Effect of Niacin Supplementation on the Concentration of Niacin in Rumen and Duodenal Digesta and in Whole Blood of Sheep

1. Niacin concentrations in rumen liquor, duodenal digesta and blood, and daily duodenal flow of niacin were measured in four wethers which were fed an oatstraw grain concentrate diet (with normal niacin content) or an oatstraw maize diet (with low niacin content). The effect of an intraruminal supplementation of 2 mmoles nicotinic acid (NIA) or nicotinamide (NAM) on concentrations of NIA and NAM in gastrointestinal contents and blood and on daily duodenal flow of NIA and NAM was studied. The animals were equipped with rumen fistula and duodenal re-entrant cannulae. 2. NIA concentration in strained rumen liquor was 384 and 264 nmol/ml and daily duodenal flow of niacin was 616 and 528 mumoles/d in animals fed normal or low niacin diet, respectively. Intraruminal administrations of 2 mmoles of NIA or NAM raised NIA concentration in strained rumen liquor for approximately 6 h. About 20% of the administered dose of NIA or NAM passed out of the rumen and resulted in a 41% increase in daily duodenal flow of niacin. The remaining 80% of the administered dose of NIA or NAM disappeared from rumen liquor without being washed out. 3. Supplemented NAM was rapidly hydrolyzed to NIA and ammonia when administered into the rumen. 4. NAM concentration in blood appeared to be unaffected by the dietary content of NIA or by niacin supplementation. 5. The NIA concentration in strained rumen liquor was positively related with niacin content of the diet. Increases in duodenal flow of niacin had no marked effect on concentration of NAM in blood. It appeared that feeding diets with different NIA content affected apparent niacin synthesis in the rumen.