Safety Evaluation Of Bupleurum Extract In Heat-stressed Dairy Feed

This study was conducted to study the effect of Bupleurum extract(BE)supplementation on physiological index,production performance,rumen fermentation,nutrient apparent digestibility,serum hormone,hematological profiles and blood metabolites in heat-stressed cows.The object of this study was to confirm the maximal tolerance dose of BE in heat-stressed cows,which provide the basis for BE safe use in dairy management.Forty-eight healthy lactating cows(207.98 ± 12.2 d in milk,30.96 ± 3.96 kg/d,and parity =1.96±1.07)were randomly assigned to 1 of 4 treatments according to a completely randomized block design.Treatments consisted of 0,0.5,2.5 or 5 g of BE/kg of dry matter(DM).Cows were individually housed in pens and fed ad libitum three times daily.The experiment lasted for 10 weeks in hot summer.Daily average temperature-humidity index was more than 72,which indicated that the cows were subjected to heat stress during 10 weeks experiment.The results showed as follows:1.Rectal temperatures responded quadratically(P < 0.05)with increasing BE concentration,and low peak value were reached at a dose of 0.5g of BE/kg;while supplementation of BE had no effect(P > 0.05)on respiration rates at any time point.2.Supplementation of BE affected,in a quadratic manner,dry matter intake and milk yield(P < 0.05),milk protein yield(P = 0.06)and Somatic cell score(P = 0.07),and the peak values were reached at a dose of 0.5g of BE/kg.The milk urea nitrogen,total solids content and milk fat concentration decreased linearly(P < 0.05)with increasing BE concentration.Supplementation of BE had no effect on 4% fat-corrected milk,energy correction milk,milk lactose or protein concentration,milk fat yield,total solid yield or feed efficiency.3.The bacterial protein content,concentrations of acetate,butyrate and total volatile fatty acids decreased linearly(P < 0.05)with increasing BE concentration.The content of ammonia nitrogen,rumen pH,acetate/propionate,the concentrations of propionate,isobutyrate,butyrate,isovalerate and valerate were not affected(P > 0.0.5)by BE supplementation.4.There were no treatment effects on the diet apparent digestibility among groups(P > 0.05).5.The white blood cell count and mean corpuscolar hemoglobin concentration decreased linearly(P < 0.05)and the platelets count increased linearly(P < 0.01)withincreasing levels of BE.Supplementation of BE had no effect on the counts of red blood cell count,lymphocyte,hemoglobin,hematocrit,mean corpuscolar volume,red blood cell distribution width,mean corpuscular hemoglobin or mean platelets volume.6.Concentrations of blood urea nitrogen,total cholesterol,high-density lipoprotein cholesterol and the albumin: globulin ratio decreased linearly(P ≤ 0.05),concentrations ofβ-hydroxybutyrate(P = 0.06)and albumin(P = 0.08)decreased linearly with the increasing levels of BE.The concentration of triglyceride increased linearly(P < 0.01)with the increasing levels of BE.The concentrations of total protein,globulin,glucose,non-esterified fatty acid and low-density lipoprotein cholesterol were not affected by BE supplementation.7.The serum concentrations of cortisol and leptin decreased linearly(P < 0.10),concentrations of prolactin(P < 0.01)increased linearly with increasing BE concentrations.Supplementation of BE affected plasma insulin concentrations quadratically(P < 0.01)and the peak value was reached at a dose 0.5g of BE/kg.The serum concentrations of T3,T4,neuropeptide Y,growth hormone,insulin-like growth factor-1 and glucagon were not affected(P > 0.0.5)by BE supplementation.Overall,supplemental BE at 0.5 g/kg could mitigate the negative effects of heat stress on production and the injury to the cow body by regulating the secretion of hormones,which has a protective effect on body.However,supplemental BE at 5 g/kg reduced rumen fermentation parameters and milk quality and was potentially harmful to cow body,especially to hepatic function.In conclusion,we recommended the safety level of BE is 5 g/kg DM.