In sacco degradability, chemical and morphological composition of 15 varieties of European rice straw

Abstract

The aim of this study was to evaluate the variability in chemical and morphological variables of European rice straw varieties and to relate these variations to changes in in sacco degradation. Fifteen rice straw varieties were analyzed for their chemical and morphological compositions. Ground (2 mm) straw was incubated in the rumen of three ruminally cannulated cows for 24 and 72 h for in sacco degradability measurements. Results were analyzed by principal component analysis (PCA) and equations are proposed for degradation of rice straw in the rumen according to morphological and chemical variables. Both chemical and morphological characteristics presented great variability. Mean values, on a dry matter (DM) basis (%), for ash, silica, crude protein (CP), ash-free neutral detergent fiber (NDF), ash-free acid detergent fiber (ADF), and acid detergent lignin (ADL), were 11.2, 6.8, 3.9, 75.8, 45.7 and 9.3 respectively. Mean values, on a DM basis (%), for stem (internodes+nodes), leaf blade, leaf sheath and chaff were 22.7, 32.7, 35.8 and 7.5 respectively. Variation in the in sacco degradation (%) of DM and organic matter (OM) was observed among straw varieties at 24 and 72 h: 30.4 (26.6–36.3) and 50.3 (43.6–57.6) for DM degradation; 29.0 (23.6–35.6) and 50.2 (42.2–58.7) for OM. The principal component analysis discriminated degradation parameters with botanical and chemical parameters. Degradation (%) was positively related to total leaves and leaf blade fractions and hemicelluloses, and negatively related to stem fraction, NDF, cellulose and lignin. Cumulative equation with both leaf blades (morphological variable) and hemicelluloses (chemical variable) explained 62 and 66% of variation in OM degradation at 24 and 72 h, respectively.