.

Evers, D.J., & Carroll, D.J. 1998. Ensiling salt-preserved shrimp waste with grass straw and molasses. An. Fd. Sc. Techn., 61: 241-249.

Fagbenro, O.A., & Bello, O.O.A. 1997. Preparation, nutrient composition and digestibility of fermented shrimp head silage. Fd. Chem., 60: 489-493.

Fagbenro, O.A., & Fasakin, E.A. 1996. Citric acid ensiled poultry viscera as protein supplement for catfish (Clarius gariepinus). Bioresource Techn., 58: 13-16.

Fagbenro, O.A, & Jauncey, K. 1998. Physical and nutritional properties of moist fermented fish silage pellets as a protein supplement for tilapia (Oreochromis niloticus). An. Fd. Sc. Techn., 71: 11-18.

Frazier, W.C., & Westhoff, D.C. 1978. Food Microbiology. 3rd Ed., McGraw-Hill.

Hadjipanayiotou, M., & Koumas, A. 1996. Performance of sheep and goats on olive cake silages. Technical Bulletin Cyprus Agricultural Research Institute, No.176. 10 p.

Le-Van-Lien, Nguyen-Thein, Le-Viet-Ly & Pryor, W.J. 1996. By-products from food industries: processing and utilisation for animal feed in Viet Nam. Exploring approaches to research in the animal sciences in Viet Nam. ACIAR Proc., 68: 149-152.

Lee, P.A., & Close, W.H. 1987. Bulky feeds for pigs: a consideration of some non-nutritional aspects. Livest. Prod. Sc., 16: 395-405.

Machin, D.H. 1986. The use of formic acid preserved meat and fish offal silages in pig and poultry feeding. PhD Thesis, Reading University. 221 p.

Machin, D.H. 1990. Alternative feeds for outdoor pigs. p. 103-114, in: B.A. Stark, D.H. Machin & J.M. Wilkinson (eds) Outdoor Pigs. Principles and Practice. Marlow, Bucks (UK): Chalcombe Publications.

Machin, D.H., Hector, D.A., Capper, B.S., & Carter, P.M. 1984. The utilisation by broiler chickens of poultry offal hydrolysed in formic acid. An. Fd. Sc. Techn., 11: 247-260.

Machin, D.H., Panigrahi, S., Bainton, J., & Morris, T.R. 1990. Performance of broiler chicks fed on low- and high-oil fish silages in relation to changes taking place in lipid and protein components. An. Fd. Sc. Techn., 28: 199-224.

Martin, A.M., & Bozoglu, T.F. 1996. Role of lactic acid fermentation in bioconversion of wastes. p. 219-252, in: T.F. Bozoglu & R. Ray (eds) Lactic acid bacteria: Current advances in metabolism, genetics and applications. NATO ASI Series, Vol. H98.

Megias, M.D., Hernandez, F., Cano, J.A., Martinez, T.A., & Gallego, J.A. 1998. Effects of different additives on the cell wall and mineral fractions of artichoke (Cynara scolymus L). J. Sc. Fd. Agric., 76: 173-178.

Myer, R.O., Johnson, D.D., Otwell, W.S., Walker, W.R., & Combe, G.E. 1990. Evaluation of scallop viscera silage as a high protein feedstuff for growing finishing swine. An. Fd. Sc. Techn., 31: 43-54.

Nikolic, J.A., & Jovanovic, M. 1986. Some properties of apple pomace ensiled with and without additives. An. Fd. Sc. Techn., 15: 57-67.

Niwa, Y., & Nakanisi, G. 1995. Research on the utilisation of food by-product to growing and finishing pigs: 2. The effects of tofu cake silage feeding on growth and body fat. Jap. J. Swine Sc., 329: 1-7.

Nour, A.A., Nour, A.M., El-Shazely, K.A., Abaza, M., Borhami, B.E., & Naga, M.A. 1981. Evaluation of some agro-industrial by-products for sheep and lactating cows. Alex. J. Agric. Res., 29: 1125-1142.

Pelz, D., & Hoffman, S. 1997. Dewatering, compacting and ensilaging of spent grains. Brauwelt, 15: 436-439.

Perez, R. 1995. Fish silage for feeding livestock. World Animal Rev., 82: 34-42.

Raa, J., & Gildberg, A. 1982. Fish Silage: A review. Crit. Rev. Fd. Sc. Nutr., 16: 383-419.

Rodriguez, A., Riley, J.A., & Thorpe, W. 1985. Animal performance and physiological disturbances in sheep fed diets based on ensiled sisal pulp (Agave fourcroydes). Trop. An. Prod., 10: 23-31.

Sander, J.E., Cai, T., & Barnhart, H.M., jr. 1995. Evaluation of amino acids, fatty acids, protein, fat and ash in poultry carcasses fermented with Lactobacillus bacteria. J. Fd. Agric. Chem., 43: 791-794.

Talkington, F.D., Shotts, E.B., jr., Wooley, R.E., Whitehead, W.K., & Dobbins, C.N. 1981. Introduction and re-isolation of selected Gram-negative bacteria from fermented edible wastes. Am. J. Vet. Sc., 42: 1298-1301.

Urlings, H.A.P., de Jonge, G., Bijker, P.G.H., & Van Logtestijn, J.G. 1993. The feeding of raw, fermented poultry by-products: Using mink as model. J. An. Sc., 71: 2427-2431.

Wooley, R.E., Gilbert, T.P., Whitehead, W.K., Shotts, E.B., jr., & Dobbins, C.N. 1981. Survival of viruses in fermented edible waste materials. Am. J. Vet. Res., 42: 87-90.

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