Up to 50% of dairy cows in high-production herds go through borderline ketosis during early lactation (Emery et al., 1964). The concentration of 3-hydroxybutyrate in serum was reduced from 1.24 to 0.74 mmol per liter after five days, when 10 g of niacin was fed to ketotic cows (Flachowski et al., 1988a). Fronk and Schultz (1979) indicated that supplementing ketotic dairy cows with 12-g doses of nicotinic acid daily had a beneficial effect on the reversal of both subclinical and clinical ketosis. More recent studies indicate that 6 g of niacin may be sufficient. Endogenous synthesis of niacin is decreased by ketones and increased by corticosteriods, leading to the hypothesis that part of the beneficial effect of adrenal corticoids on ketosis is derived from increased niacin synthesis. This suggests that niacin may be a useful adjunct to glucocorticoid therapy for ketosis.
Supplemental niacin has been reported to increase plasma insulin and glucose response to beta agonists (Chilliard and Ottou, 1995). Erickson et al. (1990) reported a trend for reduced lipolysis (area under curve for non-esterified fatty acids) in response to epinephrine challenge in cows fed 12 g per day of either nicotinic acid or nicotinamide. Skaar et al. (1989) did not find any effect of niacin on hepatic lipidosis during the periparturient period in dairy cows.
B. Milk Production
Girard (1998) summarized effects of supplemental niacin on milk production in dairy cows. Some of the individual studies and recent results are discussed below. Many of the more recent studies have tested the possible interaction of feeding niacin with or without supplemental fats.
Daily supplementation of 3 to 6 g of niacin to early lactation dairy cows resulted in slight increases in milk production. In a study involving six dairy herds, Jaster et al. (1983) found that milk production of niacin-supplemented cows peaked earlier, and milk production of high-producing cows in first lactation was greater when they received supplemental niacin. In these herds there was only a slight increase in milk fat percentage.
Muller et al. (1986) and Bartlett et al. (1983) both reported that supplemental niacin increased milk yield of cows in early lactation in commercial dairy herds. Muller et al. (1986) noted a 4% increase in milk production over the entire lactation in response to feeding 6 g of niacin per day.
Horner et al. (1986) reported that feeding whole cottonseed and most other dietary fat sources to dairy cows results in a reduction of milk protein percentage and protein yield. Diets supplemented with niacin (6 g niacin per 20.45 kg of dry matter) increased milk protein percentage in diets with 15% whole cottonseed. The authors concluded that milk protein depression with whole cottonseed was alleviated by niacin because of stimulation of mammary casein synthesis. A subsequent study reported that supplemental niacin increased milk production by 3% with no effect on dry matter intake (Horner et al., 1988). In another study, there was no beneficial effect of niacin on milk casein synthesis for cows fed whole cottonseed, which may have been due to their late stage of lactation (Lanham et al., 1992). Driver et al. (1990) suggest that niacin feeding to cows receiving heat-treated soybeans corrected a dietary oil-induced milk protein depression. Erickson et al. (1992) reported that feeding cows 12 g of niacin daily increased milk protein yield and reduced plasma ketones.
More recently, Cervantes et al. (1996), using cows in mid-lactation, found that feeding 12 g of nicotinamide daily increased milk and milk protein production, decreased milk fat percentage and had no effect on blood glucose or beta-hydroxy butyrate. Madison-Anderson et al. (1997) tested effects of feeding 0 or 12 g of nicotinic acid daily with or without supplemental fat from extruded soybeans. Milk yield was 3.3 kg per day higher for cows fed niacin, but the difference was not statistically significant. Niacin exerted some effects on fatty acid composition of milk, increasing the proportion of unsaturated and long-chain fatty acids. Milk oleic acid concentration was increased by duodenal infusion of 6 g of nicotinic acid daily with no other effects on milk yield or composition (Wagner et al., 1997). Minor et al. (1998) tested effects of supplementary niacin (0 or 12 g per day) fed with either high or moderate levels of nonstructural carbohydrate in the ration, starting 19 days prepartum and continuing through week 40 of lactation. Niacin had no significant effects on production parameters or blood metabolites. In contrast, Drackley et al. (1998), using similar rations with or without supplemental fat (whole soybeans and animal fat), and supplementing either 0 or 12 g of nicotinic acid daily for weeks four through 43 of lactation, reported increased milk production (6.2% to 7.2%), lower milk casein concentration and a trend toward higher milk protein yield in cows fed niacin.
The variation in response to supplemental niacin in dairy cows is difficult to explain. Interactions of niacin and dietary fat are predicted based on metabolism but have not been observed, although niacin has increased milk yield in diets containing supplemental fat. Tryptophan status of animals may be involved in some of the milk production responses if supplemental niacin is able to spare tryptophan for use by the mammary gland. Horner et al. (1986) reported a trend for elevated plasma levels of free tryptophan in niacin-supplemented cows. Others have noted an apparent effect of niacin in decreasing plasma calcium and increasing plasma phosphorus concentration (Dufva et al., 1983). This has led to speculation that marginal dietary calcium levels may limit the response to supplementary niacin (Harmeyer and Kollenkirchen, 1989). In addition there are the variable effects of niacin on rumen metabolism and the variations in rumen niacin synthesis and degradation to consider. Girard (1998) concludes that because of its role in energy metabolism, niacin is likely of most value when fed during early lacatation, when body lipid stores are mobilized and when nutrient deficits are most likely to occur. Retrospective analysis of some trial data has led to the theory that cows in heavier body condition, and therefore cows that will mobilize more body fat after calving, are more responsive to supplementary niacin than cows in thin condition. Overall the research results suggest that niacin be considered as a supplemental nutrient at 6 to 12 g per day in high-producing cows during early lactation, particularly with higher fat diets (>6% fat).
Responses to Niacin Supplementation — Lambs
Mizwicki et al. (1975) observed that 500 ppm of supplemental niacin improved feed efficiency of lambs fed a high-concentrate diet containing urea. Subsequent studies using 100 ppm niacin fed to growing and finishing lambs showed increased performance (Table 1), with evidence that niacin stimulates rumen microbial protein synthesis (Shields et al., 1982). These studies indicate that supplemental niacin (1) increased nitrogen utilization, (2) improved the percentage of absorbed nitrogen retained, (3) reduced urinary nitrogen excretion and (4) reduced the percentage of nitrogen found as urea nitrogen. All of these positive responses indicate improved protein metabolism with high- concentrate diets.
