S. Khajarern and J. Khajarern
Department of Animal Science, Khon Kaen University, Thailand
Livestock production in a tropical Southeast Asian farm is of secondary importance after crop production. Ruminants are raised for draught purposes and/or as the growing farm assets, while pigs and poultry are raised for cash needs and for family consumption. With this setting, potential availability of crop-residues and agro-industrial by-products is high compared with the livestock population. Among less fibrous agro-industrial by-products, energy sources from rice-milling and starch extraction and molasses are essentially adequate for pig and poultry industries of the region, whereas plant protein sources are substantially deficient and must be imported. Fibrous residues and agro-industrial by-products, such as rice-straw, sugar cane tops and leaves, banana leaves and stems, and maize stover are plenty but under-utilized. Apart from being used as feed, these resources are used as soil conditioners, in construction and for paper manufacturing and other non-feed purposes.
Rice straw is the only residue which has been used for animal feeding in small farms. Much research has been done to use other residues as feed but the practical adoption of the results is negligible. Rice straw is a poor source of roughage of low dry matter intake and nutrient digestibility. Physical treatments, such as chopping and/or soaking the rice straw prior to feeding gave positive responses in terms of increasing intake and digestibility. Supplementation of chopped straw with sweet potato chips urea and/or molasses, or with small amounts (200 g DM/d) of protein sources, such as leucaena, gliricidia and cassava leaf meals or with water hyacinth bring about a significant improvement in terms of increasing intake, nutrient digestibility, nitrogen retention and animal weight changes.
Literature reviews show that chemical treatment with alkalis, ammonia and other oxidants also increase intake and nutrient digestibility of rice straw, but these technologies seem unlikely to be practicable in SE Asian small farms. Straw treatment by ammonia released from urea/urine or by cheap alkalis as calcium oxide or hydroxide, seems to have potential applicability in the region. However, before these treatments can be put into practice at small farm level, more work is needed to devise a cheap and effective process to minimize ammonia escape during the treatment period; to establish the effective procedure(s) in calcium oxide/hydroxide treatment; and to formulate guidelines in supplementing the treated and/or untreated straw with economic and practical feeds. These are considered as first research priorities of the region.
Another high priority of research is to assess completely, in quantitative and qualitative terms, the residues that are “actually” available for feeding purpose on a year-round basis. Assessment should give information of what, where, when, how much and what quality of each residue is available. This will help the development of year-round feeding strategies. The appropriate treatments for improving the feeding value of each residue also need to be investigated.
Finally, socio-economic backed extension work for applying the residue feeding in the real small farmer's feeding systems deserves the immediate attention of all researchers.
Southeast Asian agriculture as a whole has placed more emphasis on crop rather than livestock production. The primary demand for livestock is to provide farm power, transport and household assets; and secondarily meat and milk. In general, livestock in the region is primarily raised on small farms rather than in big, commercial herds. The commercial production of swine and poultry has been developed in the past decade and contributes a minor, but rapidly increasing, portion of animal protein to the market. Ruminants, except for a few thousand head of dairy cattle in each country, graze on marginal land about the cultivated plots to obtain barely enough green forages during the rainy season. The green feed supply is generally inadequate during the dry period. During these dry months, crop residues represent the important source of feedstuffs for them. Other by-products yielded from agro-industries such as milling, sugar processing, oil and starch extracting play a relatively minor role in supplying nutrients to non-dairy ruminants. Therefore, studies concerned with the potential supply, availability as feed, methods of feeding and improving the nutritive value of these crop residues enabling their better utilization at small farm level are of prime importance for livestock development in Southeast Asia.
This paper is by no means a comprehensive review of research work dealing with the utilization of and/or methodology tested in improvement of crop residues and agro-industrial by-products for livestock feeding, it rather emphasizes work which have been conducted with the aim to apply in, and are pertinent for, Southeast Asian conditions. Again, this is by no means complete; only major crop residues and agro-industrial by-products will be emphasized.
|Production by country|
|'000 metric tons|
|Rice (Oryza sativa)||33 000||2 147||7 720||19 000||12 570||376 232|
|Maize (Zea mays)||3 991||8||3 176||3 700||540||86 570|
|Sorghum (Sorghum Vulgare)||-||-||-||380||35||20, 566|
|Sweet Potatoes Impomoca batatas)||2 079||37||1 100||348||2 400||137 108|
|Cassava (Manihot spp.)||13 726||360||2 300||17 900||3 400||47 584|
|Banana (Musa spp.)||1 556||375||893||2 021||900||14 788|
|Pineapple (Ananas comosus)||266||207||1 200||1 800||350||5 003|
|Sugar cane (Saccharum officinarum)||17 560||850||20 450||18 600||3 900||290 357|
|Soyabean (Glycine max)||653||-||8||120||64||10 320|
|Groundnuts (Arachis hypogaea)||855||23||50||112||80||11 408|
|Cotton seed (Gossypium spp.)||7||-||3||153||3||11 871|
|Coconut (Cocos nucifera)||10 800||1 207||10 050||900||350||30 803|
|Oilpalm kernels (Elaeis quineensis)||131||588||2.5||2||-||769 500|
|Rubber (Hevea brasiliensis)||937||1 590||65||510||48||3 569|
Source: F A O 1981. Production Yearbook Vol. 35, 306 pp.
POTENTIAL SUPPLY OF CROP RESIDUES AND AGRO-INDUSTRIAL BY-PRODUCTS
Table 1 presents the major crop production in five Southeast Asian countries during 1980/1981 season (FAO 1981). Data indicate that the main food crops of the region are rice, sugar-cane, cassava, maize and other plantation crops such as coconut and oil palm. The potential supply of their residues and agro-industrial by-products are given in Tables 2 and 3. It is worth noting that these crop residues and agro-industrial by-products are not totally available for feeding of livestock for three reasons. Firstly, the extraction rate which has been calculated from the primary products as given by Devendra (1979a) is a general average which in turn is subject to error due to variation in harvesting and handling methods from place to place. Secondly, accurate statistics on processing of commodities especially home processing is not complete thus making the theoretical estimation very inaccurate. Finally, the potential availability may differ greatly from what is or could actually be used for feeding due to their value in non-feed utilization. Castillo (1983) has comprehensively discussed six broad areas in utilization of fibrous residues in the Asian context. These include their utilization as animal feed, as fertilizer or soil conditioner, as fuel or sources of energy, as a source of building/construction material, as sources of herbal medicines, biologics or chemicals and for sociological or cultural applications.
|Yield by country|
|'000 metric ton|
|Rice straw||36 300||2 362||8 492||20 900||13 827||81 881.0|
|Maize stover||3 991||8||3 176||3 700||540||11 415.0|
|Maize husk||559||1.1||445||518||75.6||1 598.7|
|Sorghum head w/o grain||-||-||-||152||14||166.0|
|Sweet potato vine||624||11||330||104||720||1 789.0|
|Cassava leaves||1 098||29||184||1 432||272||3 015.0|
|Banana stem and leaves||3 423||825||1 965||4 446||1 980||12 639.0|
|Banana fruit wastes||467||112||268||606||270||1 723.0|
|Pineapple wastes||186||145||840||1 260||245||2 676|
|Sugar-cane tops and leaves||5 268||255||6 135||5 580||1 170||18 408.0|
|Soyabean stover and pods||1 306||-||16||240||128||1 690.0|
1 Extraction rate given by Devendra (1979a, 1980)
|Yield by country|
|Concentrates||'000 metric tons|
|Rice bran||3 300||215||772||1 900||1 257||7 444.0|
|Broken rice||1 650||107||386||950||629||3 722.0|
|Maize bran||360||0.7||286||333||48.6||1 028.3|
|Maize germ meal||678||1.4||540||629||91.8||1 940.2|
|Cassava wastes||7 824||205||1 311||10 203||1 938||21 481.0|
|Sugar-cane molasses||702||34||818||744||156||2 454.0|
|Cotton seed meal||3.2||-||1.3||69||1.4||74.9|
|Copra meal||4 320||483||4 420||360||140||9 723.0|
|Palm kernel meal||29||129||0.6||0.4||-||159.0|
|Rubber seed meal||515||875||36||280||26.4||1 732.4|
|Rice hulls||5 280||344||1 235||3 040||2 011.2||11 910.2|
|Maize cob||798||1.6||635||740||108||2 282.6|
|Palm press fiber||484||1871.0||8||6.7||-||2 389.7|
|Sugar-cane bagasse||3 863||187||4 499||4 092||858||13 499.0|
1 Extraction rate given by Devendra (1979a, 1980).
UTILIZATION OF CROP RESIDUES AND AGRO-INDUSTRIAL BY-PRODUCTS FOR ANIMAL FEEDING
Despite the fact that crop residues and agro-industrial by-products are currently used for various purposes, their importance as feedstuffs particularly for ruminants in small farm systems cannot be over-emphasized. With fewer fibrous agro-industrial by-products which are conventionally used in non-ruminant feeding, opportunities for offering them to ruminants or for improving their feeding value appear to be smaller and smaller due to rapid advances in nutritional sciences. Better utilization of these less fibrous feedstuffs for non-ruminant feeding in Southeast Asia can be obtained by increasing local production of protein feedstuff in order to keep up with the regional deficiency. Khajarern and Khajarern (1980) reported that the deficiency of protein concentrates in Southeast Asia was 3.9 million tons or 62.4% of the requirement. Exploitation for novel protein feeds consequently appears to be of the first priority for animal nutritionists in this region.
On the other hand, fibrous crop residues seem to be currently utilized at lower efficiency levels even though they have been used as the main forage source for ruminants in the region for hundreds of years. Among the fibrous crop residues potentially available in Southeast Asia, rice straw, sugar-cane tops and leaves, banana residues and maize stover are of primary importance whereas other crop wastes are of secondary importance (Table 2). For feeding purposes, rice straw is commonly used as main roughage, during the dry season, while other crop residues are rarely fed to livestock in Southeast Asian small farms. Traditionally, rice straw is stored, at the time of harvest, near the farmer's house either in the form of a stack or in a thatched hut. During the forage shortage, straw is fed to livestock either alone or mixed with a small supplement of green forage and generally without any concentrates. It has long been established that rice straw has low protein (3–5%), calcium (0.25– 0.55%), phosphorus (0.02–0.16%) but is high in crude fiber (26–34%) and silica (12–16%) with slightly lower lignin than other cereal straws (Jackson 1977). The TDN for cattle is relatively low (35.9 to 50.3%) (Devendra 1979b). Furthermore, the amount an animal can eat is limited to less than 3 percent of body weight due to the slow rate at which it is fermented in the rumen resulting in relatively low and variable digestibility (Table 4).
|Species||Physical form||Location||Dry matter intake||DDM %||Reference|
|Sheep||chopped (wet)||Malaysia||1.9||42.7||36.0||Devendra (1982)|
|Cattle||unknown||Philippines||-||-||42.8||Roxas et al (1975)|
|Carabaos||unknown||Philippines||-||-||44.1||Roxas et al (1975)|
|Cattle||chopped||Thailand||1.74||65.4||42.4||Wanapat et al (1982a)|
|Cattle||chopped||Thailand||2.92||86.6||44.0||Wanapat et al (1982b)|
|Water Buffalo||chopped||Thailand||1.88||70.0||48.7||Cheva-Isarakul (1983)|
In short, rice straw is a poor roughage which generally provides little or no surplus energy over maintenance requirement. Jackson (1977) concluded in his review that the only way to obtain more animal products from straw in the Asian setting was to improve digestibility and intake so that more energy was available for productive purposes.
RESEARCH AIMING FOR BETTER UTILIZATION OF CROP RESIDUES IN ANIMAL FEEDING
Research aiming for better utilization of the main crop residues in Southeast Asia, namely rice straw, has been undertaken by two major means. One is by improving the utilization of untreated straw by various supplementations including energy, protein/nonprotein nitrogen and/or minerals, whereas the other is by treatments of the residue prior to feeding with or without further supplementation. Both of these means, however, have not created appreciable impact for application in the small farm levels at present. This consequently suggests that much more work has to be done not only in the technical but also in the extension and sociological aspects.
Untreated rice straw as livestock feed
The utilization of rice straw as a significant proportion of the ration would only be successful if the limitations of low crude protein (Milford and Minson, 1968) and poor digestibility could be overcome. Supplementation with energy and protein sources is a prerequisite to increasing the efficiency of utilization. Energy sources such as molasses, cassava chips and sweet potato chips are appropriate for this purpose, while rice bran, copra cake, palm kernel cake, soybean meal, groundnut meal, fish meal, urea and other green leaves can supply protein to the level that can support the optimum dry matter intake. O'Donovan and Chen (1972), feeding untreated chopped straw (25 or 35%) with 25, 33 or 45 percent of molasses along with sweet potato chip-soybean meal-urea, obtained 0.46–0.82 kg body weight gain/day, in growing hiefers. Devendra (1975) supplemented molasses at 40 percent of ration containing 40 percent rice straw and noticed an increase in dry matter intake to 3.3% of sheep body weight. He also noted that maximum dry matter and organic matter digestibility were obtained at 20 percent rice straw with 60 percent molasses. At this level, rice straw intake and utilization were significantly increased. In a subsequent study, Devendra (1976) reported that when urea molasses was added to rice straw diets having maize as the main energy source, nitrogen intake and retention were significantly increased (Table 5).
|Level of rice straw % diet||Carbohydrate sources, % of diet||N intake g||N retention % of diet|
Source: Devendra (1976)
The favourable effect of molasses on maize is not only due to increased palatability but it is also an ideal source for urea utilization in rice straw diets. With water buffalo, Suriyajantratong et al (1974) supplemented 10 percent molasses with either 0, 1, 2, 3 or 4 percent urea to rice straw diets and observed a progressively reduced weight loss as the urea level increased. The molasses supplementation without urea, however, produced higher body weight loss than in the animals on rice straw. Rice straw consumption in the former group was significantly reduced. Similarly, Wanapat et al. (1982b) noted the decreases in rice straw intake, body weight gain and dry matter digestibility when cattle on a rice straw diet were supplied with 2 kg/hd/d of cassava chip. They explained that this adverse effect was due to the starchy nature of cassava chip which brought about the equivalent decrease of roughage intake and parakeratosis.
Devendra (1982) emphasized the importance of maintaining a balance between carbohydrate sources such as molasses with rice straw and dietary nitrogen if the maximum utilization of rice straw is to be obtained. Any diets containing less than 20 percent of rice straw supplemented with high levels of energy and protein sources would reduce the roughage utilization.
Another way to increase the utilization of untreated rice straw with low inputs of concentrates is to include in the diets forages with a relatively high crude protein content. Positive dry matter digestibility, crude protein digestibility and nitrogen retention in sheep being fed rice straw, 10–60 percent DMI of leucaena (Leucaena leucocephala) and minerals were observed by Devendra (1982). Similar responses were observed, in cattle receiving up to 50 percent DMI of leucaena, by Intramongkol et al (1983) and in cattle and water buffalo receiving rice straw rations with 2 kg/hd/d concentrates containing poultry manure up to 25 percent (Suriyajantratong et al 1983). Other high protein forages have also been demonstrated to be suitable supplements in rice straw rations. These include kenaf (Hibiscus spp.) leaves, pigeon pea (Cajanus cajan) straw and stylosanthes (Tawinprawat et al 1971), cassava leaves (Intramongkol et al 1978), and gliricidia leaves (Vearasilp 1981).
Devendra (1982) concluded in his review on the utilization of untreated straw that the optimum level of rice straw in a diet is about 20 percent and some of the aforementioned forages have potential value in increasing the utilization of straw. Further, economic justification between straw treatment to improve its nutritive value and the low cost, untreated straw-based feeding system that can combine various crop residues and non-conventional feed resources has been questioned.
Treatments to increase the utilization of crop residues by animals
Treatments of crop residues for improving their nutritional value has been undertaken since the beginning of 20th century. Since then, a tremendous effort has been geared to treat them by physical, physio-chemical, chemical or biological means to render the structural carbohydrates of the cell wall more digestible by the actions of rumen microbes and/or digestive enzymes. Donefer (1977), Jackson (1978), Sundstol (1981), Doyle (1982) and Ibrahim (1983) have comprehensively reviewed treating methods, effectiveness and applicability of methods being studied. Jayasuriya (1983) and Wanapat (1984) compared the potential and drawbacks of these methods as shown in Table 6. Apparently, some of the methods need high investment in equipment and careful health hazard precautions. Under Southeast Asian conditions however, a few methods are potentially practical at small farm level and worth looking into in detail. These include physical treatments, such as chopping and soaking (Doyle 1982) and chemical treatment with cheap chemicals, such as calcium hydroxide or calcium oxide and urea (Verma 1983) or urine (Mahyuddin 1982) as ammonia sources.
|Methods||Comments, e.g. availability and feasibility in farm use, scale of process, use of manure etc.|
|1. Physical treatment - Physical or mechanical processing, such as by grinding, pelleting etc.||Variable responses but often leads to a higher energy retention. Manure suitable for recycling on land. Inferior to chemical treatment expensive and not feasible under small farm situations.|
|2. Chemical treatment (a) Beckmann method (1921)||No complicated machinery involved, relatively less hazardous to operator than 2 (b), effective. High use of labour, alkali and water loss of organic matter, pollution due to washings, a batch process difficult to store treated material.|
|(b) ‘Dry’ method of Wilson and Pigden (1964) Spraying of a concentrated solution of NAOH||Simple, fast and effective. Can be a continuous process and possible in a small farm situation. High concentration of NaOH. Costly and hazardous to operator, manure will contain high Na + content.|
|(c) ‘Nebraska’ System (Waller & Klopfenstein 1975) using a mixture of NaOH (1–2%) and Ca(OH) (2–3%) with 50% water. Treated material stored for several weeks anaerobically at room temperature||Uses less NaOH than 2(b). Less hazardous to operator. Manure will contain less Na + content than 2(b). A slower process than 2(b). Presumably less effective.|
|(d) Torgrimsby method (1971) (as described by Homb et al. 1977)||Effectiveness and drawbacks are similar to Beckmann method, but pollution can be reduced by using less chemicals.|
|(e) Sundstol method (1981) (Dip- MaOH method)||Utilize less NaOH than Beckmann and Torgrimsby methods. Reduce treating period but may have high residual NaOH in the treated straw. May be applicable to small farm level if chemical price is cheap enough.|
|(f) Ammoniation using 3–5% aqueous or gaseous ammonia (as described by Sundstol et al 1978)||NPN added in the process, effective, manure suitable for recycling, NH, is scarce and expensive, not suitable for small farmer in the village, requires trained personnel for treating the residue.|
|(g) Ammoniation using urea solution (as described by Jayasuriya and Perera, 1982)||Simple, effective NPN added in the process. Urea is easily available and cheap in most instances. Manure suitable for recycling, slow process.|
|(h) Calcium oxide or calcium hydroxide treatment (as described by Pacho et al., 1977 and saadhulla et al., 1981)||Chemicals are cheap and readily available in S.E. Asia, but the reaction period is long and nutrient loss is high. Has high potential for application at small farm level.|
|3. Biological treatment Treatment with microorganisms, such as white rot fungi.||Method less developed, probably relatively slow. Little information available on response to treatments. Effects of fungal metabolites not known.|
|4. Physico chemical treatment - such as chemical treatment followed by grinding and pelleting||Fast and effective, uses NaOH. Therefore, more expensive than 2(g) Pelleting not feasible under most farm situations. Manure may not be suitable due to high Na+-content.|
Sources: Jayasuriya (1983) and Wanapat (1984)
Castillo et al (1982) demonstrated that chopping rice straw increased voluntary intake of this roughage by carabao; however, soaking of chopped straw did not further increase intake. In contrast, Chaturvedi et al (1973) observed increased dry matter intake when chopped wheat straw in diet was soaked prior to feeding. Doyle (1982) explained that this controversy might be due to the difference in dustiness of feeds used in these experiments. Chopping of straw prior to feeding to improve voluntary intake is not generally practised among S.E. Asian farmers. In most instances, the animals are given long straw either by grazing stubble, hand feeding, or by being allowed access to stacks. In addition, the farmers in the region are relatively conservative and are slow to adopt new ideas. The chopping and soaking of straw prior to feeding involves a significant time input in terms of labour, although it requires no other inputs. It is important for researchers to bear this in mind before attempting to transfer even such a simple technology as the chopping and soaking method if success is to be ensured.
Substantial amounts of work have been done in S.E. Asia, during the past few years, on straw treatment with ammonia which is released from urea and/or urine. This line of work, which is strongly supported by the Australian-Asian Fibrous Agricultural Residues Research Network (AFAR), is being actively undertaken in Indonesia by Djajanegara, Mahyuddin and their team at the Research Institute for Animal Production in Bogor; in the Philippines by Castillo, Roxas and their team at UPLB; in Malaysia by Devendra and his colleagues at MARDI and Azman of University Pertanian Malaysia; in Thailand by Wanapat and his team at Khon Kaen University; by Cheva-Isarakul and his colleagues at Chiangmai University; and, by Promma and his colleagues in Department of Livestock Development. Also, this network includes Jayasuriya's and Ibrahim's teams in Sri Lanka and Saadhullah and his colleagues of Bangladesh Agricultural University. The effectiveness and practicability of straw treatment with urea looks very promising. Urea at the levels from 3 to 5 percent of straw, when applied in the form of a solution to the residue to bring the final moisture content to 50 percent and ensiling for 2–3 weeks, increases the dry matter digestibility of the straw by 10 to 12 percentage units. Livestock responses in terms of improved digestibility and dry matter intake of urea treated straw obtained by some of these workers are given in Table 7. It appears, consequently, that urea treatment of rice straw gives promising results in terms of improved feed intake, digestibility and offers potential applicability. The only problem that needs to be solved with this method is devising practical and cheap equipment, enabling us to give an enclosed environment for newly urea-applied straw to ensure the minimum escape of releasing ammonia throughout the treatment period. Dolberg et al (1981a), Ibrahim (1982) and Verma (1983) outlined various devices being made of indigenous materials which seemed to be relevant to small farm application in Bangladesh, Sri Lanka and India. Similar development has been seriously looked into in Thailand by Wanapat et al (1984). However, much more work needs to be done before the practical application in S.E. Asian small farms can be realized.
|Ambar and Djajanegara (1982) Rice straw sheep-nylon bag||1 kg fresh grass 200 g of 14%/CP concentrates/hd/d||% DMD at 24 hr|
|- 4% urea stored for 4 wk||-||60.0|
|Doblerg et al (1981) Rice straw-cattle||-||% increase in dig. DMI||%DMD|
|- 3% urea treated||-||33||51|
|- 5% urea treated||-||42||52|
|Jayasuriya (1982) Rice straw-Buffalo||g DMI/Wkg0.75 (straw)||%OMD|
|- untreated||concentrates (40% of diet)||69||31|
|- 4% urea treated||95||62|
|Djajanegara et al (1983) Rice straw-sheep||200 g groundnut cake/hd/d||g DMI/hd/d (straw)||% DDM|
|- 5% urea treated||246||37|
|Wanapat et al (1982a) Rice straw-cattle||g DMI/hd/d (straw)||% DMD|
|- 5% urea treated||-||95.2||51.5|
|- 5% urea treated||2 kg/hd/d cassava chip||75.7||47.7|
|Wanapat et al (1982 b) Rice straw-Buffaloes||g DMI/hd/d (straw)||%DMD|
|- 5% Urea treated||-||98.1||58.4|
|- 5% Urea treated||200 g cassava leaves/hd/d||88.7||58.5|
UTILIZATION OF OTHER CROP RESIDUES AND AGRO-INDUSTRIAL BY-PRODUCTS IN ANIMAL FEEDING
As has been mentioned previously, other crop residues and non-conventional agro-industrial by-products are rarely used in livestock feeding at small farm level in S.E. Asia. In his review, Castillo (1983) exclusively covered research works dealing with experiments aiming to incorporate these residues and by-products, which are available in S.E. Asia, into feeding systems. Examples of these are maize stover (Castillo et al, 1970 and Roxas et al, 1973), maize cob (Castillo et al 1957; Cocjin et al 1978; and Del Rosario et al 1981), cane tops (Palo et al, 1978), cane bagasse (Roxas et al, 1969) and many more. In Malaysia, works on utilization of palm oil by-products have been studied by scientists at University Pertanian Malaysia (Aznam, 1982) and at MARDI (Devendra, 1978). In Thailand, works in this line tried to utilize local crop residues, such as cassava leaves (Khajarern et al 1980; 1982; Wanapat et al 1982a; 1984; and Sriwatanasombat and Wanapat, 1984).
It is apparent therefore that a substantial amount of crop-residues and agro-industrial by-products in S.E. Asia are still left underutilized. More research efforts should be centered on these aspects. It has recently been proposed to establish an ASEAN network to make an assessment of the feed resources (agro-industrial by-products and non-conventional feed) in the ASEAN region. This network aims to assess, in quantitative and qualitative terms, the availability of these feed resources to produce a detailed feed resource inventory, establish priorities in the use of individual feeds for development of feeding systems, including year round feeding patterns in individual countries in order to ultimately stimulate increased productivity from the animal genetic resources.
CONCLUSIONS AND SUGGESTIONS ON RESEARCH PRIORITY
Among the crop residues and agro-industrial by-products available in S.E. Asia, by-products from rice, sugar-cane, cassava, maize, coconut and oil palm are of prime importance. Among them, less fibrous by-products are fully utilized, either as food, feed or export commodities. Only the fibrous residue from rice, namely rice straw, has been widely utilized in livestock feeding systems, although at an efficiency far below its optimum potential. Much more attention has been paid, in the last decade, to improving its feeding value in order to increase livestock productivity at small farm level. Chemical treatments of straw seem to attract the attention of most of the nutritionists in the region, although no treatment method has proved to be fully applicable at S.E. Asian small farm levels. Furthermore, there has not been any solid proof, economically, in comparing treated straw feeding to that with properly supplemented untreated straw. This, along with the development of suitable equipment needed for economical straw treatments, is still challenging the researchers.
Apart from rice straw, other fibrous crop residues and agro-industrial by-products received negligible attention from small farmers in S.E. Asia. Sporadic research on using these by-products as livestock feed is still far from enabling them to be on the practical feedstuff list. If serious and systematic research efforts are put into them they may play an important role as the supplements or even the substitute for rice straw in the small farm feeding systems in the future.
With all of these, it appears that the following areas need immediate attention by research workers in this field.
There is a need to assess, quantitatively and qualitatively, all crop residues and agro-industrial by-products that are actually available for feeding purpose on a year-round basis. Their feeding value needs to be established in order to be able to develop the year-round feeding strategies in each country and location. Questions still remain inadequately answered about what by-products are fed, quantities fed and seasonality of feeding by-products, and the relationship between site of production of bulky or high moisture by-products to where they are needed as feeds.
More information is needed on the effect of proper supplementation of straw-based rations on feed intake, digestibility and production. Supplementation should be done by way of small quantities of green forages locally available, less fibrous agro-industrial by-products, non-protein nitrogen and minerals. Nutritional studies should always be accompanied with economic and sociological evaluation in order to ensure the acceptability of small farmers in the region.
Crop residues other than rice straw should be upgraded. This is the next phase after the practical adaptation of urea-ammonia treated rice straw at the farm level is established. Other means of treatments, such as lime treatment and biological treatments also need to be looked into in order to enable small farmers to utilize the most economical by-product-based rations in their feeding system.
Development of straw and other crop residues feeding systems needs immediate study in order to be relevant to small farmers. A great deal of research has frequently been irrelevant for practical application. Here again, economists and social scientists can play a very important supporting role in the process of development.
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R Parra and A Escobar
Instituto de Producción Animal Facultad de Agronomia
Universidad Central de Venezuela, Maracay, Venezuela
Crop and animal production generates a range of fibrous materials which have traditionally been called “residues”. These have been classified as: crop residues, fibrous agro-industrial residues, urban fibrous residues and animal wastes. They all have aroused considerable interest as sources of feed, energy and/or fertilizers. This paper refers to the use of such residues in Tropical America (Central America, Caribbean and Northern South America). Tropical America cannot develop intensive ruminant production systems like those of developed temperate countries due to the low availability of cereal grains, oilseed meals and high quality roughages.
Fibrous residues will become more important in tropical countries and improved ways to utilize them as feed sources have to be developed. They are produced in large quantities, but there are important limitations for their use, such as their low nutritive value, low density and high moisture content, which impose severe technological and economic constraints.
Estimations are given of the gross production of fibrous residues in Tropical America compared with the estimated energy requirements of the ruminant population in that region.
Ways of utilizing agricultural residues are discussed along with their advantages and limitations. Brief consideration is given to different ways of improving their feeding value. Special attention is given to alkaline treatment (NaOH and NH4OH) and to some aspects related to the efficiency of the alkaline treatment, which have arisen in the work carried out by the authors.
It appears that from a biological standpoint, the limitations of many agricultural residues in animal feeding could be overcome. The main problems which remain are related to the technological and economic viability of their use. At present, crop, animal and agro-industrial operations are poorly integrated in many tropical countries, making difficult the incorporation of these feed resources into animal production on a large scale.
Animal production depends on plant production as shown in Figure 1. It could be demonstrated that the opposite is also true.
Crop and animal production generates a range of fibrous materials which have traditionally been called “residues”, perhaps due to the fact that they are not utilized and have therefore not been regarded as “resources”. These materials (FAR) have been classified according to their origin as: crop residues, fibrous agro-industrial residues, urban residues and animal wastes. Fibrous Agricultural Residues (FAR) have aroused considerable interest as possible sources of animal feed, energy and fertilizer. Such uses are not mutually exclusive: a logical sequence would be to use them first as animal feed, then use the excrement as a source of energy (biogas) and, finally, the biomass from the digestor could, or should, be applied as fertilizer to the crop land.
The present paper is devoted to the use of FAR as sources of feeds for ruminants, with special emphasis on the experiences which have been accumulated in Tropical America (Central America, including Caribbean countries, and northern South America).
Tropical America cannot develop intensive animal production systems, like those of developed temperate countries, based on feed resources such as cereal grains, oil-seed meals and high quality roughage from harvested forages (alfalfa, corn silage) or grass/legume pastures.
Table 1 shows the estimated amounts of cereal grains imported and the availability of protein meals for the region.
Sources of feedstuffs for animal production
Coarse grain imports are for both human and animal consumption. There is no available information on the proportion of grain and protein meal fed to ruminants, but it should be very low due to human and non-ruminant competition. In Venezuela, more than 95% of the formulated feeds (85% cereal grains and protein meals) are directed to poultry and pig feeding.
A comparison of reported values of dry matter digestibility of temperate and tropical grasses (Figure 2) indicates the lower average of tropical forages.
Figure 2. Range in digestibility of 312 tropical and 760 temperate grasses (McDowell, 1972). The mean difference in TDN between tropical and temperate grasses is about 15 units.
Developing countries, especially those in tropical regions cannot follow the conventional approach of intensifying animal production, as common in developed temperate countries. Fibrous agricultural residues (FAR) will become increasingly important in tropical countries and suitable strategies for their use will have to be developed.
These strategies will have to do with processing and supplementing FAR and development of ruminant production systems which will allow FAR to be used efficiently. Appropriate feeding strategies are required because of the many nutritional interactions, which exist within different FAR and between them and the conventional supplements which are available in tropical regions.
IMPORTANCE OF FAR AS ANIMAL FEEDSTUFFS
When the use of FAR as livestock feeds is proposed, two questions immediately arise: first, why is so much interest expressed in them and, second, why are these materials not being used fully at the moment? An attempt to answer these questions follows.
Interest in the use of FAR arises from their wide availability and from the possibility of using them to help solve the problems of seasonal feed shortages for livestock as well as to reduce pollution caused by certain forms of crop production (Escobar and Parra 1980). In Table 2, the mean dry matter yields per hectare are summarised for the different FAR considered. Besides residues from crops and agroindustry, urban refuse and animal excreta, have also been included as a type of FAR.
If the production of crop residues, agroindustrial residues, animal excreta, urban organic refuse and the unutilized portion of pastures is taken into account, an estimated 75–80% of man's effort in present-day agriculture is represented by residues. Thus, agricultural residues represent the chief product of modern agriculture. Obviously, such an enormous volume of material and the serious problems which arise if it is not utilized, demand urgent consideration. Otherwise, agriculture will be incapable of satisfying the needs of an increasing population.
There exists a series of reasons which explain the under-utilization of FAR. From Table 2, in which certain of their characteristics are shown, it is clear that most FAR have a low density and many of them also have a high water content. This puts heavy economic and technological restrictions on their use, limiting possibilities for transport and storage. This problem is accentuated by the fact that a large proportion of FAR are to be found in areas far away from the centres of animal production.
From the nutritional point of view, the feeding value of FAR is limited by the deficiencies of crude protein, minerals and vitamins. In addition, they are high in fibre, have high lignin and/or silicon contents, low digestibilities and low voluntary consumptions by the animal. Consequently, when they are included in conventional diets in high proportions, the digestibility of the ration and the animal response are generally reduced (Figure 3).
|Coarse grains (1)||Protein meals (2)|
|Tons × 103||Tons × 103|
(1) Coarse grains includes corn, sorghum, millet and mixed grain.
(2) Protein meals include various vegetable-oil meals and fish meals.
Adapted from Wheeler et al (1981)
|Water % (as fed)||Yield tonnes (DM/ha)||Crude protein % (% in DM)||Cell wall content % (% in DM)||ME (Mcal/kg)||Density (air) (dried) kg/m3|
|Corn, stover||20 – 45||4.0||5 – 7||70 – 80||1.2 – 1.6||50–100|
|Sorghum, stover||20 – 45||4.0||4 – 7||65 – 70||1.6 – 2.0||50–100|
|Rice, straw||30 – 60||4.0||3 – 4||65 – 70||1.2 – 1.5||50–100|
|Wheat, straw||15 – 45||2.5||2 – 6||75 – 80||1.3 – 1.8||50–100|
|Cotton, stubble||20 – 30||4.0||1.5–2.5||70 – 80||1.1 – 1.6||50–100|
|Peanut, straw||15 – 30||1.3||10 – 15||40 – 50||1.6 – 2.0||50–100|
|Sugarcane, tops||50 – 80||6.0||6 – 8||65 – 75||1.7 – 2.0||100–150|
|Banana, leaves||70 – 80||2.0||10 – 15||40 – 60||1.3 – 2.0||100–150|
|Banana, pseudo stem||90 – 95||10.0||1.8 – 3.5||35 – 40||2.7 – 2.9||100–150|
|Plantain, leaves||70 – 80||2.0||10 – 15||40 – 60||1.3 – 2.0||100–150|
|" pseudo stem||90 – 95||10.0||1.8 – 3.5||35 – 40||2.7 – 2.9||100–150|
|Cassava, tops||60 – 80||3.6||20 – 25||35 – 45||2.7 – 2.9||150–200|
|Sweet Potato, vines||60 – 70||4.0||12 – 18||40 – 50||2.4 – 2.7||100–150|
|Dry beans, straw||60 – 70||1.0||4 – 6||65 – 70||1.3 – 1.8||50–100|
|Soybean, straw||60 – 70||1.5||4 – 6||65 – 70||1.3 – 1.6||50–100|
|Corn, cob||15 – 25||0.5||2.5 – 3.5||80 – 90||1.3 – 1.7||150 – 200|
|Cotton seed, hull||15 – 25||0.3||4 – 5||85 – 90||0.9 – 1.3||150 – 200|
|Sunflower, head||15 – 25||2.5||8 – 11||25 – 30||2.4 – 2.7||150 – 200|
|Sugarcane, bagasse||46 – 52||9.8||0.5 – 2.4||85 – 90||0.7 – 0.9||120 – 170|
|Sugarcane, pith||15 – 50||2.8||0.5 – 2.5||85 – 90||0.8 – 1.1||120 – 170|
|Coffee, pulp||80 – 90||0.015||9 – 13||35 – 40||1.9 – 2.2||200 – 250|
|Coffee, bean hulls||10 – 20||0.006||2 – 3||75 – 85||0.9 – 1.1||50–100|
|Cocoa, pods||5 – 15||0.500||6 – 8||50 – 55||1.1 – 1.6||200–250|
|Sisal, pulp or bagasse||5 – 90||5.9||6 – 8||35 – 40||1.6 – 2.0||100–150|
|Fruits, canning waste||80 – 90||4 – 8||20 – 35||2.7 – 2.9||350–400|
|Tomato, pomace||80 – 90||15 – 20||35 – 45||2.0 – 2.2||150–200|
|Barley, brewer's grain||75 – 80||35 – 45*||23 – 28||60 – 65||1.9 – 2.1||180–220|
|Brewery, sludge||85 – 65||3 – 5*||18 – 20||25 – 46||0.6 – 1.1||750–850|
|Poultry, manure||50 – 70||1.3**||25 – 30||20 – 30||1.8 – 2.2||250–300|
|Pig, manure||65 – 85||1.0**||11 – 15||35 – 45||1.6 – 2.0||200–250|
|Cattle, manure||70 – 85||1.0**||9 – 14||55 – 70||1.1 – 1.8||100–150|
|Urban fibrous residues|
|Paper and others||10 – 20||0.3***||0.1 – 0.4||65 – 95||0.4 – 3.1||150–200|
* kg of DM/1000 litres of beer.
** kg of DM/100/kg of liveweight per day
*** Tonnes of DM/inhabitant per day
Effedt of the level of FAR (not treated) on digestibility and weight gain in lambs (• corn stover; o Rynchilintreum rosen; ð Sorghum stover; + corn cob; D bagasse pith) (from Parra and Renaud 1972; Goiri et al 1980; Tesoro 1979; Garcia et al 1980; Parra and Medina 1975)
USE OF FAR IN TROPICAL AMERICA
The estimated amounts of FAR produced yearly in Tropical America are shown in Table 3. As we consider the different sources of FAR it is obvious that we are dealing with a volume of residues which could potentially supply important quantities of nutrients.
The annual Metabolizable Energy (ME) requirements for the domestic ruminant population of Tropical America, estimated by using FAO (1982) populations of cattle, sheep, goats and buffaloes, and Winrock's estimates of annual ruminant ME requirements (Wheeler et al 1981) gives a value of 755086 × 106 Mcal of ME which is 16% lower than the ME accumulated in FAR, as shown in Table 3.
By using 10 to 30% of the ME accumulated in FAR (Table 3), 12 to 36% of the energy requirements of the ruminant population in tropical America would be supplied.
These simple calculations underline the importance of considering FAR as feed resources to be integrated in the ruminant production systems of the region.
There are important experiences in the use of FAR in ruminant feeding in different countries of the region. These range from the highly integrated crop-animal systems in the smaller Central American and Caribbean countries to the most extensive type of use of crop residues (corn, sorghum and wheat stover) in Mexican and Venezuelan ranching systems, including the summer feeding of alkali-treated bagasse to beef and dairy cattle in Cuba and the use of fibrous agro-industrial residues (corn cob, cotton seed hulls) and crop residues (corn stover) in feed-lot operations in Peru.
These experiences and the numerous research groups actively involved in evaluating FAR processing and utilization are not integrated in a cooperative approach. A coordination effort like those developed in Africa (African Research Network for Agricultural By-Products) and Asia-Oceania (Australian-Asian Fibrous Agricultural Residues Research Network) could prove to be of great help in Tropical America, stimulating the exchange of experiences and the development of cooperative projects.
|FAR||Volume (million tonnes)||ME (Mcal × 106)|
|Banana, Pseudo Stem||8.60||23908.0|
|Plantain, Pseudo Stem||7.10||14555.0|
|Sweet Potato, Vines||1.10||2837.4|
|Dry Beans, Straw||8.00||12412.9|
|Soy bean, Straw||13.45||19639.9|
|Cotton Seed, hull||0.92||1035.6|
|Coffee, bean hulls||0.03||68.3|
|Barley, Brewer's grain||1.10||2178.0|
|Urban Fibrous Residues|
|Paper + others||97.15||170270.7|
1 Estimates from:FAO Production Yearbook 1982 Vol 36.FAO Trade Yearbook 1982 Vol 36Values in Table 2 of this paper
WAYS OF UTILIZING RESIDUES
1. Crop residues may be used by the grazing animal, that is, by allowing the animal to collect its own food. It has been pointed out that these materials can contribute to solving the problems of feed shortages at critical times of the year, which are typical of tropical environments. Crop residues, which frequently become available during the dry season of the year, may be used to reduce stocking rates on pastures and be partly used in the feeding of ruminants. Grazing is undoubtedly the simplest and cheapest form of using FAR, but it does have certain limitations.
|Days after harvest||% green leaves||Biomass (tonnes DM/ha)||In vitro DM digestibility (%)|
One of the problems associated with the use of residues by grazing is that they rapidly lose their nutritional value as the season advances (Table 4). In an experiment carried out in Venezuela with sorghum stubble (Arias et al 1980), it was shown that animals gained weight rapidly at the start of the grazing period because they were able to select the green material present. However, once the stock had consumed this highly nutritive fraction, they entered a phase in which liveweight was only maintained since the intake of digestible energy and other nutrients did not permit production above maintenance. If grazing is continued, the animals finish with the same liveweight as they had when they entered the stubble (Figure 4).
On the other hand, it has been supposed that supplementation might permit more efficient utilization of these residues. In fact the same phenomenon occurs as is widely recognised in pasture management: that of substitution. When conventional supplements are fed, between about 45 and 80 g of residue are substituted by each 100 g supplement fed to the animal. As a consequence, the biological response obtained by supplementation differs widely from the expected result. The utilization of residues by the grazing animal can only be improved by supplementation to correct deficiencies of soluble nitrogen in the rumen and of minerals such as phosphorus and sulphur, and by the use of protein or energy supplements which escape rumen fermentation. This is an important area for further research.
An alternative which deserves consideration in a more general approach to the problem is that of the use of forage legumes. In the case of crops, the primary products of which are marketed and the stubbles left for grazing, consideration should be given to the possibility of consigning part of the crop area to a forage legume and then comparing the relative profitability of the combined crop and grazing system, with and without the legume.
Weight changes of cattle grazing sorghum stover
Effect of increasing levels of non-structural carbohudrates on digestibility of fibre fractions (from Parra and Medina 1975)
From the information presented above, it is clear that these materials are under-utilized by grazing stock (25 to 50% of the total available), due to the fall in their nutritive value after harvest and possibly also to limitations caused by the physical structure of the residues in the field.
2. In the case of the other materials, the agro-industrial and urban residues which cannot be used by grazing, the alternative is to collect, transport, process and finally feed them to the livestock. When high proportions of unproccessed FAR are included in the diet, a noticeable fall in digestibility is observed, as well as in voluntary intake and in animal response, as a consequence of their usually poor nutritive value (Figure 3). On the other hand, when low proportions of FAR are included in the ration in order to guarantee good animal performance, the fibrous fraction of the FAR suffers a marked reduction in the degree of fermentation, especially when the rest of the diet contains high proportions of non-structural carbohydrates (Figure 5). In this situation, the whole purpose of using the FAR as a source of energy for animal production is lost.
As was mentioned in the case of FAR used by grazing stock, in certain situations the use of strategic supplementation to overcome deficiencies of nitrogen in the rumen and/or to supply protein or energy which escape rumen fermentation, has led to the improvement in the utilization of rations based on fibrous materials.
In view of the above, the alternatives for using FAR as a feed resource are:
METHODS OF IMPROVING THE FEEDING VALUE OF FAR
For many years a wide range of methods for improving the feeding value of FAR has been under investigation. Among these, the following deserve mention:
Brief reference has already been made to the supplementation method and only physical and chemical methods will be discussed.
Physical methods: Grinding and/or pelleting leads to a reduction in particle size, and increase in surface area and density. Associated with these changes, an increase in voluntary intake, a reduction in digestibility and increase in the efficiency of the utilization of metabolizable energy are obtained. Beardsley (1963) concluded from a review of the literature that, on average, grinding led to an increase of 25% in voluntary intake, of 98% in daily liveweight gain and of 36% improvement in conversion efficiency.
Two limitations to the application of this method must be considered: (1) the high energy cost of grinding and pelleting, and (2) the fact that when the FAR are of very low nutritional value, grinding is not an effective method of improving their feeding value.
Chemical methods (alkaline hydrolysis): Among the many alkalis which have been evaluated, sodium hydroxide (NaOH) has proved the most efficient in improving the feeding value of FAR. In second place, treatment with ammonium hydroxide (NH4OH) has generated considerable interest because of its additional advantage of incorporating non-protein nitrogen in the feed. Another advantage of NH4OH compared with NaOH is that the former does not produce pollutants while the latter may cause problems of saline soils.
|Treated (T)||Nontreated (NT)||T - NT 100 NT|
|Voluntary intake: (kg/d)||1.3 ± 0.4||1.1 ± 0.4||28.2|
|Liveweight daily gain (g/d)||122.9 ± 39.2||57.8 ± 45.2||112.6|
|Feed conversion||10.9 ± 3.1||18.3 ± 4.5||-37.2|
|% FAR in diet||64.2 ± 14.3|
|Voluntary intake: (kg/d)||7.7 ± 2.4||6.3 ± 1.9||22.2|
|Average daily gain (kg/d)||0.7 ± 0.3||0.4 ± 0.3||75.0|
|Feed conversion||10.8 ± 3.3||18.0 ± 11.4||-40.0|
|% FAR in diet||64.4 ± 17.4|
|Treated (T)||Nontreated (NT)||T - NT 100 NT|
|Voluntary intake : (kg/d)||1.8 ± 0.6||151 ± 0.5||17.1|
|Average daily gain (g/d)||131.6 ± 32.6||74.2 ± 43.4||17.5|
|Feed conversion||14.5 ± 3.7||20.8 ± 1.8||-30.2|
|Voluntary intake: (kg/d)||8.6 ± 1.9||7.6 ± 2.4||14.7|
|Average daily gain (kg/d)||0.77 ± 0.2||0.90 ± 0.3||30.5|
|Feed conversion||19.9 ± 11||16.3 ± 3.3||-27.0|
Values from sheep and cattle are average of 15 and 16 trials respectively.
A detailed discussion of the effects on the chemical composition and nutritive value of FAR caused by treatment with alkalis has been given by Escobar and Parra (1981). These authors also discussed the possible mechanisms of action of the alkalis. Alkali treatment leads to the solution of hemicellulose and this is accompanied by a breakdown of the ester bonds which link lignin to the structural carbohydrates, as well as by an increase in the saturation point of the fibre (Tarkow and Feist 1969). This results in a more rapid and complete fermentation. Escobar and Parra (1981) also reviewed the effect of alkali treatment on the response (intake, weight gain and conversion efficiency) of animals fed rations including FAR. Tables 5 and 6 summarize results reported in the literature. In general, alkali treatment leads to an increase in consumption, as well as in liveweight gain and conversion efficiency. Comparatively, treatment with NaOH is more effective than treatment with NH4OH and sheep appear to respond better than cattle. This latter aspect will be considered in more detail later on. Positive responses to alkali-treated FAR have also been reported in milking cows (Escobar and Combellas 1981; Table 7), in goats and in rabbits.
|Level of cobs (%) and treatment|
|40 N||60 T||40 T||20 T||SE x|
|Milk production (kg/d)||9.5b||10.9b||12.5a||12.9a||0.37|
|Fat corrected milk (4%) (kg/d)||9.5(b)||11.1a||12.1a||10.9a||0.31|
|Solids not fat||8.5||8.6||8.6||8.6||0.08|
|Liveweight change (kg/d)||-0.21||-0.02||-0.02||0.17||0.132|
|Intake (kg DM/d)||6.40c||8.43b||10.29ab||11.30a||0.497|
Values with different superscripts in the same row are significantly different(P< 0.01)
Some aspects to be considered in the study of the efficiency of alkali treatments. Among the many factors which influence the efficiency of alkali treatments are the following: type of FAR, level and type of alkali, ration of water to FAR, treatment conditions (pressure, temperature), reaction time, degree of grinding of the FAR, level of FAR in the ration, level and type of supplementary feed.
It is not the purpose of the present paper to give a detailed description of each of these factors, but rather to mention some of the aspects which have arisen in the work carried out in our laboratory. It is hoped that a consideration of these may lead to a better understanding of alkali treatments and of the possibilities for using FAR in animal feeding.
3.1 As may be seen from Figure 6, a strong negative correlation exists between the initial quality of the FAR and the effectiveness of chemical treatment. However, despite the relatively high responses of poor quality materials to treatment, this does not mean that the values reached are satisfactory from the point of view of animal production.
Relationship between initial in vitro organic matter digestibility (IVOMD) due to NaOH treatment ((60 g NaOH/kg) (from Escobar 1981)
3.2 It is important to point out that not all the fraction which is made soluble by the alkali is digested, as was originally thought. When we apply the Lucas test (Lucas and Smart 1959) to our data, it shows that the availability of the fraction solubilized by the alkali treatment is less than the expected value: ca 100%. The value obtained for the true digestibility of the solubles in neutral detergent of the diets which contained FAR treated with alkali was 85%. If we assume a true digestibility of ca 100% for the original solubles in neutral detergent, we can estimate a true digestibility of 50–70% for the fraction solubilized by the alkali treatment (see Figure 7).
Figure 7: Lucas test (Lucas 1959) for neutral detergent solubles of diets based on corn cob treated with NaOH (from Escobar 1981)
Hogan and Weston (1971) also report a low digestibility of the original cellular content fraction and of the alkali solubilized fraction of wheat straw treated with NaOH, and suggested that the polyphenols liberated by the treatment may be involved. An alternative hypothesis is that the dissolved fraction may be made up of short xylan chains (oligomers) and other components of the hemicellulose fraction, all of them undigestible by mammalian digestive enzymes, with a very low retention time because they are associated with the liquid phase and thus escape rumen fermentation.
3.3 The greater digestibility of the treated FAR is associated with a higher fermentation rate. The fermentation rate of the cell wall is affected considerably more than the fermentation of the potentially digestible fraction of the cell wall. The fraction of the cell wall which is made digestible by the action of the alkali apparently shows a fermentative kinetic which is similar to that of the digestible fraction of the cell wall of untreated FAR (Table 8).
|% NaOH/kg DM|
|Total cell wall|
|Potentially digestible cell wall|
K: Fermentation rate in hours-1
r: Correlation coefficient
T1/2: Half-time of fermentation in hoursValues with different letters in the same row were significantlydifferent (P< 0.05)
The mean fermentation half-times (T 1/2) show the effect of NaOH on the fermentation process even more clearly. The T 1/2 of the potentially digestible cell wall shows a difference of only 6.5 hours between the extreme levels of the alkali treatments, the difference for the whole cell wall is approximately 74 hours. Both the milling process of the FAR and the high consumptions associated with increased intake of the NaOH treated FAR (Table 9) may produce an increased rate of passage of the solid and liquid phases in the rumen and this, added to the relatively slow rate of fermentation of the material, may cause a reduction in the extent of the digestion.
Milling increases the voluntary consumption of the FAR, and this may compensate for the detrimental effect on digestibility of the reduced particle size. Alkaline treatment may have an effect on the milled material, increasing, maintaining or decreasing the digestibility compared with that of the unprocessed residue. This will depend on the quantitative relationships between the increases in the fermentation rate and in the rate of passage through the digestive tract. If the rate of passage of the solid phase is very high, the fermentation time is reduced and the expected increase in the digestibility of the FAR treated with alkali will be very small. This is illustrated in Figure 8 where the relation between the fermentation time and the efficiency of the alkali treatment is demonstrated.
Relationship between increments in in vitro digestibility of cell wall/g of NaOH added per g of DM and time of in vitro fermentation with maize cobs (Escoabar et al 1984)
|g NaOH/kg maize cob|
|Rate of passage of fiber2||2.20||2.38||2.35||2.82||3.40|
Different letters in same line indicate significant differences (P 0.05)
1 Escobar et al (1984)
2 Klopfestein et al (1979)
|Level of NaOH (%)||In vitro/in %||vivo relationship SD||No. of determinations|
Berger et al (1979) showed that the digestibility of the cell wall of corn cobs collected from abomasum (after ruminal fermentation) rose with level of NaOH used to treat the cobs, suggesting an increase in the potentially digestible fraction which escapes rumen fermentation when intake rises. However, the importance of post-ruminal fermentation (in the caecum and colon) in these situations has not been evaluated.
The evidence presented provides a partial explanation of why the digestibilities of the FAR in vitro exceed the digestibilities in vivo when the material is treated with levels of NaOH in excess of 40 g/kg DM (Table 10). It appears, in summary, that as well as an increase in the fermentation rate, a rise in the rate of passage may also take place. Depending on the relationship of these two rates, digestibility will be increased, maintained or decreased with alkali treatment. From this follows the importance of the interaction between alkali treatment and particle size (milling), since it is known that a reduction in particle size leads to an increase in rate of passage. Thus, very small particle size may reduce the efficiency of the alkali treatment.
In connection with this aspect, it is interesting to consider the possible effect of high solids consumption which is associated with increasing levels of alkali (Table 9), on the turnover rate of the liquid phase (and of very small particles) in the rumen, and the effect which this latter may have on the energetic efficiency of the growth of rumen microflora (Harrison and McAllan, 1980).
3.4 The information in Tables 5 and 6 indicates that alkali treatment of fibrous materials produces a relatively greater response in sheep than in cattle. This observation fits with the findings of Parra (1978) in a comparison of different sized herbivores. Small herbivores have greater energy requirements and smaller digestive capacity per unit body weight which leads to a higher turnover rate of the digestive contents. It seems logical that small animals (such as sheep), when fed materials of slow degradability (FAR), should show a greater response than large animals (such as cattle) if the degradation rate of the materials is increased by alkali treatment (Table 8).
This is an important consideration since, in the majority of cases, small ruminants (such as sheep and goats) are used to evaluate the animal response obtained from the treatment of fibrous materials, but these are subsequently used commercially in larger animal (cattle) feeding.
3.5 It is worth emphasizing the relatively low efficiency with which the metabolizable energy obtained from alkali treated FAR appears to be used. For example, in an experiment in which cattle were fed treated maize cobs, a liveweight gain of 700 g/day was obtained (Escobar and Parra 1984b). However, it was estimated that the metabolizable energy consumed daily was 72 MJ/head and that a liveweight gain in the order of 1 kg/day was to have been expected.
It appears that from a biological standpoint, the limitations of FAR for use in animal feeding can, on the whole, be overcome. The problem which remains is the economic viability of their use. At the present time, crop, animal and agro-industrial operations are poorly integrated in many tropical countries and it is thus difficult for FAR to be incorporated into animal feeding on a large scale. Table 11 indicates some of the considerations which must be taken into account in a study of FAR as components of animal production systems. If the cost represented by contamination is included in the economic analysis, it is possible that their use as animal feeds may be justified. Frequently animals are considered only in terms of the meat and milk they produce. This ignores a series of other functions which they may perform, among which is that of agents of decontamination.
On the other hand, it has been pointed out on various occasions that there may be other competitive uses for FAR (food, energy and fertiliser). Our belief is that the various uses are complementary and that the animal can help in the recycling of the materials within the production system. A logical sequence in their utilization should be followed, first as animal feed, then various possibilities lie open for their use as energy sources (eg. biogas) and finally as fertilizer.
From this, arises a global consideration of the uses of FAR. A stronger integration of crop and animal production systems is required in the future, in which a wide range of combinations may exist. For example, integrated crops-pastures-livestock systems would minimize the problems of transport, collection and storage of the FAR. At the same time, an improved integration of agro-industrial and agricultural operations would reduce the serious problems of contamination caused by dumping the unwanted residues.
|Availability, annually and seasonally|
|Geographic distribution of production and use|
|Price of other feedstuffs|
|Availability of other feedstuffs|
|Need and cost of processing|
|Physico-chemical characteristics of FAR|
|Managerial capacity of farmer|
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