Feed value of Tanzanian sisal wastes: Chemical composition and digestibility in vitro

Abstract

Characteristically, fresh sisal waste was found to contain 90% moisture and have a low pH of about 4, but when put in the open, the waste was very unstable and underwent a rapid fermentation which was characterised by an initial increase in pH and the emission of odorous gases; later the pH remained more or less constant and Diptera maggots developed within 88 h. The fermentation resulted in significant ( P < 0.01) increases in the proportion of crude fibre (CF), significant reductions in nitrogen free extract (NFE), dry matter digestibility in vitro (IVDMD) and organic matter digestibility in vitro (IVOMD). Formaldehyde added at rates of 4.6, 9.2 or 13.8 ml/100 g dry matter (DM) prevented these changes, but NaOH (1.54, 3.08 or 4.62 g 100 g DM ) inhibited fermentation only temporarily (< 16 hours). The recovery rates of DM and NFE after 88 h of fermentation were predominantly less than 70 and 60%, respectively, in both the control and the NaOH-treated samples, but formaldehyde increased the recovery rates to 80–90% of both DM and NFE. The recovery rates of CP and CF were of the same order, but were less consistent. In Experiment 2, sisal-waste samples were dried in the sun then winnowed and separated into fine and medium pulp and large particle pulp plus cuticles. The CF content was highest ( P < 0.01) in the large particle pulp plus cuticles, while IVDMD and IVOMD decreased with increasing particle size and the digestibility coefficients of the large particle pulp plus cuticle were extremely low. It is suggested that cutin and CF of the cuticle contributed to indigestibility.