Protein degradation in different feedstuffs labelled with 15N by using the nylon bag technique

The nylon bag technique was used to determine the Nitrogen (N) and 15N degradation of 15N labelled feedstuffs in the rumen. The N and 15N degradation values were calculated according to Orskov and McDonald (1979) and ranged from 46.8 to 92.0 and from 61.8 to 93.6%, respectively. The differences between N and 15N degradation values of high fibre content feedstuffs are the highest, thus the measuring errors were greatest here. But differences also existed in concentrates. This study indicated that especially barley had a higher proportion of microbial N in the bag residues after the washing than the other concentrates. Therefore it is necessary to correct the N degradation values not only in cases of high fibre content but also in cases of low nitrogen content of feedstuffs. The calculation of the N degradation values could be possible on the basis of crude fibre and crude protein contents of feedstuffs. But experiments with a much larger number of 15N labelled feedstuffs have to be realized to give an accurate prediction of N degradation.