USE OF N-15 DETERMINATIONS OF PURINE NITROGEN FRACTION OF DIGESTA TO DEFINE NITROGEN-METABOLISM TRAITS IN THE RUMEN

A method for direct purine N isolation and determination was modified from the method of Zinn and Owens for rapid determination of purines. By this method, N derived from purines in digesta was measured and collected for N-15 determinations. Measurements of purine N in 33 samples of ruminal contents and duodenal digesta of sheep and goats were compared with purine determinations in the same samples. The results showed that essentially all the N in the purines that could be isolated by the Zinn and Owens procedure also could be detected by N isolation and determination. Determinations of N-15 in the NH3 N, NAN, and purine N fractions in a continuous culture in vitro showed significant differences in the N-15 enrichment curves between diets based on either roasted or raw soybean meal.