Rumen degradation of straw 5. Botanical fractions and degradability of different varieties of oat and wheat straws

Straw from six varieties of oat and 12 varieties of wheat were divided into their botanical fractions of leaf plus leaf sheath, internodes, nodes and chaff, and the rumen degradabilities of the individual fractions determined by the nylon bag method. The proportions of the fractions varied between varieties, but more so within wheat than within oat straw. The proportion of leaf plus leaf sheath varied from 0·27 to 0·37 for wheat and 0·29 to 0·33 for oats with the proportion of stem ranging from 0·41 to 0·51 for wheat and from 0·55 to 0·60 for oats. There were also differences in degradation characteristics, more evident in wheat than in oats. The 48-h degradability varied from 570 to 650 g/kg for wheat leaf plus leaf sheath and from 300 to 380 g/kg for wheat stem. The respective ranges for oat straws were from 480 to 530 and from 250 to 280. Generally, the wheat straw varieties, and in particular leaf from wheat straw, were of a higher degradability than oat straw. The mean 48-h degradabilities of wheat and oat leaf were 615 and 501 g/kg respectively. There was no relationship between the nitrogen content of leaves or stems and their degradability.