1. The literature in the following areas is reviewed: ruminant protein rationing systems and methods of measurement of dietary protein degradability; rate of passage through the ruminant digestive tract; protein supplementation of diets for growing cattle; production and utilisation of fish silage and protection of dietary protein by formaldehyde treatment. 2. Eleven acidified fish silages were prepared using a range of formalin levels (0-40 cm3kg-1 fish waste). White fish filleting scrap was minced and well mixed with formic acid (1.5-2.0% v/w) before the addition of the appropriate level of formalin. The silages were stored before analysis in closed plastic containers at a temperature of 23 +/-
