Review: A Meta-Analysis of Lactation Responses to Supplemental Dietary Niacin in Dairy Cows

A meta-analysis of published data was conducted to examine the response of lactating dairy cows to supplemental dietary nicotinic acid (NA). The data set was developed from 27 studies published between 1980 and 1998 where lactation performance responses to targeted supplementation of 6 and 12 g/d NA were reported. Response variables evaluated were DMI, milk yield and composition, feed efficiency, and plasma beta-hydroxybutyric acid, non-esterified fatty acid, and glucose concentrations. No efficacy of 6 g/d dietary supplemental NA was found. Similarly, dietary supplementation with 12 g/d NA did not affect DMI, milk fat or protein percentages, or measured plasma metabolites. However, responses to dietary supplementation with 12 g/d NA were observed for 3.5% fatcorrected milk (FCM) yield, feed efficiency (when calculated with 3.5% FCM), and milk fat and protein yields. Yields of 3.5% FCM, milk fat, and milk protein were 0.5 kg/d (P=0.06), 25.8 g/d (P=0.01), and 17.4 g/d (P=0.08) higher, respectively, for NA-supplemented cows. Feed efficiency calculated with 3.5% FCM was 0.03 units higher (P=0.09). A Type I/Type II error economic analysis of the 3.5% FCM yield response showed frequencies of the observed response being greater than the break-even responses by 54 and 57% when NA costs were $0.01 and $0.005/g, respectively. Further research on transition cows and incidence of metabolic disorders, higher dosages of NA, and ruminally protected NA appears warranted.