6.2 Assessment of Protein Degradability of Forage

Abstract

A new system for calculating the protein requirements of ruminants has been proposed by the Agricultural Research Council's sub-group on protein evaluation (Roy, Balch, Miller, Ørskov and Smith, 1977; ARC, 1980) to replace the now largely discredited Digestible Crude Protein (DCP) and Available Protein system.There is little need to discuss the theory of the new system here as a number of excellent publications are now available outlining the new approach (e.g. Miller, Balch, Ørskov, Roy and Smith, 1977; Wilson and Strachan, 1981). Suffice to say that the new system requires the description of dietary crude protein in terms of rumen degradable protein (RDP) and undegradable protein (UDP) requirement for a specific energy input necessary for a particular level of production. Therefore, one of the important aspects of implementation of the new system is a description of the degradable/undegradable protein contents of feedstuffs. This not only applies to cereals, cereal by-products and protein concentrates used in the animal feed trade but also to the on-farm forages which may make up a considerable proportion of the diet of the dairy cow. It is this latter dietary component that is under consideration here but, in the first instance, it is worthwhile examining the importance of degradability overall, before considering the various aspects of forage protein degradability in particular.