| Some evidences from the cited reviews of the ruminant lactic acidosis indicated that accumulation of lactic acids in the rumen may play an important role in inducing ruminal lactic acidosis while rumen lactic acids accumulation mainly depends on the degree of rumen producing and utilizing balance of rumen bacteria in feeding high concentrate diets.This study focus on metabolic mechanism and regulation of bacteria that associated with lactate metabolism in rumen of goats in purpose to provide reference for further research of lactic acids rumen acidosis mechanism.Trial 1.To clarify rumen bacterial competition and fermentation pattern shift in rumen acidosis,acute rumen acidosis(ARA)and subacute rumen acidosis(SARA)models have been induced successfully at different starch levels(9 g/L for ARA,3 g/L for SARA and 1 g/L for normal)by mixed culture of five key rumen acidosis associated bacterial(Streptococcus bovis,Lactobacilli fermentum,Butyrivibrio fibrisolvens,Megasphaera elsdenii and Selenomonas ruminantium).The results showed as follows:1)The population of lactate producers(S.bovis,L.fermentum and B.fibrisolvens)increased with the amount of starch in a dose dependent manner(P<0.001),and the population of lactate utilizers(M.elsdenii and S.ruminantium)lower in ARA model than SARA model(P<0.001).2)The concentration of lactate,acetate,formate and propionate were significantly higher(P<0.001)in ARA model than SARA model but butyrate was significantly lower(P<0.001).3)The activity of lactate dehydrogenase(LDH)increased with the starch dose(P<0.001),while the a-amylase(a-AMY)activity was lower in ARA model compared with SARA model(P<0.001).4)In ARA model,the lipopolysaccharide(LPS)concentration was higher than SARA model and normal(P<0.001),but no significant difference between SARA model and normal(P = 0.659).Apart from it,8 adult dairy goats in dry period were choosed and were fed with high concentrate diet(50%ground corn)to induce SARA model.The results showed as follows:1)The rumen pH in SARA period was significantly lower compared with Normal period(P<0.001).2)In SARA period,the population of S.bovis,M.elsdenii and S.ruminantium were significantly higher than Normal period(P<0.001),the population of Lactobacilli lower than Normal period(P<0.001)and there was no significant difference in B.fibrisolvens population(P = 0.800).3)The concentration of lactate,formate,propionate and butyrate in SARA period were significantly higher than Normal period(P<0.01),but there was no significant difference in acetate(P =0.209).4)The activity of LDH and a-AMY and LPS concentration in SARA group were significantly higher than Normal period(P<0.001).Taken together,our findings provide that both in vitro and in vivo rumen acidosis models can be built by mix culture or high concentrate diet and S.bovis and M.elsdenii are the most important lactate producer and utilizer in rumen acidosis.Trial 2.Study on the role of substrate(starch and glucose),substrate concentration(1,3,and 9 g/L)and pH(6.5 and 5.5)in regulating S.bovis organic acids production.The results showed as follows:1)Lactate was the dominant acid produced during the fermentation,and levels increased with the amount of glucose or starch in a dose-dependent manner(P<0.001),and more lactate was produced at pH 6.5 than that at pH 5.5(P<0.001).The production of formate and acetate in the fermentation media fluctuated slightly with the dose,but accounted for small fractions of the total acids.2)The activity of LDH and a-AMY increased with the starch dose(P<0.05),and at pH 5.5,the activity of LDH and a-AMY were higher than those at pH 6.5(P<0.05),but the a-AMY activity did not change with the glucose dose(P>0.05).3)The relative expressions of genes encoding LDH,PFL(pyruvate formate-lyase),CcpA(global catabolite control protein A)and a-AMY were,in general,positively related to the substrate level.4)The fructose 1,6-diphosphate(FDP)concentration tended to increase with glucose and starch concentration(P<0.05),and at pH6.5,the FDP concentration was higher than at pH 5.5(P = 0.032).5)Compared with the shift of substrate concentration,the lactate production in S.bovis was more sensitive to pH changes.Taken together,our findings provide that the fermentation of S.bovis was regulated at the transcription level in response to substrate type,substrate concentration and pH.Trial 3.Study on the role of substrate concentration(15,30,and 90 mM)and pH(6.5 and 5.5)in regulating M.elsdenii lactate metabolism.The results showed as follows:1)Acetate was the dominant acid produced during the fermentation and followed with propionate and butyrate.2)The production of aeetate,propionate and butyrate at pH 6.5 were higher than that at pH 5.5(P<0.001).At pH6.5,the percentage of acetate was lower than that at pH 5.5(P<0.001),while the percentage of propionate and butyrate were significant higher than that at pH 5.5(P<0.001).3)The production of acetate and the percentage of acetate were all significant higher at 90 mM than the other two groups(P<0.05).The production and percentage of propionate and butyrate were all significant higher at 30 mM than 90 mM and the 90 mM also significant higher than 15 mM(P<0.05).4)The genes that encod key enzymes in lactate metabolism were all expressed significantly due to changes in pH and substrate concentration(P<0.05).Taken together,our findings provide that the metabolism of lactate in M.elsdenii was regulated at the transcription level in response to substrate concentration and pH.Trial 4.Effect of rumen perfusion of low nutrient enriched M.elsdenii in relieving SARA symptoms induced by high starch diet in goats.The results showed as follows:1)The pH in M.elsdenii group was higher than SARA group(P<0.05),and was significant lower than Normal group(P<0.05).2)The concentration of lactate and propionate in SARA group were higher than the other two groups(P<0.05),but there was no significant difference between the other two groups(P>0.05).The concentration of butyrate in Normal group was lower than the other two groups(P<0.05).The concentration of acetate in Normal group was higher than M.elsdenii group(P<0.05),but there were no significant difference between SARA group and the other two groups(P>0.05).3)In SARA group,the population of S.bovis was higher than the other two groups(P<0.05).In M.elsdenii group,the population of Lactobacilli and B.fibrisolvens were higher than the other two groups(P<0.05).In Normal group,the population of M.elsdenii and S.ruminantium were lower than the other two groups(P<0.05).4)The activity of LDH and a-AMY in SARA group were significantly higher than M.elsdenii group(P<0.05),and the activity of a-AMY in M.elsdenii group was significantly higher than Normal group(P<0.05).5)The LPS concentration in SARA group was higher than M.elsdenii group(P<0.05),and M.elsdenii group was higher than Normal group(P<0.05).Taken together,our findings provide that rumen perfusion of low nutrient enriched M.elsdenii played a very important role in relieving SARA symptoms induced by high starch diet in goats. |
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