Use of root crops as animal feed

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A factor restricting the development of animal production in many developing countries is the cost of imported feed which has often gone up several fold because of alterations in the rate of exchange of local currency with respect to world markets. As feed costs have increased, animal products have become very expensive. If part of the feed could be substituted with root crops such as cassava, then part of the maize ration could be freed for human consumption. Table 8.1 compares the nutritive value of different cassava products with sorghum and maize, as components of animal feeds. The low protein and fibre and high content of soluble carbohydrates (high digestibility) are notable features of the cassava root. Cassava tops, stems and leaves are also available as animal feed and are comparatively high in utilizable protein.

TABLE 8.1 - Nutritive value of different cassava products compared with sorghum and maize (in percentages)

Source: H.K. Lim. 1967.

The International Development Research Centre in Canada sponsored a series of investigations into the use of cassava as animal feed. On the basis of their findings it is recommended that cassava could be a substitute of up to 40 percent for maize in the nutritionally balanced rations of pigs without any deleterious effect, and up to 30 percent in poultry rations.

Gómez et al. (1984) in Colombia reported that when cassava was substituted for corn in a poultry broiler ration at levels of up to 30 percent there was no significant difference in the performance at all levels, but the 20 percent level of substitution was the most economical. It required 215 kg of feed to produce 100 kg live weight with a 20 percent substitution, whereas it required 220 kg and 224 kg respectively for the corn feed and the 30 percent substitution feed as shown in Table 8.2. High levels of cassava intake are more acceptable for broiler production than for laying hens. Egg production and quality may be adversely affected by nutritional imbalances associated with rations high in cassava.

In the case of pigs (Table 8.3) the performance was progressively better as the level of cassava in the feed was increased. Thus it required 339 kg of feed to produce 100 kg weight with corn alone, whereas it required 337 kg and 331 kg respectively with 20 percent and 30 percent cassava substitution. In the economic assessment of the rations, the least-cost broiler diets containing 20 percent cassava meal gave the largest returns while profitability increased with the level of cassava meal in the case of the pig trials (Table 8.4), with those on the 30 percent cassava substitution being the most economical.

In view of the potential value of cassava to supply energy to dairy cattle, it has been used in a great number of experiments as the main source of energy, resulting in higher milk and fat yields and live weight gains (Pineda and Rubio, 1972). Similar results have been obtained for beef cattle when steers fed on commercial concentrate and cassava-based diets gained significantly faster than those fed bran or corn and cob-based diets. Better performance of bulls has also been reported by Montilla et al. (1975) on 40 percent cassava rations rather than on maize meal. Devendra (1977) has reported similar findings for goats and sheep, cassava enhancing utilization and hence nitrogen retention.

TABLE 8.2 - Performance of broilers fed least-cost diets with varying levels of cassava meal

¹Pooled standard deviation = Error mean square.
²Initial number of chicks per treatment: 148 with an overall average body weigh of 36.3 +(-) 5g. ³Units of feed consumed per unit of body weight grin.
Source: Gómez et al., 1984.

Mattei (1984) designed a simple cassava chipping machine for production of chips for animal feed. In one version the chipper is powered by an electric motor and in the other version, by a two-stroke or four-stroke petrol engine, each with a chipping capacity of 1 tonne of cassava per hour. The drying is done on trays made of aluminium mosquito netting supported by chicken wire stretched on a strong timber frame. The dried chips are then stored in a wellventilated area to avoid moulding. The economics of the process are favourable. A good review of simple technologies for root crop processing is provided by the United Nations Development Fund for Women (UNIFEM) publication Root crop processing, 1989.

TABLE 8.3 - Performance of growing finishing pigs fed least-cost diets with varying levels of cassava meal¹

¹Overall avg initial weight: 20.0 +(-) 1.2 kg. Experimental period: 91 days
²Pooled standard deviation = Error mean square.
³One pig was eliminated during the first two weeks of the experiment.
Source: Gómez e, al., 1984

Some work has also been reported on the use of sweet potato as animal feed. Yang (1982) found it satisfactory for horses, mules and hogs, for lactating dairy cows when compounded with corn meal feed, and for poultry feed at 25 percent substitution for corn. Yeh et al. (1978) found that the digestible energy and the metabolizable energy are 91 percent of those of corn, and the nett energy is about 79 percent of that of corn as pig feed. It is not as good as corn in terms of quantity or quality of digestible protein or energy. Results in Table 8.5 indicate that sweet potato at less than 25 percent substitution will give a better result than corn alone and al about 25 percent will give a similar weight gain and efficiency as corn. Popping the chips improved starch and nitrogen digestibility as well as removing the trypsin inhibitor which might have contributed to the lowering of the feed value, but it also resulted in reducing the lysine availability. There was a significant improvement in the performance of the pig on the popped food compared to the untreated sweet potato chips. The result is also comparable to the corn diet, which improved quality and percentage lean cut, especially at the 50 percent substitution level.

TABLE 8.4 - Economic assessment of poultry piq-feeding triads¹

¹Results of biological evaluations have been used in these calculations. The figures are in Colombian pesos.
²Includes $Col 28 800 and $Col 19 800 for cost of 1 000 one-day-old chicks and fixed costs for raising them, respectively.
³See text for explanations.
Source: Gómez et al., 1984

TABLE 8.5 - Performance of fattening pigs on different proportions of corn and sweet potato chips

¹Values in the same column followed by different small letters differ significantly (P<0.01 or P<0.05)
Source: Yeh, 1982.

Chen et al. (1979) evaluated the efficiency of gelatinization of urea-sweet potato meal (GUSP) and found that came on soybean meal performed better than on GUSP or urea alone, but the feed value of GUSP was better than urea. In terms of digestibility of dry matter, crude protein, crude fibre and nitrogen retention GUSP was equivalent to soybean meal. Table 8.6 summarizes the different results obtained using sweet potato for different livestock indicating that replacement of corn by dehydrated sweet potato in the food of dairy cows could give as much milk (91-100 percent) as corn alone (Masher et al., 1948; Frye et al., 1948). If the orange-flesh variety is used the milk will contain more vitamin A and 30 percent more beta-carotene than milk produced using corn alone, another added advantage. Southwell et al. (1948) found that beef cattle fed standard rations gained 1.07 kg/day compared to 1.17 kg and 0.98 kg/day when half or all of the corn is replaced with sweet potato respectively. The feed gain ratios were 9.51, 9.31 and 9.22 respectively. Massey (1943) found in a three-year trial that substitution of corn with sweet potato led to more meat production in lamb. Lee and Young (1979) reported that chickens fed diets containing a 24 percent substitution of corn with sweet potato grew as well as on the all-coin diet, with no significant difference in carcass quality, and the egg yolk contained more vitamin A.

TABLE 8.6 - Value of sweet potato as compared to corn In various feeding trials

Sources: Yeh & Bouwkamp, 1985.

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