Department of Animal Science


Date of this Version

January 2001


Published in Nebraska Beef Cattle Report 2001, published by Agricultural Research Division, University of Nebraska Cooperative Extension, and Institute of Agriculture and Natural Resources, University of Nebraska–Lincoln.


Three experiments tested modifications of the purine assay designed to improve estimation of microbial crude protein supply. In Experiment 1, changing hydrolysis conditions from 12 normal perchloric acid to 2 normal increased purine recovery and lowered the coefficient of variation. In Experiment 2, phosphate buffer yielded greater recovery of purines than acetate buffer and using the extraction solution as a wash was less variable than silver nitrate in .005 molar hydrochloric acid. In Experiment 3, purine nitrogen:total microbial nitrogen ratios for five forages were determined by incubating NDF in situ and analyzing them before and after neutral detergent extraction.