In the US, 60% of colostrum fails to meet the minimum standard of 50g/L of immunoglobulin G (IgG). High quality colostrum is essential for the survival and future production of dairy heifers. Previous studies have shown that niacin (N) may increase vasodilation and in dairy cows, prepartum N supplementation may increase blood flow and potentially Ig flow, to the mammary gland. The objective of this study was to determine if feeding 48g/d of supplemental N to prepartum dairy cows effects colostrum quality. The experiment used 26 multiparous Holstein cows housed in a tie-stall barn. Cows were blocked by expected calving date and randomly assigned to 1 of 2 treatments 4wk prepartum: (1) 48g/d N (Lonza) or (2) 0g/d N (C), both with 52g/d of corn meal as a carrier. Total mixed ration amounts fed and refused were measured daily at 0800h to determine dry matter intake (DMI). Within 90min of parturition, colostrum was collected and weighed. IgG concentration was analyzed using a radial immunodiffusion (RID) assay (Triple J Farms). Calves were removed from their dams immediately and weighed. Calves received 3 bags of a lacteal based colostrum replacer (180g IgG, Saskatoon Colostrum Co.), fed within 2 h of birth. Blood samples were collected from calves via jugular vein at 0 and 24 h of age and analyzed for IgG concentration and apparent efficiency of absorption (AEA). No differences were observed for DMI [15.7 kg/d (C), 14.3 kg/d (N); P = 0.13], IgG yield [748.87 g (C), 773.67 g (N); P = 0.83], colostrum yield [10.64 L (C), 9.45 L (N); P = 0.19], fat % [5.5% (C), 4.72% (N); P = 0.45] and solids nonfat % [23.9% (C), 22.9% (N); P = 0.7]. No differences were observed for 24-h calf serum IgG concentration [15.9 g/L (C), 15.5 g/L (N); P = 0.8] or AEA [32.46% (C), 30.92% (N); P = 0.5]. Niacin tended to increase colostrum protein percent (14.6% (C), 17.9% (N); P = 0.09). Niacin increased IgG concentration in colostrum from 73.8 g/L (C) to 86.8 g/L (N) (P < 0.05). These results indicate that supplementing N (48 g/d) during the prepartum period improves colostrum quality.