Use of Nitrogen-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 ¹⁵N 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 ¹⁵N in the NH₃ N, NAN, and purine N fractions in a continuous culture in vitro showed significant differences in the ¹⁵N enrichment curves between diets based on either roasted or raw soybean meal.