| In the production of ruminants,increasing the level of dietary starch and the proportion of concentrate as a way to improve the production performance and feed efficiency of ruminants.The increase of dietary starch level and concentrate ratio will increase the proportion of rumen degradable starch（RDS）,increasing the concentration of organic acids in the rumen and reducing the ruminant activity and salivary secretion of animals.The increase of rumen organic acid concentration and the decrease of salivary secretion will lead to the decrease of rumen p H.Therefore,how to analyze the effects of salivary secretion and dietary RDS level on p H is an important scientific problem.In this study,the artificial rumen simulation（Rusitec）system was used to study the effects of reducing the buffer capacity（BC）of artificial saliva and the combined effect of them on feed nutrient degradation,fermentation parameters,lactate production and metabolism,microbial flora and function.Experiment 1:To explore the effects of BC reduction of artificial saliva on rumen fermentation parameters,rumen microorganisms,nutrient degradation and rumen function.Two kinds of artificial saliva（standard buffer capacity,100%BC;60%buffer capacity,60%BC）were set in the RUSITEC system.The 5 repetitions are set for each process.The results show that,compared with 100%BC treatment,60%BC artificial saliva significantly reduced the proportion of acetate and the ratio of the ratio of acetate to propionate,increased the proportion of propionate,but had no effect on the concentration and yield of total volatile fatty acids（TVFA）.Compared with 100%BC treatment,60%BC artificial saliva significantly reduced the relative abundance of fiber degrading bacteria in liquid phase and solid phase,but had no effect on the total relative abundance of starch degrading bacteria.Compared with 100%BC,60%BC artificial saliva significantly increased the relative abundance of lactate utilizing bacteria and significantly decreased the relative abundance of lactate producing bacteria.In the liquid phase,the rumen microbial diversity of 100%BC artificial saliva was significantly higher than that of 60%BC,but there was no significant difference in the solid phase.As for the degradation rates of dry matter（DM）,organic matter（OM）,neutral detergent fiber（NDF）and crude protein（CP）,100%BC artificial saliva treatment was higher than 60%BC.The 60%BC artificial saliva resulted in a significant down-regulation of the relative abundance of major functions,such as amino acid and carbohydrate transport and metabolism.Experiment 2:Effects of dietary RDS and artificial saliva BC on rumen fermentation parameters,rumen microorganisms,nutrient degradation rate and rumen function.The experiment adopted 2*2 factor design.Two artificial saliva treatments（standard buffer capacity,100%BC;50%buffer capacity,50%BC）and two RDS levels（high RDS=21.86%and low RDS=13.45%）were set in the RUSITEC system.The 4repetitions are set for each process.Compared with 100%BC artificial saliva,50%BC of artificial saliva decreased the concentration of NH3-H and the proportion of acetate in fermentation liquid,significantly increased the proportion of propionate,but had no effect on the concentration and yield of TVFA.Reducing BC in artificial saliva resulted in a significant decrease in microbial diversity.Increasing the proportion of dietary RDS resulted in significant differences in microbial diversity in 50%BC artificial saliva.Increasing the proportion of dietary RDS had impact on the relative abundance of microorganisms in three genera,while reducing artificial saliva BC caused significant changes in the relative abundance of 20 genera.Compared with 100%BC,50%BC artificial saliva significantly reduced the degradation of DM,OM,NDF and CP.The50%BC artificial saliva resulted in an increase in the number of total lactate-producing bacteria and lactate utilizing bacteria,but the increase in the number of lactate-utilizing bacteria was higher than that of lactate producing bacteria,which resulted in a significant decrease in the concentration and yield of lactate.Compared with 100%BC,50%BC artificial saliva reduced the number of total fiber-degrading bacteria,while increasing the proportion of dietary RDS resulted in a significant increase in fiber-degrading bacteria and starch-degrading bacteria.The 50%BC artificial saliva led to significant changes in the 13 functions of bacteria,while increasing the proportion of dietary RDS had no significant effect on microbial metabolic function.The above research results show that,the effects of reducing artificial saliva BC on rumen fermentation,microbial diversity and microbial function was greater than that of increasing the proportion of dietary RDS,especially on fiber degrading bacteria. |
