Increasing protein quality of forages in ruminant nutrition may contribute to reduce nitrogen losses in specialized dairy farms in Europe. Red clover is known to have high polyphenol oxidase (PPO) activity among forage legumes. The enzyme oxidizes phenols to quinones. These highly reactive quinones form stabilized quinone-protein-complexes, protecting protein from fast degradation. The objective of this study was to investigate the effect of the specific PPO activity on the protein fractions of twelve red clover genotypes in two management systems (without and with mechanical stress) in pure red clover swards. The results showed that genotype seem to be of minor importance compared to the variation in PPO activity induced by mechanical stress and particular by cut. Furthermore, with increasing specific PPO activity fraction A decreased and fraction C increased slightly. However, specific PPO activity was poorly related to the protein fractions, expressed by a low R²
