Cassava as a total substitute for cereals in livestock and poultry rations

Z. Müller, K.C. Chou and K.C. Nah

Brazil, the world's largest producer of cassava, depends primarily on human labour for planting and harvesting.

Cassava is the name widely used in English-speaking regions of North America, Europe and Africa for the shrubby tropical root crop Manihot esculenta Crantz. Other common regional names are manioc (in French-speaking areas), tapioca (in English-speaking southeast Asia), mandioca (in Brazil) and yuca (in Spanish-speaking South America).

Cassava is believed to have originated in tropical Brazil. It is an all-season subsistence food crop, with a high photosynthetic potential, an ability to tolerate drought and poor soils and a high resistance to weeds and pests. It is only in recent years that concerted efforts have been made to exploit its full potential; however, its chronic toxicity has always remained a major limiting factor (Nestel, 1973).

Cassava requires a sandy soil and a warm tropical climate. The optimum growing temperature is about 27°C. When the temperature drops to 15°C, growth stops; at 8 to 10°C the plant dies. The optimum rainfall is 700– 1 000 mm.

Dr. Z. Müller is with the UNDP/SF Project SIN 67/505 in Singapore; K.C. Chou is Head, and K.C. Nah is Assistant Principal Primary Production Officer, of the Pig and Poultry Research and Training Institute, Singapore.

The plant is photosensitive, with a high sunshine requirement. The cyanogenetic glucoside content increases with nitrogen fertilization and drought, but decreases with potassium or organic fertilizers. Shading young plants increase the glucoside content in the leaves but not in the root. The bark of the tubers has a relatively higher level of glucoside than the interior (Bruijn, 1973). In Africa, cassava is sometimes planted together with maize, yams, citrus, coffee or cocoa; in Indonesia, with yams, rubber, oil palms and on the bunds surrounding paddies. In South and Central America it is often planted with legumes and melons. The cassava plant has a reputation for exhausting soils. The uptake of nutrients by a 50-ton yield of tubers is approximately 120 kg P₂ O₅, 450 kg K₂O and 250 kg CaO. This explains the significance of fertilization. Small farmers in southeast Asia usually start to grow cassava on virgin forest clearings. When productivity drops (two to three years later) they abandon the land.

Some of the new commercial varieties contain as much as 38 percent starch and yield, on average, 40 tons per hectare. A number of improved varieties have recently been planted in South America, Africa and Asia, due to the efforts of international organizations concerned with the development of Cassava production (the International Institute of Tropical Agriculture in Nigeria, Centro Internacional de Agricultura Tropical in Colombia, and the United Nations, particularly FAO).

To produce 1 ton of dried cassava products requires about 3–4 tons of fresh cassava roots. The fresh tubers are highly perishable and deteriorate within two or three days of harvest, unless dried or properly stored.

The following are the main commercial feed products available in dried form from the cassava plant:

Cassava chips: irregular slices of root, 4 or 5 cm long;

Broken cassava roots: 12 to 15 cm long and of varying thickness;

Cassava roots in bars: rectangular bars, 0.8 × 0.8 × 5.0 cm;

Cassava cubes: about 1 × 1 × 1 cm;

Cassava pellets: in cylindrical form, about 2 cm long and 0.5 to 0.8 cm in diameter;

Cassava meal: a fine powder from the manufacturing of chips and/or starch;

Cassava refuse (or waste): residual pulps separated from the starch;

Cassava leaf meal: dried aerial part (or leaves only) of the plant.

Table 1. Chemical composition of cassava-root meal compared with maize meal and a mixed cassava-so, bean meal

Source: Pig and Poultry Research and Training Institute, Singapore.
¹ Cassava 85 percent, soybean 15 percent
² January 1974 prices at Singapore.

The pelleting of cassava products is becoming increasingly popular because it decreases volume by about 25 percent. This simplifies transport, handling and storage, and produces a uniform product which is less fragile for overseas shipment.

It is estimated that annual world production of cassava roots is about 100 million tons. Brazil, Indonesia and Zaire together grow approximately half this output. Although Brazil is the world's largest producer, most of the crop is utilized locally and very little is exported. Thailand, which grows only about 3 percent of total world production, is the largest exporter. The biggest importers include the countries of the European Economic Community (particularly the Federal Republic of Germany). where about 2 million tons of cassava meal are consumed as livestock feed. Recent feed shortages have greatly stimulated demand for cassava, as a substitute for grain in cattle feedlots and in manufactured feed in general.

Table 2. Caloric values of cassava and maize, on dry matter basis

Source: Draft Feeding Standard, Republic of Singapore, 1972.

The nutritive profile

The chemical composition of cassava root meal is given in Table 1: however, there is considerable variation according to variety, age of plant and processing technology. The caloric value of the meal (see Table 2) and the digestibility of cassava starch are relatively high compared with cereals. The protein, mineral and vitamin content of the root product is nutritionally insignificant. The amylolytic activity of cassava meal is about one third that of maize and about half that of rice bran Cyanides are the most undesirable constituents of the cassava plant. The content in fresh tubers varies from about 0.01 to 0.04 percent, with the bitter varieties containing 0.02–0.03 percent and the sweet less than 0.01 percent. Free hydrogen cyanide is liberated from the cyanogenetic glucosides by the action of the enzyme, linamarase, which is found in the plant. However, the glucosides and linamarase come into contact only when the plant tissue is damaged in storage, or during processing and handling. The importance of methionline as a moderator of the toxic side-effects of cassava products in poultry diets has been reported by many authors, and recent studies by Maner and Gomes (1973) have also demonstrated the detoxification effect of methionine on rats and pigs. In cassava-growing regions, the aerial part of the plant may offer a new perspective for livestock and poultry development. As cassava leaves produce about 10 to 15 tons of dry matter per hectare, they could become an important source of protein in the form of protein extracts for monogastrics, while the voluminous, fibrous residue could be used as forage for cattle. Although the protein value of cassava leaves is well established, the usual objection to their use as food or feed has been the cyanide content. In human nutrition this problem was elucidated by Rogers and Milner (1963). Recent studies by Eggum (1970) and Hutagalung et al. (1973) have shown that cassava leaves have also a good potential as an alternative source of protein for animals; the amino acid pattern is similar to that in grass or legume meals (Table 3). However, cassava leaf protein is deficient in methionine and marginal in tryptophan and isoleucine, although rich in lysine. The true availability of the amino acids is somewhat variable and only about 60 percent of the total methionine has been found to be available (Eggum, 1970).

Table 3. Protein value of dehydrated aerial part of cassava plant and some tropical grasses, compared with soybean meal (on dry basis)

Source: Draft Feeding Standard, Republic of Singapore, 1972.

	Above: Cassava and rice growing together in Indonesia. Cassava leaves produce 10 to 15 tons of dry matter per hectare.
	Left: Cassava tubers, neatly packed in special baskets, being transported by bicycle in Indonesia.
	Below: Cassava pellets. Producers have been responsive to European demands. From 1962 to 1973 EEC cassava imports rose from 413 000 to 1900 000 metric tons; the proportion imported in pellet form grew from 0 to 90 percent.
PHOTO: IDRC, OTTAWA

Cassava-based diets for pigs

The first serious scientific approach to substituting cereals with cassava in commercial pig rations began during the early years of the second world war. It was soon recognized by European farmers, especially in Germany, that cassava could solve the postwar shortage of grains. Nutritional studies were geared to the maximum substitution of cereals with raw or dried cassava root products, and it was generally recommended that cassava could replace cereals at a 20–40 percent level of the dry matter in pig rations. However, in some experiments, even low levels of cassava were found to depress growth noticebly. Thus, Vellose et al. (1967) observed that 22 percent cassava root meal in pig diets significantly affected growth and feed efficiency. When Maust et al. (1969, 1972) replaced maize with 36 percent cassava meal, appetite declined and the rate of weight gain decreased rapidly; the pigs developed parakeratosis during the fourth week, and this disorder was eliminated only by the addition of 100 mg ZnCO₃/kg of diet. Maner et al. (1969, 1970) fed fresh chopped cassava with different protein supplements offered ad libitum. These trials clearly demonstrated a satisfactory feed intake and liveweight gain. In later studies, Maner and Gomes (1973) proved conclusively, with large numbers of pigs, that cassava may fully replace cereals without any negative effects when the diets are properly balanced. In a short-term experiment (seven weeks) conducted in Venezuela (Chicco et al., 1972), maize was gradually substituted with cassava meal up to a level of 58.5 percent. Levels over 40 percent reduced liveweight gain, but feed efficiency at the 40 and 58.5 percent levels remained the same. There were no differences in digestibility of the organic matter and in nitrogen retention when the diets were based on maize or cassava. Carcass evaluations and chemical analyses of carcasses did not show any significant differences.

Aumaitre (1967) compared pig diets based on wheat, barley, maize and cassava. The cassava-based diets were clearly superior in weight gain and feed efficiency, and there was a drop in the incidence of diarrhoea. Numerous experiments have also been conducted in Singapore from 1969 to 1974 (Müller et al., 1972, 1974). The replacement of cereals with cassava meal in proportions of from 40 to 75 percent of the total diet had no adverse effects on the pigs. However, cassava-based rations presented in mash form were generally disliked by the animals. On the other hand, pelleted cassava diets were more readily accepted by the pigs than conventional maizebased diets. The results of nine experiments (see Table 4) proved conclusively that overall performance, health and carcass quality were not significantly influenced by any level of cassava meal, when the diets were pelleted and carefully balanced in relation to all limiting factors. Similar results with a 50 percent cassava-based diet, fed either in mash or pelleted form, were recently reported in Brazil by Peixoto and Farias (1973), and in Malaysia by Hutagalung et al. (1973).

A cassava market in southern India. Fifty-five million tons of cassava are consumed annually in the tropics.

Table 4. Comparative results of experiments on pigs fed maize and cassava diets, as mash or pellets

Source: Pig and Poultry Research and Training Institute, Singapore.
¹ P < 0.05.
² P < 0.025.

Cassava-based diets for poultry

Experiments with cassava meal in poultry diets date back to 1935 in the Philippines. Considerable emphasis was given to the replacement of cereals in poultry diets during the second world war. But feeds containing more than 10 percent cassava meal resulted in visibly poorer performance than those based on cereals. Similarly, in Germany and other countries, a significant growth depression was recorded when the level of cassava meal was higher than 10–20 percent of the total diet, although in some experiments there was already a tendency to substitute cassava for cereals at levels up to 50 percent. It was suggested that glucosides remained in the cassava, and that a phosphorylase inhibitor in the rind of the cassava tuber could also have been responsible for the growth depression (Vogt, 1966). Somewhat better results were obtained when cassava-based diets were fortified by methionine. High levels of cassava meal in poultry diets were only recently introduced by Singapore and Malaysian workers (Chou and Müller, 1972; Hutagalung et al., 1973). While pelleted diets containing the meal (up to 58 percent in broiler rations and 75 percent for replacement birds) resulted in performances similar to those with maize-based diets, poorer growth and feed efficiency were recorded for all cassava-based diets when they were fed in mash form. The results of the Singapore broiler experiment are summarized in Table 5. The possibility of replacing maize with cassava meal in diets for laying hens was also studied recently. It was concluded that at levels of up to 50 percent in the rations the meal did not affect either performance or the quality of the eggs; any significant drop in yolk pigmentation can be easily overcome by adding synthetic xanthophylls. The literature on the use of cassava in poultry rations may thus appear conflicting. Cassava-based diets must meet not only the physiological aspects of nutrient balance but also the physical requirements of the diet. Therefore, volume as a factor controlling feed intake usually has greater importance than the nutritive make-up of the diet. This is of very great importance, particularly in the tropics where feed intake is already seriously affected by climatic interference, and represents a key factor in the nutrition of laying hens.

Potential in cattle feeding

The shortage of grains has given an important stimulus to the use of cassava root products in all-mash feedlots and in feed concentrates for dairy cattle. The release of energy from cassava starch and of nitrogen from urea has a very close timing, and this is of great importance for the maximum utilization of NPN compounds in cattle diets and for effecting significant savings in protein feedstuffs. In green-lots, a concentrate consisting of 85 percent cassava root meal, 6 percent molasses, 8 percent urea and 1 percent mineral supplement, for instance, could effectively supplement tropical forages and supply all the deficient nutrients required for optimum performance. In drylots, a combination of cassava pellets and grass-meal pellets may totally substitute cereals. Fresh cassava roots, when properly processed, may also serve as a basic caloric source for intensive cattle feeding. In tropical regions, cattle development is usually hampered by inadequate forage, the quality of which changes too rapidly to meet the physiological requirements of ruminants and permit economic performance. Under such conditions, the use of fresh or dried cassava products, preferably the latter, could effectively solve this feeding problem.

Table 5. Different levels of cassava in broiler rations compared with maize-based diets

Source: Pig and Poultry Research and Training Institute, Singapore.
¹ 100 birds in each group.
² Maize diet.

Conclusions

The following conclusions may be drawn from the experiments conducted on substituting cassava for cereals in pig and poultry diets:

1. In cassava-based diets the cassava must be fed either as pellets or in a wet or liquid form. While pellets facilitate a once-a-day feeding system, wet or liquid diets require two or preferably three feeding intervals a day in order to obtain reasonable performance. However, under field conditions pelleted diets will always produce more reliable results.
2. Pellets eliminate irritation of the respiratory organs and infections of the eye, and ensure optimum feed intake. Feeding time for poultry consuming pellets is about 20–30 percent of that for mash.
3. Pelleted rations have a higher digestibility of starch and fibre than those fed in mash form. The digestibility of fibre increases probably because the heat generated by both pressure and steam treatment releases the cellulose from the lignin-cellulose bond.
4. Cassava products of lower quality may, to some extent, be used in pelleted diets, because nutrient requirements could be regulated by higher feed intake.
5. The heat generated by steam treatment and high pressure during pelleting destroys many of the growth inhibitors of microbial origin (moulds, fungi and other contaminants, during sun-drying or storage). Thus, pigs fed on mash suffer almost continuously from a mild type of diarrhoea, but this does not occur when the cassava is fed in pelleted form.
6. Cassava-based diets must be formulated with more care than cerealbased diets. Special attention must be paid to the level of crude fibre and ash in cassava-root meal, as this product is often adulterated with lime, chalk, sand, etc. An excess of crude fibre and ash decreases the digestibility of the ration as a whole, and limits the choice of other feed ingredients. Cassava roots having more than 4 percent fibre are not suitable as a total substitute for cereals in high-energy diets. Great care must be taken to ensure a balance of the limiting amino acids, essential fatty acids (linoleic acid for layers), basic minerals, microelements (such as zinc and iron) and vitamins.
7. Poultry diets based on cassava roots must be fortified by natural and/ or synthetic xanthophylls (preferably a combination of both yellow xanthophylls from grass/legume meals and synthetic red xanthophylls).
8. Economic considerations are obviously of prime importance, and the replacement of some cereals with cassava is only feasible when the price of a nutritionally equivalent mixture of cassava and protein feeds is lower than that of the cereal grain to be substituted.

References

Aumaitre, A. 1967. Futterwert von Tapioka und verschiedenen Getreidearten in Futterationen für frühzeitig abgesetzte Ferkel. Zeit. Tierphysiol. Tierernühr. Futtermittelk, 23: 41–43.

Bruijn, G.H. 1973. The cyanogenic character of cassava (Manihot esculenta). In Chronic cassava toxicity. Ottawa, Canada, Int. Dev. Research Centre.

Chicco, C.F., Garbati, S.T., Müller-Haye, B. & Vecchionacce, H.I. 1972. La harina de yuca en el engorde de cerdos. Rev. Agron. Trop., 12(6): 599– 603.

Chou, K.C. & Müller, Z. 1972. Complete substitution of maize by tapioca in broiler ration. Proceedings of Australasian Poult. Sci. Conv., Auckland, New Zealand.

Eggum, E.O. 1970. The protein quality of cassava leaves. Br. J. Nutr., 24(3): 761–768.

Hutagalung, R.I., Phuah, C.H. & Hew, V.F. 1973. The utilization of cassava (tapioca) in livestock feeding. Third Int. Symposium on Tropical Root Crops, IITA, Ibadan, Nigeria.

Maner, J.N., Buitrago, J. & Jimenez, I. 1969. Utilization of yuca in swine feeding. First Int. Symposium on Tropical Root Crops. University of the West Indies, Trinidad.

Maner, J.N., Buitrago, J. & Callo, J.T. 1970. Protein sources for supplementation of fresh cassava (Manihot esculenta) rations for growing-finishing swine. J. Anim. Sci., 31(1): 208, abs. 203.

Maner, J.N. & Gomes, G. 1973. Implications of cyanide toxicity in animal feeding studies using high cassava rations. In Chronic cassava toxicity. Ottawa, Canada, Int. Dev. Research Centre.

Maust, L.E., Warner, R.G., Pond, W.G. & McDowell, R.B. 1969. Rice brancassava meal as a carbohydrate feed for growing pigs. J. Animal Sci., 29(1): 140, abs. 149.

Maust, L.E., Pond, W.G. & Scott, M.L. 1972. Energy value of a cassava-rice bran diet with and without supplemental zinc for growing pigs. J. Anim. Sci., 35: 953–957.

Müller, Z., Chou, K.C., Nah, K.C. & Tan, T.K. 1972. Study of nutritive value of tapioca in economic rations for growing/finishing pigs in the tropics. UNDP/SF Project SIN 67/505, Pig & Poultry Research & Training Institute, Singapore (Pigs), R-672: 1–35.

Müller, Z., Chou, K.C. & Nah, K.C. 1974. Cassava as a total substitute for cereals in livestock and poultry rations. London, England, TPI Conf., Animal Feeds of Tropical and Subtropical origin.

Nestel, B. 1973. Current utilization and future potential for cassava. In Chronic cassava toxicity. Ottawa, Canada, Int. Dev. Research Centre.

Peixoto, P.R. & Farias, J.V. da Silva. 1973. Estudo da influencia da prensagem (pellets) em racoes con elevado teor de farinha de mandioca pra porcos em crescimento e terminacão. X. Reuniao Anual da S.B.Z. I Congresso Brasileiro de Forrageiras, P.A.R.S. 241–242.

Rogers, D.J. & Milner, M. 1963. Amino acid profile of manioc leaf protein in relation to nutritive value. Econ. Bot., 17: 211–216.

Vellose, L., Rodrigues, A.J., Becker, M., Neto, L.P., Scott, W.N., Kalil, E.B., Melotti, L. & Da Rouche, G.L. 1967. Substitucão parcial e total do milho pelo farelo de mandioca em racoes se suinos em crescimento e engorda. Bolm. Ind. Anim., 23(1965/66): 129–137.

Vogt, H. 1966. The use of tapioca meal in poultry rations. World Poultry Sci. J., 22: 113–125.

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