PART II (Contd.)

CHAPTER 10
UTILIZATION OF AGRO-INDUSTRIAL BY-PRODUCTS IN AFRICA

by

A.A. Adegbola

Department of Animal Science, University of Ife
Ife-Ife, Nigeria

Resumen

El documento señala la importancia que tienen los subproductos agroindustriales en el fomento de la producción pecuaria en Africa para completar el escaso desarrollo de los recursos de pastos y subsanar la falta de principios reconocidos de ordenación de pastos y de prácticas de manejo del ganado, y reducir la competencia por los limitados cereales disponibles para el hombre y el ganado.

El desconocimiento general existente en Africa sobre los usos posibles de subproductos agroindustriales para la alimentación de animales puede atribuirse a factores como la falta de información sobre su composición y valor nutritivo, la carencia de medios suficientes para la manipulación y elaboración, las diferencias de composición, los problemas de disponibilidad en cantidades suficientes y carácter estacional de los suministros, la necesidad de transporte y elaboración.

Se estudia el uso actual y potencial de los productos siguientes:

Los subproductos de molienda y de industrias almidoneras y cerveceras sirven como fuentes de energía, proteínas y vitaminas para rumiantes, cerdos y aves de corral. Es probable que el gluten de maíz de Guinea, los resíduos de tapioca y las peladuras de yuca y ñame lleguen a utilizarse como piensos especialmente en Nigeria y el Africa Oriental durante el próximo decenio.

Los dos principales subproductos de la elaboración del azúcar -- melazas y bagazo -- pueden utilizarse en la alimentación del ganado vacuno y, de pequeños rumiantes. El bagazo tratado al vapor puede satisfacer las necesidades del mantenimiento y de la gestación del ganado vacuno, pero deberá ser completado cuando se utilice para el crecimiento y la producción de leche.

Hay una falta general de mataderos centrales en Africa, con las excepciones de Kenia, Uganda y algunas zonas del norte de Nigeria, lo que hace dificil la utilización de subproductos de matadero. Además, por razones sociales, económicas y de otra índole, algunos productos como la sangre se utilizan para el consumo humano directo. El que aumente la utilización de resíduos de origen animal dependerá en último término de una mejor organización y posiblemente, de la mecanización de los sistemas de matanza y elaboración de las aves de corral, aunque el desarrollo reciente del sistema de producción de huevos en baterias comienza a plantear problemas de evacuación del estiércol de las aves, especialmente en algunas partes de Nigeria, Ghana y Kenia.

La producción mundial de cacao asciende a 1,5 millones de toneladas y el 70 por ciento de la misma procede de Africa. Recientemente se ha empezado a estudiar las posibilidades de utilizar como pienso la cáscara del cacao, la cubierta del grano de cacao, así como los granos de cacao enteros que se descartan. La presencia de teobromina, así como el bajo contenido de cistina y metionina, parecen ser los factores más importantes que limitan el empleo de estos productos. La cáscara del cacao puede substituir en parte a los cereales en la alimentación de rumiantes y no rumiantes. Las harinas de grano de cacao pueden substituir en un 50 por ciento a los cereales en la alimentación de engorde de pollos jóvenes y cerdos.

Trabajos realizados en Kenia, Uganda y Tanzania demuestran que el ganado vacuno no ingirió menos pienso porque se incluyera hasta un 20 por ciento de cascarilla de café en los suplementos dados al ganado para carne. El alto contenido de cafeina puede Limitar el rendimiento del animal, aunque puede evitarse este inconveniente con la deshidratación o el ensilaje de la pulpa y la cascarilla.

La cáscara de semilla de algodón se está convirtiendo en un importante resíduo agrícola en Africa, a medida que aumenta La molturación de Las semillas en la región. La harina de semillas de algodón se emplea en gran medida en Africa oriental y occidental en La alimentación de bovinos de engorde en dosis que representan hasta el 30 por ciento de la ración. En las granjas lecheras de Uganda se utiliza como alimentación de producción la semilla de algodón en cuanto tal, mezclada con tallos de banano machacados, especialmente durante los periodos de sequía. Se ha empleado la harina de semilla de algodón en la alimentación de cerdos de engorde con el suplemento de metionina y lisina.

En Africa tradicionalmente se utiliza mucho la torta de maní como alimento proteínico en la alimentación de los cerdos y aves de corral. La torta de almendra de palma que contiene más fibra que la de maní se limita más a la alimentación de rumiantes.

Al desarrollarse la elaboración de zumos de fruta en Africa occidental, empieza a disponerse de productos como pulpa de agrios, subproductos de la elaboración de la piña, semillas de mango y resíduos de tomate, que pueden constituir una buena fuente de nutrientes.

La producción de harina de semillas de cauchotero para su empleo en la alimentación de pollos jóvenes es actualmente objeto de atención en Nigeria. En las raciones para pollos jóvenes puede incluirse hasta un 25 por ciento de harina de semillas de cauchotero.

Introduction

It has often been noted that the shortage of feed during periods of drought in Africa still constitutes one of the most limiting factors to increasing the production of livestock in that continent. Grassland resources are vast but relatively poorly developed and inadequately managed, while water and health facilities for livestock are in short supply. Further, with the increase in the population of Africa, currently estimated at 384 millions or 124% of the 1963 figure (FAO, 1974) and 69% of whom are largely agricultural, there is a rise in demand for the major food crops since many African countries show a deficit in their food balance sheets. This shortage of food, especially of the major cereals, will prevent any significant development in the production of poultry and pork products as these stock depend largely on a constant supply of maize, guinea corn and millet as a basic source of energy.

Under the traditional system of livestock management in Africa, a few crop residues form part of the feed, especially for cattle, sheep and goats. These animals are usually offered groundnut hay, cowpea hay, cotton residue, millet and sorghum residues where these are available, particularly during the dry season, when standing forage usually shows a low protein content of about 2% (van Raay and de Leeuw, 1974). In Nigeria, under the backyard system of sheep and goat management, these animals are occasionally offered leaf-wrappings, cassava and yam peels resulting from the processing of these food crops for human consumption. In the Kenyan highlands, livestock grazings are traditionally supplemented with maize stalk, been haulms, sweet potato tops as well as cuttings of napier grass (Said, 1971).

Over the past decade, agricultural production in many African countries has begun to be better organized, as more and more development plans give priority to food production for domestic use. Consequently, larger acreages are being mechanized, with a resultant increase in the number of agriculture-based industries. Further, urban abattoirs have been built in several cities in East, West and Central Africa.

This welcome trend in development has led to the gradual availability of agro-industrial by-products, some of which can find use as direct feed for livestock or as components in feed-compounding industries.

The major agro-industrial by-products to be considered in this paper include the by-products of milling, starch and brewing industries, such as wheat bran, middlings, rice bran, rice polishings and husk, brewers' dried grain, maize gluten meal, and abattoir waste products, all of which can serve as sources of energy, protein and vitamins for ruminants as well as pigs and poultry. The two by-products of the sugar processing industry under experimentation for use as livestock feeds are molasses and bagasse. Waste products of cocoa, coffee, as well as cotton may also become important as livestock feeds, especially for ruminants. The use of by-products of the fruit processing industry, including banana wastes and citrus pulp, will also be considered. A brief mention must also be made of the potential value of rubber-seed meal, cashewnut meal and other forest products in ruminant rations.

Factors limiting the use of agro-industrial by-products in Africa

Attention must be drawn to some of the factors that limit the increased use of agro-industrial by-products in livestock production in Africa. In most countries, there is the need to modify or in fact totally replace the traditional system of livestock production in favour of one which will establish some sort of stratification in the systems of production and permit the sustained introduction and effective utilization of agro-industrial waste products into the system. There is now, in Africa, a general lack of awareness of the possible uses of some of these by-products as livestock feeds. Items such as cocoa husks or discarded cocoa beans cannot be obtained readily for inclusion in livestock rations, owing to the peasant pattern of cocoa production, which makes the collection and processing of large quantities of this by-product difficult. Similarly, groundnut husk or rice by-products are not often readily available, since their production is largely in peasant hands. The heterogeneous nature of most of the products makes their inclusion in formulated rations difficult, while lack of information on their composition and nutritive value, as well as on the levels acceptable for use in animal diets, may also limit the use of most by-products, especially those of cocoa, citrus, cashewnut and other forrest products.

Most agricultural wastes can potentially contribute to pollution, and while this may not be of major significance in Africa at present, owing probably to the vastness of the area, the fast rate of decomposition in the tropics and the underdeveloped nature of agricultural production in general, it can become a sizeable problem within a very short time. Projected increases in agricultural production in Africa suggest that unless adequate plans are made to channel agro-industrial wastes into productive systems it may become increasingly difficult to dispose of large quantities of them without an unfavourable repercussion on the environment. Livestock production offers a good method of using these by-products and preventing pollution.

Flour mill, brewery and rice mill by-products

There is evidence that these by-products are being considered to replace cereals that form the main energy portions of poultry and swine rations in various parts of Africa.

Although the production of wheat is small (4.64 million metric tons) compared to world production, African countries are installing quite sizeable capacities for flour milling, especially in East and West Africa: Nigeria alone has four flour mills producing, with three more planned to come into production by 1980. These are based largely on imported wheat, but some locally-produced wheat is also milled. Considerable amounts of wheat residues are thereby becoming available. An estimated 213 000 metric tones were available in 1975, and availability is expected to rise to 321 000 tons by 1980. Rations have therefore been formulated to use this product in place of maize in dairy as well as in growing-finishing pig rations. Unfortunately, the local demand for wheat-processing wastes is low and most of the product is currently exported, very little going into livestock feeds. A typical dairy ration in Nigeria contains 50% wheat bran, 35% groundnut cake, 12% maize or guinea corn and 3% mineral supplement. Beef animals as well as fattening lambs can also handle up to 20% of their rations as wheat residues. Olsen et al., (1970), In Ghana, measured the performance of pigs on diets containing 50% maize, 20% wheat bran and 30% maize bran, using large white and local black breeds of swine; they concluded that replacing one half of the maize with maize bran or wheat bran did not reduce liveweight gains.

Rice production in Africa is at present of the order of 7.60 million metric tons. Assuming that 10% of the whole crop is bran, a production of 760 000 metric tons of bran can be estimated, 80% being soft bran and 20% rough bran. Regrettably, most of this is not available for inclusion in animal feed, since not more than 20% of African rice production is milled commercially, the rest being processed in scattered small-scale mills in the various countries. Besides rice bran, small quantities of rice polishings as well as broken rice also become available, and these have been used in livestock feeds.

Although soft rice bran is traditionally included in poultry rations at low levels in starter (4%) and grower (5–6%) diets in Nigeria (Ademosun, 1973), it can in fact form the basis of rations for pigs at levels of up to 15% for weaners and 30% for growing-finishing pigs, according to Campabadal et al, (1976). These workers found that a 40% rice-bran diet could be fed to weaner pigs without reducing performance and that the addition of fat to rice-bran diets improved performance, apparently by increasing palatability and/or digestibility. The authors observed inflammation and ulceration of the gastrointestinal tract lining in the pigs fed, but could not establish the effect of this condition on the pigs' performance.

Rice polishings have been used to replace 10% of maize or guineacorn in chick starter diets, while up to 40% of maize in a broiler diet can be replaced without a resultant depression in growth and diarrhea (Ogunfowora et al., 1975).

Large breweries have recently been established in Africa, especially in East Africa and in most West African countries. Nigeria alone has fifteen breweries, with a potential production of 18 800 metric tons of spent grain by 1980. At present, most of this potential feed resource is dumped, resulting in pollution. Apart from lack of storage capacities, most breweries also lack of facilities for drying the by-product. Nevertheless, wet brewers' grains are already in use in several urban dairies near breweries, at levels between 26 to 55% of the production rations. Studies conducted in Nigeria with poultry (Ademosun, 1973) showed that 10 to 15% of brewers' dried grain can replace maize in starter and grower rations, but that birds from 8 to 18 weeks of age should not be fed brewers' dried grain in excess of 30% owing to the high crude-fibre content of the feed. Since it has a high content of protein and amino acids (Almquist, 1972), governmental action is necessary to ensure its collection, drying and inclusion in poultry and swine rations in Africa.

Other starch-milling by-products

Beside the above products of milling, maize meal from traditional processing of the crop to starch often becomes available and has been used as supplement for sheep and goats in West Africa. Spurling et al, (1972) also reported its use as part of the concentrate for stall-feeding experiments with cattle in South Malawi. With a production of 26.76 million metric tons of maize as grain in Africa, an estimated 10% can be available as meal from processing for starch representing another untapped potential for livestock feed. Similar observations can apply to guineacorn germ meal as well as cassava starch residues, the processing of which crops is however largely in peasant hands.

Sugar processing by-products

The production of sugar from sugarcane reached about 3 million metric tons in Africa by 1974, representing a production of about 30 million metric tons of canestalk. Sugar manufacture will yield about 4% of the cane-stalk as final molasses and 25% as bagasse. These by-products are at present inadequately utilized in Africa. Nigeria projects 1980 production at 92 000 metric tons of molasses and 483 000 metric tons of bagasse. Lawrence and Mugerwa (1974) estimated an annual production of 100 000 tons of molasses in Uganda, 90% of which is wasted. The final molasses in Nigeria and Rhodesia (Zimbabwe) have a lower content of ash than Trinidad molasses and slightly lower total sugar contents than the final molasses from Cuba and Trinidad (see Table 10.1).

Final molasses has considerable value as a source of energy in pig, sheep and cattle rations. In Kenya, daily gains of 0.95 kg have been achieved in steer fattening lots based on the use of final molasses. At Mokwa, Nigeria, molasses has been fed in feedlots to fattening steers of Keteku and N'Dama breeds. These animals achieved daily weight gains of 0.8 kg when they received 4 kg molasses plus 2 kg cottonseed in addition to bush grazing (Ogunfowora et al., 1975).

Experience with incorporating molasses plus urea into dairy rations in Uganda has not proved satisfactory. The ration used contained 20% molasses on a dry matter basis, with 2.1% urea and 26% cotton-seed cake. Milk yields of animals on the urea-molasses ration were compared over a period of 24 weeks with those of animals on a commercial feed. The concentrate was fed at 100 and 110% of total digestible nutrient requirement. The results showed that the urea-molasses concentrate stimulated a greater milk yield during the first eight weeks of lactation, producing 4.5% more milk (6 280 kg of 4% FCM). There was however no significant difference in milk yield over the entire 24-week period.

Baustad (1973) fed diets containing 20 and 39% molasses to pigs from 25 kg to 100 kg liveweight and concluded that growth rates were higher in the group of pigs receiving molasses than in the control group. Pigs on a 20% molasses diet had better feed conversion efficiency (3.81 kg feed/kg gain) than pigs on the 39% diet (4.15 kg feed/kg gain). Molasses supplied 17 and 34% respectively of the metabolizable energies in the rations.

¹ After Finchan J.E. (1966), Unsworth E.F. et al. (1976), and Ogunfowora et al. (1975).

This result is confirmed by experience in Nigeria, which indicates that up to 20% of the cereal grains in diets for growing and finishing pigs can be economically replaced by final molasses (Ogunfowora et al., 1975).

Bagasse is burned as fuel in sugar mills in Africa almost without exception, yet this product has potential for use as roughage in the feeding of ruminants. Of relevance in this context is the work done in the United States of America which indicated that steam treatment of bagasse may render it useful for cattle as a maintenance ration when mixed with molasses and cereal (Wayman et al., 1953).

Cocoa processing by-products

Current world production of cocoa beans has been put at 1.5 million metric tons, 70% of which comes from Africa (208 000 metric tons from Nigeria and twice as much from Ghana). The first product obtainable from cocoa is the cocoa husk, which in dry matter represents 75% of the entire fruit. As local processing of cocoa beans increases, a new product, referred to as cocoa meal, has been developed; it is described by Owusu-Domfeh (1972) as composed of fragments of the bean, including the cocoa bean plus shell, collected from the chocolate factory. This product is different from the cocoa bean shell, which is the thin skin immediately surrounding the cocoa nib and accounts for 10% of the weight of the bean. Another product, known as discarded cocoa-bean meal, was obtained by Adegbola and Omole in 1973 from the hot-water treatment of cocoa beans discarded as unfit for export.

The occurrence of theobromine and caffeine in plant parts of cocoa has limited the direct use of most of these products in livestock rations. Senanayake and Wijesekera (1971) showed that these methyl-xanthines occur more in the cotyledons than in shells. They occur only in traces from the formation of the pod up to about 3 1/2 months, and both purine bases increase steadily in shell until maturity, there being more theobromine than caffeine. The content also varies with varieties. The theobromine content of cocoa husk is however quite low when compared with its content in the shell. Additional processing of the husk, apart from grinding, may not be necessary for its incorporation into livestock rations. The theobromine contents of cocoa meal and cocoa shell must however be reduced through processing before the by-products can be offered to livestock.

After an hour's treatment with hot water, cocoa bean showed only a slight reduction in crude protein, a lower fat content and higher levels of free amino acids when compared with untreated ground cocoa beans (Table 10.2).

¹ after Adegbola and Omole, 1973.

Pigs averaging 21.5 kg bodyweight were fed to a final average of 80 kg bodyweight on rations shown in Table 10.3. The animals gave daily growth rates of 0.48 kg/day on the control diet while pigs fed diets containing 25, 50, 75 and 95% discarded cocoa meal (DCM) had growth rates of 0.43, 0.36, 0.26 and 0.13 kg/day respectively (Table 10.4). It was apparent that addition of DCM beyond the 50% level will require a critical balance of amino acids in the rations for growing pigs. There are at present no reports on work that includes DCM in poultry rations.

Cocoa-bean shell is reported by Owusu-Domfeh (1960) in Ghana to have a feed value about that of a good roughage and to be a source of Vitamin D (28 I.U./g). He recommends that it be fed to small stock at 0.9 kg per day because of its high content of theobromine (1.3%). No attempt has thus far been made to detheobromize this product through boiling, as has been done with cocoa meal.

Cocoa husk has successfully been fed to sheep and goats as well as to layers. Adeyanju et al. (1976a) fed maintenance rations to wethers and castrates in which dried and ground cocoa husk constituted 0, 20, 40 and 50% of the basic ration respectively. They observed no significant changes in the body weights of all animals after 63 days on the experimental diets, indicating that all the rations were adequate for maintenance. They also showed that both in sheep and goats, the substitution of cocoa husk for maize in maintenance rations in a ratio of 2 : 1 was the best for crude-fibre digestibility.

The inclusion of cocoa husk in poultry rations is also currently under investigation at the University of lfe. Preliminary results (Adeyaniu et al., 1976) indicate that compared with the control diet, egg production almost doubles when up to 15% of dried and ground cocoa husk replaced maize in the layers' ration. Above this level, egg production was delayed and subsequently decreased. Rations containing 10, 15 and 20% cocoa husks were cheaper in terms of feed cost.

¹ After Omole and Adegbola, 1975.
² Average of three measurements (shoulder, loin and backfat).

A, b, c, d values in each row with a common letter or no letter are not significantly different (P 0.05).

Coffee by-products

Investigations into the use of coffee hulls for livestock feed have not received much attention in Africa, probably owing to the fact that they can only be obtained in small quantities from peasant farms. The feed also has high fibre and caffeine contents. Nevertheless, Rogerson (1955) attempted to feed coffee hull; he observed that dried coffee hulls were palatable to sheep in East Africa. Working in Uganda in 1972, Ledger et al. reported their attempt to include this by-product in cattle fattening rations in place of maize. They concluded that the addition of 10 to 20% of coffee hulls did not affect feed intake, feed conversion and liveweight gains of Boran steers. Gains were however reduced when coffee hulls amounted to 30% of the ration, which included 8% cottonseed and 5% cane molasses.

Coffee pulp can also be used following dehydration or ensiling designed to reduce the caffeine content of the product. When ensiled with grass and molasses for upward of four months, coffee pulp silage has very good organoleptic properties and should form a good ration for cattle during the dry season (Ogunfowora, 1975). Dried coffee pulp can be fed to young and adult ruminants up to 20% of the total ration without adverse effects.

Oil-seed processing by-products

The products of cotton harvesting and processing, delinted whole cottonseed and cottonseed meal have long been used in East and West Africa in cattle dry-season feeds and dairy production rations. Traditionally, dairy farmers in Uganda and Kenya feed whole cottonseed to milking herds as a source of protein in the concentrate mixture. Generally, cottonseed products are used in combination with groundnut cake, another traditionally important protein source of livestock, or more recently with urea. The availability of these products depends largely on the oil-crushing capacity for these crops, and cottonseed hull is becoming more available in Africa as local crushing increases. There is however a lack of understanding of the best ways of using this product. Since it is high in crude fibre, it has found its greatest use in diets for ruminants. Thus, it was included at a 26% level in a production ration for lactating animals in Uganda (Lawrence and Mugerwa, 1974) and levels of up to 30% have been included in rations for fattening stock at lbadan in Nigeria (Ogunfowora et al., 1975). Caribbean experience also shows that ground cottonseed fed at 0.43 and 0.5 kg/day produced average weight gains of 0.12 and 0.11 kg/day in grazed sheep.

The use of supplementary diets of whole delinted cottonseed to prevent weight loss of up to 300 g/day by zebus grazing dry-season pasture, at a rate of 747 g cottonseed or 314 g groundnut cake per day, has also been reported by Zemmelink (1973). Weight losses of 300 to 400 g/ day can also be prevented by these animals if they received 287 g of a 50 : 50 mixture of groundnut cake and cottonseed per day.

¹ Cruickshank, 1971.

¹ After de Leeuw, 1973.

Using breeds of Angoni, Barotse and Boran cattle in Zambia, Cruickshank (1971) fed daily supplementary ration composed of 2.7 kg snapped maize bran plus 0.68 cottonseed meal plus 106 g urea to heifers to prevent dry-season weight loss.

He noted that liveweight gains were lowest where urea was added to the cottonseed meal and maize bran or snapped maize rations, and obtained the best financial returns from animals fed the maize bran/ cottonseed meal diets (Table 10.5).

In a series of feedlot steer-fattening trials involving 80 animals, steers that received low levels (45%) of raw undelinted cottonseed gained at a faster rate than steers receiving much higher levels (65 to 74%) (de Leeuw, Koch and Schalles, 1973). The authors suggested that the poor performance of steers on diets containing more than 45% cottonseed was probably due to the excessive oil in the ration, since these animals would have consumed more than 1 kg of oil per day. They also noted that animals fed the low level of cottonseed approached or surpassed their expected gains (Table 10.6). The use of cottonseed meal in the feeding of growing pigs has recently been investigated by Baustad (1974), who noted that cottonseed meal is the cheapest and most easily available source of protein in Kenya, but that its use in pig rations may be limited by its low content of lysine, methionine and cystine and its high content of gossypol, which can be toxic to pigs when taken in large quantities. Baustad (1973) observed that cottonseed meal was superior to both groundnut meal and soybean meal when fed to growing pigs at 16% of a ration fortified with meat- and bonemeal. The diets contained low levels of gossypol (about 44 ppm), so that the addition of ferrous sulphate to control the toxic effect of gossypol was of no benefit in the ration The addition of 0.2% lysine or methionine to the ration improved the efficiency of feed utilization slightly (Table 10.7).

a = standard deviation.

¹ After Baustad, 1974.

There is little doubt that cottonseed meal can be profitably included in compound rations as a protein source for growing and finishing pigs in Africa.

Groundnut cake (product of the expeller process containing 5% oil) cannot truly be regarded as a new feed resource in Africa, as it has been used extensively in compounding rations for poultry and swine, as well as in supplementary diets for ruminants.

Virtually all palmkernel cake derived from oil processing is exported from lvory Coast, which is now the greatest world producer of palm oil, and from other West African palm-oil producing countries. A small amount of the product is used in the rations of ruminants, especially dairy animals, where it serves as the main protein source. Levels of up to 60% in combination with 30% wheat bran, 8% molasses and 2% mineral supplement have been fed in Northern Nigeria (Ogunfowora et al., 1975). Sheep and goats can also use the by-product as a source of protein in maintenance rations.

A recent report from Nigeria (Babatunde et al., 1975) suggests that palmkernel meal does not prove a good source of protein in pig diets for weaners, for which it was particularly unsuitable, or for fatteners, which tolerated it better. The authors noted that it was a fibrous feed, with fairly low levels of lysine, leusine, threonine and phenylalanine, and concluded that its inclusion in pig diets should be supplemented with bloodmeal and/or fish-meal as sources of these amino acids.

The use of oil-palm sludge recovery as animal feed has not been given any consideration in Africa. Experience in other countries (Webb, 1975), indicates however that this product can yield economically an animal feed of better quality than maize through a complex integrated process known as the ‘Censor’ process, which can also include a fermentation stage capable of providing a higher-grade feed. Further processing of agro-industrial by-products definitely requires more attention in African countries.

Fruit processing by-products

Very few reports exist on the use of agroindustrial by-products of fruit processing from many African countries, and this topic can therefore only be discussed from the standpoint of possibilities. African fruit production is of the order of 23.37 million metric tons per annum, comprising mainly grapefruit, citrus and bananas. There is also evidence of increasing activity in the processing of citrus, pineapple, mangoes, and tomatoes in some East and West African countries, resulting in such waste products as citrus wastes, pineapple pulp, bran and tops, mango seeds and tomato wastes. Considerable quantities of banana waste also become available from Cameroun. Assuming that only 10% of the total fruit produced in African countries is processed, and wast age of 50% of the whole fruit during processing, and estimated 600 000 metric tons of wastes can become available annually for animal feeds.

Citrus wastes can serve as energy sources and have been used in developed countries for feeding beef and dairy animals They can also be incorporated into grass and/or legume silages, combined with mixed pellet feeds or even dried to citrus pulp. Cattle can eat fresh grapefruit readily, but find oranges and tangerines unpalatable because of the bitter oil in their peel. Yearling cattle have been fattened on 1.8 to 4.5 kg of dried citrus pulp and 1.0 to 1.4 kg of cottonseed meal, with access to mineral salt lick (Kirk and Davis, 1954).

Similarly, pineapple products have found use in livestock feeding in India and Southeast Asia as supplements for dairy animals as well as sheep and goats. There is need to encourage the use of these products in local fattening operations where a constant supply can be guaranteed.

The potential value of waste bananas for livestock feed, especially in pig diets, has been highlighted by Maner (1973) and Clavijo and Maner (1974 as it related to the Latin American countries. Bananas production in Africa is of the order of 4 million metric tons, and rejected bananas can serve as an energy source for pigs. Daily gains of 0.68 kg have been obtained for finishing pigs from an intake of 2.31 kg of ripe bananas supplemented with about 30% protein (Maner, 1973).

In Zambia, ripe bananas and plantain trunks are usually chopped into bits and fed to beef and dairy animals during periods of drought. It is not quite clear whether this practice is adopted as a means of providing animals with high-moisture feed to minimize the effects of drought, or whether it also serves to supply some minerals. Ankrah (1974) has shown that the trunks of plantains and bananas have high contents of potassium, calcium, phosphorus and iron.

Animal-processing by-products

Although a few abattoirs exist near major cities in such countries as Kenya, Uganda, Zambia, Nigeria, Ghana and Senegal, the general lack of centralized abattoirs in Africa makes the handling and processing of products such as bloodmeal, meat meals, tankage and steamed bonemeal difficult in many African countries. Further, in some countries a few of these products, especially blood, are required for direct human consumption. In general, the distinction between edible and inedible components of animal carcasses in Africa depends on such factors as the socio-economic conditions of the region, religious beliefs, taboos and dietary habits. There is a consumer preference for warm meat in many African countries; hence, slaughtering is done in scattered slaughter slabs or in small numbers in slaughter-houses which are usually not mechanized. This creates problems of effectively salvaging, collecting and processing animal by-products for use in compounding livestock feeds, as well as of obtaining these products in sufficient quantities and in good quality. Increased use of waste products of animal origin will ultimately depend on a better-organized and possibly mechanized system of livestock slaughtering and processing in Africa.

Similarly, very little use is made of the by-products of poultry processing, since less than 5% of the total broilers or table birds are slaughtered through organized dressing systems. The use of feather and offal meals, which according to reports from the United States, can be recycled into the diets of broilers (Jackson and Fulton, 1971) and be used for caged laying hens in place of fishmeal (Jackson, 1971), in Africa will have to await the development of large-scale broiler industries.

Recent developments in commercialized deep-litter and battery systems of egg production are beginning to create problems of poultry manure disposal in urban centres. Poultry manure has been shown to be of value, if further processed, as a source of energy (about 2 000 kcal/g) and protein (about 16.5% on a dry basis) for sheep and cattle. It is also being used in the developed countries to replace soybean meal in ruminant diets (Bhattacharya and Taylor, 1975).

Most of the fishmeal used in poultry and pig rations in Africa is imported. Recently, such countries as Nigeria and Ghana have been looking into the question of producing fishmeal. The use of this product has heretofore been limited by its lack of availability, and this in turn has limited the ability of the feed-compounding industries in African countries to expand and to meet the growing demand for their products. Fishmeal can be derived from the waste products of fish processing or from the direct processing of unsaleable fish species. Laksesvela et al. (1971) tested the value of Lake Rudolph fish-meal from unsaleable species, e.g. Citharinus spp., Dischodus niloticus, Lates nilotious and Tilapia niloticus, which occur in the lake. They concluded that at 10 to 15% levels in the diet, this fishmeal gave satisfactory growth and feed efficiency use for chicks, weaner and grower pigs when compared with an imported fishmeal, meat and bone meal as well as an all-vegetable meal. There is need to encourage the production of animal by-products in all African countries in order to stimulate the development of both poultry and pig production.

Other by-products of potential value

There are a number of agro-industrial by-products that can be used in Africa but are apparently burnt or disposed of in other unproductive manners, sometimes adding to the problem of pollution. One such product is sawdust resulting in West Africa from the processing of timber for export. A tremendous amount of sawdust accumulates in the yards of a large number of sawmills to be found throughout the forest region. With appropriate treatment by steam heating, ball milling, fungal fermentation, or alkaline solutions, Hartley et al. (1974) have shown that sawdust of beech oak, poplar or barley straw gave improved organic-matter digestibilities of the order of 4 to 10 times compared with untreated sawdust and that the products of these treatments can be used as ruminant feed. There is every possibility that sawdust can serve as a source of energy for ruminants in West Africa as well, but there is need for research into this area of utilization.

There are a number of other African oilseeds which occur in abundance in both East and West Africa but which so far have not been used for livestock feed except in a few instances. For example, Mba et al. (1974), reporting on the approximate chemical composition and amino acid content of meals of conophor seed (Tetracarpidium conophorum, Hatch) and the African oilbean (Pentachethra macrophylla, Benth), concluded that the former is rich in cystine, methionine and tryptophan, while the latter contains adequate levels of lysine. It appears that a judicious combination of both can be used in poultry and pig rations. In a similar evaluation of the nutritive value of cashewnut (Anacardium occidentale) extraction meal, Piva et al. (1971) concluded that it has good-quality protein (42% crude protein), containing 4.6% lysine, 1.6% methionine, 1.3% tryptophan, and a higher content of the sulphur amino acids than soybean and groundnut meals. They obtained higher efficiency of feed utilization of this feed from pigs. Cashew trees are adapted to most parts of East and West Africa and will thrive even under adverse soil and moisture conditions. The seed is a source of oil and the resulting meal can be of value as a livestock feed.

For some time, rubber-seed meal has been made available in Malaysia for livestock feed. It has been incorporated at levels between 10 to 15% in chick diets and up to 25% for growers. Rubber seeds from plantations in Nigeria, Ghana and Liberia currently go to waste, as no known facilities exist for crushing in these countries. Yet the seed contains adequate oil for commercial extraction for use in the soap industry, while the cake can be used as a protein supplement. Adequate quantities of rubber seed are available from the plantations already existing in West African countries. Preliminary work at Ibadan, Nigeria, indicates that the meal has low contents of lysine and methionine but is fairly high in tryptophan. Its use in poultry rations will therefore require supplementation with the sulphur amino acids.

References

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Adeyanju, S.A., D.B.A. Ogutuga, J.O. llori and A.A. Adegbola (1975). Potentialities of cocoa husk in livestock feeds. (In press) Proceedings of the Fifth international Cocoa Research Conference. University of Ibadan, Nigeria.

Adeyanju, S.A., D.B.A. Ogutuga, J.O. llori and A.A. Adegbola (1975). Cocoa husk in poultry diets. (in press) Malaysian Agric. Res. J.

Adeyanju, S.A., D.B.A. Ogutuga and J.O. llori (1976). Further studies on the utilization of cocoa husks in ruminant rations. Niger. J. Anim. Prod. 3: (2).

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Ankrah, E.K. (1974). Chemical studies of some plant wastes from Ghana. J. Sci. Fd. Agric. 25, 1229–1232.

Babatunde, G.M., B.L. Fetuga, O. Odumosu and V.A. Oyenuga (1975). Palmkernel meal as the major protein concentrate in the diet of pigs in the tropics. J. Sci. Fd. Agric 26 (9) 1279–1291.

Baustad, B.M. (1973). A preliminary note on the use of molasses in the feeding of growing pigs. East Africa Agric. For. J. 39 (2), 203.

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Bhattacharya, A.N. and J.C. Taylor (1975 Recycling animal waste as a feedstuff: A review. J. Anim Sci 41, (5) 1438–1457.

Campabadal, C., D. Cresswell, H.D. Wallace and G.E. Combs (1976). Nutritional value of rice bran for pigs. Trop. Agric (Trinidad) 53(2) 141–149.

Clavijo, H. and J.H. Maner (1974). The use of waste bananas for swine feed. Series EE No. 6, Centro Internacional de Agricultura Tropical, Call, Colombia, S.A.

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Jackson, N. and R.B. Fulton (1971). Composition of feather and offal meal and its value as a protein supplement in the diet of caged laying hens. J. Sci. Fd. Agric 22(1) 39–42.

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Laksesvela, B., H. Bergh and J. Haug (1971). Lake Rudolph fishmeal. Chick and pig test of a sample from Citharinus citharus. East Afr Agric. For. J. 37(1), 38–45.

Lawrence, M.P. and J.S. Mugerwa (1974a), Utilization of urea and molasses for dairy cattle feeding (2) Urea-molasses supplement for lactating dairy cattle grazing improved pastures in Uganda. East Afr. agric. For. J. 39(3) 228–239.

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Mba, A.U., M.C. Njike and V.A. Oyenuga (1974). The proximate composition and the amino acid content of some Nigeria oilseeds. J. Sci. Fd. Agric 25, 1547–1533.

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CHAPTER 11
UTILISATION DES SOUS-PRODUITS DES INDUSTRIES AGRICOLES ET ALIMENTAIRES DANS LES PAYS MEDITERRANEENS ET DU PROCHE-ORIENT

par

M. Skouri

Office de l'Elevage et des Pâturages
30, rue Alain Savary, Tunis, Tunisie

Resumen

Los paises mediterràneos y del Cercano Oriente disponen de una gama bastante amplia de productos agrícolas, sobre todo frutas y hortalizas, que se destinan a la transformación industrial. La transformación de estos productos origina una cantidad importante de subproductos que pueden utilizarse para la alimentación de animales, bien directamente, bien previa aplicación de tratamientos apropiados.

Por desgracia, estos países han dedicado hasta ahora poco interés a la utilización de tales subproductos para la alimentación del ganado, lo que se debe a distintas razones:

1. El hecho de que la ganadería se haya mantenido en un estadio extensivo tradicional, en el que la alimentación proviene en gran parte de la utilización de los recursos de pastos y de los resíduos de los cultivos (rastrojos, paja, barbecho), ya que, incluso en las zonas donde se han desplegado esfuerzos importantes para intensificar los cultivos, la ganadería se ha beneficiado poco de tales esfuerzos.

2. El desconocimiento del potencial nutritivo que representan los subproductos disponibles.

3. La insuficiencia de estudios e investigaciones relacionados con las posibilidades de utilizar como piensos algunos subproductos específicos de la región.

4. La escasa concentración y el bajo nivel de integración de las industrias agrícolas y alimentarias que hacen que la producción esté demasiado dispersa en el tiempo y en el espacio para que la recuperación de subproductos pueda efectuarse en buenas condiciones technológicas y económicas.

Entre los subproductors disponibles en la región, nos limitaremos a los más importantes, sea porque su utilización no plantea problemas particulares o porque se trata de productos muy abundantes y que pueden contribuir, por tanto, a acrecentar los recursos de alimentos para animales.

1. Subproductos de cereales: se utilizan relativamente poco porque la industria de los piensos está poco desarrollada en el país o porque la ganadería no es todavia suficientemente intensiva.

2. Subproductos de la aceituna: Los orujos tienen poco valor nutritivo porque contienen un elevado procentaje de cáscara completamente lignificada y porque la pulpa misma tiene principios tóxicos que inhiben la actividad microbiana en el rumen.

3. Subproductos de la vinificación: su principal elemento es el orujo y presentan caracterísiticas nutricionales comparables a los orujos de aceituna. La poca digestibilidad del orujo de uva parece deberse a la presencia de taninos en la película de la fruta y en los escobajos.

4. Subproductos de conserva de frutas y hortalizas: entre los que abundan en la región, merecen atención particular dos productos: la pulpa de agrios y la pulpa de tomate. La pulpa de agrios constituye un buen complemento energético para los rumiantes, mientras que la pulpa de tomate, que es más rica en materias nitrogenadas, puede suministrar un aporte suplementario de nitrógeno.

5. Subproductos de cultivos industriales: pueden desempeñar un papel cada vez más importante en la alimentación del ganado debido al desarrollo que van a conocer algunos cultivos, como el girasol y la remolacha azucarera. La presencia de estos subproductos es un factor muy favorable para intensificar la producción pecuaria.

6. Subproductos de origen animal: los disponibles en la región son bastante limitados, pero ello no es óbice para que una mejor recuperación de estos productos contribuya eficazmente a mejorar la alimentación del ganado.

Los problemas que se plantean en lo que respecta a la utilización de los distintos subproductos varían según el tipo de producto y el grado de evolución del sistema de cría así como según el estado de desarrollo de la industria de los piensos en un país determinado. Por ejemplo, en lo que respecta a los subproductos de la aceituna, los problemas que se plantean son ante todo de orden científico y tecnológico; mientras que en lo que se refiere a los subproductos de cereales, los problemas son sobre todo de orden económico y estructural.

Es importante dediçar al estudio de estos productos medios suficientes que permitan abordar simultáneamente los distintos aspectos tecnológicos bioquímicos, nutricionales y económicos, a fin de llegar a soluciones prácticas que puedan interesar a los industriales. Los países mediterráneos en conjunto deberían adoptar medidas concertadas para realizar investigaciones.

INTRODUCTION

L'élevage a gardé, dans la majorité des pays de la région méditerranée et du Proche-Orient, son caractère extensif traditionnel. Il a de surcroît subi les méfaits de l'extension de la céréaliculture et de l'arboriculture fruitière, résultant de l'accroissement démographique et de l'utilisation de plus en plus répandue de la traction animale d'abord et du tracteur par la suite.

La “marginalisation” de l'élevage vers les zones les plus défavorisées et vers les secteurs les plus arriérés a pour effet de diminuer la productivité du cheptel, et d'augmenter le déficit en produits animaux de la plupart des pays de la région.

Par ailleurs, l'élevage n'a que peu bénéficié de l'intensification de la production résultant de la mise en oeuvre des techniques nouvelles faisant appel à l'utilisation de certains facteurs de production tels que les engrais minéraux, les pesticides et l'irrigation. Ce sont surtout les secteurs maraicher et de l'arboriculture fruitière qui ont bénéficié de l'utilisation de ces nouveaux facteurs, réalisant ainsi des performances assez remarquables.

Parallèlement à l'intensification de l'activité dans ces secteurs, on a enregistré une augmentation considérable de la part de leur production qui est destinée à la transformation industrielle.

C'est ainsi que le secteur des industries agro-alimentaires a connu un essor important dans la majorité des pays de la région, donnant lieu à des quantités importantes de sous-produits, mais malheureusement les industriels n'ont pas accordé toute l'attention voulue aux possibilités de leur valorisation. Les éleveurs, enfermés dans un système d'économie de cueillette, n'ont pas cherché de leur côté à diversifier les sources d'alimentation de leur cheptel et à exploiter rationnellement les nouvelles ressources que représentent les sous-produits des industries agro-alimentaires.

LES PRINCIPAUX SOUS-PRODUITS DISPONIBLES DANS LA REGION

La gamme des sous-produits agro-industriels disponibles dans les pays de la région méditerranéenne et du Proche-Orient est assez diversifiée et reflète la diversification de la production agricole dans la région.

On se limitera ici à examiner les sous-produits les plus importants, et plus particulièrement ceux qui sont produits en grande quantité et qui sont susceptibles, de ce fait, de contribuer à l'accroissement des ressources pour l'alimentation animale dans la région.

Parmi ces sous-produits il y a lieu de mentionner--

• les sous-produits de céréales: sons et issues de meunerie;

• les sous-produits de l'olive: les tourteaux d'olives (grignons);

• les sous-produits de vinification; marc de raisin;

• les sous-produits des conserves de fruits et de l'égumes: pulpe d'agrumes, pulpe de tomates, etc.;

• les sous-produits des cultures industrielles “nouvelles”: betterave sucrière, plantes oléagineuses, etc.;

• les sous-produits d'origine animale; farine de poisson, farine de sang,

La composition chimique de certains entre eux figure en tableau 11.1.

Les sous-produits des céréales: sons et issues de meunerie

Les pays du bassin méditerranéen et due Proche-Orient sont de gros consommateurs de produits céréaliers; même si la production céréalière de la zone est inférieure aux besoins, le complément est le plus souvent importé sous forme de céréales brutes qui sont transformées sur place. La transformation des céréales produites dans la région ou importées donne naissance à une quantité importante de sous-produits (petit blé, sons et issues de meunerie, etc.) qui sont très intéressants pour l'alimentation des animaux. Les sous-produits du blé, la céréale la plus utilisée dans la région, représentent environ 20 pour cent du volume de céréales transformées. Cette ressource est relativement bien connue et son utilisation ne pose pas de problèmes particuliers si ce n'est le faible développement des industries des aliments de bétail dans les pays où l'élevage n'est pas suffisamment intensifié.

Les sous-produits de l'olive

Les olives constituent une production typiquement méditerranéenne; la production mondiale, de l'ordre de 9 à 10 millions de tonnes par an, provient en majeure partie de la zone méditerranénne et du Proche-Orient (FAO, 1974). Le grignon, résidu résultant de l'extraction de l'huile du fruit entier trituré selon le procédé classique, représente environ 30 pour cent de la production d'olives. Il est constitué de la pellicule du fruit (épicarpe), de la pulpe (mésocarpe), de la coque du noyau (endocarpe et de l'amandon, qui est la graine. Si l'extraction se fait par pression, le résidu conserve un pourcentage élevé de matière grasse (20 à 30 pour cent du grignon séché) dont une partie importante est récupérée au moyen d'une extraction aux solvents. Les fractions disponibles pour l'alimentation animale, qui sont les pulpes et les pellicules d'une part et les amandons d'autre part, representent respectivement 15 et 6 pour cent des grignons frais (Levi di Léon, 1962).

Références: ¹ Laboratoire de Zootechnie I.N.R.A., Tunisie
- ² APRIA, 1969.
³ APRIA, 1969.
- ⁴ Paraloran, 1971.

Les essais effectués pour déterminer la valeur nutritive et les conditions d'utilisation des tourteaux d'olive dans l'alimentation animale ont montré que les constituants de ces tourteaux ont une digestibilité très faible (Cordier, 1947; Maymone et al., 1962).

Les pulpes et les pellicules, qui constituent la fraction la plus importante, ont une valeur nutritive très faible: cette fraction contient des principes toxiques qui inhibent l'activité microbienne dans le rumen (Thériez et Boule, 1970). C'est pour cette raison que les sous-produits de l'olive, disponibles en grande quantité dans las région méditerranéenne et au Proche-Orient, sont peu utilisés dans l'alimentation animale.

Les différentes études effectuées dans plusieurs pays de la région ont permis de mettre bien en évidence les effets négatifs de l'adjonction d'une importante quantité de tourteaux d'olive dans la ration des ruminants mais n'ont pas encore abouti à des solutions permettant d'éliminer les principes toxiques. Des études biochimiques et nutritionnel les plus approfondies seraient nécessaires pour mieux connaître ces facteurs toxiques et pour mettre au point des moyens permetant d'eliminer ou du moins de réduire leur effet.

L'autre fraction, constituée par l'amandon, ne semble pas contenir des principes toxiques; le tourteau d'amandon a en effet une bonne valeur nutritive aussi bien pour les monogastriques que pour les ruminants (Thériez, Skouri, de Montrichard, 1968). Il convient de souligner cependant qu'il existe peu d'installations traitant séparément la puple et le noyau qui contient l'amandon. Là aussi des procédés technologiques seraient à mettre au point à l'échelle industrielle.

Le tourteau d'amandon convenablement purifié a une valeur nutritive comparable aux tourteaux classiques (soja, arachide).

Les sous-produits de vinification: marc de raisin

Le marc de raisin, résidu de la transformation du raisin à cuve, est également un sous-produit très important dans la région méditerranéenne, qui est l'une des principales régions viticoles du monde. Les trois pays européens riverains de la Méditerranée qui sont gros producteurs de vin (France, Italie, Espagne) ont une production annuelle de marc de raisin de l'ordre d'environ 3 500 000 tonnes, en comptant 15 kg de marc pour 100 kg de raisin pressé (Bremond, 1965). Dans les trois pays viticoles d'Afrique du Nord (Algérie, Maroc, Tunisie) cette production atteint environ 170 000 tonnes par an.

Malgré son abondance, ce produit est peu utilisé dans l'alimentation du bétails, à cause de sa faible valeur nutritive, qui s'explique par la haute teneur en constituants membranaires (rafles fortement lignifiées) et par la faible digestibilité des matières azotees, due à la présence de tanins et autres facteurs qui inhibent l'activité microbienne dans le rumen.

Les sous-produits des conserves de fruits et de légumes

Le climat de la zone méditerranéenne est assez propice aux productions fruitières et légumières, destinées soit à la consommation en frais soit à la transformation industrielle. Parmi ces productions nous nous limiterons à celles qui laissent des quantités importantes de résidus susceptibles d'être utilisés dans l'alimentation animale, les agrumens d'une part et les tomates d'autre part.

Les pulpes d'agrumes

La production annuelle des agrumes dans la région méditerranéenne se situe entre 8 et 10 millions de tonnes, soit à peu près le quart de la production mondiale (FAO, 1974).

Le volume des agrumes fraîches destinées à la transformation industrielle est en progression rapide, représentant à peu près le tiers de la récolte mondiale. Pour la compagne 1971/72, ce volume a atteint environ 1 200 000 tonnes pour quatre pays membres du Comité de liaison de l'agrumiculture méditerranéenne (CLAM): Espagne, Israël, Italie et Maroc.

La pulpe quirésulte de la fabrication de jus d'oranges peut être utilisée soit à l'état frais soit sous forme ensilée ou déshydratée. La pulpe déshydratée à 8 pour cent d'humidité représente environ 6, 5 pour cent du produit frais de départ (Hendrickson et Kesterton, 1965). Avec une valeur énergétique relativement élevée (2 770 kcal par kg pour les ruminants), elle constitue un bon aliment pour les ruminants et peut entrer jusqu'à concurrence de 20 pour cent dans la composition de la ration (Blair, 1974).

Les pulpes de tomate

Comme pour les agrumes, une bonne partie de la production de tomates est destinée à la transformation industrielle; la proportion transformée se situe aux alentours de 40 pour cent mais peut dépasser 50 pour cent dans beaucoup de pays (FAO, 1970). Le bass in méditerranéen produit à peu près la moitié de la récolte mondiale.

Le résidu de la transformation de la tomate n'est pas constitué de pulpe mais de pellicules et de pépins; cette fraction représente environ 13 pour cent de l'extrait sec total. Ce résidu peut être utilisé à l'état frais ou sous forme d'ensilage ou déshydraté.

La composition chimique du produits déshydraté est comparable à celle d'une excellente farine de luzerne, mais sa valeur nutritive est beaucoup plus faible, du fait de la faible digestibilité tant des constituants membranaires (pellicules fortement cellulosiques) que des matières azotées. Il semble renfermer des facteurs toxiques analogues à ceux rencontrés dans le tourteau d'olives ou dans le marc de raisin et qui ont pour effet de reduire l'activité de la flore microbienne du rumen.

Des études en vue d'améliorer la valeur nutritive de ce produit seraient à souhaiter.

Les sous-produits des cultures industrielles “nouvelles”: betterave sucrière et plantes oléagineuses annuelles

Les pays de la zone méditerranéenne et du Proche-Orient déploient, dans le cadre de la diversification de leur production, un effort important pour développer certaines cultures industrielles telles que la betterave sucrière, le lin, le tournesol et le coton. Si l'objectif de ces cultures est de produire du sucre, de l'huile ou des fibres, il n'en reste pas moins que de leur transformation proviennent des quantités importantes de sous-produits particuliérement intéressants pour l'alimentation des animaux. C'est ainsi qu'au Maroc la production de betterave sucrière est passée de 86 000 tonnes en moyenne entre 1961 et 1965 à 1 950 000 tonnes en 1974. Une évolution similaire a été enregistrée pour les plantes oléagineuses: en Espagne, par exemple, la production des graines de tournesol est passée de 11 000 tonnes en 1964 à 316 000 tonnes en 1974 (FAO, 1974).

Il faut souligner cependant que la vulgarisation de l'utilisation des sous-produits de ces cultures dans l'alimentation animale est restée parfois insuffisante et qu'elle n'a pas suivi l'évolution de l'extension de ces cultures. Un effort particulier est à déployer pour assurer une meilleure valorisation de ces produits dans les pays producteurs.

Les sous-produits d'origines animale

Les pays de la zone méditerranéenne et du Proche-Orient accusent un grand déficit en protélines de haute valeur biologique nécessaires notamment au développement de l'aviculture. Or ce secteur, en forte expansion dans la zone, reste en grande partie tributaire pour son alimentation de l'importation tant de céréales que de ressources protéiques. Il importe donc de réduire cette dependance en mobilisant toutes les ressources disponibles dans la région et plus particulièrement les sous-produits de la pêche et des abattoirs, concernant lesquels il n'existe que peu de données chiffrées.

Même si les ressources en poissons de la zone sont assez limitées, il y a lieu d'accroître les possibilités de recupération des sous-produits de la pêche. Il en est de même des déchets d'abattage: il faudra améliorer les techniques d'abattage et le foncitionnement des abattoirs.

DISCUSSION ET CONCLUSIONS GENERALES

Les problèmes que pose l'utilisation des sous-produits des industries agro-alimentaires varient en fonction du type de produit considéré et en fonction du degré d'évolution des systèmes d'élevage et de l'état du développement de l'industrie des aliments de bétail dans un pays déterminé.

C'est ainsi qu'en ce qui concerne les sous-produits de l'olive, disponibles en grande quantité dans la région, les problèmes qui se posent sont d'abord d'ordre scientifique et technologique, alors que ceux qui concernent les sous-produits des céréales sont plutôt d'ordre économique et structurel.

La faible valeur nutritive de la plupart des sous-produits examinés est souvent liée à la faible digestibilité de la fraction azontée, qui serait elle-même liée à la présence de facteurs inhibiteurs de l'activité microbienne dans le rumen, facteurs qui peuvent provenir en partie de la présence de certains composants tels que les tanins de l'altération du produit avant son ingestion par l'animal. Etant donné qu'il s'agit de produits rapidement fermentescibles il y a lieu d'accorder une attention particulière aux problèmes de conservation. Les sous-produits humides tels que les tourteaux d'olives, le marc de raisin, la pulpe de tomates ou la pulpe d'agrumes, devront être ensilés ou déshydratés le plus rapidement possible pour éviter leur altération. D'autres traitements chimiques ou mécaniques pourront être envisagés pour améliorer la qualité des produits et les possibilités de leur conservation.

La déshydratation des sous-produits humides serait certainement une solution techniquement valable, mais elle présente l'inconvénient d'être coûteuse, surtout s'agissant de produits de faible concentration nutritive.

Dans l'état actuel de nos connaissances il n'est pas réaliste de baser des systèmes d'élevage sur l'utilisation des sous-produits mentionnés ci-dessus. Toutefois, ils peuvent constituer des compléments pour des rations alimentaires classiques ou se substituer à une partie des constituants de ces rations.

En zone méditerranéenne, ces sous-produits peuvent jouer le rôle d'aliments de sauvegarde pendant les périodes de disette, fréquentes en raison des fluctuations de la pluviométrie. En effet, en période de disette l'objectif est beaucoup plus d'assurer la survie des animaux que de chercher les performances zootechniques, de sorte que même des aliments de faible valeur nutritive permettent de limiter ses effets.

Il est également possible de constituer des régimes alimentaires valables en combinant judicieusement différents sous-produits ayant des caractéristiques nutritionnelles complémentaires et en apportant les correctifs nécessaires, notamment sous forme de minéraux et de matières azotées; car les tourteaux mis à part, la plupart des sous-produits sont peu pourvus en matières azotées digestibles et ont une composition minérale déséquilibrée.

Il convient de souligner cependant que des études et des recherches sont encore nécessaires pour préciser et améliorer les conditions de récupération et d'utilisation de ces sous-produits. Elles devront porter aussi bien sur les aspects biochimiques, nutritionnels et zootechniques que sur les aspects technologiques et économiques, de façon à aboutir á des solutions opérationnelles susceptibles d'intéresser tant les industriels que les utilisateurs.

Etant donné que ces études nécessitent des moyens qui ne sont pas à la portée d'un seul pays, une action concentrée devrait être entreprise au niveau de l'ensemble des pays méditerranéens pour développer les recherches relatives aux sous-produits disponibles en grande quantité dans la région, tels que les grignons d'olive notamment.

REFERENCES BIBLIOGRAPHIQUES

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