The apparent digestibility of crude protein by the ruminant: II. The general equation and some of its implications

Abstract

The general equation, y = 70 log x − 15, connecting y, the digestibility coefficient, to x, the percentage of crude protein in the dry matter of the feed of ruminants, which was proposed in an earlier paper, has been shown to fit all the directly determined world data for cattle, sheep and goats which have been published by Schneider (1947). It is applicable to rations composed of both single and mixed feeds for it is the total percentage of crude protein in the ration which determines its digestibility.The equation is of general application, irrespective of climate or feed, and for the first time a link is provided between the large bulk of data from temperate regions and those hitherto neglected and apparently aberrant data from the tropics and subtropics.The equation adequately explains a large part of the variability of results obtained by the ‘by difference’ method. In particular, attention is drawn to its value in explaining ‘associative effects’ in mixed feeds.It would seem to have several practical applications; one being the ready determination of the average digestibility of crude protein in rapidly growing grasses and herbages at different stages of development; another being the evaluation of average crude protein digestibility of single or compound feeds in those parts of the world where adequate facilities for digestibility studies are not available. It can also be used in computing maintenance and production rations for meat and milk.