Sugarcane and byproducts

Saccharum officinarum

Sugarcane tops

Sugarcane tops (SCT) are a major byproduct of the sugarcane industry which is left in the field after harvest and widely used for feeding draught animals or cattle owned by workers on the sugar estates or by the sugar companies. The `top' is removed from the cane at a very arbitrary point and this results in important variations in composition, especially of fibre content. Millers hold widely differing opinions on the optimum topping point but the concensus is that it should be at the highest fully formed node. SCT, therefore, consists of 3 distinct parts: the green leaves (blades, the bundle sheath and variable ammounts of immature cane.

SCT production varies considerably with variety, age, growing conditions and management practices. SCT represents up to 18% of the aerial biomass in Mauritius and Hawaii, giving a conservative estimate of 5 tonnes DM per ha (26% DM). This is theoretically sufficient to provide forage for 1 livestock unit (1 LU = 500kg) per ha.

In countries where sugar production is seasonal, livestock depend heavily on SCT, especially in the winter when the productivity of most other forage species is at its lowest. The seasonal availability of SCT, however, represents a constraint on its use and various methods of preservation (ensiling) have been tried.

Sugar-cane tops can be ensiled for better utilization of the large quantities available during the harvest season. Chopped sugarcane tops are easy to ensile and provide a palatable silage. Leaves from the cane plant can be included in the silage, but they lower the digestibility. The methods range from small plastic bag silos, below ground trench silos, above ground low-cost silos (1-4 tonnes), small concrete silos (2-6 tonnes) and large concrete silos (100-4000 T).

Loss of ensiled materials is low (5%) and the quality of the preserved material is very good. Silage made with cane tops and

1-5% (w/w) molasses and 1% ammonium sulphate compares very well with temperate crops silage. Preserving cane tops with ammonia, produced in situ from urea, has been successfully applied in small concrete silos (1-4 T) at small cowkeeper sites in Mauritius but it is possible to make good silage without additives.

Sugarcane tops are highly palatable with good intake characteristics but are low in protein and require supplementation. Fed on their own, animals either lose condition or just maintain themselves or at best have very low levels of production. It has been estimated that SCT can provide for maintenance and 2-4 litres of milk in Mauritius [Sansoucy, 1972!]. The reasons why low-

moderate levels of production are achieved in the latter case is because the small cowkeepers peel the cane tops, keeping the succulent central portion only, and the animals in turn select the succulent bundle sheath and eat very little green leaf. This is achieved by luxury feeding of the cane tops (up to 90 kg/head/day) to allow for selection by the animals.

Attempts to improve SCT by alkali treatment or with ammonia/urea does not produce the same improvement in feed value as with cereal straws. Fine chopping decreased, rather than improved intake. Ensiling with urea has the benefit of increasing the nitrogen content and hence the rumen nitrogen balance for cattle. Small silos are an economic method of achieving this, with a requirement of approx 5 tonnes of silage to feed 2 cows for 1 month.

The principles of supplementing SCT-based diets are essentially the same as decribed for whole sugar cane (satisfying the needs of rumen microbes for fermentable nitrogen (ammonia) and trace nutrients, and providing sources of protein, glucose precursors and long chain fatty acids able to bypass the rumen fermentation to balance the needs of production.

Pate [ref] obtained ADGs of 0.52 kg/day by supplementing SCT with 1 kg cottonseed meal while animals just maintained weight without it. Ferreiro and Preston [ref] obtained ADG of 0.84 kg/day when zebu bulls were fed 1 kg rice polishings with SCT. In Mauritius, SCT silage with 1 kg copra cake, 0.2 kg fishmeal, 0.5 kg rice bran and molasses/urea (3%) at 3 per kg per 100 kg LW gave ADGs of 0.57-0.67 kg [Deville et al. ref] but lower gains (0.41 kg/day) were obtained with SCT silage, molasses and copra meal [Tuazon]. However, all these results are still below the genetic potential of the animals.

With correct balance of both rumen nitrogen and by-pass nutrients, gains of over 1 kg per day have been obtained (590) on ad lib SCT and molasses but with different sources of nitrogen: urea, poultry litter and wheat bran. In Mauritius, gains of over 1.4 kg/day were obtained with finishing beef cattle on 15 kg SCT silage + molasses/urea (4%) at 1.5 kg per 100 kg LW + 14 kg brewers' grains + 1 kg cottonseed cake.

For milking cows, a UNDP-funded project has demonstrated the benefits of the judicious use of cottonseed cake as a supplement to SCT for small cowkeepers in Mauritius [Boodoo et al]. 1 kg cottonseed cake in late pregnancy and 0.25 kg per litre of milk were equally as effective as twice the quantity of commercial concentrates (maize/bran/CSC or GNC etc.). It clearly demonstrated that cowkeepers can increase their milk production from 5 litres per day to 13 litres per day by using the protein supplement.