Effects Of Artificial Saliva PH And Addition Of Aspergillus Oryzae Culture On Fermentation Parameters And Ruminal Bacteria In Rusitec

Feeding an amount of degradable carbohydrates for ruminants causes organic acids to accumulate in the rumen and decreases the ruminal pH,leading to subacute rumen acidosis(SARA).The grain-induced SARA and pe NDF-induced SARA had the difference between fermentation with ruminal bacteria community because of the substrate.The artificial saliva induced SARA avoiding the substrate.Therefore,studying the influence of artificial saliva pH on fermentation and ruminal microbial flora,which will help clarify the relationship between diet and pH in order to regulate the environment of the rumen.The purpose of this experiment is to study the effect of artificial saliva pH in Rusitec system on nutrient digestion,fermentation parameters and ruminal bacteria community.On this basis,the second experiment is to study the effect of the addition of Aspergillus oryzae culture in the diet on the SARA in vitro.The first experiment aimed to investigate the effect of artificial saliva pH on nutrient digestion,fermentation patten and ruminal bacteria community.The Rusitec system composed of 8 fermenters,which was divided into two groups according to the composition of the buffer solution.One is the high pH(pH = 6.8)group,the other is the low pH(pH = 6.2)group.The per group has 4 repetitions.The experiment periods were 13 days,including 9 days of adaptation and 4 days of sampling period.The results showed that:1.Compared with high pH,low pH significantly decreased DM,OM,NDF,ADF and CP degradation rate(P < 0.001).The proportion of propionate was significantly decreased in the low pH group(P < 0.001).The proportion of butyrate(P = 0.008),isovalerate(P = 0.012),valerate(P < 0.001),and the ratio of acetate to propionate(P <0.001)were increased in the low pH group.The TVFA concentrations had a decrease trend in the low pH group(P = 0.080).2.The number of Ruminococcus flavefaciens,Fibrobacter succinogenes and Ruminococcus albus was significantly decreased(P < 0.001)in the low pH group.The number of Selenomonas ruminantium has a decreased trend(P = 0.065)in the low pH group.The amount of Butyrivibrio fibrisolvens in the solid-associated bacteria had a tendency to decrease in the low pH group(P = 0.081),but the amount of Butyrivibrio fibrisolvens in the liquid-associated bacteria was significantly decreased in the low pH group(P = 0.022).3.In the solid-associated bacteria,the abundances of Spirochaetes(P = 0.001)and Synergistetes(P = 0.004)were increased in the low pH group,while the abundance of Verrucomicrobia was decreased(P = 0.004).In the liquid-associated bacteria,the abundance of Proteobacteria(P = 0.005)was increased significantly in the low pH group,while the abundance of Planctomycetes(P = 0.001),Spirochaetes(P = 0.002),Tenericutes(P = 0.012)and Lentisphaerae(P = 0.031)were decreased.The abundance of Lactobacillus(P = 0.050)was higher in the low pH group compared with the high pH,while the abundance of Schwartzia(P = 0.002)in the solid-associated bacteria was lower.In the liquid-associated bacteria,the abundances of Succinivibrio(P < 0.001)and Prevotella＿1(P = 0.001)was increased in the low pH group.The second experiment aimed to investigate effect of adding Aspergillus oryzae culture on nutrient digestion,fermentation parameters and ruminal bacteria in Rusitec system.The Rusitec system composed of 8 fermenters,and fermented 2 batches.The per treatment had randomly 4 replicates.The treatments were high pH(pH 6.8),low pH(pH 5.5),low pH(pH 5.5)+ 1.25% Aspergillus oryzae culture group and low pH(pH5.5)+2.5% Aspergillus oryzae culture group.The results showed that:1.The OM degradation rate was higher in 2.5% Aspergillus oryzae culture group(P=0.040)compared with low pH group.The addition of Aspergillus oryzae culture in diet had no effect on the DM,NDF,ADF and CP degradation rate(P > 0.05).2.The addition 2.5% of Aspergillus oryzae culture in diet has a tendency to increase the number of Selenomonas ruminantium(P = 0.058)and Fibrobacter succinogenes(P = 0.089)compared with low pH group.In summary,low artificial saliva pH decreases degradation rate of the diet and the number of cellulolytic bacteria.Low artificial saliva pH increased the proportion of butyrate and decreased the proportion of propionate,which changes the fermentation patten.The addition of 2.5% Aspergillus oryzae culture in diet increase the degradation rate of OM in Rusitec system,but has no effect on fermentation parameters.The addition of 2.5% Aspergillus oryzae culture increase the number of Selenomonas ruminantium and Fibrobacter succinogenes.