by
C.C. Balch
National Institute for Research in Dairying,
Shinfield, Reading, United Kingdom
| Summary | Résumé |
| The roughages to be considered are those so high in lignified cellulose that they are virtually without nutritive value for non-herbivorous animals; this would include materials supplying no more energy than poor-quality hay, less than 7.5 MJ metabolizable energy per kg dry matter. Poor-quality roughages can be divided into herbage from poor range grazings, the residues, straws, haulms, vines etc., remaining after removal of grain, fruits, tubers and roots from crop plants, and stover remaining after removal of sugar from sugarcane. The range grazings of the world appear to offer possibilities for improved utilization by ruminants. The typical present pattern of production from such areas is of declining live-weights throughout long dry periods interspersed by periods of rapid growth of the animals in the period of rains and plant growth. Supplementation with non-protein nitrogen and minerals can reduce dry-season losses. Provision of sufficient energy and other nutrients to support substantial growth at these times markedly depresses the intake of the poor herbage. Substantial improvements in the utilization of poor range grazing are unlikely to be achieved without improved agronomy; this must include the improvement of the quality of grazing and the cultivation of limited areas of crops for stock. The amounts of poor roughages as byproducts of crop production have been calculated. In the world the major straw crops are maize, wheat and rice; the developed countries produce 36% of the straws, countries with centrally-planned economies 35% and developing countries only 29%. The main straw yields of the developing countries are rice, maize, wheat and sorghum. It is calculated that the developing countries produced 42M tons of sugar cane tops and 56M tons of bagasse. The poor-quality roughages, including much range grazing, are low not only in available energy, but also, with few exceptions, in nitrogen and minerals. Within the groups of plants there are great variations in both the proportions of cellulose, hemicellulose and lignin and in the composition and properties of each of these fractions. It is important to stress that after removal of lignin the digestibility and nutritive value of the residues vary greatly between the different crops. Poor-quality roughages are not readily consumed, and their utilization is severely limited by the low voluntary intake of the animals and by their bulk, which makes transport costly per unit of nutritive value. Alone and untreated the poor roughages cannot sustain effective animal production, many being consumed in amounts insufficient even to support maintenance. Improvements in digestibility and intake of many coarse roughages can be effected by supplementary feeding to provide an optimum environment for the rumen microflora. The potential for utilizing the world's supply of poor roughage cannot be gauged merely from the total production of these materials in each region or country; it depends much more on the opportunities for creating situations in which ample supplies of roughage coincide with supplies of suitable supplementary feeds, with the opportunity to treat the roughage, with supplies of suitable animals and with possibilities for efficient management. Intake and utilization of poor roughages may be increased by reserving supplementary energy feeding for critical parts of the life cycle, such as the finishing period of beef cattle; little opportunity exists for extensive use of untreated poor-quality roughage in the diet of high-yielding dairy cows or rapidly growing beef cattle. The improvement of digestibility and voluntary intake resulting from NaOH treatment of cereal straws appear to be sufficient to allow treated straw to replace perhaps 15 or 20% of the diet of dairy and beef animals in typical semi-intensive systems. This could represent an important net saving of food consumable by man. It is necessary to establish the financial cost of this system as well as the energy cost, including the energy involved in NaOH production. Treatment of poor-quality roughages should be regarded as a potential means of reducing the amounts of concentrates required in cattle production; it cannot replace concentrates completely. | On envisage les fourrages dont la teneur en cellulose lignifiée est telle qu'ils sont pratiquement sans valeur nutritive pour les animaux non herbivores; l'on rangerait parmi ceux-ci des produits ne donnant pas plus d'énergie métabolisable par kg de matière sèche. Les fourrages grossiers peuvent se répartir entre l'herbe des parcours de médiocre qualité et les résidus, pailles, fanes, sarments, etc., de l'égrenage et de la récolte des fruits et des tubercules, les racines des plantes à racines, et la bagasse de la canne à sucre. L'utilisation des pâturages par les ruminants semble offrir des possibilités d'amélioration dans le monde entier. La conduite de l'élevage typique de ces régions est caracterisée actuellement par la baisse des poids vifs pendant de longues périodes de sécheresse interrompues par des périodes de croissance rapide des végétaux et des animaux pendant les pluies. En complétant l'alimentation animale avec de l'azote non protéique et des minéraux, l'on peut réduire les pertes imputables à la saison séche. L'apport d'aliments énergétiques et d'autres nutriments en quantités suffisantes pour favoriser une croissance substantielle pendant cette saison a pour effet de réduire notablement la ration prélevée sur des herbages médiocres. Vraisemblablement, l'utilisation des parcours médiores ne fera guère de progrès sans de meilleures méthodes agronomiques; celles-ci doivent comporter l'amélioration de la qualité des pâturages et la production de cultures destinées au cheptel sur des aires limitées. L'on a calculé les quantités de fourrages grossiers constitués par les sous-produits de la production végétale. Les principales plantes à paille cultivées dans le monde sont le maís, le blé et le riz; les pays développés produisent 36 pour cent et les pays en développement 29 pour cent seulement. Les gros rendements en paille obtenus dans les pays en développement sont ceux du riz, du maís, du blé et du sorgho. L'on estime que les pays en développement produisent 42 millions de tonnes de sommités de canne à sucre et 56 millions de tonnes de bagasse. Les fourrages grossiers de qualité médiocre, dont une bonne partie consiste en herbe pâturée sur les parcours, sont pauvres non seulement en énergie assimilable, mais aussi, à quelques exceptions près, en azote et en minéraux. Au sein des groupes de végétaux il existe de grandes variations, tant dans les proportions de cellulose, d'hémicellulose et de lignine que dans la composition et les propriétés de chacune de ces fractions. Après l'élimination de la lignine la digestibilité et la valeur nutritive des résidus présenteront une forte variation entre les différents végétaux. Les fourrages de qualité médiocre sont de consommation difficile, et leur utilisation se ressent fortement de leur faible taux d'absorption volontaire par les animaux, et aussi de leur masse, qui rend le transport coûteux par unité de valeur nutritive. Distribués seuls et non traités, les fourrages de qualité médiocre ne peuvent entretenir efficacement la production animale, et nombre d'entre eux sont consommés en quantités qui ne suffiraient même pas à assurer l'entretien du bétail. L'on peut apporter des améliorations à la digestibilité et au taux d'absorption de nombreux fourrages grossiers au moyen d'aliments de complément qui fournissent un environnement optimal à la microflore du rumen. On ne peut évaluer ce potentiel d'utilisation des disponibilités mondiales en fourrages grossiers simplement en se fondant sur la production totale de ces substances dans tel pays ou région; il dépend beaucoup plus de la possibilité de faire naître un concours de circonstances telles que d'amples disponsibilités en fourrage coïncident avec des approvisionnements adéquats en aliments de complément, ainsi qu'avec les moyens de traiter ces fourrages, la présence d'un cheptel appropriè et l'existence de conditions favourables à une conduite de l'élevage efficace. L'on peut accroître l'absorption et l'utilisation des fourrages grossiers de qualité médiocre en distribuant des aliments énergétiques de complément aux points critiques du cycle biologique, par exemple lors de la finition des bovins; il n'est guére possible d'utiliser massivement les fourrages grossiers de qualité médiocre non traités dans l'alimentation des vaches laitiéres à fort rendement ou des bovins à viande à croissance rapide. L'amélioration de la digestibilité et de l'absorption volontaire par le bétail résultant du traitement des pailles de céréales à l'hydroxyde de sodium semble suffisante pour permettre aux pailles traitées de servir de produits de remplacement à concurrence de 15 à 20 pour cent dans l'alimentation du cheptel laitier et des bovins à viande dans les systèmes d'élevage semi-intensif typiques. Cela pourrait représenter une substantielle économie nette d'aliments susceptibles d'être consommés par l'homme. Il importe d'établir le coût de ce système tant en termes financiers qu'en valeur énergétique, en tenant compte de l'énergie utilisée dans la production de l'hydroxyde de sodium. Le traitement des fourrages grossiers de qualité médiocre devrait être considéré potentiellement comme un moyen de réduire les quantités de concentrés qui sont nécessaires dans la production animale, sans toutefois qu'il permette de les remplacer entièrement. |
Resumen
Se propone tomar en consideración aquellos forrages duros que tienen tanta celulosa lignificada que virtualmente carecen de valor nutritivo para los animales no herbívoros. Se trata de forrajes que no producen más energía que el pasto seco de calidad inferior, o sea, menos de 7,5 MJ de energía metabolizable por kilogramo de sustancia seca.
Los forrajes duros de calidad inferior se pueden dividir en herbajes de montes de calidad inferior, residuos tales como paja, rastrojos, sarmientos, etc., que quedan después de las cosechas de cereales, frutas, tubérculos y raíces comestibles y los residuos de la caña.
En los montes de todo el mundo probablemente es posible lograr una mejor utilización del pasto por parte de los rumiantes. La forma típica de producción en los montes se caracteriza por una disminución del peso vivo durante los largos períodos de sequía y por un rápido aumento en la época de las lluvias y en el período de desarrollo vegetativo. Las pérdidas de peso de la época de sequía se pueden aminorar administrando suplementos de nitrógeno no proteínico y minerales. El suministro de suficientes alimentos energéticos y de otros nutrientes, a fin de lograr un aumento de peso sustancial durante la epoca de la sequía, hace disminuir notablemente la ingesta de herbajes de calidad interior. No es probable que se pueda lograr un aumento sustancial de la utilización del herbaje de calidad inferior sin una mejora agronómica, la que debe consistir en una evaluación de la calidad del herbaje y en el cultivo de forrajeras en una superficie limitada.
Se calculó la producción de aquellos forrajes duros de calidad inferior que son subproductos agrícolas. En todo el mundo las pajas producidas son principalmente de maíz, trigo y arroz. Los países desarrollados producen el 36 por ciento de las pajas, los de economía centralizada planificada, 35 por ciento y los paises en desarrollo sólo 29 por ciento. Las pajas que producen principalmente los países en desarrollo son de arroz, maíz, trigo y sorgo. Se calcula que los países en desarrollo produjeron 42 millones de toneladas de cogollos de caña de azúcar y 56 millones de toneladas de bagazo.
Los forrajes duros de calidad inferior, incluso los herbajes de muchos montes, no sólo tienen poca energía utilizable sino también, salvo raras excepciones, poco nitrógeno y minerales. Entre los grupos de plantas hay gran variación en cuanto a la proporción de celulosa, hemicelulosa y lignina que éstas contienen y en cuanto a su composición y a sus propiedades. Después de quitaries la lignina, varían mucho la digestibilidad y el valor nutritivo de las diferentes plantas cultivadas.
Como el ganado no consume fácilmente forrajes duros de calidad inferior, su utilización se ve muy limitada por el escaso volumen que los animales ingieren voluntariamente y porque son voluminosos y el costo de transporte por unidad de valor nutritivo, elevado.
Por sí solos y sin ningun tratamiento, forrajes duros de calidad inferior no pueden servir de base a una producción ganadera eficaz, porque la cantidad consumida es insuficiente incluso para mantener el peso.
Se puede aumentar la digestibilidad y la ingesta de muchos forrajes duros con suplementos capaces de crear un ambiente óptimo para la microflora del rumen. El potencial de utilización de los forrajes duros de calidad inferior producidos en todo el mundo no se puede evaluar limitándose a determinar la producción total de cada región o país, a depender mucho más de la posibilidad de crear situaciones en las que, junto con grandes disponibilidades de forrajes duros, haya también grandes disponibilidades de suplementos, posibilidades de tratamiento de los forrajes duros, ganado idóneo y posibilidades de manejo eficiente. La ingestión y la utilización de los forrajes duros de calidad inferior se puede acrecentar guardando suplementos energéticos para períodos críticos del cicio biológico tales como la etapa final de engorda del ganado vacuno de carne. Son escasas las posibilidades de utilización extensiva de forrajes duros de calidad inferior no tratados en la dieta de las vacas lecheras de alto rendimiento o del ganado vacuno de carne de crecimiento rápido. El aumento de la digestibilidad y de la ingesta voluntaria que se logran tratando la paja de cereales con NaOH, al parecer, es suficiente para lograr reemplazar con paja tratada del 15 al 20 por ciento de la dieta de los vacunos de leche y de carne en los sistemas semi-intensivos corrientes. Así se podrían economizar muchos alimentos de consumo humano. Es necesario determinar los costos financieros del sistema y los costos de la energía, incluida la necesaria para la producción del NaOH.
El tratamiento de los forrajes duros de calidad inferior se puede considerar como un medio potencial de reducir la cantidad de concentrados necesaria para la producción de vacunos, pero no para sustituir completamente los concentrados.
Part I of this book studies the various physical, chemical and biological methods by which the value of poor-quality roughages can be improved, how such improved materials can be incorporated into animal production systems, and whether this incorporation can be made to pay. The poor roughages that so often go to waste, are no new feed resource, but there is certainly a very urgent need for new thoughts on methods of utilizing them.
What is meant by poor quality
This discussion covers plant materials that are so high in fibre that they are virtually useless to non-herbivorous animals. It follows that only the ruminants, and possibly the horse, are able to utilize them. Our concern is to establish their value for ruminants and the extent to which this value can be improved by treatment or management, and to identify management practices and systems which promise to utilize roughages maximally. For this purpose, 'poor quality' includes those roughages which supply ruminants with no more energy than poor quality grass hay; their dry matter has a metabolizable energy content of 7.5 MJ or less per kg, a TDN of less than 50% and a starch equivalent of less than 29%.
The heterogenous materials that can be thus defined as poor roughages are all highly fibrous. Adapting from Van Soest and Robertson (1976), the dietary fibre can be assumed to be the insoluble structural matter of plants resistant to enzymes of animal origin. It is immediately evident that this category of feeds is entirely non-uniform in both the physical and chemical sense. Fibre is cellwall material consisting of cellulose, hemicellulose and lignin. Their chemistry will be described in detail later in this book; it must be emphasized here, however, that both the proportions of these fractions and their properties vary greatly depending on the source. Although delignification almost always raises digestibility by ruminants of cell wall constituents, there is great variation in the digestibility and nutritive value of the remaining material. There is a strong case for insisting that attempts to introduce chemical methods for the improvement of roughages should be supported by frequent laboratory and animal tests, including digestibility trials. It should not be assumed on the basis of known roughage sources that the nutritive value of a new roughage source will be improved to the same extent.
It is convenient to divide the vast range of poor-quality roughages into two main classes; range plants, including poor hays and browse, and straws, by which is meant the residue remaining after removal of the grain or seed from crop plants; various vines, haulms and straw from other crops, including root and tuber crops, can be conveniently grouped in this class. A third category, which includes residues left after plant materials have been subjected to industrial processes, will be discussed later in this book, but bagasse will be included here for comparative purposes. Sugarcane has been included in Part 1, however, on the basis of utilization of the whole plant and Dr. Donefer's paper discusses the potential for physical treatment of that crop.
Poor-quality grazing and browse
McDowell (1972) concluded that the natural grasslands of the humid, subhumid and semi-arid areas of Australia, Asia, Africa and Latin America consist principally of bunch-type grasses, with some fine-stemmed grasses but few if any legumes. The utilization of natural grasslands is determined by the seasonal distribution of herbage, caused by moisture availability and soil fertility. In many of the more arid regions it is accepted that browse may supplement the nutrients obtained from grazing.
Pattern of production and utilization
The vast range of plants and plant associations falling under this general heading creates a problem: it is very difficult to generalize and equally hazardous to extrapolate from specific instances. Without doubt the range grazings of the world, especially those in the arid, subtropical regions, have considerable potential for improved utilization.
McDowell (1972) has estimated (Table 1.1) the limitations that affect use of the world's land resources for arable agriculture and grazing; the output of all but 9% of the grazing area is limited by temperature, moisture or both. McDowell also estimated that the regions between 30°N and 30°S of the equator comprise 50% of the potential arable and approximately 52% of the non-arable area, whose grazing varies from desert grasses and shrubs to tall prairie grasses. He concluded that the N-S 30° area could contribute much more to feed supplies for livestock than it does at present. There is a need for statistics relating to the amount, type and potential of range grazings.
The typical pattern of production in range grazings consists of rapid growth during a wet period, rapid maturation of the herbage and long periods with mature material in which no further growth occurs. Matching this, the growth pattern of ruminants dependant on such herbage shows rapid growth coincident with the herbage growth, followed by a long period in which the animals typically lose weight. Conservation of herbage appears to be unusual in areas of range grazing and presents special problems in the hot humid tropics. Grass tends to be left as 'standing hay' to be consumed in the dry season.
Nutritive value of poor range grazing
The nutritive value of range pasture species, and indeed of planted tropical grasses, tends to be lower than that of temperature grasses. Digestibility of the new growth is high for a very short period and declines rapidly as the plant matures; the content of protein and other nutrients is low and may decline during long dry periods. In tropical and subtropical grasses the relationship between digestibility and voluntary intake is not close; low voluntary intake is a constant problem with widespread consequences on all aspects of grass utilization.
The utilization of poor grassland roughage is dependant on the action of the rumen microflora; the organisms concerned require, for optimum growth, certain levels of nitrogen and a range of minerals; shortages of any of which result in suboptimal digestibility and intake. Accordingly, it is often possible to improve both digestibility and intake by providing nitrogen or other nutrients that may be lacking. Whether this nitrogen should be given in the protein or non-protein form requires further study.
| Limitations | Potentially arable | Non-arable | Total | |
| Grazing | Other | |||
| Temperature | 820 | 940 | 2950 | 4710 |
| Moisture | 1300 | 1500 | 1360 | 4160 |
| Moisture & temperature | 550 | 920 | 1640 | 3110 |
| Not limited by temperature or moisture | 500 | 330 | 360 | 1190 |
| TOTAL | 3170 | 3690 | 6310 | 13170 |
Source: FAO data, summarized by McDowell, 1972.
It would, presumably, also be possible to improve the utilization of poor herbage by chemical or other treatment. For the purpose of this book it is probably safe to assume that the costs, and in some cases the impossibility, of collecting grassland herbage are likely to preclude such treatment.
Potential for improved utilization of poor range grazing
The utilization of the world's natural grasslands probably includes some of the least controlled and most unsystematic exploitation of a world resource. FAO has been struggling for many years to overcome the problems created by such practices as uncontrolled grazing (whether over-grazing or under-grazing), pasture destruction resulting from overstocking with goats and failure to utilize the herbage at its more nutritious stage.
The present distribution of the various species of domesticated ruminants is given in Table 1.2. Cattle are the most numerous and most evenly distributed species. Buffaloes and camels are largely confined to developing countries, while large numbers of both sheep and goats are found in the arid regions of Africa and Asia. The sheep is also an important utilizer of poor grazings in South America, Europe and Australia. In considering the potential for improving the utilization of poor range grazing it is very frequently necessary to decide whether improvements should involve replacing sheep and goats by cattle. If means of improving the utilization of range grazing are to be suggested, an indication must be given of the extent to which, with improved grazing management, improved utilization and improved pasture quality are compatible, and with which species of ruminant.
The management of poor range grazing is usually difficult: rough terrain unsuitable for machines and lack of water, fencing, fertilizers and shade are typical of the problems to be faced. Nevertheless, it would be unrealistic to suggest that nutritional technology can substantially improve the utilization of the world's poor-quality grazings without marked improvements in agronomy. In the history of agriculture the inevitable solution to the problem of poor herbage has been to grow something better. There is no reason for supposing that some other long-term solution will be found to the problems of poor range grazings.
| Species | World | Africa | N & C America | S.America | Asia | Europe | Oceania | USSR | Developed | Developing | Centrally planned economies |
| Cattle | 1178.9 | 148.1 | 190.0 | 207.3 | 352.6 | 133.8 | 40.8 | 106.3 | 297.2 | 675.5 | 206.2 |
| Buffaloes | 130.3 | 2.1 | - | 0.2 | 127.2 | 0.4 | - | 0.4 | 0.2 | 97.7 | 32.4 |
| Camels | 13.3 | 9.5 | - | - | 3,6 | - | - | 0.2 | - | 12.4 | 0.9 |
| Sheep | 1032.7 | 148.8 | 23.5 | 117.9 | 273.5 | 125.2 | 201.2 | 142.6 | 341.9 | 428.2 | 262.6 |
| Goats | 397.9 | 116.8 | 13.1 | 29.3 | 221.1 | 11.5 | 0.2 | 5.9 | 15.6 | 310.8 | 71.5 |
Source: FAO, 1974
A few precautions can, however, be taken to ensure that existing, unimproved materials are utilized to their maximum potential. This is no place to reiterate the principles of good grazing management, but a few key points deserve emphasis. First, it is obviously important to encourage systems of animal management that minimize the shortcomings of the feed supply, rather than to overload the feed supply by systems which necessitate a more nutritious diet. It should be accepted, for example, that poor herbages of low digestibility, or indeed straws, can play little part in the diet of even medium quality cows in the early months of lactation or of beef cattle in the fattening period. Such materials, especially if suitably supplemented with nitrogen and minerals, can be used for store periods at about the maintenance level, provided that growth is adequate at times of better pasture and that long rearing periods are acceptable.
In 1971 FAO organized a consultation on the value of non-protein nitrogen (NPN) for ruminants consuming poor herbages. It was reported (FAO, 1971) that the weight gains of cattle subsisting on poor-quality herbages are usually restricted by shortage of both energy and protein. In some instances small improvements in growth rates have been obtained with supplements of NPN alone: these result from the combined effects of raising digestibility and voluntary intake. Larger responses have been obtained with supplements providing energy and NPN, especially if supplies of minerals are adequate. If, however, substantial energy supplements are given, there will be reductions in the intake of the poor herbage.
The consultation concluded that NPN supplements can serve a useful purpose in reducing losses in weight during the dry season and in ensuring that beef cows are gaining in weight when mated. The meeting was impressed however by the small extent to which the cost of supplements was justified by increased financial returns.
A good example of how beef cattle raised on extensive systems, utilizing poor herbage, can be brought to marketable condition by a short period in a feed lot, was provided by the FAO Beef Industry Development project at Nakuru, Kenya and its subsequent expansion into a stratified beef industry (Squire and Creek, 1973). The authors stress that a scheme such as this, that passes profits back to the original cattle breeders, can provide an incentive for the gradual improvement of the extensive systems under which the cattle are reared.
The important principles demonstrated by the Nakuru project is that the potential of poor feeds may be best utilized by giving them, ideally with NPN and mineral supplements, at certain periods of the life cycle of the animal, and then changing to a better diet, containing no poor roughage, at other critical periods With this procedure, more value seems to be obtained from the poor feed than if the same weight of better feeds were distributed more evenly over the life cycle. Similarly, with milking cows, poorer feeds, if unavoidable, can be used in the rearing period, especially if it can be extended to three or more years. Work at Shinfield has emphasized that where nutrients are in short supply for dairy cows, the best diet should be reserved for the first three months of lactation and for late pregnancy, rather than spread more evenly over the lactation cycle (Broster, 1972).
Poor-quality roughages originating from crops
A vast range of crops are here involved, some cultivated worldwide, others of purely local occurence and importance. The by-products of crop production consist of stems in the form of straw, haulm, vine, etc., with a greater or lesser amount of leaf, glumes, cobs, pods and other residues from the seedbearing part of the plant. The amount of all these residues varies with the crop and with cultivating and harvesting methods.
Pattern of production
The amounts of cereal straws available in the various regions of the world have been calculated from the values for cereal grain production given in the FAO Production Yearbook 1974; it was assumed, following Owen (1976), that for wheat, rice, barley, rye and oats the weight of straw approximately equals the weight of grain. For maize, millet and sorghum it was assumed that the straw or stover approximates to twice the weight of grain. The resulting estimates are given in Table 1.3.
These estimates do not include cereals grown for cutting green or as whole crop hay or silage; such products would be expected in general to have a higher quality than the roughages now under consideration; they do nevertheless represent a very important source of roughage.
The estimates also exclude other residues of grain crops: chaff, glumes, awns, cobs, etc., which may or may not become available as feeding stuffs depending on the method of harvesting and threshing, in the world, the estimates indicate, maize, wheat and paddy rice are the major straw crops. As a whole, straw production is divided fairly evenly among the developed and developing countries and the countries with centrally-planned economies.
| Crop | World | Africa | N & C America | South America | Asia | Europe | Oceania | USSR | Developed | Developing | Centrally planned economies | ||||
| Wheat1 | 360.2 | (21) | 8.5 | 65.8 | 10.2 | 90.0 | 90.5 | 11.4 | 83.8 | 139.2 | (39) | 72.0 | (20) | 149.1 | (41) |
| Paddy rice1 | 323.2 | (19) | 7.6 | 6.9 | 10.2 | 294.3 | 1.9 | .4 | 1.9 | 23.2 | (7) | 174.9 | (54) | 125.1 | (39) |
| Barley1 | 170.9 | (10) | 4.8 | 15.6 | 1.0 | 31.7 | 60.5 | 3.1 | 54.2 | 65.9 | (39) | 16.6 | (10) | 88.3 | (51) |
| Maize2 | 586.0 | (35) | 53.5 | 261.0 | 58.2 | 100.3 | 88.2 | .5 | 24.3 | 317.3 | (54) | 142.8 | (24) | 125.9 | (22) |
| Rye1 | 32.6 | (2) | <.1 | 1.0 | .3 | .6 | 15.5 | <.1 | 15.2 | 5.8 | (18) | .9 | (3) | 25.9 | (79) |
| Oats1 | 51.2 | (3) | .2 | 13.0 | .5 | 3.3 | 17.8 | 1.1 | 15.3 | 26.9 | (52) | 1.0 | (2) | 23.3 | (46) |
| Millet2 | 92.4 | (5) | 18.1 | .4 | .5 | 67.4 | .1 | .1 | 5.8 | .1 | (0) | 38.6 | (42) | 53.7 | (58) |
| Sorghum2 | 93.8 | (5) | 18.5 | 38.0 | 14.6 | 19.3 | .9 | 2.2 | .2 | 36.3 | (39) | 57.1 | (61) | .4 | (0) |
| Total cereal straw | 1710.3 | 111.2 | 401.7 | 95.5 | 606.9 | 275.4 | 18.8 | 200.7 | 614.7 | 503.9 | 591.7 | ||||
| (100) | (6) | (24) | (6) | (35) | (16) | (1) | (12) | (36) | (29) | (35) | |||||
| (million metric tons dry matter) | |||||||||||||||
| Sugarcane | |||||||||||||||
Tops3 | 49.9 | 4.0 | 12.0 | 12.2 | 19.9 | - | 1.7 | - | 4.9 | (10) | 41.9 | (84) | 3.1 | (6) | |
Bagasse4 | 66.5 | 5.4 | 16.0 | 16.3 | 26.6 | - | 2.3 | - | 6.5 | (10) | 55.9 | (84) | 4.1 | (6) | |
1 Assuming straw:grain ratio of 1:1 (Owen, 1976)
2 Assuming straw:grain ratio of 2:1 (Owen, 1976)
3 Assuming tops:cane ratio of 1:4 (Owen, 1976)
4 Assuming bagasse:cane ratio of 1:5 (Owen, 1976)
Values in brackets show percentages of world totals.
Basis: FAO Production Yearbook 1974 values for production of individual crops.
The distribution of the different crop species varies greatly. The developing countries provide 61% of the sorghum, 54% of the rice and 42% of the millet straws, but only 24% of the maize stover and 20% of the wheat straw. It is worthy of note that only 6% of the world's straw is produced in Africa; four times as much is produced in North and Central America, while the major straw-producing continent is Asia.
The main straw yields of the developing countries are rice, maize, wheat and sorghum.
Estimates of the production of sugarcane tops and bagasse are also given in Table 1.3. They are mainly produced in developing countries; the total production are equivalent to 8% of the cereal straws on a dry matter basis.
There appear to be no estimates of the potential production of roughage in the form of by-products from other crops. In Table 1.4 are listed the 1974 productions (FAO, 1974) of roots and tubers, pulses, soybeans and groundnuts; there are however a number of less important crops that may be locally important as producers of roughage. From the table it is reasonably easy to calculate the relative production in the various regions of any by-products edible by ruminants. For some crops, e.g., potatoes remaining in the ground after the death of the haulm, there is virtually no by-product roughage.
Nutritive value of poor-quality roughage from crops
Some examples of values for the composition and digestibility of the major roughages in this category are given in Tables 1.5, 1.6, 1.7 and 1.8; the values for British straws and chaffs in Table 1.8 have been included to show metabolizable energy values.
With the exception of a small number of feeds, such as pea and sweet potato vines, cassava leaves and possibly groundnut haulms, the by-products of the crops listed are of very low nutritive value, The high ligno-cellulose contents are reflected by the high levels of relatively indigestible crude fibre, acid-detergent film and cell walls. Protein levels are low and digestible protein values extremely low. In most instances the Ca and P values are also low compared to better quality roughages. Lucerne hay is included for comparison.
A further factor that severely limits the usefulness of most of the poor feeds under consideration is voluntary intake. Whether offered alone or in combination, most of them are unpalatable, and their voluntary intake by ruminants, even when very hungry, is limited. This appears to be due both to the heavy work of chewing during eating and ruminating, required to produce particles small enough for passage from the reticulo-rumen and, in the case of feeds fed alone, to the low level of nitrogen and other nutrients in the feed, that limits the rate of breakdown by the rumen micro-organisms and may lead to deficiency symptoms, one of which is depressed appetite, in the host animal.
| Crop | World | Developed countries | Developing countries | Centrally-planned economies |
| Roots and tubers | 1559.9 | 81.7 | 169.7 | 308.5 |
| Pulses | 244.1 | 3.9 | 22.0 | 18.2 |
| Soybeans | 56.8 | 34.1 | 9.8 | 12.9 |
| Groundnuts in shell | 17.6 | 2.4 | 12.4 | 2.8 |
1 Potatoes, 52%; sweet potatoes, 24%; cassava, 19%; yam, 3%.
2 Dry beans, 26%; broad beans, 12%; peas, 26%.
Source: FAO, 1974.
| Roughage | Total digestible nutrients | Crude fibre | Digestible crude protein | Ca | P | K |
| Wheat straw | 44 | 40 | 0.3 | 0.23 | 0.08 | 0.85 |
| Rice straw | 45 | 36 | 0.6 | 0.21 | 0.08 | 1.32 |
| Barley straw | 47 | 42 | 0.8 | 0.36 | 0.12 | 1.47 |
| Maize straw | 57 | 34 | 2.3 | 0.32 | 0.06 | 0.50 |
| Rye straw | 45 | 42 | 0 | 0.28 | 0.10 | 0.97 |
| Oat straw | 50 | 40 | 0.8 | 0.21 | 0.11 | 1.51 |
| Millet straw | 47 | 42 | 1.7 | 0.09 | - | 1.60 |
| Field bean straw | 51 | 45 | 3.4 | 1.87 | 0.15 | 1.14 |
| Pea vines | 47 | 37 | 3.5 | - | 0.11 | 1.19 |
| Soybean straw | 43 | 46 | 1.4 | - | 0.14 | 0.70 |
| Lucerne hay, fair1 | 56 | 33 | 9.0 | 1.25 | 0.20 | 1.97 |
| Grass hay, good1 | 58 | 35 | 3.9 | 0.54 | 0.24 | 1.34 |
Source: Morrison, 1947
| Roughage | Total digestible nutrients | Crude protein | Crude fibre | Acid-detergent fibre | Cell wall |
| Barley straw | 47 | 5 | 42 | 59 | 80 |
| Maize bran | 83 | 11 | 14 | 16 | 60 |
| Maize cobs | 47 | 2 | 35 | 39 | 89 |
| Maize stover | 58 | 7 | 34 | 39 | 67 |
| Cottonseed hulls | 33 | 4 | 50 | 71 | 90 |
| Oat hulls | 36 | 4 | 32 | 42 | 78 |
| Oat straw | 50 | 4 | 40 | 47 | 70 |
| Rice hulls | 11 | 3 | 45 | 72 | 82 |
| Rice straw | 46 | 4 | 36 | 49 | 64 |
| Soybean hulls | 80 | 13 | 40 | 46 | 67 |
| Soybean straw | 43 | 4 | 39 | 44 | 58 |
| Wheat straw | 44 | 3 | 41 | 54 | 85 |
| Lucerne hay1 | 57 | 17 | 32 | 40 | 52 |
Source: Van Soest, 1973
| Roughage | Total digestible nutrients | Crude protein | Crude fibre |
| Sugarcane tops | 59–66 | 6 | 33 |
| Sugarcane bagasse | 45 | 1–2 | 45–50 |
| Groundnut haulm | 69 | 10 | 21 |
Source: Göhl, 1975
| Roughage | Metabolizable energy (MJ/kg DM) | Digestible crude protein (g/kg DM) | Crude fibre (g/kg DM) |
| Barley straw, spring | 7.3 | 9 | 394 |
| Barley straw, winter | 5.8 | 8 | 488 |
| Bean straw (including pods) | 7.4 | 26 | 501 |
| Buckwheat straw | 6.6 | 27 | 455 |
| Clover straw, red | 5.6 | 48 | 531 |
| Maize straw | 7.3 | 20 | 461 |
| Oat straw, spring | 6.7 | 11 | 394 |
| Oat straw, winter | 6.8 | 9 | 402 |
| Pea straw | 6.5 | 50 | 410 |
| Rape straw | 6.5 | 21 | 450 |
| Rye straw, spring | 6.2 | 7 | 429 |
| Rye straw, winter | 6.3 | 7 | 465 |
| Soybean straw | 7.5 | 44 | 311 |
| Tare or vetch straw | 6.3 | 48 | 472 |
| Wheat straw, spring | 5.6 | 1 | 417 |
| Wheat straw, winter | 5.7 | 1 | 426 |
| Linseed chaff | 5.0 | 16 | 460 |
| Lupin pods | 7.4 | 39 | 334 |
| Millet chaff and husks | 5.2 | 19 | 464 |
| Oast chaff, spring | 6.4 | 26 | 265 |
| Rice husks | 2.5 | 5 | 421 |
| Rye chaff | 5.8 | 13 | 515 |
| Soybean pods | 8.6 | 30 | 340 |
| Wheat chaff | 5.9 | 13 | 322 |
Source: MAFF, 1975
Using the predictions and values given in Table 1.8, an attempt has been made to group the major straws into classes according to the concentration of metabolizable energy (ME). The predictions of probable intake for each of these classes, in Table 1.9, are based on the probable voluntary intake of more nutritious diets at lower ME concentrations in direct proportion to the fail in intake. Comparison with a few available experimental results suggests that this rudimentary procedure is acceptable for the purpose. At any one energy concentration a slightly lower proportion of maintenance will be provided at ad lib consumption, for animals of weights less than 300 kg or above 500 kg. If nitrogen and minerals are lacking, intakes are likely to be less than the ranges indicated in Table 1.8.
Although approximate, calculations of the kind leading to the values in Table 1.9 demonstrate that where poor roughages are expected to provide a maximum contribution to cattle diets, much benefit might result from the adoption of plant varieties, cultural methods, harvesting dates and any other procedures likely to lead to more digestible straw. Selection of a spring barly straw of 7.3 MJ/kg DM in preference to a winter barley straw of 5.8 MJ/kg DM could make it possible to obtain full maintenance from straw rather than 0.6 or 0.7 maintenance.
The increase in utilization of poor-quality roughages fed ad lib, resulting from improvements in digestibility, is proportionately much greater than that improvement.
Finally it must be noted that as a class the straws have the disadvantage of being extremely bulky, making the cost of transporting straw high per unit of nutritive value. One of the advantages of treatment processes that involve fine chopping or grinding is to reduce the bulk of the material and thereby to facilitate its transport in the pelleted form.
Feeds Information
Mean values of the kind given in Tables 1.5, 1.6, 1.7 and 1.8 are useful for general discussions of nutritive value and feed utilization. Detailed planning of feeding systems requires information more directly related to the feeds available in the region. For some of the less widespread crops and grazed species information is scarce. Göhi (1975) has provided short summaries of factual information about a very large number of feeds and tables of data on their composition and nutritive value. The good reception accorded to this publication has encouraged those who are developing the international Network of Feeds Information Centres (INFIC), a project under FAO leadership, for worldwide coordination in the computerized collection of factual information and numerical data about all types of feedingstuffs. Most of the difficulties have now been overcome, and the Centres in Utah and Stuttgart should shortly provide, from a single data base, printouts of sets of data covering, for example, a single feed, a group of feeds, or the feeds of a region. A major problem, the construction of an adequate set of feed names and descriptions, has now been ironed out, and output can be printed in English, French, Spanish, German or Portuguese, as required. A data bank of this kind can be extremely useful to workers engaged in attempts to improve the utilization of the world's feed resources; the INFIC project merits endorsement, and producers of suitable data and information should be encouraged to make their output available to the network.
| Straw type | ME concentration (MJ/kg DM) | Probable intake of energy (ME % of maintenance) |
| Winter barley, clover, wheat | 5.6 – 6.0 | 0.5 – 0.8 |
| Pea, rape, rye, tare or vetch | 6.1 – 6.5 | 0.7 – 0.9 |
| Buckwheat, oats | 6.6 –7.0 | 0.8 – 1.0 |
| Spring barley, maize, soybean | 7.1 – 7.5 | 1.0 – 1.2 |
Derived from MAFF, 1975
Potential for improved utilization of roughages derived from crops
Traditionally, straws have largely been put to uses such as bedding and thatch, other than as feeds. Their use in ruminant feeding has been limited to acting as “fillers” rather than as essential sources of nutrients. It would be unrealistic to suppose that, even with treatment, means will suddenly become available to convert straws into the major feeds of effective animal production systems. It is more logical to examine the opportunities for increasing the use made of straws in existing systems. The question is: Could greater use be made of straws, in the natural state or after treatment, in extensive, intensive or intermediate systems of cattle management, and how great could be the resulting saving in cereals?
The potential for increased use of untreated coarse roughages is limited. There may be opportunities in more extensive animal production systems for these materials to play a useful role in reducing weight losses in times of pasture shortage. In the U.K., during the exceptionally dry summers of 1975 and 1976, much barley straw was given to grazing beef cattle and dairy heifers, and indeed as a source of fibre and bulk to milking cows receiving concentrates.
As even the better straws cannot be expected to contribute more than maintenance, it is necessary to decide, in each particular extensive system, whether straw would contribute most if supplemented by other feeds throughout the growing period or if it were reserved for “store” periods, the better feeds being used for critical parts of the growing period of the animal. In any system making extensive use of straw, it is important to ensure that adequate levels of nitrogen and minerals are provided in some form of supplement, to ensure optimal digestion of the straw in the reticulo-rumen, as well as optimal intake.
The scheme of practical allowances for cattle currently in use in the U.K. (MAFF, 1975) suggests that the minimum ME concentration for beef cattle diets to support 0.5 kg gain/day will vary from 9.8 MJ/kg DM for animals of 100 kg, to 7.5 MJ/kg DM for animals of 300 to 350 kg, rising to 8.1 MJ for animals of 600 kg.
This encourages the hope that diets containing fairly substantial proportions of coarse roughage can be used where such modest gains would suffice; the possibilities would clearly be greatest for better quality samples of straw and for treated straws, and in the middle part of the rearing period. It is essential, however, that potential feeding systems based on increased use of poorer feeds be tested under local conditions before wide application is attempted.
In reporting their investigations into the value of poor-quality roughages, Smith and Broster (1976) emphasized the need to avoid preconceived ideas on the limitations of straws; they demonstrated how the potential of these materials can be overcome by improved technical knowledge and judicious supplementation and food preparation. They were especially concerned with dietary protein, and their experiments suggest that in growing heifers the response to added protein is greater with high-fibre diets (containing 56% barley straw) than with diets containing 35% barley straw. With diets high in straw the daily response was 223 g extra live weight from 200 g crude protein; with low-fibre diets the response was 58 g extra gain from the same protein supplement. The correct ratio of roughage to concentrates depends on the class of stock and the desired level of production, coupled with the quality of the roughage and the composition of the concentrate portion of the diet. Any process that will increase appetite or nutritive value, or both, will allow a widening of this ratio or permit a higher output from the same ratio (Smith and Broster, 1976). It is very important to know whether the responses to nitrogen are greater with protein than with NPN.
Potential for treated roughages in existing cattle production systems
What are the opportunities for utilizing treated roughages as a means of reducing the amounts of more expensive feed currently used in intensive and semi-intensive methods of keeping beef and dairy cattle? Substantial amounts of concentrates are used for these purposes in most of the main beef and milk-producing countries. Since these also tend to be the main areas of cereal straw production, the possibility is encouraging, although it must be expected that, as in a country such as the United States, great distances may separate the main grain-producing and milk-producing districts.
In the United Kingdom, the firm of BOCM Silcock has recently made available results of experiments with ground barley straw treated with 5 to 6% NaOH and extruded as pellets. This treatment improved the digestibility of the dietary energy from 35% to 50%. The results suggest (Wilson, 1976) that inclusion of up to 30% treated straw in complete diets has not depressed production of milk or beef; inclusions of about 15% are however being recommended at this stage for practical feeding; 20% would seem feasible in many situations. One plant has been treating 25 000 tons annually for two years and two further plants are to be built in other straw-producing areas of the U.K. From digestibility trials, with goats, the treatment is claimed to give a product with an average ME content of 8.9 MJ/kg DM. The long-term value of this process and of alternative treatment processes will depend on many factors, including financial costs and energy costs, which must include the cost of energy involved in NaOH production.
The potential for using treatment processes must depend markedly on the occurrence of situations in which ample supplies of roughage coincide with supplies of suitable supplementary feeds, with the opportunity to treat the roughage, with supplies of suitable animals and with possibilities for efficient management. Determinations on these questions would be useful to those who must assess the potential for treat ment processes in developing countries.
Owen (1976) calculated that in theory alkali treatment which raised mean ME from 6.6 to 9.2 MJ/kg DM would provide, if applied to all the cereal straws produced, from 15% (South America) to 158% (North and Central America) of the maintenance requirements of the cattle population of the various regions; the values for Africa were 22.5% and for Europe 86.9%. Nevertheless, in view of the tremendous problems that would be involved in arranging for, say, 10% of the straw in a developing country to be treated and utilized, it is evident that the importance of the increase in nutrients that can be expected from chemical treatment should not be exaggerated.
References
Broster, W.H. (1972). Effect on milk yield of the cow of the level of feeding during lactation. Dairy Sci. Abstr., 34, 265.
FAO (1971). Ad hoc Consultation on the value of non-protein nitrogen for ruminants consuming poor herbages. FAO Meeting Report AGA: 1971/4. FAO, Rome.
FAO (1974. Production Yearbook 1974. FAO, Rome.
Göhl, B. (1975) Tropical feeds. FAO, Rome.
McDowell, R.E. (1972). Improvement of livestock production in warm climates. San Francisco, Freeman & Co.
MAFF (1975). Energy allowances and feeding systems for ruminants. Min.Agric.Fish & Fd, Tech.Bull. No. 33.
Morrison (1947). Feeds and feeding. 21st edn. Ithaca, N,Y., Morrison Publishing Co.
Owen, E. (1976). Farm wastes: (a) Straw and other fibrous materials in human food chains and nutrient cycles. (Duckham, A.N., Jones, J.G.W. & Roberts, E.H., editors). Amsterdam, North Holland Publishing Co.
Smith, T. & Broster, W.H. (1976). Wld Rev. Anim.Prod. In press
Squire, H.A. & Creek, M.J. (1973). Custom feeding of cattle: a proposal for a standardized package approach to project formulation. Wld Anim. Rev. No. 8, 8.
Van Soest, P.J. (1973). Revised estimates of the net energy value. Proc. Cornell Nutr. Conf. 1973, p.11.
Van Soest, P.J. & Robertson, J.B. (1976). Proc. Nutr. Soc. Canada. In press
Wilson, P.N. (1976). Unpublished
by
E. Donefer
Department of Animal Science, MacDonald Campus of McGill University,
Ste Anne de Bellevue, Quebec, Canada
| Summary | Résumé |
| Limiting factors in the utilization of poor-quality roughages as productive feed are related both to their low digestibility and low voluntary intake. Although grinding usually results in an increased voluntary intake, digestibility is either not affected or may actually be reduced. Ground poor-quality roughages (straw, wood) have been successfully used to replace a major portion of the forage fraction of ruminant ration, but the levels of productive performance obtained with these rations depend on their content of energy feed such as cereal grains. This therefore limits application in areas deficient in food grains. Other physical treatments such as vibratory or ball milling and irradiation, shown to be very effective in increasing poor-quality roughage digestibility in vitro offer little practical value application because of excessive treatment costs. Since 1970, many workers have investigated the treatment of poor-quality roughages with high pressure/high temperature saturated steam. In vitro digestibilities of wood, straw and sugarcane bagasse have been markedly increased when temperatures have been used in excess of 160°C (requiring total steam pressures in excess of 6 kg/cm2). The treatment process (232° C at a pressure of 28 kg/cm2) developed by the U.S. Department of Agriculture, has been the most extensively tested both in vitro and in vivo with a wide range of roughages; animals fed these treated materials performed poorly (as compared to in vitro results), thus limiting the applicability of this relatively expensive treatment. Conflicting results are available when high pressure/high temperature treatments have been used in combination with alkali treatments, with additive effects only observed in some cases. The mechanism of action of high pressure/high temperature treatments appears related to the delignification action of organic acids derived from liberated acetyl groups from the ligno-cellulose structure. Alkali addition under these conditions could thus be counterproductive as some neutralization would take place. In summary while various physical methods have been shown to be effective in increasing digestibility of poor-quality roughages under laboratory conditions, this has not been verified in limited feeding trials where these feeds constitute the major portion of the ration. Because of the equipment and investment necessary these treatments presently appear unfeasible at farm levels and questionable at commercial levels. | Les facteurs limitant l'utilisation des fourrages pauvres comme aliments productifs sont leurs faibles digestibilité et ingestibilité. Bien que le broyage résulte d'habitude en une augmentation de leur ingestibilité, un tel traitement non seulement n'en améliore pas la digestibilité mais peut au contraire la réduire. Des fourrages de qualité médiocre (foin, bois) broyés ont remplacé avec succès unr majeure partie de la fraction fibreuse de la ration alimentaire des ruminants, mais les performances animales obtenues avec de telles rations dépendent de leur contenu en aliments énergétiques comme les céréales. Ceci freine donc l'application de cette pratique dans les régions pauvres en céréales. D'autres traitements physiques comme le broyage par vibration ou par billes et l'irradiation, se sont montrées efficaces dans l'amélioration de la digestibilité des fourrages de qualité inférieure en laboratoire, mais offrent peu de débouchés pratiques en raison des coûts excessifs du
traitement. Depuis 1970 de nombreux chercheurs ont enquèté sur le traitement des fourrages de qualité inférieure par l'application de vapeur saturée à la haute température combinée à une pression élevée. Les digestibilités “in vitro” de bois, foin, bagasse, ont été nettement améliorées par des températures excédant 160°C (impliquant une pression de vapeur totale supérieure à 6 kg/cm2). Le procédé (232°c à une pression de 28 kg/cm2) mis au point par le Département d'Agriculture des Etats-Unis à été de loin le plus testé, aussi bien “in vitro” que “in vivo” avec une grande variété de fourrages, toutefois les performances réalisés par les animaux alimentés avec ces produits ont été médiocres en comparaison avec les résultats obtenus “in vitro”; cela limite donc l'application pratique de ce traitement relativement onéreux. Des résultats contradictoires ont été obtenus en combinant des traitements de haute pression - haute température avec des traitements chimiques (alcalis); des effets additifs ne se produisant que dans un nombre de cas infime. Le mécanisme d'action des traitements haute pression - haute température apparaìt relié à l'action digestive (délignification) d'acides organiques dérivés de groupes acétyliques libérés de la structure lignocellulolytique. L'addition d'alcalis dans de telles conditions pourrait donc ètre antiproductive puisqu'une certaine neutralisation interviendrait. En résumé, bien que de nombreuses méthodes physiques se soient avérées capables d'augmenter la digestibilité de fourrages pauvres en laboratoire, cela n'a jamais été vérifié, dans les essais alimentaires restreints, dans les régions ou ces ingrédients constituent la majeure partie de la ration alimentaire. En raison du capital et de l'équipment nécessaires ces traitements apparaissent aujourd'hui comme peu rentable au niveau des exploitations agricoles et douteux à un niveau commercial. |
Resumen
Los factores que limitan la utilización de los forrajes de baja calidad como alimentos productivos están relacionados tanto con su baja digestibilidad como con su bajo consumo voluntario. Aunque la molienda empleada como un tratamiento físico simple resulta generalmente en un aumento en el consumo voluntario, la digestibilidad sea no se afecta o puede incluso disminuir. Forrajes de baja calidad molidos (paja, madera) han sido empleados exitosamente para reemplazar una parte importante del “volumen” y “fibra” de las raciones para rumiantes, pero los niveles de producción obtenidos con estas raciones han dependido de su contenido de alimentos energéticos tales como granos de cereales. Esto, por tanto, limita la aplicación de esta práctica en áreas en las cuales existe deficiencia de granos. Otros tratamientos físicos tales como molienda muy fina (molino vibratorio) e irradiación, que se han demostrado como muy efectivos en mejorar la digestibilidad de forrajes de mala calidad bajo condiciones de laboratorio tienen poco valor práctico por los costos excesivos de los tratamientos.
Desde 1970, muchos investigadores han estudiado el tratamiento de forrajes de baja calidad con vapor sobre-saturado a alta presión y alta temperatura. Las digestibilidades in vitro de madera, paja y bagazo de caña de azúcar se han incrementado marcadamente cuando se han empleado temperaturas sobre 160°c (que requieren presiones de vapor de más de 6 kg/cm2). El proceso (232°C a una presión de 28 kg/cm2) desarrollado por el Departamento de Agricultura de los Estados Unidos ha sido el más estudiado tanto in vitro como in vivo con un amplio rango de forrajes. Sin embargo, los animales alimentados con los forrajes procesados tuvieron un bajo comportamiento productivo (al compararlos con los resultados in vitro) limitando así la aplicabilidad de este tratamiento relativamente caro. Cuando se ha empleado tratamientos de alta presión/alta temperatura en combinación con tratamientos químicos (álcali) los resultados han sido conflictivos, observándose efectos aditívos sólo en algunos casos. El mecanismo de acción de los tratamientos de alta presión/alta temperatura parece estar relacionado con la acción degradativa (“delignificación”) de ácidos orgánicos derivados de la liberación de grupos acetilos de la estructura ligno-celulósica. La adición de álcali en estas condiciones podria por tanto ser contraproductiva ya que podría producir cierta neutralización.
En resumen, aunque se ha demostrado que varios métodos físicos han sido efectivos, incrementando la digestibilidad de forrajes de baja calidad en condiciones de laboratorio, esto no ha sido verificado en el número limitado de experimentos in vivo en los cuales estos forrajes han constituido la parte principal de la ración. Debido al equipo e inversiones necesarios estos tratamientos no parecen actualmente factibles al nivel de granja y son cuestionables a niveles industriales.
Poor-quality roughages are characterized by their low available energy content, which is related to the highly lignified state of their cellulose and hemicellulose fractions. Although a variety of techniques can be employed' to alter the state of lignification of a poor-quality roughage, this procedure has been generally limited to the realm of the researcher, and there is only limited information indicating their commercial utilization for animal production purposes.
Reduction in particle size
Perhaps the simplest of physical treatments is the grinding of roughages, often with subsequent pelleting. When finely ground roughages constitute a major portion of the ration (over 50%), a marked increase in voluntary intake is consistently observed, with digestibility usually reduced (Minson, 1963; Donefer, 1973). This indicates that while intestinal rate of passage and subsequently voluntary intake is increased, the treatment has no effect on lignification. It appears that physical delignification is possible by utilizing the extreme reduction in particle size made possible by ball milling, but this increased digestibility has only been observed in vitro, the expensive nature of the process precluding any practical testing, let alone application (Millett et al., 1970).
Another possible application of ground poor-quality roughages is as a partial replacement of other forages in a ration consisting primarily of energy-rich grains and by-products. In this situation the nutritive contribution of the ground roughage is limited, or nil, the major effect being one of ration dilution. For satisfactory results it is necessary to grind the roughage finely, and even then Swan and Clarke (1974) reported that use of ground straw at levels over 30% of the ration did not result in any further increase in liveweight gains. When ground and pelleted sugarcane bagasse was used at a level of 15% in a high-concentrate ration in Floride in beef-feeding trials, lower weight gains were observed (Chapman and Palmer, 1972). Bagasse pellets have been successfully used as the sole source of roughage to constitute up to 40% of a complete ration for dairy cattle, with ground corn as the other major ingredient (Roman-Ponce et al., 1975).
Irradiation of roughages
Several studies in vitro have demonstrated that gamma radiation can substantially increase digestibility of forages and wood (Pidgen et al., 1966; Huffman et al., 1971), but in vivo results with oat straw indicated no effect of radiation on voluntary intake and a depression in dry matter digestibility (McManus et al., 1972). Millet et al. (1970) showed electron irradiation to be an effective method of enhancing aspen wood digestibility, but these workers considered the process too expensive for commercial application, a conclusion similar to that of others in reference to gamma irradiation.
High pressure/high temperature steam treatment
A number of reports have appeared since 1970 relating to the use of saturated steam under high pressure to increase effectively the in vitro digestibility of a wide variety of poor-quality roughages.
Bender et al. (1970) studied the effect of steaming with different time and pressure combinations and reported an in vitro dry matter digestibility of 56.6% for aspen wood treated at 165°C for 2 hours. In subsequent trials with sheep, steamed aspen was found to be superior in digestibility to full-bloom alfalfa hay, and levels of 45% treated wood (55% grain) resulted in liveweight gains similar to those obtained through use of a similar level of hay (Heaney and Bender, 1970). This treatment procedure is being developed on a commercial level (termed STAKE process); the calculated cost of processing is stated to be 14.33 Canadian dollars per metric ton with the possibility that the value of by-products (furfuraldehyde) could offset all processing costs (Bender, 1975). To date no extensive feeding trial data are available to demonstrate the efficiency of this process as a practical means of utilizing high levels of treated roughages.
Extensive research on a high-pressure steaming process has been reported by the Western Regional Research Laboratory (California) of the U.S. Department of Agriculture. Guggolz et al. (1971) demonstrated marked increases in in vitro digestion for a variety of grass straws treated for 3 minutes at 232°C and 28 kg/cm2 in specially constructed pressure vessels. When this process has been used to treat different roughages for animal feeding trials, the results have not been satisfactory. Rice straw treated for 90 seconds exhibited reduced digestibility and voluntary intake, and a 20-second treatment resulted in no significant difference in gain or intake over an untreated rice-straw control (Garrett et al., 1974). Although large increases in both in vitro and in vivo organic matter digestibility were observed when sugarcane bagasse was treated for 45 seconds (Wayman et al., 1972), chemical studies indicated extensive degradation of cellulose and hemicellulose and the production of undesirable phenolic compounds. A further report by the same group, based on sheep-feeding trials in Hawaii, indicated that a level of 39.7% of steam-treated bagasse with 55.2% rolled barley resulted in a decreased ration intake and digestibility as compared to a control ration containing alfalfa and barley (Campbell et al., 1973). These workers suggested that depressed intake of the treated bagasse may have been due to a large increase in polyphenolic-like compounds, which increased from 0.43% for raw bagasse to 5.30% after treatment. In summarizing various processing methods studied to improve the feeding value of rice straw, a recent article by the California group stated that the high-pressure steam process was not effective unless alkali was combined with the steam treatment (Hart et al., 1975).
In studies in Mauritius with steamed bagasse, Cheong et al. (1974) observed that treatment temperatures of 198°C were necessary for the bagasse to obtain in vitro digestibilities as high as preflower setaria grass. In further work in Mauritius, Preston (1974) indicates that steam-treated bagasse, supplemented with urea and molasses, would provide the nutrient requirements needed-for maintenance and pregnancy but that more molasses or further processing of the bagasse was necessary to meet requirements for growth or milk production.
Martin et al, (1974) in Cuba have observed that although steam pressure (up to a temperature of 158°C) increased in vitro digestibility of bagasse and bagasse pith (bagacillo), the response was significantly lower than when alkali treatment (NaOH) was used at 90–100°C (atmospheric pressure).
Dhinsa and Donefer (1976) have observed an increased in vitro digestibility of bagasse with increasing steam pressures up to 21.5 km/cm2 (and thus increasing temperatures). Addition of NaOH to the steam treatment resulted in decreased digestibility at higher pressure levels (see Fig. 2.1).
This is explained by the fact that organic acids liberated during the high-pressure treatment counteract the effect of the alkali. This result is contrary to that of Millett et al. (1970), who observed an additive effect when high pressure and alkali were used in combination. Further work from our laboratory (Donefer and Pathirana, 1976), with a series of 14 bagasse samples obtained from four countries, indicated a wide variation in chemical content and in vitro cellulose digestibility. The average digestibility of untreated bagasse samples was increased from 24.6±10.6% (SD) to 39.9±8.2% and 42.0±8.0% when 4% NaOH and high-pressure steam (8 kg/cm2 at 170°C) were used, respectively. The in vitro digestion of the pressure-treated bagasse samples was highly correlated (r = 0.80) with titratable acidity after treatment.
Figure 2.1. Effect of NaOH and increasing steam pressure on the in vitro cellulose digestion of sugarcane bagasse.
Economic feasibility of treatment procedures
Because of the very limited information available on the use of physically treated roughages in livestock rations, it is not possible to determine the economic feasibility of these methods at this time. Another factor making economic projections difficult is the widely varying situations found in different areas, particularly in developing countries where these processes might find their most important use.
It is important however at least to list the various factors which will help to determine economic feasibility:
Economic value of food produced for domestic use or export
Local government constraints (fixed prices, etc.)
External constraints (import embargos, etc.)
Local socio-economic effects (creation or loss of jobs, etc.)
Currency exchange constraints (external purchase of equipment, supplies, expertise)
Conclusions
While various physical methods have been shown to be effective in increasing digestibility of poor-quality roughages under laboratory conditions, this has not been verified in limited feeding trials where these feeds constitute the major portion of the ration. Because of the equipment and investment required, these treatments presently appear unfeasible at farm levels and questionable at commercial levels.
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