An approach to the determination of rumen degradability of nitrogen in low-grade roughages and partition of nitrogen therein

Summary Rumen degradability of dry matter (D.M.) and N in wheat straw, rice straw and local grass hay, containing 5·16, 6·37 and 4·58 mg N/g D.M. respectively, was estimated by rumen fermentation measurements at 3, 6, 9, 12, 24 and 48 h using the nylon bag technique. The degradability of D.M. at an assumed rumen outflow rate of 0·025/h was 21·7, 34·9 and 22·4 for wheat straw, rice straw and grass hay, respectively. Theestimation of degradability of N was confounded by thedeposition of ruminal microbial nitrogen in the nylon bag. A correction was made by measuring the accumulation of N when N·free fibre and cellulose were incubated in the nylon bags. The effective degradability of N in the roughages at the assumed rumen outflow rate was 54·5, 36·9 and 42·8% respectively, showing that the roughages contain rumen-degradable N for microbial nutrition. The undegradable nitrogen (UDN) values in wheat straw, rice straw and grass hay were 2·35, 4·02 and 2·62 mg/g D.M., and after correction for unavailable acid detergent-linked N, the available UDN values were 0·58, 2·95 and 1·32 mg/g D.M., respectively.