Cassava (Manihot esculenta Crantz) is widely grown in the tropical regions. It is estimated that most (65 percent) of the cassava crop is used for human consumption while the remainder is used for animal feed, starch, and industrial applications. Some European countries are using cassava pellets, imported mainly from Thailand, in animal feeds, particularly for swine. Although the commercial production of dried cassava chips and pellets in most tropical countries is still insignificant, there is a considerable potential to expand the use of cassava in local animal feed markets.
The purpose of this paper is to review the most relevant information on the use of cassava products, mainly fresh, ensiled, and dried root chips or cassava meal, in swine feeding programmes. Most of the data herein reported has been obtained with, either; whole roots of 10- to 12-months-old plants, of cassava cultivars grown at CIAT or cassava pellets imported to Hawaii from Thailand.
NUTRITIONALCHARACTERISTICS OF CASSAVA ROOT PRODUCTS
Whole fresh cassava roots contain approximately 65 percent water and have to be dried or processed to extend their shelf life or to preserve them. Contents, expressed as percentages in parentheses, of crude protein (1–2), ether extract (0.2–0.5), crude fibre (0.8–1.0), and ash (1–2) are generally low in the fresh roots, with the nitrogen-free extract (30–35) or total soluble carbohydrates as the second most important chemical constituent after water (Gomez 1979).
Cassava whole-root chips can also be safely stored in airtight silos, and the resulting biomass has a chemical composition similar to that of fresh roots (Gomez et al. 1988).
If cassava is not consumed fresh or stored in silos, the roots can be converted into stable dried products such as chips or pellets that can be subsequently used for industrial purposes or in composite animal feeds. Although all chemical constituents are concentrated in the dried cassava product, the most important component is starch, which accounts for 70 to 80 percent of its composition (Gomez 1979).
Dried cassava chips have less than half the protein content, and consequently lower amino acid contents than feed grains. The low concentration of sulfur amino acids and the relatively high content of arginine are common features of all cassava products analyzed (leaves, foliage, and whole-root chips), (Gomez and Noma 1986).
Of major concern with the use of cassava products, as animal feed, are their cyanide content. Most of the cassava cyanide is found in the form of a cyanogenic glucoside known as linamarin. A wide range of total cyanide concentrations (140 to 890 ppm dry matter basis) have been found in the fresh whole-root chips of several cassava cultivars (Gomez et al., 1984b), though most of them have a cyanide content below 300 ppm. Processing of cassava roots (sun-drying, oven-drying, ensiling) reduces the cyanide content in the final products to levels lower than the permissible maximum amount of hydrocyanic acid (100 ppm) set by the Council of the European Community (Ingram 1975). For example, cassava pellets imported from Thailand have a low cyanide content. No major problems have been encountered in feeding fresh, ensiled, or dried cassava roots to pigs in Latin America, because most of the cassava cultivars grown in this region have a low cyanide content.
FRESH CASSAVA ROOTS IN SWINE FEEDING PROGRAMMES
Fresh whole-root chips have been fed, ad libitum, either separately or mixed with a protein supplement. The basic difference in the different feed use was that a certain amount of protein supplement was saved when it was mixed directly with the fresh chips (Buitrago 1964); though, the extra labour required to do the mixing could outweigh the advantage of this method.
Experimental information obtained at the Centro International de Agricultura Tropical (CIAT) and the Instituto Colombiano Agropecuario (ICA) in Colombia has shown that fresh cassava can be used successfully throughout all the periods of the swine life cycle. However, sows fed fresh cassava during gestation and lactation had a slightly inferior breeding performance than sows fed a corn-soyabean meal-based diet (Maner 1972).
The consumption of chopped fresh cassava by growing-finishing pigs varies according to the protein content of the supplement. The daily intake of cassava throughout the growing-finishing period was greater when the protein supplement (fed free choice) had a higher protein level (Table 1). At the same time the intake of the supplement decreased (Job 1975), though a tendency to overconsume protein was observed as the protein content of the supplement increased (Table 1).
|Parameter||control diet||Fresh cassava +|
|20% PS||30% PS||40% PS|
|Daily gain (kg)||0.63||0.70||0.67||0.65|
|Daily feed intake (kg)|
|Total feed (90% DM)||2.08||2.08||2.07||2.04|
|Protein in diet (%)||14.3||14.6||16.6||17.3|
Pigs do not readily consume fresh bitter roots. When a protein supplement was supplied ad libitum with fresh, chopped, bitter roots, the pigs consumed an excess of the supplement to compensate for a reduced intake of the bitter roots. When fresh bitter roots were mixed with the supplement, pigs did not consume enough feed and lost weight during the experimental period (Gomez et al. 1976).
The management of feeding programmes based on fresh cassava roots is an important aspect to be considered. For example, pigs more readily consume chips produced using a chipping machine (such as the Malaysian model), which cuts the roots into relatively regular chips, and reduces the loss of starch in the chipping process, than ground fresh roots. Also, self-feeding systems based on, free choice-ad libitum consumption of fresh chopped roots and protein supplement, usually lead to an excess intake of the supplement. A proportioned supply of chopped cassava mixed with the protein supplement would restrict the excess protein consumed to normal levels, though the additional labour required must be taken into account in an economic evaluation.
Experimental results obtained during the different periods of the swine life cycle suggest that fresh cassava roots are an excellent source of energy for swine feeding when properly supplemented with protein, minerals, and vitamins.
CASSAVA ROOT SILAGE AS A SWINE FEED
Little information is available on the ensiling process and on the nutritive quality of the stored product. Work at CIAT has shown that cassava whole-root chips can be safely stored in airtight silos for at least six months. The ensiling process is an efficient means of reducing the cyanide content and the resulting biomass can be fed to pigs (Gomez and Valdivieso 1988).
Pigs fed cassava whole-root silage with a protein supplement, either premixed or separately, performed similarly to pigs fed a control sorghum-based diet (Gomez et al. 1988). Furthermore, any of three protein supplements evaluated (soybean meal-cottonseed meal, soybean meal-fish meal, and cottonseed meal-fish meal (Table 2) proved to be effectivly used when fed in combination with cassava whole-root silage.
Limited data available on the use of ensiled cassava chips for gestating and lactating sows as well as for growing-finishing pigs indicated that results were comparable to those obtained with chopped fresh cassava roots (Maner 1972).
|Soybean meal (SBM)||43.5||40.4||0.0|
|Cottonseed meal (CSM)||43.5||0.0||42.5|
|Fish meal (FM)||0.0||40.4||42.5|
|Calculated analysis (%)|
Ensiling of cassava whole—root chips could be a relatively inexpensive solution to the postharvest deterioration of the roots, particularly in humid tropical areas where drying of root chips would not be always feasible. Furthermore, storage of cassava root chips in silos would ensure a continuous supply of cassava for on-farm animal feeding programmes. However, more research on the ensiling of cassava root chips is needed to find the most appropriate silage method to preserve and enhance the high quality of cassava starch.
USE OF CASSAVA MEAL IN SWINE FEEDING PROGRAMMES
The most convenient and practical way of handling cassava is to dry the whole—root chips and grind them into a meal, which can be easily incorporated into composite diets. Dried cassava chips, pellets, and meal can be stored in a well-ventilated area for a long time without deterioration in their nutritive value. Cassava meal is an excellent energy source because of its highly digestible carbohydrates (70–80 percent), mainly in the form of starch; however, its protein content (2–4 percent) is low.
Experimental research at CIAT was conducted to study the effects of a cassava meal-soybean meal-feeding programme throughout the life cycle of the pig, with emphasis on the gestation and lactation periods. The results showed a consistent trend of the cassava feeding programme to produce lower reproductive performance and number of pigs farrowed (8.4 vs. 10.0) and weaned (6.6 vs. 9.4) than the control, yellow cornsoybean meal diets (Maner 1972, Gomez et al. 1976, Gomez 1977). The factors responsible for the lower reproductive performance of gilts fed the cassava meal-based diets were not clear, but a shortage of methionine was suspected to be one of the responsible factors.
The effect of methionine supplementation in cassava-based diets both for gestating and lactating gilts as well as for growing-finishing pigs was subsequently ascertained (Gomez et al. 1984a). The experimental results showed that the extra amount of methionine (0.3 percent) added to the cassava meal-based diets did not improve gilt or litter performance (Table 3).
|Parameter||Corn + SBM||Cassava meal + 0.0% Met||Soyben meal + 0.3% Met|
|No. gilts farrowed||14||10||10|
|Data at farrpwomg|
|Avg. pig weight (kg)||1.09||1.06||1.07|
|Data at weaning (56 days)|
|Avg. pig weight (kg)||16.7||16.2||16.5|
|Total litter weight (kg)||117.0||128.5||132.0|
A comparison of previous experimental conditions with those of the latter experiment suggested that handling of the feed supply during the gestation period could explain the difference in the results. Previously (Maner 1972, Gomez et al. 1976), the amount of daily feed (1.8 kg diet/gilt) required for each experimental group was spread on a concrete platform in the shaded area of a pasture lot, but the amount consumed per gilt could not be controlled, and consequently feed intake may not have been uniform.
Although the same group-feeding system was used with the control diet (corn-soybean meal), it appeared that with this diet the feed intake per gilt was more uniform than with the cassava-based diet. Diets containing high levels of cassava meal have a more dusty or floury texture and lower density than the corn-based diets. Feeding management, therefore, appears to be an important factor that may affect the performance of gestating and lactating gilts or sows fed diets containing high levels of cassava meal.
Although cassava meal can be satisfactorily used as the main energysupplying ingredient, especially when combined with soybean meal, leastcost diet formulation will take into consideration the nutrient supply as well as the cost of available feedstuffs. Under practical conditions, cassava meal would be between 20 and 40 percent of the diets at a price equivalent to approximately 80 percent of the current price of corn or sorghum. Performance of gestating and lactating gilts, their litters, and growing-finishing pigs fed least-cost diets containing cassava meal were also similar to that obtained with practical commercial diets based on sorghum (Gomez et al. 1984a).
Because of the physico-chemical characteristics of cassava starch (a small-diameter granule, a low amylose content, and an X-ray diffraction pattern of the A-type) (Szylit et al. 1977), which facilitate an efficient amylolytic degradation of the starch, cassava-based diets appear to be highly digestible and particularly suitable for baby pig feeding. A palatability test with baby pigs fed diets containing different levels of cassava meal (0, 20, and 40 percent) throughout the lactation (42 days) and post-weaning (42 to 56 days) periods, using the free choice method, clearly showed a definite preference for the diet containing the highest level of cassava meal throughout the entire experimental period (Table 4) (Gomez and Valdivieso 1983). However, there was no significant difference between the cassava- and sorghum-based diets when they were compared by the single feed method.
|Feed intake||% Cassava meal in diets||Total|
|Kilograms of feed consumed|
|% of total||17||30||53|
Data from recent experimental studies with nursery pigs (from weaning to 20–25 kg liveweight) at the University of Hawali have shown the following: a) diets containing 20 to 30 percent cassava meal produced pig performances similer to or slightly better than taht of pigs fed a control diet based on corn-soybean meal, b) diets containing 30 percent cassava meal in combination with either 10, 15, or 20 percent dried whey produced results similar to those obtained with a control diet based on corn with 20 pecent dried whey, c) a combination of 30 percent cassava meal with soyabean meal and fish meal led to better nursery pig performance than that obtained with either soybean meal alone or in combination with meat and bone meal or a combination of all three protein feeds, and d) the physical form (meal, crumbled, pelleted) of a diet based on 30 percent cassava meal in combination with soyabean meal and fish meal did not significantly affect pig performance (Gomez, unpunlished results).
Because of its low protein content, cassava meal-based diets require higher amounts of protein-supplying ingredients such as soybean meal to obtain an adequate balance of protein and amino acids. Therefore, the economic feasibility of using cassava as a substitute for conventional energy sources would depend not only on the relative price of cassava but also on the price of protein supplements needed to balance cassava-based diets.
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