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The present study was conducted to investigate the effects of 24 g niacin (nicotinic acid (NA)) supplementation over 40 weeks with two forage-to-concentrate ratios (60% concentrate vs. 30% in the total diet) on performance variables of energy metabolism such as plasma concentrations of non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), glucose and nicotinamide (NAM), and the fatty acid profile in rumen fluid. In a 2 x 2 factorial design, 64 German Holstein cows were divided postpartum into four dietary groups: i) 60% concentrate supplemented with 24 g NA (Group 60 + NA); ii) 60% concentrate without NA (Group 60−); iii) 30% concentrate with 24 g NA (Group 30 + NA) and iv) 30% concentrate without NA (Group 30−). The experiment started on the day of calving and continued for 40 weeks. Niacin supplementation did not affect milk yield or composition. The plasma niacin content increased in the supplemented groups, especially Group 30 + NA. Niacin supplementation led to decreased plasma glucose concentrations. The interaction of concentrate x niacin enhanced the molar proportion of propionic acid in rumen fluid in Group 60 + NA. Total short-chain fatty acid (SCFA) concentrations were increased by level of concentrate, niacin supplementation and the interaction, concentrate x niacin. Plasma levels of NEFA and BHB remained unaffected. In sum, concentrate level, niacin supplementation and the interaction of concentrate x niacin increased plasma NAM concentration, whereas plasma glucose concentration was decreased by niacin supplementation. Keywords: Milk performance, nicotinic acid, plasma metabolites, rumen fluid composition

Effects of niacin supplementation (40 weeks) and two dietary levels of concentrate on performance, blood and fatty acid profiles of dairy cattle