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T.R. Preston


Research at the Cuban Institute of Animal Science in the late 1960s led to the development of molasses-based feeding systems for both cattle and pigs, which have been applied on a widespread scale, in many tropical countries (Preston and Leng, 1986).

Molasses had been used previously in animal feeds, but always at relatively low levels (usually less than 20 percent of the diet). The Cuban research was the first to show that molasses could seriously be considered as an alternative to cereal grains as a means of intensifying animal production in the tropics.


Molasses is a term applied to a variety of by-product feeds derived from sugar-rich crops. To avoid confusion, the different kinds of molasses that are produced by the sugarcane industry are listed in Table 1. The Spanish names are used in the case of products derived from the “panela” industry as there are no English equivalents.

From the nutritional standpoint, the major differences in the various “molasses” by-products are in the amount of soluble ash as a proportion of the total dry matter. In this respect, final molasses stands apart from the rest with an ash content between 10 and 15 percent of the dry matter. As is to be expected from the method of manufacture, “B” molasses is in a position intermediate between final and high-test molasses. The “cachaza” and “melote” from “panela” production resemble the raw cane juice and cane syrup, respectively; they differ in their higher content of impurities, mostly as protein and mineral matter complexed with “tannins” from the bark extracts used to clarify the juice.

The concentration of soluble ash in the molasses derived from industrial manufacture of crystalline sugar, and the impurities in “cachaza” and “melote”, are the factors which apparently determine the degree to which these feeds can be incorporated in the diets of monogastric animals. All the different types of molasses can be fed safely to ruminants, even at high levels (> 70 percent of the dry matter).


It is important to distinguish between low and high level usage of all types of molasses. At low levels (<20 percent of the diet dry matter), the effect of the soluble carbohydrates in the molasses tends to be complementary rather than competitive and there appears to be little or no depression in the degree to which the basal feed resource is fermented. Beyond a concentration of 20 percent in the diet dry matter, there is increasing competition for substrate by the rumen microorganisms, with the result that the basal diet is used less and less efficiently according to the amount of molasses that is fed.

When molasses accounts for more than 50 percent of the diet, the digestibility of all types of feeds that accompany the molasses is depressed often to the point of only half the value recorded when molasses is not given (Encarnación and Hughes-Jones, 1981). These effects are obviously undesirable if the accompanying feed is composed mainly of cell wall carbohydrate: however, if the feed is rich in protein, starch or lipids-which can be digested by gastric enzymes in the small intestine-then depressing the extent to which these nutrients are fermented in the rumen becomes an advantage to the host animal.

Final molasses as a supplement

It is frequently claimed that small amounts of molasses in a roughage-based diet stimulate rumen fermentation. However, this appears to be unlikely in view of recent evidence that sources of digestible cell walls, rather than soluble carbohydrate, are the most appropriate supplements for this purpose (e.g. Gutierrez and Elliott, 1984; Silva and Orskov, 1985).

The most appropriate role for small amounts of molasses in ruminant diets is as a vehicle for other nutrients (e.g. urea and minerals). A drought feeding strategy based on the use of liquid molasses supplements containing from 8 to 10 percent urea is now an established practice in Australia (Nicol et al., 1984) and has been introduced sucessfully in Africa (Preston and Leng, 1986).

The incorporation of urea and other nutrients in molasses-based (multi-nutritional) blocks promises to be an even more attractive technology, especially for smallholder-village farmers, for supplementation of locally available crop residues which are of low digestibility and also deficient in fermentable nitrogen (Leng and Preston, 1984; Sansoucy et al., 1986).

Final molasses as the basis of the diet

The Cuban research in the late 1960s had, as its objective, the development of livestock feeding systems in which molasses was the principal ingredient. At the outset it was decided that molasses should be fed in its original liquid state in order to reduce processing costs and to facilitate transport and storage. The successful development of the high molasses-fattening system for cattle (Preston et al., 1967a) exemplifies the application of the basic principles of ruminant digestion and metabolism on low-N, high-CHO feeds, namely:

The original system utilized forages such as Elephant grass, pangola grass and often sugarcane tops as the roughage source. Forage was restricted (0.8 kg dry matter/100 kg liveweight) to encourage the animal to consume high levels of molasses. The urea level was set at 2.5 percent of the fresh weight of the molasses to provide a ratio of fermentable nitrogen to carbohydrate close to the theoretical requirements of efficiently growing rumen microorganisms. Sulphur supplementation was not required as sulphur dioxide is used in clarification of cane juice and residual sulphur is concentrated in the molasses. In the first widespread commercial application of the feeding system, fishmeal (Peruvian) was the bypass protein supplement. The dramatic effect of this supplement in raising animal productivity on a molasses-based diet is shown in Figure 1. The data in Tables 2 and 3 summarize the results obtained when the molasses fattening programme was commercialized in large scale feedlots and under conditions of restricted grazing on State farms.

Subsequent developments in the use of molasses-based diets have been directed to the use of:

There is evidence that on molasses-based diets, poultry litter influences the pattern of VFA formation by increasing the proportions of propionate and decreasing the butyrate (Fernandez and Hughes-Jones, 1981; Marrufo, 1984). This would be a partial explanation of the improved growth rates and feed conversions associated with the use of poultry litter in molasses-based diets (Figure 2) see also Meyreles, 1984 and Herrera, 1984).


High-test molasses

High-test molasses differs from final molasses in that it is the concentrated sugarcane juice, from which no sugar has been extracted, but which has been clarified and filtered (to remove impurities) and partially inverted (conversion of sucrose to its constituent reducing sugars, glucose and fructose), to prevent crystallization of the sucrose. It is thus richer in total sugars and has a much lower content of soluble ash than final molasses, which as the name implies is the residual solubles of the cane juice after most of the sucrose has been extracted. High-test molasses is not laxative and gives rise to faeces which have normal consistency.

The successful feeding of pigs with liquid diets in which high-test molasses was the only source of carbohydrate, and contributed up to 70 percent of the ration dry matter, was first reported from Cuba (Preston et al., 1968). High-test molasses supported similar rates of liveweight gain as final molasses in one experiment with fattening steers in Cuba (Preston et al., 1967b).

“Cachaza” and “melote” (sugarcane scums)

“Cachaza” is the flocculated matter and associated cane juice removed from the boiling cane juice during the artisanal production of “panela”. Its composition is similar to that of cane juice differing only in the higher percentage of protein and minerals and other substances (including tannins) present in the bark extracts added to aid the flocculation process. It may be fed fresh but usually it is concentrated to about 60 percent solids so as to give a stable product which can be stored (the fresh “cachaza” begins to ferment after 24 h). The concentrated product is called “melote” in Latin America.

There seem to be no reports in the scientific literature concerning the nutritive value of “cachaza” or “melote” in animal feeds; however, they are widely used at least in Latin America as a feed for pigs and for the mules that traditionally transport the feed for pigs and for the mules that traditionally transport the sugarcane from the fields. Practical observations are that they satisfactorily replace cereal grains in the diet of finishing pigs but cause diarrhoea in younger pigs and are not suitable for lactating sows (T.R. Preston, unpublished observations).

In Colombia, steers given free access to “melote”/urea (2.5 percent urea), and restricted quantities of rice polishings, poultry litter, sugarcane tops and foliage from the legume tree, Gliricidia sepium, had average liveweight gains of 800 g/d (T.R. Preston and R. Botero, unpublished data).


Three metabolic diseases may occur in cattle and sheep fed diets in which molasses is used as a supplement (as a vehicle for urea) or as the basis of the diet. These are: urea toxicity, molasses toxicity and bloat.

Urea toxicity

With ad libitum feeding of molasses/urea mixtures, urea intakes may reach as high as 300 g/d (e.g. in a 500 kg dairy cow consuming 10 kg/d of the molasses/urea mixture). Even in these cases, there is rarely any risk of urea toxicity since the sugars in molasses and ammonia from urea are quickly used in microbial cell growth. Animals which have never previously consumed urea can be safely permitted free access to mixtures of molasses containing up to 3 percent urea without fear of toxicity. The principle underlying the use of molasses with 8–10 percent urea is that the high urea concentration inhibits consumption of the mixture (Figure 4). Toxicity will only occur if the urea is not uniformly mixed or if the mixture has a high water content which may encourage the animal to “drink” rather than “lick” the mixture.

Molasses toxicity

This used to be the most serious problem associated with ad libitum molasses feeding. For example, in the first year following the introduction of the molasses/urea fattening system in Cuba, mortality and emergency slaughter rates in a 10 000 head feedlot increased from 0.1 percent and 0.4 percent (when a forage-based diet was fed) to 1 percent and 3 percent respectively, when the diet was changed to high levels of molasses/urea (see Table 2).

Cattle suffering from molasses toxicity salivate, stand apart in a “dejected” posture, usually with their head lowered; and frequently are found “leaning” against the fence or feed trough. Invariably, eye-sight is affected and often the animal is blind. When disturbed they have an unsteady and uncoordinated gait and this led the “cowboys” in Cuba to refer to the affected animal as “borracho” (i.e. drunk!!).

The nervous symptoms and blindness, that were a feature of molasses toxicity, indicated damage to the brain and it was subsequently shown (Verdura and Zamora, 1970) that the clinical syndrome was indistinguishable from that of cerebro-cortical necrosis (CCN) also known as polioencephalomalacia (Edwin et al., 1979). The necrosis in the brain is readily seen and this allows rapid diagnosis. The cause of the necrosis is likely to be a decrease in the energy supply to the brain either because of an absolute deficiency of alimentary thiamine, binding of thiamine analogues produced in the rumen and/or through the action of thiaminase in the rumen (Edwin et al., 1979); or a deficiency of glucose (Losada and Preston, 1973).

Treatment and prevention

In high-molasses feeding systems, it is usual to restrict the supply of forage (either to stimulate molasses intake or because of the greater cost of forage compared with molasses). Inadequacies in the forage supply, either in quantity or “quality”, appear to be the main causative factors of molasses toxicity. Thus, the incidence of molasses toxicity was less when wheat or barley straw, rather than sorghum forage or maize silage, were used as the forage sources in molasses-based feedlots (T.R. Preston, unpublished data). Furthermore, there have been no reports of toxicity when high protein forages (e.g. leucaena, and cassava and sweet potato leaves) have been used. Equally, the feeding of palatable forage with a high protein content appears to be the best cure for affected animals. The recent developments in the molasses feeding system have emphasized the technical and economic advantages of giving high protein forages, especially from leguminous trees like leucaena, gliricidia and erythrina, as a combined source of both “roughage” and “bypass” protein (Preston and Botero, 1986). Such procedures are also likely to offer the most cost-effective solution for molasses toxicity. The above discussion emphasizes the critical role of management in any feeding system where economic constraints dictate a less than optimum degree of supplementation.


Bloat, which is the retention in the rumen of gas, either free or entrapped in foam, occurs in almost all feeding systems. It is more frequent in the diet of other carbohydrate sources which have little or no fibre but which are highly digestible, such as raw sugar (MacLeod et al., 1968) and maize grain (Fermin et al., 1984).


Two approaches are possible:

Molasses as a component of traditional feeds

Including molasses in conventional cereal grain-based feeds is established technology, but has limited economic significance in developing countries because of the relatively small proportion (5 to 10 percent of the feed) of molasses than can be accepted by most mixing systems in conventional feed mills.

Molasses as the basis of new feeding systems

Final and “B” molasses have been the basis of commercial pig diets in Cuba since the late 1960s (Perez, 1986). The molasses is fed in liquid form, partially diluted with water and is combined with a protein supplement usually of saccharomyces, yeast and fishmeal.

The most widescale example of molasses usage is as a component of a “soup” prepared by boiling urban organic refuse (mostly food and vegetable wastes) and using this enriched with “B” molasses as the only feed for pigs (Perez, 1986).

Although technically feasible (e.g. Perez et al., 1968), there has been no commercial application of molasses feeding as the basis of diets for poultry, mainly because of management difficulties caused by the viscous nature of the molasses.


Edwin, E.E., Makson, L.M., Shreeve, J., Jackman, R. and Carroll, P.J. 1979 Diagnostic aspects of cerebrocortical necrosis. Veterinary Record, 104:4–8.

Encarnación, 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.

Fermin, D., Fermin, R., Pila, A. and Mena, A. 1984 Sugarcane juice as a substitute for maize and molasses in diets for fattening pigs. Tropical Animal Production, 9:271–274.

Fernandez, A. and Hughes-Jones, M. 1981 Rumen fermentation and rumen function in bulls receiving a basic diet of molasses/urea supplemented with poultry litter, sweet potato forage or wheat bran. Tropical Animal Production, 6:360.

Ffoulkes, D. and Preston, T.R. 1978 Cassava or sweet potato forage as combined sources of protein and roughage in molasses based diets: effect of supplementation with soybean meal. Tropical Animal Production, 3:186–192.

Gutierrez, E. and Elliott, R. 1984 Interacción digestiva de la pulpa de henequén (Agave fourcroydes) y el pasto estrella de Africa (Cynodon plectostachyus) In: Alternativas y valor nutritivo de algunos recursos alimenticios destinados a producción animal. Informe provisional No. 16. International Foundation for Science, Stockholm, pp 229–246.

Herrera, F. 1984 Evaluación de diferentes niveles de Leucaena leucocephala en dietas basadas en melaza/urea, con y sin gallinaza, en la engorda de novillos In: Alternativas y valor nutritivo de algunos recursos alimenticios destinados a producción animal. Informe provisional No. 16 International Foundations for Science: Stockholm pp 199–204.

Losada, H. and Preston, T.R. 1973 Effect of forage on performance, content of the reticulo-rumen and VFA in rumen and caecum of calves fed diets based on molasses-urea. Revista Cubana ciencia Agricola (English edition), 7:185.

Leng, R.A. and Preston, T.R. 1984 Nutritional strategies for the utilization of agro-industrial by-products by ruminants and extension of the principles and technologies to the small farmer in Asia. In: Proceedings 5th World Conference on Animal Production, Tokyo, pp 310–318.

MacLeod, N.A., Preston, T.R., Lassota, L.A., Willis, M.B. and Velazquez, M. 1968 Mieles y azúcares como fuentes energéticas para puercos. Revista Cubana Ciencia Agricola, 2:205–210.

Marrufo, D. 1984 La Leucaena leucocephala: su productividad en la zona henequenera de Yucatán y su uso como suplemento en diets a base de melaza/urea. Tesis de Maestria, Universidad de Yucatán.

Meyreles, L. 1984 La gallinaza como suplemento en dietas de melaza/urea para el ganado bovino. In: Alternativas y valor nutritivo de algunos recursos alimenticios destinados a producción animal. Informe provisional No. 16 International Foundation for Science, Stockholm, pp 147–158.

Meyreles, L., Pound, B. and Preston, T.R. 1982 The use of Leucaena leucocephala or sugarcane tops as sources of forage in cattle diets based on molasses/urea, supplemented with chicken litter and/or wheat bran. Tropical Animal Production, 7:92–97.

Meyreles, L. and Preston, T.R.1982 The role of poultry litter in molasses/urea diets for the fattening of cattle. Tropical Animal Production, 7:138–141.

Morciego, S., Muñoz, F. and Preston, T.R. 1970 Commercial fattening of bulls with molasses/urea and restricted grazing. Revista Cubana de Ciencia Agricola (English edition), 4:97–101.

MuÑoz, F., Morciego, F. and Preston, T.R.1970 La ceba commercial de toros con miel/urea, harina de pescado y forraje restringido en condiciones de cebadero. Revista Cubana de Ciencia Agricola, 4:99–104.

Nicol, D.C., Venamore, P.C. and Beasley, R.C. Fortified molasses 1984 systems for beef properties. Animal Production in Australia, 15:216–219.

Perez, R., Preston, T.R. and Willis, M.B. 1968 The replacement of cereals by sugar or molasses for broilers raised on wire or litter. Revista Cubana de Ciencia Agricola (English edition), 2:101–108.

Perez, R. 1986 Molasses as feed for non-ruminants. In: FAO Expert Consultation on Sugarcane as Feed (Editors: R. Sansoucy, G. Aarts and T.R. Preston) FAO, Rome.

Preston, T.R., Elias, A., Willis, M.B. and Sutherland, T.M. 1967a Intensive beef production from molasses and urea. Nature, 216:721.

Preston, T.R. Willis, M.B. and Elias, A. 1967b Intensive beef production from sugarcane by-products. 2. Comparison between normal and invert molasses as a supplement to forage or concentrates. Revista Cubana Ciencia Agricola (English edition), 1:41–48.

Preston T.R., MacLeod, N.A., Lassota, L., Willis, M.B. and Velasquez, M. 1968 Sugarcane products as energy sources for pigs. Nature, 219:727–728.

Preston, T.R., and Willis, M.B. 1974 Intensive beef production (2nd Edition). Pergamon Press.

Preston, T.R. and Leng, R.A. 1986 Matching Livestock Systems with Available Feed Resources. International Livestock Centre for Africa, Addis Ababa, pp 331.

Preston T.R. and Botero, R. 1986 Resultados parciales de Programa CIPAV (Enero-Abril 1986) Fundación del Desarrollo Integral del Valle del Cauca, Cali, pp 23.

Sansoucy, R., Aarts, G. and Leng, R.A. 1986 Molasses-urea blocks as multinutrient supplements for ruminants. In: FAO Expert Consultation on Sugarcane as Feed (Editors: R. Sansoucy, G. Aarts, and T.R. Preston) FAO, Rome.

Silva, A. and ørskov, E.R. 1985 Effect of unmolassed sugar beet pulp on the rate of straw degradation in the rumens of sheep given barley straw. Proceedings Nutrition Society 44:50A

Silvestre, R., MacLeod, N.A. and Preston, T.R. 1977 Voluntary intake and liveweight gain of cattle given chopped sugarcane and solutions of molasses containing different concentrations of urea. Tropical Animal Production 2:1–12.

Verdura, T. and Zamora, F. 1970 Cerebro-cortical necrosis in beef cattle fed high levels of molasses. Revista Cubana Ciencia Agricola (English edition), 4:209–212.

Figure 1: Addition of fish meal to a basal diet of ad libitum molasses/urea and restricted forage dramatically improves growth rate and feed conversion of cattle in Cuba.

Figure 1

Figure 2: In a cattle fattening diet based on ad libitum molasses, sugarcane tops and wheat bran (1 kg/day), urea was a more effective source of fermentable-N than poultry litter. Poultry litter stimulated growth rate when added to the diet (with urea), which was apparently adequate in fermentable-N.

Figure 2

Figure 3: Contrasting effects of legume and grass as the roughage supplement in a diet based on ad libitum molasses/urea with or without supplements of wheat bran (1 kg/day) and/or poultry litter (1.5 kg/day).

Figure 3

Figure 4: Intakes of steers (250 kg) given free access to chopped sugarcane and molasses with different concentrations of urea.

Figure 4
Table 1. Sugar-rich by-products derived from the processing of sugarcane
ProcessNameApproximate composition (% fresh basis)
SucroseReducing sugarsAshDry matter
Crystalline “B” molasses(i) 5–880–90
(Industrial)Final molasses(ii)33–3715–1910–1580–90
 Cane syrup(iii)45–555–101–255–60

(i) Concentrated soluble residue following the secondcentrifugation to remove the “B” sugar
(ii) Concentrated soluble residue after the last centrifugationto remove the “C” sugar; also known as “C” and blackstrapmolasses
(iii) The clarified cane juice concentrated to the point where thesucrose is almost ready to crystallize
(iv) The concentrated cane syrup that has been partially inverted toavoid crystallization
(v) A mixture of “scums” and cane juice that is “skimmed off” theboiling juice following addition of a flocculating agent(usually extracts from the bark of resin-rich trees) whichcauses coagulation of the protein and mineral matter
(vi) Cachaza which has been concentrated to a point that preventssubsequent fermentation

Table 2. Economic data from a commercial cattle feedlot (10 000 head) in Cuba during the years when a change was made from an ad libitum forage (Pangola grass) plus concentrate diet to one based on ad libitum molasses/urea and restricted forage and fish meal. The high losses for emergency slaughter and mortality in the first year of high molasses feeding were due to molasses toxicity (Cerebro-cortical necrosis, see Preston and Willis 1974).
Total liveweight gain (kg/day)3 7248 29513 797
Liveweight gain (kg/head/day)0.430.880.89
Feed conversion (DM)151110
Deaths (%)
Emergency slaughter (%)

Source: Muñ et at. (1970)

Table 3. Performance of bulls fattened commercially in Cuba on ad libitum molasses/urea, fish meal and restricted grazing (3 hours/day). Results are for 11 units each with 400 animals.
Liveweight gain (kg/day) Conversion
MolassesFish meal (kg/kg)Urea

Source: Morciego et al. (1970).

Table 4. Leucaena foliage was as effective as groundnut meal in supporting high growth rates in young Friesian bulls fed a diet based on molasses/urea. The Leucaena replaced both the forage (native grass) and the groundnut meal, and thus served as a combined source of protein and roughage.
(% LW/day)
Groundnut cake
Liveweight gain (g/day)790740847597742
Feed conversion (kg/kg gain)
Molasses (% of diet)7968627353

Table 5. The foliages of cassava or sweet potato were used as the roughage supplement in a molasses-urea diet for fattening bulls in the presence or absence of soyabean meal. With cassava supplementation there were no benefits from additional protein indicating that it was a better source of bypass protein than sweet potato foliage.
ForageSweet potatoCassava
Soyabean meal (g/day)04000400
Liveweight gain (kg/day)0.650.850.850.87
Molasses (kg/day)5666
Forage (kg/day)13131010

Source: Ffoulkes and Preston (1978).

T.R. Preston

En los países productores de caña, la melaza es el nombre genérico que se da a una serie de productos y subproductos con gran contenido de azúcar, que van desde la melaza de mejor calidad, pasando por las clases “A” y “B” hasta la melaza “C” o “final”, que se producen en las etapas sucesivas del proceso actual de fabricación del azúcar.

En la producción de azúcar no centrifugado (denominado panela y gur en América Latina y el subcontinente indio, respectivamente), los subproductos son la cachaza apartada del jugo hirviente después de haber añadido un agente de floculación para eliminar la materia proteínica y mineral contaminante. En América Latina, la cachaza puede concentrarse para producir un producto parecido a la melaza denominado “melote”.

Puede utilizarse todo tipo de melaza en la dieta de los rumiantes. La suplementación es decisiva para lograr niveles altos de productividad, y debe proporcionar (i) los nutrientes complementarios necesarios para la actividad de los microorganismos del rumen, (ii) los estímulos físicos necesarios para lograr un funcionamiento adecuado del rumen, (iii) nutrientes sobrepasantes para equilibrar los productos de digestión del rumen, con arreglo a las necesidades del animal. En la práctica, estas necesidades pueden satisfacerse con menor costo añadiendo urea en la melaza (25 g urea/kg melaza) y suministrando cantidades limitadas de un forraje con alto contenido de proteínas (por ejemplo las hojas de un árbol leguminoso), que puede ser al mismo tiempo una fuente de nutrientes para el rumen y para el animal.

Los productos de fermentación de la melaza en el rumen padecen un desequilibrio particularmente acusado de precursores de glucosa (baja proporción de propionato y alta de butitato) que pueden ser un factor inductor de desórdenes metabólicos (toxicidad de la melaza) que provoquen necrosis cerebral y la falta de idoneidad de una dieta a base de melaza para la producción de leche. La alimentación con gallinaza aumenta la productividad animal y la eficiencia de los piensos en las dietas a base de melaza, al parecer porque cambia la estructura de los ácidos grasos volátiles hacia proporciones más elevadas de propionato.

En el caso de los cerdos y las aves, las tasas de rendimiento (y la humedad de los excrementos) están en función directa de la proporción de sacarosa y/o azúcares reductores en la melaza. Los mejores resultados se obtienen con melaza rica y los peores con las melazas finales.

Se utilizan comercialmente sistemas de alimentación a base de melaza con los cerdos, pero no con las aves de corral.

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