Compositional analyses and rumen degradability of selected tropical feeds

Abstract

The chemical composition (nitrogen fractions, fibre components, phenolic compounds, neutral sugars and uronic acids) and rumen degradability of the dry matter (DMD) and neutral detergent fibre (NDFD) of six crop by-products (raw palm oil mill effluent (POME), dried POME, palm kernel cake, palm press fibre, cocoa pods and rice straw) and the leaves of two legumes ( Leucaena leucocephala and Gliricidia sepium) were measured. Univariate and multivariate statistical analyses were used to compare and classify the feeds according to chemical composition and degradability. Lignin poorly differentiated between feeds and was poorly related to 48 h DMD; the major anomalies were with rice straw and Gliricidia (low lignin, low DMD) and cocoa pods (high lignin, high DMD). The xylose: arabinose ratio, an indicator of hemicellulose digestion, was higher in the legumes than in the by-products. The ratio of rapidly degradable (arabinose + glucose) to slowly degradable (xylose + uronic acids) sugars was not a good indicator of cell wall digestion; the correlation with 48 h NDF degradability (NDFD) was only 0.69. Cluster analysis showed that conventional classification of the feeds into by-products and legumes did not reflect their compositional or degradability attributes. These attributes were also poorly related to each other. Two unusual feeds were identified, cocoa pods and palm kernel cake.