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).
MOLASSES AS A FEED FOR RUMINANTS
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:
- optimization of rumen fermentation by supplying fermentable-N (urea) and some high quality green forage;
- balancing the nutrients available for metabolism, by providing bypass nutrients.
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:
- high protein forages which supplied much, and sometimes all, of the bypass protein as well as the roughage characteristics (Figure 3, Tables 1 and 5);
- Supplementation with poultry litter (Figure 2).
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).