The apparent digestibility of crude protein by the ruminant: I. A synthesis of the results of digestibility trials with herbage and mixed feeds

Abstract

The apparent digestibility of crude protein by cattle and sheep of different breeds and types, both temperate and tropical, has been studied by means of an analysis of the results of feeding trials with herbages and mixed feeds in many parts of the world. No matter whether herbages or mixed feeds are used the digestibility coefficient (y) is shown to be related to the percentage crude-protein content of the feed (x) by means of an expression of the form y = a + b log x. The particular equation y= 70 log x − 5 is shown to give a reasonable fit of all the available data.The digestibility of crude protein in the feed is shown to increase very rapidly at low protein levels (from about 2 to 9%), and there after it rises more slowly as the crude-protein content increases.There is close agreement between the equations for herbage fed alone and for mixed feed which suggests that the total percentage of crude protein in the feed, irrespective of its nature, determines the digestibility of the protein.