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 ?rskov 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.