Effects of supplemental niacin on the performance and biochemical parameter of serum of heat-stressed dairy cows.

To determine the effects of supplemental niacin on the performance,physiological and biochemical parameter of serum of heat-stressed dairy cows,an experiment was carried out using three health Chinese Holstein cows in latter lactation under hot environment.According to a 3×3 Latin square design,the basal diets supplemented with 0,8,15 g/d niacin in each cow were used as negative control group A,experimental group B,and C,which were carried out for 63 days.The results showed that supplemental niacin had no effects on the rectal temperature and respiratory rate.Compared to the negative control A,milk yield of group B and C was increased by 29.9%(P 0.05) and 22.0%(P0.05),respectively.The 4% fat corrected milk yield was increased by 28.5%(P0.05) and 21.5%(P0.05),respectively.No significant difference between group B and C(P0.05) was observed.Dietary niacin had no effect on the content of milk fat,milk protein and milk sugar.The serum levels of COR could be kept stable,and the content of serum cholesterol and triglyceride decreased insignificantly at the Niacin level of 8 g/d and 15 g/d(P0.05).As performance,part of serum physiological-biochemical parameters was 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.