Sugar cane feed by-products: molasses, juice and stalk compared

Why tropical feed researchers turned to sugar cane#

The paper opens by describing sugar cane as a crop with strong agronomic credentials for the tropics: it copes with varied soil types, grows back year after year without replanting, and resists many pests, alongside a well-developed breeding and management base. For most of its history it had been grown almost solely to make sugar, but the paper notes that the preceding decade's energy crisis had pushed researchers and industry to look seriously at other uses for the crop and its residues.

Underlying the whole review is a stark economic contrast. Tropical countries that grow most of the world's sugar cane were typically exporting molasses at low prices, under $80 per tonne, while importing cereal grain for livestock at prices above $150 per tonne. That price gap, the paper argues, created a strong case for building feeding systems around home-grown molasses and juice rather than imported grain.

To organise the analysis, the paper sets out the various ways sugar cane can be processed and the feed-relevant residue each pathway leaves behind: conventional factory sugar milling, small-scale farm boiling for unrefined sugar, a derinding process aimed at particle-board manufacture, and schemes growing cane mainly as fuel. Each pathway, it argues, needed its own dedicated feeding trials because the by-products differ markedly in composition and handling requirements. This index holds the paper among the RAAN Conference Proceedings, alongside other work from the same conference series.

How the evidence on sugar cane feed by-products was assembled#

Rather than a single experiment, the paper brings together results gathered over many years of trials run mainly in Cuba, Barbados, Mauritius, the Dominican Republic and Mexico, with additional material from a feeds research centre in Trinidad. The species studied ranged widely, from crossbred cattle to pigs, chickens, ducks and turkeys, reflecting how differently each type of animal might make use of liquid or fibrous cane residues.

The trials measured outcomes such as liveweight gain, feed conversion, carcass yield and, in some comparisons, how firm or loose the animals' faeces were. Several of the tables set feeding regimes directly against each other: different molasses types compared in pigs and ducks, maize compared with a concentrated cane juice product in turkeys, and whole chopped cane compared with the separated stalk interior in growing cattle. Basal diets of molasses, juice or fibre were tested with a wide variety of added protein and forage sources across the different trial sites.

The review draws a clear line between by-products judged to have real commercial promise, among them ordinary and concentrated molasses, the central portion of derinded stalk, raw cane juice, pressed fibre left after juice extraction, and the leafy tops of the plant, and two by-products it treats as largely unsuitable for feed: the burnt fibrous residue from milling and the muddy filtration waste, both described as poor in nutritive value.

What the molasses-based trials showed#

The Cuban trial that opened this line of research achieved growth rates over 800 g/day in crossbred Zebu bulls on rations drawing most of their energy and nitrogen from molasses and urea. That result led to commercial-scale feeding arrangements in both feedlots and semi-confinement systems, and later work found that adding only small amounts of fish meal, under 400 g/day, to these high-urea rations was an early practical demonstration of protein that survives rumen breakdown and is absorbed further along the digestive tract.

Subsequent studies in other countries refined the basic molasses system by substituting better forage for part of the ration. In Mauritius, fresh leaf material from a tropical legume tree took the place of native pasture and groundnut meal in molasses rations for growing bulls. In the Dominican Republic, forage grown from cassava or sweet potato plants supplied protein and bulk alongside molasses and urea, and adding poultry litter to a basal diet further lifted cattle performance.

Even so, the paper is explicit about where molasses falls short. Its digestible energy value, around 13 MJ/kg DM, sits close to that of sorghum grain at 14.6 MJ/kg DM, yet its usefulness only holds when it makes up a small share of the diet, under 10%; beyond that point its relative value compared with grain drops away, a decline the paper describes as worse for milk output than for beef production. It links this to reduced microbial protein reaching the animal under heavy protozoal activity in the rumen, and to a shortage of compounds needed for glucose supply because the rumen fermentation of molasses tends to favour butyrate production rather than letting sugars bypass fermentation entirely.

Derinded stalk versus whole cane, and the promise of cane juice#

Trials conducted in Barbados fed young dairy cattle a diet built around the ground central portion of stalk left after rind removal, with added cane tops, urea and a protein meal, and recorded very strong growth. Yet the paper notes this approach never moved into commercial practice, largely because the equipment needed to separate rind from pith is costly and complex, poorly matched to the farm scales found in the developing countries where it would matter most.

A second problem proved just as important: once both diets were properly supplemented, the derinded stalk gave little advantage over simply chopping the whole cane plant, even though the separated stalk material digests more fully in the rumen than the whole plant. Later Dominican Republic work confirmed that, without added forage or protein, derinded stalk actually performed worse than whole cane, suggesting the rind contributes nutrients that the pith alone lacks.

Cane juice offered a more encouraging path. A simple single-pass mill, extracting roughly 60% of the available juice, was proposed as a low-cost, farm-scale alternative to full factory milling, leaving behind a fibre residue richer in sugars than ordinary mill waste. In Mexico, crossbred cattle grew faster and converted feed more efficiently on cane juice than on molasses, and pig trials found similar growth on cane juice to maize-fed controls but better feed conversion and carcass yield, a difference the paper links partly to savings in how much true dietary protein was needed.

Judging the weight of this evidence#

The review draws on a wide spread of trials run over roughly two decades, across several countries, species and farm scales, rather than reporting one controlled study with a single fixed protocol. That breadth helps when judging how far a feeding approach might transfer elsewhere, since similar positive responses to molasses-urea and cane juice systems turned up repeatedly in quite different settings. All the same, we think this body of work is better read as a set of converging pointers than as proof that any one ration will perform identically on a new farm, given how much the supplementation details, animal genetics and trial scale vary between the studies cited.

The paper itself flags an important qualification. It suggests that the drop in feeding value seen with high levels of molasses appears to be a bigger issue in molasses coming from very efficient sugar factories, naming Australia and Mauritius as examples, possibly because less sugar and more soluble ash remains in their molasses. That detail matters for Australian readers, since results from Caribbean or Cuban trials may not translate directly if local molasses composition differs.

A further caveat concerns the leafy tops of the cane plant. The review notes that tops are only available as a meaningful feed source where cane is cut by hand, because most leaf material is destroyed when fields are burnt ahead of mechanical harvesting. This ties the feed value of this particular by-product closely to harvesting method rather than to any inherent property of the plant.

Practical implications for feeding systems#

The paper lays out a staged picture of what different levels of supplementation can achieve. On their own, neither chopped whole cane nor derinded stalk supported more than maintenance of liveweight. Adding just urea and minerals allowed some weight gain on chopped whole cane, though derinded stalk needed some additional long roughage before urea and minerals alone would support any gain at all. Higher growth rates were described as achievable only once good-quality forage and a nutrient source able to bypass rumen fermentation were both included alongside the basic urea and mineral supplement.

On the fibre left over after juice extraction in the on-farm system, the review reports that this residue still holds a substantial share of sugars in its dry matter because extraction is incomplete, and that treating it with alkali can unlock a further portion of the cell wall carbohydrate, producing a feed with over 50% readily fermentable material. A ration built from this pressed residue, a legume forage including Canavalia ensiformis, and poultry litter, after alkali and urea treatment, was reported to break down faster in the rumen than fresh elephant grass. This index separately catalogues Canavalia ensiformis as a tropical legume for livestock feed (Dixon 1983).

Taken together, the paper judges final molasses and cane juice as the two by-products with the greatest promise for replacing cereal grain in intensive tropical livestock production, while noting that molasses still needs further work to overcome its limits, particularly for dairy production, and that cane juice systems depend mainly on finding an economic use, whether as fuel or ruminant feed, for the fibre left behind after juice extraction. The paper sits within this index's broader Recent Advances in Animal Nutrition community of conference proceedings.

Sources and further reading#

• Trove library search: find a library that holds the paper
• Meat & Livestock Australia: red meat industry research and marketing body
• Integrity Systems (NLIS and LPA): which runs NLIS, LPA and the National Vendor Declaration
• Feedipedia animal feed database: an open-access database of animal feeds

Questions#

— The Livestock Library team