Rumen degradation of straw 2. Botanical fractions of straw from two barley cultivars

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Abstract
Two varieties of barley straw, Corgi and Gerbel, which varied in degradability when incubated in the rumen in nylon bags, were chosen for further examination of botanical fractions and to see how each fraction responded to treatment with ammonia. The straws were separated into leaves, internodes, nodes and chaff. The average proportions of these fractions were respectively 0·499, 0·380, 0·055 and 0·065 in Corgi straw and 0·404, 0·512, 0·059 and 0·025 in Gerbel straw. For both varieties the degradability of the botanical fractions were leaves > chaff > nodes > internodes. Despite a similar chemical composition, the dry-matter loss (DML) values of leaves, internodes and nodes of Corgi were higher than those of Gerbel straw. The differences between varieties were larger for internodes and nodes than for leaves. The difference in DML of the two varieties at 48-h incubation was 132 g/kg DM. Of this difference, 25 g were due to differences in distribution of the botanical fractions and 107 g to differences in DML of the fractions. Ammonia treatment significantly increased the DML of all fractions except the nodes. The overall improvement due to ammonia treatment of the different fraction was internode > chaff > leaves > nodes.