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Fattening beef cattle on molasses in the tropics

T.R. Preston*

Molasses vs grain

From an agricultural point of view, the tropical regions of the world are probably the richest in potential for crop production, and subsequently for animal production. Nevertheless, until rather recently, there has not been the development of intensive feedlot fattending that has taken place in the developed and developing countries in more temperate regions of the world, e.g., the United States and Yugoslavia. The only exception to this is perhaps Hawaii, but this is atypical since the cattle industry there is based almost entirely on imported grain from North America.

* Formerly of the Instituto de Ciencia Animal, Calle 30 No 768-1, Nuevo Vedado, Havana, Cuba; now Animal Production and Health Division, FAO, Rome.

It is the absence of indigenous grain production which, more than anything else, has delayed development of fattening systems in tropical regions. Rice is certainly one cereal that can be grown in the tropics, but this is the staple of the human diet in such areas, and very rarely has it been grown for animal feeding. Other more typical feedgrains, such as maize and sorghum, can be and are produced in the tropics but, up to the present, success with these crops has only been on a subsistence basis, and the techniques for their largescale mechanized production have yet to be developed.

Work in Cuba aimed, among other things, at developing intensive beef production systems, and following the pattern of developments elsewhere, early attention was concentrated on the production of feedgrains. However, it soon became apparent that economic viability of such a programme was likely to be, at best, a long-term operation, requiring development, among other things, of locally adaptable varieties, suitable to the climate and resistant to the considerable insect and fungal attacks which are commonplace in the tropics. There was also the need to evolve appropriate agronomic procedures to establish such crops and maintain them free of weeds in the hot and humid climate typical of the wet tropics. Such a programme would have required many years of research and development before the large-scale production of cereal grains capable of supporting an intensive animal industry could be considered.

It was the realization of this situation that led the writer to examine the possibilities of using other energy sources which, although perhaps somewhat exotic from the point of view of their current use for livestock production in other parts of the world, nevertheless had the advantage of being available in large quantities as by-products of other established industries. Sugarcane molasses was the obvious choice for development, in view of the fact that in almost all tropical countries sugarcane is grown both to satisfy national requirements for sugar and also to serve as the principal earner of foreign exchange from exports. Development of livestock feeding systems based on sugar by-products was particularly appropriate to Cuba, in view of its preeminent role as the world's major exporter of cane sugar. In Cuba, since approximately 1 ton of molasses is produced for every 3 tons of sugar, this is equivalent to the availability of some 2 million tons of what, theoretically, is a highly valuable source of energy from the point of view of chemical composition.

Development of a molasses feeding system

On examining the literature related to feeding molasses to cattle it was apparent that, although its use in livestock feeding had been known for a considerable time, it was rarely expected to provide more than 5 to 10 percent of the total ration. In fact, recommendations by such eminent authorities as Morrison suggested that the maximum limit of molasses in the diet should be 10 percent, since at higher levels, for example up to 30 or 40 percent, its feeding value could be expected to decline by almost 50 percent.

Another feature of its use, at least in developed countries, has been as an integral component of an otherwise dry ration. For a developing country, this would seem an unprofitable source of development since, because of its highly viscous nature, considerable mixing difficulties would be bound to arise as soon as attempts were made to include high levels in the ration. The fact that feed mill facilities are also invariably limited in these countries was another reason for not pursuing this line of thinking.

It was, therefore, decided that from the outset the system must be based on feeding the molasses in liquid form, apart from the other more bulky components of the diet. Free choice feeding in simple open containers was another prerequisite as this would ensure minimum trough space requirements. It also seemed unnecessary to have the complicated feeding devices, said to be necessary to avoid overeating—a completely undocumented claim— but which certainly would have involved the country in considerable expense, were the system to be developed and applied on a countrywide basis.

Another initial-decision was that the known protein deficiency of molasses (normally containing only some 3.5 percent of N×6.25) should be supplemented by nonprotein nitrogen, specifically urea. The reasons for this were that indigenous sources of true protein were almost nonexistent in Cuba, and urea, being highly soluble, could easily be distributed uniformly (and hence safely) in the liquid molasses.

Cereal grain and fresh forage were examined as other possible ingredients to be fed along with molasses. The results shown in Table 1, obtained with Brahman type cattle given free access to molasses/urea and either freshly cut elephant grass or a cereal grain mixture, indicated the following. While performance was best when molasses was used as a supplement to cereal grain, actual molasses intake was almost insignificant, comprising no more than some 15 to 30 percent of total metabolizable energy (ME) intake. As a supplement to forage, molasses intake was much higher—of the order of 50 percent of ME. However, with this combination, animal performance was less than half of that achieved on the grain-based diet. It was also clear that molasses was not a particularly palatable ingredient at other than relatively low concentrations of the total diet, and was much less acceptable by the animal than grain.

Table 1. Performance of Brahman bulls given free access to molasses with 3 percent urea and either ground sorghum grain or fresh elephant grass1

 Molasses urea and:
Number of bulls80246
Initial weight194218
Final weight368398
Daily gain0.970.59
Daily intake  
Feed conversion, (Mcal ME/kg - gain in LW)18.843.0

1 Source: Preston and Willis. 1969.

Figure1. Crossbred Brahman bulls on molasses feeding in a 10 000-head feedlot in Camagüey province

Figure 1

Figure 2

Figure2. Molasses tanker replenishing the feed troughs. Note the roof to protect the molasses from rain and sun

Nevertheless, relative palatability of a feed is a poor measure of its value to the animal which, if given no choice, may eventually eat as much of the apparently less palatable feed as of what would be more acceptable. To assess the validity of this alternative, it was therefore decided to restrict consumption of the other components of the diet in the hope that this would lead to greater intake of molasses and, as a result, to better performance.

Table 2. Performance of Brahman bulls given ad libitum molasses with 3 percent urea and either ad libitum forage (maize) or restricted forage (1.5 percent of LW) and concentrate supplement (0.4 percent of lw)

Ad libitumRestricted
Number of bulls2423
Initial weight220210
Final weight385390
Daily gain0.630.76
Feed intake  
Feed conversion (Mcal me/kg gain)32.820.6
Killing out51.752.3

1 Source: Martin et al., 1968.

In fact, the latter decision proved to be the breakthrough point for the development of the molasses feedlot system. The results in Table 2 show the considerable improvement in animal performance due to restricting forage intake to approximately 1.5 percent of the animal's live weight (on a fresh weight basis) as opposed to providing forage ad libitum. By this procedure, the daily intake of molasses was increased by some 50 percent. However, of greater significance was the improvement in animal performance, particularly with respect to the feed conversion rate.

Importance of supplementary true protein

The nutritional aspects of this new feeding system showed not only that molasses was contributing some 80 percent of the total dietary energy but that the associated urea represented some 50 percent of the total dietary nitrogen intake. The latter was at variance with generally accepted recommendations for nonprotein nitrogen (NPN) use in beef cattle fattening, which is that this should not exceed about 30 percent of total nitrogen requirements. At about the time that such traditional thinking on the extent of NPN utilization by ruminants was thus being challenged, R.E. Hungate in California had begun to make some theoretical estimates of expected rates of rumen microbial protein synthesis based upon in vitro findings. He concluded that the limitation to NPN utilization was the amount of the dietary energy made available in the rumen, and proposed that for every 100 grammes of dietary organic matter potentially digestible within this organ, one could expect a microbial synthesis equivalent to some 7 grammes of crude protein. A molasses-based diet was particularly appropriate for this type of calculation since the bulk of its energy contents was in the form of soluble sugars, which could be expected to be completely available for rumen fermentation.

On the basis of Hungate's calculations and assuming the feed intakes recorded in Table 2, it was estimated that the potential rate of microbial protein synthesis would be of the order of 250 grammes daily. When this figure was compared with expected protein requirements for a daily gain of 1.0 kilogramme (some 700 to 800 grammes daily), according to National Research Council Standards (NRC, 1970), it was apparent that considerable amounts of additional protein were needed in order to supplement that of microbial origin.

Figure 3

Figure 3. Simple open troughs are all that is needed when molasses is fed ad libitum

The nature of the protein supplement was obviously an important consideration since, to act effectively as a complement to the microbial protein produced by the rumen organisms, the supplementary protein should itself not be degraded during passage through the rumen. In this way it would reach the abomasum and small intestine as more or less “intact” protein, so that the constituent amino acids could contribute to the animal's requirements, with minimum loss. Since it is now widely understood that the degree of degradation of a protein in the rumen is a direct function of its solubility, the first restraint was that the protein should be of low solubility. It was also clear that its value to the animal would be a direct function of its balance of essential amino acids; therefore the second restraint was that it should have a high biological value.

In view of these considerations, it was decided that the most appropriate source of protein would be an animal protein which had received considerable heat treatment during its manufacture. Fish meal seemed the best in terms of the required characteristics.

The next stage was to determine the minimum amount of feed needed in order to achieve optimum animal performance, and specifically to confirm the accuracy of the calculations based on Hungate's theoretical predictions. The theoretical amount of supplementary protein required daily was 700 - 250 = 450 grammes. It was therefore decided to evaluate experimentally a range of levels from zero to the stated figure. The outstanding results of this trial are shown in Figure 4. In broad terms, the data support the proposed hypothesis relating to the need for supplementary protein over and above that resulting from microbial synthesis. Specifically, the implication is that Hungate's original estimates were on the low side. More realistic revised values, in line with these experimental findings, have since been proposed by D.J. Walker of Australia, i.e., that in practice maximum economic response is likely to be obtained by giving, on average, some 400 to 500 grammes of fish meal daily to animals in the weight range used here (i.e., 200 to 400 kilogrammes).

Figure 4. Effect on gain (x) and conversion (o) of substitution of urea by fish meal in molasses-based diets for fattening bulls (from Preston and Martin, 1971)

Figure 4

Table 3. Input-output data (January-June) for fattening bulls1 on molasses-based compared with forage-based diets in a 10 000-head capacity feedlot2

 Forage-based diet. 1969Molasses-based diet. 1970Improvement due to molasses
Daily live-weight gain per:KilogrammesPercent
Unit feed DM intake
Mortality0.11.0- 1 000
Emergency slaughter0.43.04- 780

1 Mean initial and final weights were 284 and 396 kilogrammes; breeds were Brahman and Holstein × Brahman.
2 Source: Muñoz et al., 1970.

Commercial application of molasses fattening in feedlots

The broad findings of this experimentation now form the basis of the national plan for beef cattle fattening in Cuba. Large-scale commercial evaluation of the system began in October 1969 and, in the current dry season, probably some 200 000 animals will be receiving this type of feeding.

The data in Table 3 show the economic results of the first largescale trial of the molasses fattening system applied in a 10 000-head feedlot from January to June 1970. A comparison is made with the comparable period in 1969, when the feeding system was ad libitum forage and restricted molasses and concentrates. With respect to the most important economic parameters — live-weight gain per animal, per worker, per tractor and per unit of food consumed — there have been very important improvements in productivity as a result of adopting the molasses feeding plan.

Molasses toxicity

The negative component is clearly the higher incidence of loss due to death and emergency slaughter. Almost all the problems have been associated with a metabolic upset — molasses toxicity — which appears to have something in common with the nervous disease known in Europe as cerebrocortical necrosis and in the United States as polioen-cephalomalacia, the end result of which is brain damage due to interferences with the animal's supply of thiamin — a vitamin of the B complex — which has an essential role in an enzyme system supplying the brain with energy. The local term for this is borrachera, meaning “drunkenness,” since animals affected by the condition take on a specific drunken appearance. The disease is not so much related to excessive consumption of molasses as it is to an inadequate forage intake, since it can be induced simply by removing forage from the diet entirely. Management is thus very important in reducing the incidence of the disease to a minimum. For example, it is essential that the feeding procedure is such that all animals are able to consume at least minimum amounts of forage daily. They also recuperate rapidly if given access to forage, and if molasses is removed from the ration. Thus it is vital that in any commercial feedlot animals should be carefully watched for disease symptoms, so that those affected can be removed from the pens and given a change of diet as quickly as possible. In fact, some 80 percent of affected animals can be expected to recover provided remedial measures are applied rapidly.

The precise etiology of the disease is still not known with certainty, but related factors are high consumption of ethyl alcohol — caused by fermentation of the molasses prior to consumption — and an extreme type of rumen fermentation characterized by the production of very large amounts of butyric acid and only minimum quantities of propionic acid (the major precursor of glucose, the only energy metabolite that can be used by the brain).

Prophylactic measures recommended are: (a) ensuring that all animals receive some forage in the diet (a minimum equivalent to 1 to 2 kilogrammes of dry matter daily); (b) using only the minimum amount of water to dissolve the urea prior to incorporating it in the molasses, and avoiding rainwater entering the storage or feed troughs (the latter should be roofed in the rainy season); (c) where economically feasible, feeding from 0.5 to 1.0 kilogramme of ground maize (or sorghum) daily in an attempt to increase indirectly the supply of glucose.

Molasses fattening with restricted grazing in the dry season

When the decision was made in Cuba to apply molasses fattening on as large a scale as possible, it was obvious that the first limitation was feedlot capacity. At the time there was only space for some 70 000 head in the traditional type of feedlot, whereas in fact there were molasses and animals equivalent to some 150 000 to 200 000 head. A slight modification in the system was therefore proposed whereby the animals, instead of having the forage cut and transported to them, as in the conventional feedlot, were made to seek their own forage by grazing. A simple wire-fenced enclosure was constructed in the centre of, or adjacent to, a grazing area divided into 4 to 8 paddocks. Since this modification was designed for use only in the dry season — accumulation of mud would have made it impossible during the rainy season — a fairly low stocking rate had to be used, that is, some 4 to 8 animals per hectare. The usual size of a unit was some 400 head, and for this, the respective enclosure and grazing areas were approximately 2 to 3 and 50 to 100 hectares, respectively. The management procedure was to make freely available in the central corral the molasses and urea and the mineral mixture. The animals were confined in the corral except for two grazing periods, each of one to two-hour duration, morning and evening. When the animals were out grazing, the appropriate allowance of fish meal was mixed into the surface layers of the molasses/urea. Results from a sample of such units operated during the dry season of 1969/70 are summarized in Table 4. They show that performance on the restricted grazing plan was as good as in the feedlot; in fact, disease losses were considerably reduced, possibly because the animals had more opportunity to consume their minimum forage requirements.

Table 4. Input-output data for fattening bulls given ad libitum molasses/urea, restricted grazing and fish meal supplementation (3 500 bulls in 11 units)1,2

Daily live-weight gain(kg)1.040.830.74
Conversion (kg) feed/kg gain)   
Fish meal
Emergency slaughter0.00.441.33

1 Mean initial and final weights were 313 and 403 kilogrammes; breeds were Brahman and Holstein × Brahman.
2 Source: Morciegoet al., 1970.

Current recommendations

The present procedure for molasses fattening under feedlot conditions is shown in Table 5. The recommendations relating to phase feeding of the protein also holds good for the restricted grazing system.


The success of molasses fattening of beef cattle in Cuba has resulted, above all, from the enthusiasm and dedication of certain individuals, and the foresight and confidence of various state organizations, all working together.

It is not possible to name all who contributed to its success but acknowledgements are due specifically to Ing. Arabel Elías, for important contributions in the early experiments, and to Sr. Leonardo Rodriguez, whose unfailing interest and active assistance helped to ensure that a promising experimental result successfully made the transition to a viable commercial venture.

Mention should also be made of the Institute of Animal Science, where the original research was carried out, and the Livestock Group of the Ministry of Agriculture of Camagüey province, who steered the feedlot system through the difficult “teething” stages and who made the major contribution to the development of the restricted grazing modification for use in the dry season.

Table 5. Recommended procedure for feedlot fattening of cattle on molasses-based diets

Weeks of fatteningDaily allowance (kg)
Fresh forageFish mealMolasses/urea1Minerals2
FirstAd lib0.5Ad libAd lib
Second150.5Ad libAd lib
Third100.5Ad libAd lib
Fourth100.5Ad libAd lib
Fifth to eighth100.4Ad libAd lib
Ninth onward100.3Ad libAd lib

1 Contains (percent): 2.5 urea, 0.5 common salt, 1.5 water, 95.5 final (blackstrap) molasses (first dissolve the urea and salt in the water at 50°C prior to adding this to the molasses).
2 Contains (percent): 50 dicalcium phosphate (or bone meal), 50 common salt (add 0.1 percent cobalt sulphate if soil is deficient in this element).


Hungate, R.E. (1966). The rumen and its microbes. New York. Academic Press.

Martin, J.L., Preston, T.R. and Willis, M.B. (1968). Intensive beef production from sugar cane. 6. Napier or maize as forage sources at two levels in diets based on molasses urea. Rev. cubana Cienc. agric. (Eng. ed.) 2: 175.

Morciego, S., Muñoz, F. and Preston, T.R. (1970). Commercial fattening of bulls with molasses/urea and restricted grazing. Rev. cubana Cienc. agric. (Eng. ed.) 4: 97.

Morrison, S.H. (1967). 1967-68 ingredient analysis and estimated feed value table for beef, sheep rations. Feedstuffs. 25 Nov. p. 39.

Muñoz, F., Morciego, S. and Preston, T.R. (1970). Commercial fattening of bulls on molasses/urea, fish meal and restricted forage under feedlot conditions. Rev. cubana Cienc. agric. (Eng. ed.) 4: 91.

nrc. 1970. Nutrient requirements of beef cattle. Publ. No. 4. Natl. Acad. Sci. Washington, D.C.

Preston, T.R. and Martin, J.L. (1971). Replacement of urea with fish meal for cattle fattened on molasses-based diets. (In preparation)

Preston, T.R. and Willis, M.B. (1969). Sugar cane as an energy source for the production of meat. Outlook in Agric. Vol. 6, p. 29.

Walker, D.J. (1970) (cited by Hogan, J.P. and Weston, R. H. (1970). Quantitative aspects of microbial protein synthesis in the rumen. In Physiology of digestion and nutrition of ruminants (Ed. A.T-Phillipson). Newcastle-on-Tyne. Oriel Press.

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