8. FEASIBILITY OF USING CASSAVA VERSUS MAIZE OR WHEAT

8.1 Cassava as partial or total substitute for other energy sources

Energy sources constitute between 15 and 60 percent of compound livestock feeds and concentrates. Presently, maize constitutes the bulk of the energy source in such rations. Other grains, which are used to a lesser extent, include sorghum, millet, wheat, barley and oats. The difficulty in obtaining foreign exchange in many African countries has considerably reduced the imports of maize and other cereals. At the same time local production of cereal grains remain grossly inadequate for food and feed industries. Their shortages have therefore resulted in astronomical increases in the price of grains in the last decade. Cassava production has been rising steadily in many African countries and its availability has only to be matched with competitive pricing to make its use in livestock feeds feasible. Where it is a cheap carbohydrate source it is capable of supplying adequate calories and therefore offers great potential as animal feed. However, due to certain limitations such as its low content of protein, vitamins and some minerals and lack of sulphur, containing amino acid such as methionine, it is often rated as inferior to maize or wheat. Research on cassava as an animal feed which commenced in 1903 with the study of Tracy on pigs in the USA, has over the last century shown the importance of cassava in animal nutrition and its suitability as an energy source in compound rations when properly balanced in proteins, vitamins and minerals. Presently its competitive pricing with maize is the major limitation to its large-scale use in commercial feed milling. Prices of cassava should range between 60 and 70 percent of that of maize to be economically feasible as reported in different countries (Table 43). Other factors that need to be considered in formulating balanced cassava rations include:

• oil supplementation or pelletizing in order to reduce its dustiness and the latter to improve the starch utilization in cassava feeds. Also addition of fats, molasses or pelletizing have been found to improve palatability of cassava diets which is due to its powdery nature;

• adequate supplementation of monogastric rations with sulphur amino acids to detoxify residual hydrocyanic acid and supply enough for productive purposes;

• there is a need to synchronize the release of proteins in forage with energy from cassava in ruminant rations in order to obtain favourable productive responses;

• the advantage of non-protein nitrogen in the form of urea nitrogen or poultry droppings to provide cheap protein in cassava rations for ruminants will reduce supplementation costs.

There has recently been a significant drive to improve the energy availability of cereals and cereal by-products particularly from maize and wheat. This is through supplementation of such cereal-based rations with polysaccharidase enzymes specific to break the non-starch polysaccharidic bonds in complex and unavailable fibrous components in such cereals and by-products. The feasibility of these is still under test in some countries of sub-Saharan Africa. The relative advantage of such supplementation still remains very doubtful. Cassava as a cheap energy source can play a vital role in energy supplementation as a partial substitute for maize or wheat in such cereals or by-product-based rations. Its readily available carbohydrate as an energy source can therefore be tapped to complement such efforts being directed to cereals and cereal by-products.

8.2 Satisfactory levels of cassava in relative feed rations for poultry, pigs and ruminants

The practicability of life cycle feeding of cassava to different livestock species has been demonstrated if the cassava-based diets are adequately supplemented with proteins, minerals and vitamins.

- Poultry: poultry feed constitutes the largest proportion of the commercial ration produced by feed millers for intensive livestock production. The use of cassava as a substitute for maize or wheat will therefore have its greatest impact if it can be incorporated into commercial poultry feeds. Satisfactory growth response has been obtained for growing chicks on inclusion of between 5-10 percent cassava flour in chick ration in most of the reported trials (Table 26). A recent study in Nigeria by Tewe and Bokanga (2001) revealed the importance of the form of feeding cassava on the performance of birds. A cassava root-leaf mixture in a ratio of 4:1 was used to replace maize and offered in the dried marsh or pelletized forms. The cassava level was 47 percent of rations as shown in Table 37. The performance revealed satisfactory egg production and body weight gain with complete substitution of maize with cassava. Egg yolk colour was also markedly improved on the pelletized ration due to the higher carotenoid content imparted by the cassava leaves which was mixed into the cassava pellet or marsh. There was a consistent cost-saving of the cassava plant-based rations as compared with the maize-based rations.

In the European Union a 20 percent inclusion of cassava in poultry rations is recommended for satisfactory poultry production (Wood, 1992). Pelletizing is also recommended as dustiness of cassava feedstuff can reduce feed intake in poultry, which adversely affects productivity. Tolerable levels of hydrocyanic acid in cassava chips and pellets imported into the EU have been fixed at a maximum of 100 mg/kg as shown in Table 39. The cassava quality requirements for cassava products imported into the European Community countries are shown in Table 38.

- Pigs: the suitability of cassava root meal as a total replacement for maize in growing/finishing and gestating pigs has been demonstrated in many studies as shown in Table 26. Precautions to be taken to guarantee satisfactory performance include removal of cyanide through boiling, grating, soaking, fermenting and drying or a combination of these processes to produce final products containing no more than 100 mg/kg hydrocyanic acid and the prevention of microbial activity during sun-drying, particularly in a humid environment.

Another feeding trial in Nigeria by Tewe and Bokanga (2001) involved feeding of growing pigs with maize or cassava-based feed supplements. The cassava mix which also contained whole (unpeeled) cassava root and leaf meal in a ratio of 4:1 was presented in various forms. As shown in Table 39, the cassava mix supplement was presented in the threshed, milled or pelletized forms. The feeds were compared with a cereal-based supplement and also a diet which consisted of palm kernel cake solely fed to growing pigs. The performance showed that feed intake, body weight gain and feed conversion were highest on the pelletized cassava plant-based supplement. Indeed the period to attain market weight of 100 kg body weight was 195 days (6.5 months) on the pelletized cassava supplement as compared with 234 days (7 months, 24 days) on the cereal-based supplement and 366 days (12 months) on the sole palm kernel cake ration. Earlier studies in Nigeria (Tewe and Oke, 1983) with growing pigs showed satisfactory performance on diets containing 40 percent dried cassava peel and discarded small storage roots. With cassava peels alone performance was best at 10 percent inclusion. Leaner carcasses and cost reduction of feed were obtained in the cassava diet compared with maize.

In the European Union cassava chips are incorporated in growing swine rations at up to 40 percent of ration with satisfactory performance (Table 40). The inclusion level of cassava root meal or pellets in livestock feeds used in two European Community countries is presented in Table 41. Apart from dried cassava, pigs can also be fed with fresh, boiled or ensiled cassava roots as is commonly practiced in small- and medium- scale pig farming enterprises in many African countries.

- Ruminants: ruminant responses to cassava-based rations demonstrate that when cassava foliage was used as a supplement to Pennisetum purpureum, performance of fattening steers in terms of weight gain, feed intake and feed efficiency were markedly improved (Moore, 1976). An acceptable level of substitution of the basal grass ration was 50 percent cassava foliage. It is a common occurrence to see cattle grazing on foliage in cassava farms in Nigeria, particularly in the dry season when foliage is very scarce;

- dried cassava peel fed as a supplement to Pennisetum purpureum basal ration for sheep, revealed satisfactory weight gain, feed intake and dry matter digestibility with 30 or 70 percent substitution with dried cassava peels (Fomuyan and Meffeja, 1987).

Fresh cassava roots fed as a supplement to gliricidia and leuceania for goats, improved growth rate only when the feeding of the cassava roots was synchronized in such a manner that its feeding time was close to that when:

- the basal diet of browse or grass is fed. Thus, cassava should be split fed three times daily to ensure its synchronization with forage (Smith, 1992).

Dairy cattle's rearing in small homestead farms is a common feature in western Kenya. A study in Kenya by Sanda and Methu (1992) revealed that complete replacement of maize with cassava flour and nitrogen supplementation of the cassava diets with urea gave similar milk yield and butter fats on cassava or maize-based concentrates. Cost reduction of US$10/tonne on the cassava diets was also reported. Cassava roots and leaves therefore have high potentials in smallholder and commercial dairy farms in different parts of sub-Saharan Africa.

Table 38. Current quality requirements for cassava products imported into European Community countries.

General requirements for straight feedstuffs (12 percent moisture basis):

Aflatoxin: 0.05 mg kg^-1 or less
Cyanogens: 100 mg HCN equivalent kg^-1 or less

Source: Wood, 1992

Table 39. Composition of maize and cassava-based feed supplements for pigs (cassava mix presented in various forms)

Source: Tewe and Bokanga, 2001

Table 40. Typical raw material inclusion levels in livestock feed (%) used in two European Community countries.

Source: Wood, 1992

8.3 Price relationship between cassava, maize, other cereal substitutes, soybean meal and other protein supplements

Cassava competitiveness with maize in some African countries has been largely dictated by its form of presentation as a dry cereal (garri) and the advantageous price differential between this product and the conventional cereal-based foods. Indeed, these factors have promoted the transformation of cassava into a cash crop for urban consumption in Ghana and Nigeria. As shown in Figure 1, while the price of cassava is consistently lower than that of maize for the period 1993 to 2001, the price trends show a similar paradigm for both crops. This established the relationship between the energy sources. On the other hand, the price of wheat which is largely imported is not only consistently higher than maize, but its price fluctuation is largely determined by import policies in Nigeria.

The price trends of maize, cassava chips, soybean meal and groundnut cake in the Nigeria feed milling industry between 1990 and 2002 are shown in Figure 2. For the years 1990, 1993, 1994, 1997 and 2001, cassava chips were not used in the Nigeria feed milling industry because the market price was much higher than giving an economical mix in livestock rations. These periods coincided with the years that followed the cycle of glut when farmers cut back on cassava production following unfavourable market prices. The price relationship of cassava to maize as presented in Table 41 shows that for the years when cassava was used, the percentage of cassava chips to maize varied from 38.9 percent in 1992 to 76.2 percent in 1998. This finding tallies with the recommended prices of cassava in livestock feed in different studies. Reported levels of the price of cassava as a proportion of the price of maize as presented for different countries in Table 42 varies between 60 percent in Nigeria and Thailand and 75 percent in Côte d'Ivoire.

Indeed, in the European Union the feasibility of using cassava as livestock feed largely depends on the prices of protein. Supplements, notably soybean meal, are used to complement the protein of cassava in different mixes. The price of the protein concentrates, soybean meal and groundnut cake as illustrated in Figure 2, shows a rising trend particularly with soybean meal. This is due to stiff competition for this concentrate even in food industries in the country. Full fat soybean is also particularly useful in the cassava mixes used in the Nigerian poultry industry as its high oil content dowses the dustiness of cassava in the compounded rations. The rising price trends of the protein supplements therefore call for greater efforts to reduce the cost of cassava chips for the feed milling industry if it is to compete favourably as a substitute for maize or other cereals. Current studies by Tewe and Bokanga (2001) demonstrated the feasibility of producing cassava chips at market prices 40 percent lower than maize.

Fig. 1. Market prices of maize, cassava storage roots, soybean, shelled groundnuts and wheat in Nigeria (1993-2001)

Fig. 2. Price trends of maize, cassava chips, soybean meal and groundnut cake in Nigeria feed milling industry (1990-2002)

Table 41. Cassava chip prices as percentage of maize price in Nigeria (1990-2002)

N/A = Data not available.

Table 42. Reported levels of the price of cassava as a proportion of the price of maize in different countries

Source: Tewe et al. (2002)