Rumen degradation of straw 9. Effect of cellulase and ammonia treatment on different varieties of rice straws and their botanical fractions

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Abstract
The composition and degradability of four varieties of rice straw were examined. The varieties were tall or short and early or late maturing. The straws and their botanical parts (leaf blade plus leaf sheath, internode, node and chaff) varied in acid-detergent fibre, ash and silica contents, but not in nitrogen and neutral-detergent fibre. There were some trends but no significant difference in proportions of parts between varieties. Milled samples of whole straw and its parts were either untreated, treated with a cellulase preparation plus propionic acid, treated with ammonia, or treated with cellulase then ammonia. Rumen degradability was measured by incubating the samples in polyester bags suspended in the rumen of sheep. The soluble fraction and potential degradability were greater in untreated short and early than in tall and late varieties, but rates of degradation did not vary significantly. Internode was more degradable than leaf. Cellulase and/or ammonia treatments increased the soluble fraction, especially in tall and late varieties, and increased potential degradabiiity except in internode. Degradability correlated positively with ash and silica contents.