Passage of ribonucleic acid along the intestine of sheep

Sheep (Flemish female x Texel male, 55 kg BW), fitted with a PVC cannula in the dorsal rumen and single T-shaped PVC cannulas in the proximal duodenum, distal duodenum, mid-jejunum and terminal ileum were fed hay or hay-concentrate diets at various levels of nitrogen and cell walls (NDF) (22 to 32 g N/d; 150 to 699 g NDF/d). Co-EDTA and Cr-NDF were used as markers to measure the flow rate of digesta. Ribonucleic acid (RNA) intestinal digesta and in rumen bacteria was determined with orcinol after extraction with sodium chloride, precipitation with tungstophosphoric acid and alkaline hydrolysis. The RNA:total N ratio in bacteria, harvested from the rumen, amounted to 0.70 (CV 4.4%). The apparent digestibility of RNA in different sections of the intestine was higher than of total N. About 6% of RNA entering the duodenum disappeared between the proximal and distal duodenum. At jejunum, the net disappearance of RNA amounted to 68% of the quantity which entered the proximal duodenum. A higher result of 71% was obtained at the ileum. Total net disappearance of RNA between the proximal duodenum and rectum averaged 75%. Sixteen percent of RNA leaving the ileum was apparently digested in the large intestine. The true digestibility of RNA between the proximal duodenum and the terminal ileum, as estimated by multiple regression analysis, amounted to 78%. Of the amount of RNA entering the ileum, 24% was of endogenous origin. At ileum, the RNA passage was positively related to the ileal flow of NDF (R2 = 0.67) and N (R2 = 0.94). The passage of RNA increased by 3 mg RNA per g ileal indigestible NDF. Ileal endogenous N consisting of approximately 2% of endogenous RNA-N. In conclusion, the digestion capacity in the first part of the small intestine is high. Rising flows of indigestible cell walls and nitrogen increase the loss of ileal RNA. Further, using RNA as a microbial marker to assess the amount of microbial protein entering the duodenum of ruminants, digesta samples should be collected immediately post pylorus at the proximal duodenum, in order to avoid underestimation of the microbial protein synthesis in the rumen.