Sweet potatoes as animal feed in developing countries: present patterns and future prospects
by G.J. Scott

INTRODUCTION

Many developing countries are under increasing pressure to make more effective use of available resources in the agricultural sector both to satisfy the growing demand for livestock products and to raise rural incomes by generating additional value added through processing. The cost of balancing domestic demand for livestock products with feed or livestock imports has become prohibitively expensive. The prospects for increases in the output of cereals of the magnitude required to meet livestock and human requirements remain problematic. Consequently, alternative sources of livestock feed both to spur domestic livestock production and to free cereal supplies for human consumption are receiving closer attention. Interest in the potential for a expanded use of sweet potatoes as animal feed in developing countries has arisen in this context.

This paper focuses on the following key questions:

1. What are current production and utilization patterns for sweet potatoes in developing countries?

2. Where, how and to what extent are sweet potatoes used for animal feed?

3. What is the potential for expanded use of sweet potatoes as animal feed?

As will be indicated below, the last two decades have witnessed some dramatic increases in the use of sweet potatoes for animal feed. Furthermore, the potential for greater utilization of sweet potatoes in this form would also appear to be bright.

PRODUCTION

Sweet potato is among the five most important food crops in developing countries in terms of total production (Horton 1988). Although the sweet potato Ipomoea batatas (L.) Lam is of New World origin, over 90% of developing country production is produced in Asia; 85% in China alone (Table 1). While sweet potato production and area planted in Africa practically doubled over the last three decades, they remain less than 5% and 15% respectively of developing country totals. Latin America accounts for about 2% of output and 3% of area planted.

a percent of total production/area planted/average yield for all developing countries

b Africa not including South Africa

c Africa-(Morocco, Algeria, Tunisia, Egypt, Libya)-(South Africa)

d Asia_ (Israel Japan)+Oceania-(Australia,New Zealand)

e North and Central America + South America-(Canada,USA).

Source: FAO Basic Data Unit, unpublished statistics

Sweet potatoes are grown in some 98 developing countries (Table 2). However, the 15 countries with the largest production account for nearly 97% of this total (Table 3). These countries also account for 98% of the change in output since 1961.

a FAO includes various sites (e.g. Hong Kong) in the “developing countries” category. These figuresreflectthat categorization.

Source: FAO Basic Data Unit, unpublished statistics

Recent trends in sweet potato area planted and production have been highly uneven. In a number of countries, output and area have fallen (e.g. China, Indonesia, Philippines, Brazil) since the mid-1970's (Table 3). Reasons cited for this include: (i) expansion of production infrastructure (i.e. irrigation) for other crops, (ii) switching to higher value vegetable crops in response to, (iii) growth in urbanization, incomes and the associated demand for more diversified diets (see, e.g. Calkins 1979; Chin 1989). Trends in sweet potato production have been just the opposite in several other countries.

a 1=(1973–75 vs 1961–63); 2=(1986–88 vs 1973–75); 3=(1986–88 vs 1961–63).

Source: FAO Basic Data Unit, unpublished statistics

Sweet potato output expanded rapidly during the last decade in various locations including Vietnam, Kenya, Rwanda, Burundi, the Democratic Republic of Korea and Madagascar (Table 3). Rapid population growth resulting in increased pressure on farm land was a prime factor explaining this trend in some countries e.g. Rwanda (see von Braun et al. 1988) while economic and political disruptions of other agricultural activities probably contributed to this growth in other countries e.g. Vietnam (Mackay 1989).

UTILIZATION

Information about the utilization of sweet potato in developing countries is generally harder to come by and less reliable than is the case with other roots and tubers e.g. cassava, potato (see Horton et al. 1984). International statistics indicate that approximately one third of sweet potato production in developing countries currently goes to animal feed, although the overall average is highly inflated due to the importance of China and Brazil that use huge amounts of sweet potatoes for feed. This percentage appears to have steadily increased from about 10% in the early 1960s (Table 4).

^aData are for the 15 countries with the largest sweet potato production

Source: FAO Food Balance Sheets, unpublished statistics

Growth in production and availability of cereals and the rising demand for meat products have induced sweet potato producers to look for alternative outlets for the crop, especially in Asia where this trend has been particularly pronounced. Sweet potato use for animal feed is, with a few notable exceptions, less than 10% of output in sub-Saharan Africa and Latin America.

Amongst the 15 largest producers, FAO statistics indicate sweet potato use for animal feed is 40% of total output in China, 35% in Brazil, 30% in Madagascar, 17% in the Republic of Korea and 5% or less in the remaining 11 countries (Table 4). The estimated percentages have remained stable during the last three decades in all the countries except China (12% in 1961–63) and Korea (2% in 1961–63).

Recent Chinese estimates indicate as much as 65% of sweet potato output now goes to animal feed. Explanations for this sharp increase include growth in cereal production, meaning less sweet potato is needed to supplement cereal consumption; rising demand for meat products (principally pork) for which sweet potatoes serve as a feed component, and changes in government policy e.g. the introduction of the “responsibility system” which permits the sale of agricultural surpluses for profit. Furthermore, an EEC bilateral agreement allowed China to export up to 600,000t of dried sweet potato chips to member countries duty free during the 1980s (see Calpe, 1991).

It also should be noted that estimates of “processing” or “waste” as a percentage of sweet potato production are difficult to interpret. In many countries, waste in the form of damaged roots and vines are processed or fed to livestock. On the other hand, some production is lost due to physical or autolytic processes, microbiological attack, pest damage, and so on (see NAS 1978). Furthermore, postharvest losses for sweet potatoes like other root and tuber crops would appear to be higher than for the cereal crops, given their higher water content and bulkiness, (see Coursey 1982). But little quantitative information is available other than those based on inferences of an a priori type (i.e. sweet potatoes are perishable, therefore a certain percentage of the harvest is lost) or desktop “guesstimates”. Consequently, available statistics are unreliable when it comes to calculating the volume of unutilized supplies that might be converted into animal feed.

FEED PRODUCTION AND USE

Sweet potato is almost always used, in some form and amount, as an animal feed wherever it is produced in developing countries. Unfortunately, information about the exact nature, extent and evolution of these practices is handicapped by a lack of knowledge about the crop generally and the use for animal feed specifically. With that observation as a caveat, the meager evidence available about present practices suggests that sweet potato is most commonly used as animal feed on the farm itself. Roots, vines, and foliage are fed principally to pigs and cattle in unprocessed form. With certain notable exceptions, animal feed currently constitutes a minor share of the total utilization of sweet potato production.

Asia

Roots for pigs and vines for cattle are the most commonly cited forms of sweet potato utilization as animal feed in Asia (Table 5). Both are employed in a variety ways. Visually all feed production from sweet potato takes place at the farmer or village-level. Only limited quantities of composite feeds are produced industrially.

Uncooked roots are fed to pigs in China, parts of Indonesia (Irian Jaya), Korea, Papua New Guinea, Thailand, and Vietnam (see CIP 1989). These roots may be used fresh or after storage. Some farmers in China slice up the fresh roots to make them more digestible or feed them mixed with vines, other household feed sources (e.g. rice hulls, corn husks) or even purchased protein supplements. In Korea, these fresh roots include culls left from sales to the market (Chin 1989). In Papua New Guinea, pigs will forage for roots or culls left in the field (Kanua and Rangat 1989).

Some farmers in China and the Philippines prefer to boil the roots first and then use them as pig feed. This practice reportedly improves digestibility. Cooked root-leftovers from human consumption serve as one form of pig feed in Papua New Guinea.

n.a.= not available

Source: CIP 1989; Mackay et al, 1989

Many sweet potato farmers in northern China slice and then dry sweet potato roots before using them as pig feed (Lu et al.1989). This type of simple processing often takes place in the field itself. Slicing, then sundrying of the roots is a well-known procedure for production of pig feed from sweet potatoes in Taiwan (Calkins 1979; Tsou et al.1989). It has also been done on a more limited basis in the Philippines, (Palomar et al. 1989) and Vietnam (Hoang et al. 1989).

In China, sweet potato roots are also ground by various types of smallscale machines and used to make starch for noodles (see Tang et al. 1990). After draining off the starch, the remaining pulp is then used as is, fermented, dried, or stored to make pig feed. Waste water from village-level starch and noodle production also is fed to pigs.

Sweet potato vines and/or foliage are also used as animal feed throughout Asia (Table 5). These parts of the plant are fed as is or after ensilage to cattle in Bangladesh, China, India, Indonesia (Java), and the Philippines (see CIP 1989; Mackay et al. 1989). They also serve as a form of pig feed in Papua New Guinea, Vietnam and are fed to poultry in China. In Bangladesh, India, and Indonesia, vines and/or foliage serve as a principal source of animal feed from sweet potato production. Nevertheless, available estimates indicate only a tiny fraction of sweet potato output used for this purpose.

Africa

Information about the use of sweet potato for animal feed in Africa is particularly sparse. The limited reports suggest that nearly all roots are for human consumption with only damaged ones being fed for livestock e.g. Rwanda (see Ndamaga 1988). Vines and foliage from the sweet potato plant are fed principally to cattle in a number of countries however (see CIP 1988).

In Egypt, Kenya, Mozambique, Rwanda, and Uganda vines and/or foliage are utilized as green fodder for cattle principally, but also for pigs and other small animals (Table 6). Two reasons why this practice is not more widespread are : i) farm households eat the vines in boiled form as a source to put on the basic staple (e.g. in rice in Sierra Leone); ii) farmers willl leave vines in the field to improve soil fertility.

Source: Boy et al, 1988; CIP 1988,1988a.

Latin America

Sweet potatoes roots, vines and foliage are used for animal feed in a number of Latin America countries (Table 6). As the crop is typicallky grown on small farms, often for household consumption, Argentina, ]Brazil and Peru are notable exceptions, statistics on utilization patterns for animal feed are clearly guesses. An estimated 35% of sweet potato production is used for animal feed in Brazil (Table 6), about 15% in the Dominican Republic (Baez 1988). This percentage is negligible for other countries in the region except in those cases where total sweet potato production in absolute terms is itself insignificant.

Roots are fed generally to pigs. Except in Brazil (Franca 1988) and Peru (Burga 1988) where the roots are used for cattle. In Argentina, the roots are thge culls left after grading for market (see Boy et al. 1988). In Haiti, pigs will dig up the roots that remain in the field after the final harvest (Polynice 1988). In every instance, these roots appear to be utilized in fresh form i.e. without cooking or drying. Sweet potato vines and foilage are also used as animal feed. In Argentina, Brazil, Ecuador, the Dominican Republic, and Peru, the vines and foliage are fed prinicpally to cattle, but also to pigs and rabbits (Peru) and to goats (Ecuador). In Argentina, Brazil, and the Dominican Republic in particular, fodder from sweet potatoes has served as an emergency supply of cattle feed for farmers in periods of drought or during the dry seasons (see Boy et al. 1988; Franca 1988; Baez 1988). The vines and foliage are used in unprocessed form in every instance except in the Dominican Republic where they are first ground and then mixed with sugar cane by-products before being to fed to livestock.

POTENTIAL FOR SWEET POTATOES AS ANIMAL FEEDD

Expanded use of sweet potato as animal feed appears to be promising for both agro-biological and socio-economic reasons. On the agro-biological side, sweet potato has a relatively short vegetative cycle (4-5 months).

Hence, it fits nicely into tight cropping systems. It therefore also products much more dry matter per hectare and per day than cassava (see Horton 1988). Sweet potato is widely adapted to diverse altitudes (up to 2000m) and temperature conditions. It requires pratically no cash inputs and minimal horticultural practices. Sweet potato also competes better with weeds than other root and tuber crops. It also has more potential for greater mechanized harvesting than cassava.

Improvements in yield, dry matter content, and digestiblity of the crop should make sweet potato incresingly more trractive as a source of animal feed. Average yields for sweet potatos in developing countries doubled over the last twenty-five years primarily because of developments in China (Table 1). Yet the yield increases in the People's Republic appear to have been largely the result of changes in cultural practices (i.e. increased plant density) rather than the utilization of improved varieties or of chemicl fertilizers and pesticides (Mackay 1989).; Moreover, average yeilds in China (17t/ha) are fifty percent or less of what is commonly achieved on experiment stations in developing countries. Up until recently, sweet potatoes have received relatively few resources for research and development in these countries. As pressure mounts on farmers to raise productivity, the potential gains to be made from improved sweet potato varieties and modern inputs should be more widely realized.

Most sweet potatoes currently cultivated in developing countries have a dry-matter content of around 30%. Results of research at the Asian Vegetable Research and Development Center show that “the mean dry matter content of breeding lined imporoved from, 25.9 percent to 35.1 percent in five years. Theoretically this program increased ship yield for animal feed by 40 percent.” (Tsou et al. 1989). Moreover, the international germsplasm collection for this crop includes vareities whose drymatter content is as high as 45%. Clearly the potential is there to raise the sweet potato's utility for porocessing by incorporating varieties with higher dry-matter content into the material available to growers in developing countries.

Digestibility appears to be a problem in some countries for some varieties that are grown under certain types of conditions and for some types of animal feed (see, e.g. Tsou and Hong 1989). Improved digestibility of sweet potato varieties through bio-technology, or as Tsou et al (1989) point out “through selection of varieties with low trypsin inhibitor activities”, should also help expand the plant's potential for wider use as an animal feed in developing countries.

SOCIO-ECONOMIC FACTORS

Sweet potato's potential for animal feed will also depend on socioeconomic factors including: i) growth in population and incomes, ii) growth in demand for cereals for human consumption and for animal products, and iii) the capacity of a given country to cover food deficits through imports.

Growth in population can affect the prospects for sweet potato utilization as animal feed in various ways. If population growth outstrips growth in cereal production, then those cereals currently sed for livestock feed will be required for sustaining levels of cereal consumption so as to minimize the need for expanded food or feed imports. Population growtgh in the countryside may induce farmers away from expanded cereal production to more high valued crops so as to maintain incomelevels. Growth in incomes may further aggravate this situation to the extent that consumers utilize these higher incomes in an effort to raise their consumption of both cereals and livestock products.

Growth in the demand for cereals for human consumption and livestock products will also influence the prospects for sweet potato use as animal feed. The 1980s witnessed a slowdown in the rate of increase of production of cereal crops in a number of developing countries partly because the rate of increase in yields became more difficult to sustain. Should population growth rates fail to decline, the prospects for meeting domestic food requirements with local supplies become more problematic. Furthermore, if consumers, particularly in Africa and Asia, try to improve their diets by increasing consumption of livestock products at the same time, the pressure on the agricultural sector to meet the demand for livestock products through development of alternative production schemes could well increase utilization of sweet potatoes for animal feed.

Many countries have witnessed dramatic reversals of governemnt policy as regards food and feed imports over the last few years partly as a result of chages in world markets, the burden of accumulated debt, or in an effort to create more oppurtunities for domestic agricultural production. These policy changes and similar changes in the years ahead will strongly influence the potential for sweet potato use as animal feed.

It will take time to feel the full impact odf several of the agro-biological and socio-economic factors outlined above. In the meantime, the prospects for the expanded use of sweet potatoes as animal feed would appear to be greatest in those regions and coutries where a substantial supply of the commodity already exists, where feed shortages have already materialized and where continued or expanded imports of feed do not appear sustinable for economic or political reasons. A number of countries in Asia (e.g.China, phillippines) and to lesser extent in Latin America (e.g. Brazil, Peru, Dominican Republic) would appear to meet these criteria. Unfortunately, a detailed assessment of the marketing for sweet potatoes as animal feed in these countries is currently not availble. That task is what merits immediate attention.

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Appendix 1. Sweet potato production ('000 t) in developing countries, 1986–88.

Appendix 1. (Continued)

^o Among 5 most important crops in terms of annual production (fresh weight)

* Less than 500 t

Source: FAO unpublished statistics