Abstract: 【Objective】 This experiment was conducted to investigate the effects of nicotinamide on performance and apparent digestibility of nutrients in lactating dairy cows.【Method】 Forty healthy Holstein cows with similar lactation days, parity and milk yield in middle and late lactation were randomly divided into 4 groups with 10 cows in each group, which were divided into control group (CK group) and experimental groups (NAM7, NAM11 and NAM15 groups), respectively.Dairy cows in CK group were fed a basal diet, in NAM7, NAM11 and NAM15 groups were given 7, 11 and 15 g/d niacinamide solution on the basis of CK group, respectively.The experiment lasted for 75 days, including 15 days of prefeeding-period and 60 days of trial.Milk production was recorded every 15 days.At the same time, milk, feed and blood samples were collected on the 1, 30 and 60 days of the trial period to determine milk composition such as milk fat, milk protein and lactose, somatic cell count, and conventional nutrients such as dry matter, organic matter and crude protein in the feed, and acid insoluble ash content and niacinamide content in plasma and milk, respectively.At the last 3 days of the experiment, fecal samples were collected by rectal fecal extraction method to determine the apparent digestibility of nutrients such as dry matter, organic matter and crude protein.【Result】 The results showed as follows:①Compared with CK group, milk yield and 4% standard milk yield in NAM7, NAM11 and NAM15 groups were extremely significantly or significantly increased (P<0.01 or P<0.05), the somatic cell scores were extremely significantly decreased (P<0.01).The milk fat percentage in NAM7 group was significantly increassed (P<0.05), and milk fat, lactose and milk protein yields were extremely significantly increased (P<0.01).Milk fat yields were extremely significantly increased (P<0.01), lactose and milk protein yields were significantly increased (P<0.05) in NAM11 group, and milk fat and milk protein yields were significantly increased (P<0.05) in NAM15 group. ②Compared with CK group, the apparent digestibility of crude protein, crude fat, total energy, neutral detergent fiber and calcium in NAM7 and NAM11 groups were significantly increased (P<0.05), and the apparent digestibility of dry matter and phosphorus had an increasing trend (0.05<P<0.10).The apparent digestibility of crude protein and total energy in NAM15 group was significantly increased (P<0.05).The apparent digestibility of acid detergent fiber in NAM7 group was significantly higher than that in CK and NAM15 groups (P<0.05).③The plasma nicotinamide content in NAM15 group was extremely significantly higher than that in CK group (P<0.01).Milk nicotinamide content in NAM15 group was extremely significantly higher than that in CK, NAM7 and NAM11 groups (P<0.01), and that in NAM11 group was extremely significantly higher than that in CK and NAM7 groups (P<0.01).【Conclusion】 Niacinamide could increase milk yield and improve milk quality of lactating dairy cows.At the same time, the apparent digestibility of crude protein, crude fat, neutral detergent fiber, energy and calcium were improved, and the effect was the best in NAM7 group.It was suggested that the appropriate amount of niacinamide used in production was 7 g/d.

Key words: niacinamide; lactating dairy cows; production performance; apparent digestibility