Sugarcane molasses is extensively used in feeding ruminant, both as a binder for compound feeds or to supply additional energy to the diet (Pate et al., 1989). It is usually mixed to the feed, but it may be sprayed on low quality roughage to improve its palatability and increase intake (Leclerc, 2003).
When used as an energy feed, for example to replace grain, moderate amounts of molasses are usually recommended (10-20% of the diet DM). Variable animal responses have been observed at these levels, depending on the relative proportions of the other diet ingredients (forage:concentrate ratio, starch content, etc.). For instance, in temperate areas, 10% molasses is recommended for animals fed energy-rich diets, but it is possible to include up to 15% if the diet contains straw or hay. The following inclusion rates have been proposed in Western Europe (Leclerc, 2003):
||0.25-0.5 kg/d for animals up to 200 kg LW
1-2 kg/d for animals over 200 kg
Many studies showed equal or greater animal performance when molasses was substituted for maize grain (Morales et al., 1989). When molasses accounts for less than 20% of the total DM intake, their carbohydrates contribution tends to be complementary, rather than competitive with the others ingredients of the diets (Preston, 1986). Small amounts of molasses in a roughage-based diet stimulate rumen fermentation and the rumen cellulolytic potential is maintained or improved with low quality forage diets. For instance, an early study in Australia with Friesian and Jersey cows, grazing irrigated and N-fertilized pangola grass (Digitaria eriantha), found that supplementation with molasses/urea raised milk yield by an average of 0.67 kg milk/kg molasses with Friesians, and 0.39 kg milk/kg molasses with Jerseys. Molasses supplementation generally increased lactation length and the percentage of non-fat solids in the milk (Chopping et al., 1976). In a study with growing tropical bulls fed rice straw, the best growth (982 g/d vs. 682 g/d) was obtained with 15% molasses + urea; however, 30% molasses depressed growth. 10% molasses improved the daily gain of animals fed rice straw and a grass-legume mixture (Huque et al., 1995). When fed alone to cattle or mixed with only 3% urea, the palatability of molasses was not affected and therefore it should be restricted to 2-3 kg/d. If used as a carrier for higher concentrations of urea, the bitterness of the urea serves as an auto-regulator causing the cattle to consume about 1 kg/d (Pérez, 1995).
Higher amounts of molasses (above 20%) in the diet can be detrimental to animal response, particularly in the lactating dairy cow. Rumen turnover increases, possibly due to higher intakes caused by better palatability. Molasses can depress performance in comparison to isoenergetic grain-based concentrates, and reduction in milk yield or milk fat yield has been observed in cows fed 15 to 22% (diet DM) molasses (Granzin et al., 2005). As stated above, with the bull study 30% molasses depressed growth (Huque et al., 1995). Depression in the efficiency of metabolic energy utilisation for net energy has been observed. This has been attributed to modifications in the production of volatile fatty acids in the rumen, resulting in reduced fibre digestion and lower forage intake (Granzin et al., 2005). Competition between the faster-growing amylolytic bacteria in the rumen and cellulolytic micro-organisms results in a decrease in the number of cellulolytic micro-organisms present, leading to a reduction in fibre digestion. Inclusion of large amounts of molasses is not always negative: in a study with crossbred steers fed cottonseed meal and hay, including up to 30% molasses (diet DM; 2.8 kg/d DM of molasses) resulted in an increased rate of growth (850 g/d vs. 540 g/d). However, the daily gains obtained with molasses were lower than those obtained with the same proportion of soybean hulls or maize grain (Royes et al., 2001).
Molasses is deficient in nitrogen and, therefore, N supplementation is often required to optimize rumen fermentation and to provide by-pass protein to balance the nutrients available for the animal's metabolism. Adding urea to molasses is a common method to improve its nitrogen status (Preston, 1986).
A number of trials have shown that molasses-based liquid supplements containing urea tend to be inferior to supplements providing natural protein. However, in tropical regions, liquid supplements formulated with urea can be less expensive and economically advantageous (Kalmbacher et al., 1995). Urea has to account for 2.5% of the fresh weight of molasses to provide the ratio of fermentable nitrogen to carbohydrates required for the efficient growth of rumen micro-organisms. No toxicity is observed up to 3% urea in the fresh molasses (Preston, 1986), but 8-10% results in a decrease in feed intake. To prevent urea toxicity, the equivalent crude protein from non-protein nitrogen in a molasses-based feed should not exceed 15% of total crude protein, unless it is a formula that limits intake (Pate et al., 1989).
Nitrogen supplementation is not always required. Feeding molasses to cattle grazing green pasture with a high nitrogen content is beneficial and does not necessitate additional fermentable nitrogen (Preston et al., 1987).
The sulfur content of molasses is high and may antagonize liver tissue accumulation of Se in cattle. A daily intake of 2.5 mg of supplemental Se from sodium selenite or selenite yeast sources would be needed for cattle consuming sugarcane molasses (Arthington, 2008).
As molasses is deficient in phosphorus, it is necessary to add phosphoric acid to the mixture or provide livestock with mineral supplementation (Pérez, 1995).
Molasses are rich in potassium and should not be mixed with other potassium-rich ingredients such as whey (Leclerc, 2003).
Example of utilization in Cuba
A commercial beef fattening system, developed and used in Cuba since the 1970s, is based on free-choice final molasses mixed with 3% urea, restricted fish meal or another protein source, restricted forage (3% LW) and a free-choice mineral mix of 50% dicalcium phosphate and salt. The molasses/urea mixture, which represents about 70% of the total diet DM, contains 91% final molasses and 6.5% water. Urea and salt are first dissolved in water before being mixed with the molasses; this mix is top-dressed, once daily, generally with 70 g of bypass-protein (fish meal) per 100 kg LW. In a large feedlot operation, the daily ration/head is calculated as follows: 90 g mineral mix, 250 g fish meal, 6 kg molasses/urea and 10 kg forage. The average daily gain ranges between 0.8 and 1 kg/d. However, under average feedlot conditions the gains are between 0.7 and 0.8 kg/d. Although molasses can completely replace cereals in a beef feedlot operation, such is not the case with milk production, particularly with high producing dairy cows. In this case, the molasses/milk system does not perform adequately. It has been postulated that the problem could be one of insufficient glucose precursors related to the digestion of the molasses, particularly since the demand for this nutrient is greater in milk than in beef (Pérez, 1995).