KINETICS OF NIACIN SUPPLEMENTS IN LACTATING DAIRY-COWS

The kinetics of niacin supplements in lactating dairy cows and the sta bility of supplements during in vitro fermentation were examined. Four multiparous Holstein cows (200 DIM) with ruminal and duodenal cannula s were fed a TMR either unsupplemented or supplemented with 12 g/d of nicotinic acid, 12 g/d of nicotinamide, or 6 g/d combination of each n iacin source in a 4 x 4 Latin square design. Ruminal and duodenal conc entrations of nicotinic acid increased with niacin supplementation, bu t DMI, yields of milk and FCM, most measures of milk composition, rumi nal VFA, and plasma NEFA and BHBA concentrations were unaffected by ni acin supplementation at this stage of lactation. Apparent digestibilit ies of most nutrients were greater when both sources of niacin were su pplemented than when either source was supplemented separately. Duoden al nicotinic acid concentrations were higher for cows supplemented wit h nicotinamide than for cows receiving nicotinic acid, but the opposit e was true for nicotinic acid concentrations in plasma. The results of both experiments indicated that nicotinamide was converted rapidly to nicotinic acid by microorganisms in the reticulorumen. Supplementatio n with either nicotinic acid or nicotinamide effectively can increase the amount of nicotinic acid available to the cow; however, some sourc e effects remain to be explained.