Niacin in dairy and beef cattle nutrition.

Niacin functions metabolically as a component of the coenzymes NAD and NADP. Sources of niacin are feedstuffs and the enzymatic conversion of tryptophan and quinolinic acid into niacin. Niacin is synthesized by the microflora in the rumen of ruminants. Recent research suggests that microbial production of niacin may not be sufficient for the requirements of high producing cows. Supplemental niacin given to cows in early lactation may reduce the rate of fat mobilization, decrease the concentration of ketones in blood and increase blood glucose level. Niacin supplementation may increase propionate concentration and decrease butyrate concentration in rumen liquor. Ruminal microbial protein synthesis was enhanced by niacin. Not all experiments showed such clear results. The positive metabolic effects of niacin supplementation have resulted in most studies in an improved milk yield (3-4%) especially during early lactation. The milk constituents were mostly uninfluenced or only minimally increased. Reasons for the high variations of results are differences in ration formulation, level of milk performance, stage of lactation, age of cows, body conditions, level and duration of niacin supplementation and specific experimental conditions. Niacin supplemented cows lost less body weight during early lactation, were less days open and required fewer pellets per pregnancy. It would appear that niacin supplementation of about 6 grams per animal per day (200-400 mg per kg dry matter) for the first 60 to 100 days of lactation may be beneficial in selected high producing cows or heifers. In beef cattle niacin supplementation would appear to be beneficial (approximately 1 g per animal per day or about 100 mg per kg dry matter) when the body weight of bulls is lower than 300 kg, when the diets are poor in protein (10 tp 12% crude protein of dry matter) and during dietary adaptation periods.