Measurement of the bacterial nitrogen entering the duodenum of the ruminant using diaminopimelic acid as a marker

1. A technique for the separation and colorimetric estimation of 2, 4-diaminopimelic acid (DAP) using automated ion-exchange chromatography coupled with an acid ninhydrin detection system is described. 2. Only traces of DAP were found in rumen protozoa and no DAP was detected in rumen fluid prepared by ultracentrifugation or dialysis. 3. The concentration of DAP in rumen bacteria from sheep on a constant feeding regimen, and the ratio of nitrogen to DAP for these bacteria were found to be constant over a 3-month period. 4. The method has proved suitable for the estimation of bacterial N in the duodenal digesta of ruminants. 5. The contribution of bacterial N to the total N leaving the abomasum of a lactating cow fitted with a permanent re-entrant cannula in the duodenum was found to be 50%.