Influence of Supplemental Niacin on Performancer and Ion Chroma of Serum for Dairy Cows in the Condition of Heat-stressed

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 0,8,15 g/d niac in each cow as control group A,group B,group C on performance,maintenance behavior and ion chroma of serum.The feeding experiment had been carried out for 63 days.The results showed :① compared with control group A,milk yield of group B and C was increased by 29.9%(P0.05),22.0%(P0.05),respectively,and 4% fat corrected milk yield was increased by 28.5%(P0.05),21.5%(P0.05),respectively,there was no significant difference between group B and C(P0.05);dietary niacin had no effect on the content of milk fat,milk protein and milk sugar;②compared with control group,there was no effect on the hours of standing and lying,the number of micturition and defecation,the number of drinking-water,but rumination time was significantly increased(P0.05).Also,there was no significant difference between group B and group C(P0.05);③compared with control group A,the Ca2+,K+,Na+ chroma of serum of group B and group C was increased in diffferent extent,but there was no significant difference between group B and group C(P0.05).The Mg2+ chroma of serum was increased,and the Cl-chroma of serum was decreased,but not reached significant levels(P0.05).As performance,maintenance behavior and ion chroma of serum were concerned,niacin supplementation with 8 g/d in the ration of lactating cows had the best effect and released the effect of heat stress in hot environment.