Effects of Supplemental Niacin on Performance and Serum Biochemical Parameters of Lactating Dairy Cows in Hot Environment

An experiment was conducted using three Chinese Holstein cows in early lactation under hot environment,in a 3×3 Latin square design,to determine the effects of the basal diets supplemented with 0,6,12 g/d niacin each cow as control group,group B,group C on performance and serum biochemical parameters.The results showed 1) supplemental niacin had no significant effect on the rectal temperature and respiratory rate(P0.05);2) compared with control group,milk yield of group B and C was increased by 13.20%(P0.05),9.39%(P0.05) respectively,but 4% fat corrected milk yield was not significantly influenced (P0.05);dietary niacin had no effect on milk fat and protein percentage(P0.05);3) compared with control group,the content of serum cholesterol in test groups decreased(P0.05);the content of serum glucose of group B and C increased by 37.89%(P0.05) and 51.93%(P0.05) respectively,there was no significant difference between group B and C(P0.05);the content of serum urea nitrogen decreased significantly at the niacin level of 12 g/d(P0.05);the content of serum triglyceride was no significant difference between the treatments of supplemental niacin and the control group(P0.05);the content of free fatty acid of group B and C decreased by 23.89% (P0.01),10.39%(P0.01) respectively.As performance and serum biochemical parameters were concerned,niacin supplementation with 6 g/d in the ration of lactating cows had the best effect and released the effect of heat stress in hot environment.