Improvements in nitrogen efficiency in ruminants are needed. Correct feed evaluation is a prerequisite and protein degradation in the rumen is one of the most important factors to consider. This project aims at developing a routine assay for protein degradation in ruminant feeds, where gaseous hydrogen sulfide (H2S) released from cysteine (a protein amino acid) is monitored automatically by a sensor. The method developed would replace the in sacco assay, which is unsuitable for many of our domestic feeds with high proportions of soluble protein, such as peas, field beans, rapeseed cake and haycrop silages. The developed method could easily be adapted to existing, small-scale gas in vitro equipment with automated recording of gas production. More precise determination of degraded protein would allow greater proportions of home-grown protein feeds in dairy rations, which would be of great benefit for the farmer and the environment.