Harvest of sugar cane straw : drying and composition, ammonia/urea treatment and use for feeding dairy heifers

On account of the large areas involved, sugar cane is an abundant source of biomass for feeding animals. CIRAD has undertaken research on three aspects: (1) harvest and baling/storage of sugar cane residues, (2) improvement of feed value by ammonia treatment, and (3) feeding of store animals with this fodder. During straw drying, the trend of dry matter (DM) content is an increasing logarithmic function of the cumulative saturation deficit of the air (r2=0 .91). Bales harvested are mainly composed of leaves; unlike the leaves, which dry very well, the stem pieces and cane tops do not. Several tests were performed on different methods of treatment. For treatment in the baler (4.8% urea in relation to straw DM), the resulting product is uniform, giving a 16% increase in digestibility. For application in stacks, the result is less homogeneous (the lower part of the bales being less well treated). The increase in digestibility is 12% for an addition of water of 70 l per bale and a urea/DM ratio of 6% and 26% with a water addition of 100 l per bale with a urea/DM ratio of 8.4%. Two feeding trials have been conducted on growing Holstein dairy heifers. In trial 1, 11 heifers were given urea treated sugarcane straw plus 1 kg molasses (treatment U1), and 11 heifers were given untreated sugarcane straw plus 1 kg molasses urea mixture (treat. C1). In addition, both groups received 3 kg concentrate plus a mineral and vitamin mixture daily. The voluntary dry matter intake (DMI) of the roughage was greater for U1 than for C1: 1.8 and 1.4 kg per 1OO kg live weight (LW) respectively. The daily weight gain (DWG), 896g/d and 741g/d for U1 and C1 respectively, was significantly different (P< 0.05). In the second trial, 20 heifers were given urea treated sugarcane straw plus 0.5 kg molasses (treat. U2) and 20 heifers were given untreated sugarcane straw plus 0.5 kg molasses urea mixture (treat. C2). In addition, both groups received 4 kg concentrate plus a mineral/vitamin mixture daily. The DMI was the same as in trial 1 for both U2 and C2 group. The DWG was not significantly different (P>0.05), with 700g/d and 679g/d for the U2 and C2 groups respectively. More investigations are needed in order to determine the ideal supplementation for such a roughage. (Résumé d'auteur