The effects of N fertilizer application, cutting stage, pre-wilting, fermentation temp. and formic acid or formaldehyde additives on protein and amino acid degradation in Italian ryegrass, cocksfoot, red clover and lucerne silages were studied in model experiments. An av. of 50% of the protein in the fresh forage was degraded. Pre-wilting and formic acid retarded proteolysis. Pronounced amino acid degradation was associated with butyric acid fermentation. Amino acid content was best maintained by addition of formic acid.