INTRODUCTION
There is a long practice in the feeding of sugarcane to all classes of livestock, especially for cattle during the dry season when availability of conventional forage resources is scarce. Nevertheless, the techniques used have been mostly rudimentary and there has been little appreciation of the critical role of supplements as a means of improving the efficiency of utilization of the sugarcane plant as animal feed.
It is only in the last 10–20 years that serious attempts have been made to understand the constraints that limit the expression of the nutritional potential of this feed, especially for ruminants. Our present vastly increased understanding in this area of nutrition stems in large part from research and development done in Cuba in the late 1960s on the feeding of molasses to cattle (Preston and Willis, 1974). The economic crisis affecting sugar producers, which began in the mid-1970s and which continues with little sign of abatement, has also been a major stimulus to the increased activities in the area of alternate uses of the sugarcane crop; and has been one of the major reasons for this Consultation.
FEED BIOMASS FROM SUGARCANE
The potential of sugarcane, and its intrinsic advantages over other tropical grasses, as a converter of solar energy into biomass is the rationale for the concept of “energy cane” (Alexander, 1985). However, sugarcane has other characteristics which make it especially appropriate as a feed reserve for livestock in the tropics, and superior to almost all other forage crops.
Its outstanding characteristics are:
Its perennial growth habit.
The quantity and nutritional quality of sugarcane increase with harvest interval, with optimum values being reached at a harvest interval of between 12 and 18 months. This is in marked contrast with almost all other tropical forage crops, which deteriorate in yield and quality as the interval between successive cuts is increased. For this reason sugarcane has been called “ensilaje vivo” in many Central American countries.
The dry matter content of mature sugarcane averages 30 percent which exceeds that of most other forage grasses (the average for Elephant and King grasses is closer to 17 percent). Thus harvest, transport and processing costs per unit dry matter are less for sugarcane than for most other forages.
It is easy to separate sugarcane into different components (e.g. juice and fibre), which can be exploited to permit flexibility in end-product usage (Preston, 1986).
There is a long tradition in sugarcane agronomy, especially in breeding, pest control and cultural practices. Admittedly this has been mainly directed to enhanced production of sucrose rather than total sugars which is the criterion for animal feed. But the implication of this practice in terms of the loss of potentially promising varieties is one of degree rather than direction, as there is direct compatibility between sucrose yield and feed value.
Sugarcane is widely tolerant of soil and climatic characteristics and by maintaining a canopy of green leaves (or a mulch of dead ones) throughout the year helps to combat erosion, giving it a distinct advantage over competitive forage crops such as cassava and maize.
SUGARCANE PITH
The stimulus for the research which led to the development of feeding systems based on whole sugarcane was undoubtedly the invention by Tilby and Miller (Lipinsky and Kresovich, 1982) of the Canadian-designed separator.
The idea of separating the more fibrous rind from the cane stalk, and using it for the manufacture of particle board and paper, led to the possibility of using the residual pith as the basis of animal feed (Pigden, 1972). Sadly this novel approach to sugarcane processing has still not proved to be commercially viable largely because of the high investment and operational costs of the separator and the apparent difficulties in converting the rind into suitable raw material for board and paper manufacture. Furthermore, as the basic diet for ruminants, chopped whole cane proved to have almost the same potential as the pith, and the technology required was both simpler and cheaper (Preston et al., 1976).
TECHNOLOGIES FOR COMMERCIAL USE OF SUGARCANE IN ANIMAL FEEDING
The issues to be considered are not technical but economical, and concern: a) The economics of harvesting, transporting and processing whole cane b) Supplementation.
Harvest, transport and processing
Methods of getting whole sugarcane from the field to the animal range from the entirely manual through combinations of hand cutting and mechanical loading, transport and processing to the use of machines which carry out the entire operation of cutting, chopping and loading direct into forage wagons. Choice of any one or combinations of systems will depend on socio-economic factors such as rates of unor under-employment, minimum wage scales, the nature of the terrain where the cane is grown and transported, costs of machinery and fuel and the economics of converting the processed cane into animal products. Transport of cane stalks by mules and horses is still the dominant system for small scale producers in Colombia; in the Dominican Republic, ox carts predominate at least at the level of field to rail or road. There is infinite choice, although in many developing countries there is an increasing realization that animal traction is usually the cheapest when distances are short and daily needs are relatively small (e.g. less than 2 tons daily).
Processing can be done by traditional slowly revolving chaff cutters, by high speed disintegrators employing knives and beaters or by the precision chopping chamber of a forage “double chop” harvester; effects on nutritive value due to different methods of processing appear to be negligible (Montpellier and Preston, 1977).
Supplementation
Correct supplementation is the key to animal productivity on sugarcane. The principles are well established and are based on:
Satisfying the needs of rumen microbes for fermentable nitrogen (ammonia), trace nutrients (peptides, amino acids, minerals and vitamins) and the physical attributes of an efficient rumen ecosystem (small quantities of readily fermentable fibre).
Sources of protein, glucose precursors and long chain fatty acids able to bypass (or escape) the rumen fermentation so that the end products of fermentative digestion can be balanced according to the needs of the particular production function (Leng and Preston, 1986).
Feeds and/or chemical substances capable of manipulating the rumen fermentation so as to:
Increase propionate relative to the other VFA.
Eliminate (or reduce) protozoal populations in the rumen.
Optimum levels of rumen ammonia appear to be provided by the equivalent of 30 g urea per kg of sugarcane dry matter (Alvarez and Preston, 1976a) (Figure 1).
Trace nutrients for rumen microbes and the “physical” attributes of a good rumen “ecosystem” are conferred by highly digestible green forages such as sweet potato tops and foliages from legume trees such as leucaena (Meyreles et al., 1979; Hulman and Preston, 1981). Although there have been no comparative studies, suitable amounts seem to be the equivalent of 600 g dry matter per 100 kg liveweight.
Rice polishings have proved to be the best sources of bypass nutrients because of their richness in essential amino acids, starch and lipids (Figure 2). However, other supplements and combinations of supplements have given good results (e.g. cottonseed cake or combinations of maize grain and fishmeal).
The principles are that the active ingredients (amino acids, starch and LCFA) are in a form which permits them to escape to a major degree the degradative action of rumen microbes. Thus cassava root meal (Silvestre et al., 1977) and molasses (Pigden, 1972) which are rapidly degraded by rumen microorganisms (Santana and Hovell, 1979; Encarnacion and Hughes-Jones, 1981) are less effective than maize meal as sources of glucose precursors.
Animal response to supplementation of sugarcane with bypass nutrients is curvilinear, and economically optimum supplementation strategies will depend on cost relationships between product (meat or milk) and supplement, and the dimensions of the biological response curve. For example, the most economic levels of rice polishings have proved to be between 500 and 1 000 g/animal/day.
The interaction between supplements which act in the rumen or in the animal is apparent from the data reported by Alvarez and Preston (1976a) and Ferreiro et al. (1977). Neither urea nor rice polishings was effective when given alone, yet both had dramatic effects on rate of animal performance when given together.
Foliages from legume trees such as Gliricidia sepium, Leucaena and Erythrina glauca, although proven sources of bypass protein (and possibly lipids also) in molasses-based feeding systems (Preston and Botero, 1986) have yet to be evaluated in diets based on whole sugarcane.
MEAT OR MILK
With only moderate levels of supplementation (maximum of 25 percent of the diet dry matter), it is technically feasible to achieve growth and feed conversion rates in cattle only slightly less than the maxima set by the genetic potential of the cattle breeds on test (Pigden, 1972; Meyreles et al., 1979; Preston et al., 1976). Comparable levels of performance have not been reached with milking animals fed sugarcane and the realizable yields are probably less than 50 percent of genetic potential (MacLeod et al., 1976). The reasons are likely to be the higher requirements for both glucose and amino acids for milk synthesis, and the imbalance in the proportions of these nutrients relative to total VFA energy, in the end products of fermentative digestion of cattle fed a basal diet of sugarcane.
However, if the milk production system is“matched with the feed resource” (i.e. the cattle are dual purpose crossbreds), then economical milk production systems can be established with sugarcane as the basal diet (Table 1). In such a system restricted grazing on a legume bank of Leucaena leucocephala permitted economies in the amounts of supplement (rice polishings) needed (Table 1).
ENSILING AND/OR UPGRADING OF SUGARCANE
The growth characteristics of sugarcane are such as to make it unnecessary to ensile this crop, since its nutritive value is highest in the dry season when other forages are in scarce supply, and it can be left in the field as a standing crop until required. A possible advantage from ensiling appeared to be indicated by the finding that young actively growing cane was inferior in feed value to mature cane, apparently because of the higher sugar content of the latter. It was argued that if sugarcane was to be used as the basis of a year-round confinement feeding system, then there could be advantages in certain climatic situations of ensiling cane in the dry season, when its nutritive value was high, and feeding the ensiled material in the wet season when the standing cane was of low nutritive value.
The precautions to be taken in the ensiling of sugarcane were established by Alvarez and Preston (1976c), who showed that when ensiling was performed without additives, a high proportion of the soluble sugars was converted to alcohol, and nutritive value was seriously depressed (Alvarez et al., 1977). Protective measures to ensure development of lactic acid-producing bacteria, rather than yeasts, included incorporation of ammonia (24 g/kg of sugarcane dry matter), or mixtures of urea and cattle faeces allowed to pre-ferment before being incoporated into the chopped sugarcane.
FUTURE RESEARCH
The following topics merit increased research in order to improve the utilization of sugarcane for animal production:
The effects of age/maturity on its nutritive value
Upgrading the nutritive value of cane with ammonia and other acids and alkalis.
Supplementation with foliages from forage trees.
Control/elimination of protozoa in ruminants fed sugarcane.
REFERENCES
Alexander, A.G. 1985 The energy cane alternative Elsevier, Amsterdam, pp 1–509.
Alvarez, F.J. and Preston, T.R. 1976a Studies on urea utilization in sugarcane diets: effect of level. Tropical Animal Production, 1:194–201.
Alvarez, F.J. and Preston, T.R. 1976b Leucaena leucocephala as protein supplement for dual-purpose milk and weaned calf production on sugarcane-based rations. Tropical Animal Production 1:112–119.
Alvarez, F.J. and Preston, T.R. 1976c Ammonia/molasses and urea/molasses as additives for ensiled sugarcane. Tropical Animal Production, 1:98.
Alvarez, F.J., Priego, A. and Preston, T.R. 1977 Animal performance on ensiled sugarcane. Tropical Animal Production, 2:27.
Alvarez, F.J. Wilson, A. and Preston, T.R. 1978 Leucaena leucocephala as protein supplement for dual purpose milk and weaned calf production on sugarcane-based diets: comparisons with rice polishings. Tropical Animal Production, 3:51–55.
Encarnacion, C. and Hughes-Jones, M. 1981 The rate of degradability of feeds in rumen bags in animals receiving diets with or without molasses. Tropical Animal Production, 6:362–363.
Ferreiro, H.M., Preston, T.R. and Sutherland, T.M. 1977 Investigation of dietary limitations on sugarcane-based diets. Tropical Animal Production, 2:56–61.
Hulman, B. and Preston, T.R. 1981 Leucaena leucocephala as a source of protein for growing animals fed whole sugarcane and urea. Tropical Animal Production, 6:318–321.
Leng, R.A. and Preston, T.R. 1986 Constraints to the efficient utilization of sugarcane and its byproducts as diets for production of large ruminants. In: FAO Expert Consultation on Sugarcane as Feed (Editors: R. Sansoucy, G. Aarts and T.R. Preston) FAO, Rome.
Lipinsky, E.S. and Kresovich, S. 1982 Sugarcane stalks for fuels and chemicals. Progress in Biomass Conversion, 2:89–126.
MacLeod, N.A., Morales, S. and Preston, T.R. 1976 Milk production by dual purpose cows grazing unsupplemented pangola or fed in drylot on sugarcane and molasses/urea based diets. Tropical Animal Production, 1:128.
Meyreles, L., Rowe, J.B. and Preston, T.R. 1979 The effect on the performance of fattening bulls of supplementing a basal diet of derinded sugar cane stalk with urea, sweet potato forage and cottonseed meal. Tropical Animal Production, 4:255–262.
Montpellier, F.A. and Preston, T.R. 1977 Digestibility and voluntary intake on sugarcane diets: effects of chopping the cane stalk in particles of different sizes. Tropical Animal production, 2:40.
Pigden, W.J. 1972 Evaluation of comfith as a commercial livestock feed in the Caribbean. In: CIDA Seminar on Sugarcane as Livestock Feed. CIDA, Ottawa.
Preston, T.R. 1986 Fractionation of sugarcane for feed and fuel. In: FAO Expert Consultation on Sugarcane as Feed (Editors: R. Sansoucy, G. Aarts and T.R. Preston) FAO, Rome.
Preston, T.R. and Willis, M.B. 1974 Intensive beef production. (2nd Edition). Pergamon Press.
Preston, T.R., Carcano, C., Alvarez, F.J. and Gutierez, D.G. 1976 Rice polishings as a supplement in a sugarcane diet: effect of level of rice polishings and processing the sugarcane by derinding or chopping. Tropical Animal Production 1:150–163.
Preston, T.R. and Botero, R. 1986 Resultados parciales de Programa CIPAV (Enero-Abril 1986) Fundación del Desarollo Integral del Valle del Cauca:Cali, pp23
Santana, A. and Hovell, F.O. De B. 1979 Degradation of various sources of starch in the rumen of Zebu bulls fed sugarcane. Tropical Animal Production, 4:107–108 (Abstract).
Silvestre, R., MacLeod, N.A. and Preston, T.R. Effect of meat meal, dried cassava root and groundnut oil in diets based on sugarcane/urea. Tropical Animal Production, 2:151–157.
Figure 1: Relation between urea concentration in the diet and Liveweight gain, feed intake and feed conversion.
Figure 2: Effects of supplementation with rice polishings (bypass protein, bypass starch and oil) on growth rates of Zebu bulls in Mexico fattened on basal diets of whole sugarcane which had been chopped or derinded by the “Tilby” separator process.
Source: Preston et al, (1976).
| Alvarez and Preston, 1976b: | |||
| Rice polishings (kg/d) | 2 | 1 | - |
| Leucaena grazing (3 hr/d) | No | Yes | Yes |
| Milk yield (kg/d) | 5.9 | 6.2 | 4.6 |
| Calf growth (kg/d) | 0.60 | 0.58 | 0.63 |
| Weight change of cows (kg/d) | 0.34 | 0.32 | -0.23 |
| Alvarez et al. 1978: | |||
| Rice polishings (kg/d) | 2 | 1 | 0.5 |
| Leucaena grazing (hr/d) | - | 3 | 3 |
| Milk yield (kg/d) | 5.1 | 6.9 | 6.9 |
| Calf growth (kg/d) | 0.50 | 0.52 | 0.49 |
| Weight change cows (kg/d) | 0.12 | 0.04 | 0.02 |
La antigua práctica de alimentar al ganado con caña de azúcar se ha racionalizado en los últimos 10–12 años hasta tal punto que actualmente constituye la base de sistemas de producción pecuaria económicamente viables para rumiantes de gran tamaño.
Las características esenciales de los sistemas de alimentación animal a base de caña son las siguientes: utilización de caña madura (el jugo no deberá tener menos de 12–16 grados brix); picadura de toda la cosecha en partículas no más largas de 10–20 mm; y suplementación con urea (10 g de urea/kg de caña fresca).
Cuando es el único elemento de la dieta, este pienso servirá para el mantenimiento del ganado, y cuando se utiliza como suplemento del pasto cabe prever aumentos de peso de hasta 200 g/animal/día.
A fin de lograr mayores niveles de productividad, se requieren suplementos adicionales que ofrezcan un medio más favorable a la actividad microbiana en el rumen y para equilibrar los productos de digestión del rumen (nutrientes sobrepasantes). Para lo primero, son alimentos apropiados la gallinaza y el follaje de cultivos alimentarios (por ejemplo, yuca y batata) y/o árboles leguminosos (por ejemplo, Leucaena, Gliricidia y Erithryna spp) en una proporción del 20 por ciento aproximadamente de la materia seca; para el segundo fin, los suplementos preferidos son los subproductos ricos en lípidos y proteínas de la molienda de cereales (por ejemplo, polidura de arroz) y de la elaboración de semillas oleaginosas (por ejemplo, torta de algodón).
Los niveles recomendados de ambos tipos de suplementos son hasta del 20 por ciento de la materia seca de la dieta.
Las tasas potenciales de productividad correspondiente a las cantidades máximas de suplementos recomendadas son de unos 800 g/día de aumento de peso en vivo en el caso de los toros de engorde y de 6–8 litros de leche/día en las vacas de cruzamiento.
Generalmente no se recomienda el ensilaje de la caña ya que el valor nutritivo de ésta aumenta con la madurez y el comienzo de la estación seca.
Si ha de conservarse, es esencial utilizar aditivos para evitar el desarrollo de levaduras, que convierten a los azúcares en acídos orgánicos y alcohol y reducen su valor nutritivo. Alcalis como el amoníaco y el hidróxido de sodio conservan los azúcares y aumentan la degradabilidad de la fibra.
