| Ruminants such as high-yielding dairy cows often receive high-grain diets to meet their high energy requirements.The disease incidence causing by subacute ruminal acidosis(SARA)is approximately 30 to 40%.What effective strategies are use to prevent or control rumen acidosis in production has become a crucial issue?it has become a highlight research that using plants and their extracts to relieve ruminal acidosis in animal feeding in recent years.This study was focused on investigating the effect of dietary ?-sitosterol supplementation on rumen fermentation,microbiota,blood biochemical parameters and serum immune indexes under SARA condition.The aim of this study was to determine the optimal dietary ?-sitosterol supplementation and provide scientific basis for sheep rearing.This study included three experiments.Trial 1:Effects of beta-sitosterol on the growth of Ruminant M.elsdenii in vitroMicrobroth dilution assay were used to determine the minimum inhibitory concentration of ?-sitosterol against M.elsdenii.It was found that ?-sitosterol didn't inhibit M.elsdenii at concentration of 0.25?2.0 mg/mL,and proliferation were promoted with increasing?-sitosterol concentration.Trial 2:Effects of beta-sitosterol level on the rumen fermentation and microbial structure in sheep under SARA conditionEight Hu sheep with ruminal cannulas were used in a Latin square trial.Treatment diets consisted of three ?-sitosterol levels:0.25 g/kg,0.5 g/kg,1.0 g/kg.The trial period comprised 14 days of adaptation and 7 days for sampling.During the adaptation period,the proportion of NFC/NDF in diet was increased gradually until SARA occurred.Sample collection was on the last day.pH value,NH3-N concentration,volatile fatty acid,lactic acid and rumen microflora at 6 h were determined.The results showed that:1)The pH of T(1.0)group was significantly higher than that of control group at 3 and 6 hours after feeding(P<0.05),and adding 1.0 g/kg?-sitosterol shortened the duration of SARA.2)At 3h after feeding,there was no significant difference in the molar concentration of TVFA among each group(P>0.05),the concentration of NH3-N in T(0.25),T(0.5)and T(1.0)groups was significantly higher than that in control group(P=0.05).3)At 3?9 h after feeding,the acetate ratio in T(0.5)and T(1.0)groups was significantly higher than that in control group(P<0.05).At 3?12 h after feeding,the propionate ratio in T(1.0)group was significantly lower than that in the control group(P<0.05);At 3 h after feeding,there has a declining trend in A/P ratio(P=0.06).4)3?12 h after feeding,lactic acid concentration in T(0.5)and T(1.0)groups was significantly lower than that in control group(P<0.05).5)ACE index and Chao 1 Index in T(1.0)group were significantly lower than those in control group(P<0.01),but there was no significant difference in Shannon index and Simpson index(P>0.05).6)T(0.5)group significantly increased the relative abundance of Bacteroides(P=0.05),T(0.5)group and T(1.0)group significantly decreased the relative abundance of Cyanobacteria in rumen fluid of sheep(P<0.01).In summary:Rumen pH can be significantly increased by adding 1.0 g/kg p-sitosterol under SARA condition.There was no significant difference in TVFA molar concentration among each group,rumen fermentation could be regulated by the increased acetate ratio and NH3-N concentration,and reduced propionate ratio,A/P ratio and lactic acid concentration.Adding ?-sitosterol can change the microflora structure of rumen microorganisms by increasing the relative abundance of Bacteroides,Lachnospiraceae and Ruminococcus,and reducing the relative abundance of Cyanobacteria.Trial 3:Effects of beta-sitosterol supplementation on immune responses in sheep under SARA conditionBlood sanples were collected before morning feeding from the sheep of trial 1.Then blood biochemical indexes and the serum cytokine levels were measured.The results showed that:1)There was no significalt difference in the concentration of globulin(GLO),albumin/globulin ration(A/G),total cholesterol(TC),triglyceride(TG),high density lipoprotein(HLD)and low density lipoprotein(LDL)among each group(P>0.05),and there has a decreasing tended in globulin(ALP)(P=0.09).2)Total protein and album concentration were decreased by adding 1.0 g/kg ?-sitosterol(P<0.05)and alkaline phosphatas concentration was increased(P=0.05).3)Adding 0.5g/kg and 1.0 g/kg?-sitosterol significantly increased serum levels of TLR4and IL-1?(P<0.05).In summary:Adding 0.5 g/kg can alleviate the chronic inflammation under SARA condition.In conclusion,the addition of ?-sitosterol can regulate the fermentation of subacute rumen acidosis.It can alleviate the occurrence of rumen acidosis by increasing rumen pH,acetate ratio and NH3-N concentration,reducing propionate ratio,A/P ratio and lactic acid concentration,altering rumen microbial structure and reducing chronic inflammatory reaction. |
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