Every 7.67 seconds the world gains three extra people and loses one hectare of arable land. The irony is the demand for agricultural land is on the rise as the world needs to produce enough food to feed its inhabitants.
Chronic undernourishment affects some 800 million people, i.e., 17% of the population of developing countries, and 34% in sub-Saharan Africa. Increased agricultural trade and efficient utilisation of available food resources will be a key to the future food security of the world. With an increasing level of affluence in some countries, such as China and India, the shift of diets towards livestock products has been significant.
For example, the average meat consumption in the developing countries has increased by 5-6% per annum over the past few decades (FAO, 2004). The driving force for the growth in meat consumption has been the monogastric livestock industry, in particular, the poultry sector, which has seen a threefold increase in per capita consumption since the 1960s. However, grain production is static while feed demand is rising each year. This disparity can only be addressed through significant gains in efficiency in utilising nonconventional ingredients and by-products.
This review discusses the type and availability of nonconventional or alternative feed resources, as well as technologies available to alleviate the nutritional constraints to these ingredients for monogastric animals.Non-conventional ingredients and their availability
The so-called non-conventional ingredients here refer to the by-products of roots and tubers; of vegetable oil sources such as coconut, sunflower, safflower, groundnut (peanut), palm kernel; of alcohol and rubber processing. Compared with conventional feed ingredients such as cereal grains and vegetable protein sources, these ingredients are usually cheaper, contain higher levels of anti-nutrients, have poorer pelleting quality, and are more variable in quality. In addition, the quality of by-products is influenced by processing.
Two of the amino acids most adversely affected by processing conditions are lysine and cystine. Too high or prolonged heat during the extraction process will destroy essential amino acids in protein meals. Miller (1976) indicated that the proteins in oilseed meals are particularly susceptible to damage by heat treatments involved in oil extraction because of the high carbohydrate content of the oilseeds. However, the correct heat processing of oilseeds makes nutrients highly available and destroys anti-nutritional factors (Göhl, 1981; Kalinowski, 1993). Anti-nutritional factors contained in alternative protein meals will negatively effect the performance of animals, even though some efforts have been made to reduce or eliminate these factors (Cheeke and Shull, 1985). Most alternative ingredients contain high levels of non-starch polysaccharides (NSP), which are the most important limitation to their effective use in monogastric diets.
Many other factors, including mould contamination and associated toxins, can impair the nutritional value of alternative protein sources. The detrimental effect of mycotoxins in feed has been thoroughly reviewed by Smith and his colleagues over the past 20 years (Smith et al., 2004). The energy and animo acid composition of alternative ingredients have been comprehensively reviewed by Hutagalung (2001).ETHANOL INDUSTRY CO-PRODUCTS
One of most abundant grain by-products is the so-called distillers’ grains. This co-product is further classified into distillers’ dry grains (DDG), the dried residue of distillers’ grains, and distillers’ dry grain with solubles (DDGS), the DDG with syrup added. DDG accounts for approximately 30% of dry grains for ethanol production, and it contains 25-28% protein, 8-9% fat, 5% ash and the remainder is non-starch polysaccharides (NSP). It is estimated that the world produces as much as 60 million tonnes of DDG each year. The nature of the NSP is not known, but it may be deduced that they would be composed mainly of cellulose and arabinoxylans. Currently DDG is used predominantly in cattle feed although in some countries it is also used in swine rations.COPRA MEAL
Copra meal is the residue of coconut oil production. The world production of coconuts was approximately 53 million tonnes in 2002, which yielded some 1.8 million tonnes of copra meal (Table 1). Despite its 20% crude protein, the use of copra meal in monogastric diets is limited due to a very high level of NSP (Purwadaria et al., 1995). The NSP make up 45 to 60% of the dry matter and consist predominantly of mannans (galactomannans and mannans), just over 10% cellulose and trace amounts of other polymers (arabinoxylogalactans arabinomannogalactan and galactoglucomannans) (Sattagaroon et al., 1983; Zamora et al., 1989). Sattagaroon et al. (1983) reported that approximately 30% of the copra NSP is soluble in hot water, but their nutritional properties are yet to be defined. The glucomannans are comprised of ß(1,4)- linked glucose and mannose units, whilst the galactomannans consist of a ß(1,4)-mannan backbone substituted with single units of a(1,6)-galactose.Table 1. Major copra cake-producing countries.
An aspect of the nutritional components receiving a lot of attention lately is the high level of arginine in copra meal. It is believed that a high arginine:lysine ratio can alleviate heat stress in animals (Creswell, personal communication). Information on the use of enzymes in diets containing copra meal is scarce. Purwadaria et al. (1995) reported an increased fibre digestibility in vitro after incubation of copra meal with Aspergillus niger.
Palm kernel cake is a common feed ingredient in Asian feed mills. Malaysia is the largest producer of palm kernels, accounting for 44% of world production. Malaysia, Indonesia and Nigeria together produce 85% of the world’s palm kernels. The kernel contains approximately 50% oil (Omar and Hamdan, 1998) and around 70-80% of the oil is removed by extraction.
The by-product of oil extraction is known either as palm kernel cake or as palm kernel meal depending on the processing method. Expeller extraction produces the former, whereas solvent extraction produces the latter. The two products differ in calcium, oil and fibre content.
Omar and Hamdan (1998) reported oil and crude fibre levels of 12.3% and 9.8% for the cake and 16.6% and 5.2% for the meal, respectively. The commercial palm kernel meal contains about 16% of crude protein and at least 60% of NSP. An NSP content of as high as 74.3% has been reported for palm kernel cake (Omar and Hamdan, 1998). The NSP are believed to be insoluble linear mannans (78% of total NSP) with very low galactose substitution, followed by cellulose (12%) and a small amount of 4-O-methyl-glucuronoxylans (3%) and arabinoxylans (3%) (Düsterhöft et al., 1992).
Supplementation of commercially available glycanases to palm kernel-containing diets yielded inconsistent results (Daud et al., 1997). The linear mannan is a highly crystallised, cellulose-like polysaccharide (Figure 1) and it is extremely difficult to cleave the ß-(1-4) linkage unless it is totally hydrated and its crystalline structure somehow disturbed.
The world produced 3.75 million tonnes of palm kernel cake in 2002, with Malaysia, Indonesia and Nigeria producing 87% of total production (FAO, 2004). Table 2 shows palm kernel cake production in seven countries, which accounted for 92% of world production in 2002.PEANUT MEAL
The peanut (Arachis hypogaea) is a tropical legume that is also known as the groundnut, earthnut, monkey nut, Manilla nut, Chinese nut, pindar or goober pea (Göhl, 1981; Evans, 1985). The world production of peanuts (in shell) in 2002 was 36 million tonnes (FAO, 2004). China, India, Nigeria, the United States, Indonesia and Sudan are the major producers. Peanuts are grown for the confectionery trade and, periodically, peanuts are available for stockfeed (Evans, 1985).
Peanuts are also crushed for oil and the subsequent byproduct meal is then available as a stockfeed, as are the shells.Figure 1. A typical molecular structure of a ß(1,4)-mannan.Table 2. Major palm kernel cake producing countries.
Peanut meal is the by-product of the oil-extraction process and contains 42-47% protein, which is deficient in sulphur amino acids and lysine (Miller, 1976; Evans, 1985). One of the major constraints to the use of peanut meal in monogastric diets is its susceptibility to mycotoxin contamination. In addition, peanut meal contains a considerable amount of fibre, which may interfere with nutrient digestibility and absorption. For example, Evans (1985) reported a crude fibre content of 8.7% for peanut meal, which could represent up to 30% of NSP. There are also no data on the use of enzymes in diets containing peanut meal.SUNFLOWER MEAL
The interest of the feed industry in sunflower seeds has been growing in recent years because a large amount of sunflower meal is available on the market at a low price.
In 2004, the world production of sunflower was 26.2 million tonnes. Oil extraction of sunflower seeds produces approximately 40% meal (Han et al., 1992).
Nine countries accounted for over 40% of world sunflower seed production in 2004 (Table 3).Table 3. Countries that produce more than a million tonnes of sunflower seeds per annum.
The nutritive value of sunflower meal, as for most nonconventional ingredients, is affected by its high NSP content. Irish and Balnave (1993) reported 27.6% NSP in sunflower seeds, of which 4.5% was soluble. The soluble NSP were mainly the uronic acids. Assuming the rate of oil extraction at 40%, the amount of NSP in the meal could be as high as 46%. The NSP consist of 42% cellulose, 24% pectic polysaccharides, 24% 4-Omethyl- glucuronoxylans, 5% (gluco)-mannans and 4.5% fucoxyloglucans (Düsterhöft et al., 1992).
Supplementation of diets containing high levels of sunflower meal with a number of commercial enzymes had little or no effect on performance of broiler chickens (Gerendai et al., 1997; El Sherif et al., 1997).KAPOK SEEDS
Kapok is grown for its fibre, thus it is also called ‘tree cotton’ in China. The amount of kapok seeds available for use in animal feed is not large (341,450 tonnes in 2004), but it is a uniquely southeast Asian product and produced almost entirely by Indonesia and Thailand. It contains 16% protein and, presumably, a very high level of cellulose. The protein contains a high level of arginine and has a poor essential amino acid balance.ROOTS AND TUBERS
The term ‘roots and tubers’ refers to potatoes, sweet potatoes, cassava, yams, taro (cocoyam) and other root plants. These are not only important human foods, but also very significant feed sources for animals. The world production of roots and tubers (dry equivalent) in 2002 was approximately 168 million tonnes, of which 42 million tonnes (25% of the total) were used as feed (Table 4). The nutritive value of roots and tubers can be highly variable.Table 4. Production of roots and tubers (dry equivalent) in countries producing over a million tonnes per annum in 2002.
Most of the roots and tubers are used as alternative energy sources for pigs and poultry. Cassava, also known as tapioca, manioc and mandioca, contains approximately 85% starch and 10-15% fibre.
Sometimes a by-product of cassava starch extraction is also available for use as a feed ingredient. It is called onggok in Indonesia and contains 15-20% starch and a very high level of NSP. The nature of the NSP is not known. As shown in Table 4, countries such as the Netherlands, Spain, Belgium and Luxembourg use large amounts of roots and tubers for feed; in some instances, feed use exceeds production. This indicates the high amounts of importation of the materials for feed use in these countries.
The quality of root and tuber starch products varies widely with some products containing up to 20% NSP. Occasional occurrence of increased concentration of cyanide in some products is also known although detrimental levels are not reported. The starches from potatoes and cassava contain 20% and 16.7% amylose and have gelatinization temperatures between 50-68oC and 49-65oC, respectively (Rogel, 1985).Conclusion
Non-conventional feed ingredients are available in large quantities around the world, particularly in Asia. The most important problem in relation to the use of these materials is variability in their chemical composition and nutritive value. This lack of consistency is due mainly to the way the original material is processed.
The fibre, or more precisely, the non-starch polysaccharides, makes up the bulk of these ingredients and represents the major cause of variation. The challenge ahead is to characterise the chemical structures of these carbohydrates, identify their strategic use in various stages of monogastric production, and ultimately increase their use as efficient energy sources for monogastric animals.
Author: MINGAN CHOCT
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School of Rural Science and Agriculture, The University of New England, Armidale, NSW, Australia