The Ruminal Manipulation Strategies For Enhancing Propionate Fermentation And Their Dynamic Effects On Carbohydrate Metabolism

Ruminants ultimately convert human-indigestible plant resources into human digestible milk or meat products,but the bioconversion efficiency is still at relatively low level.Not only becase they intake more structural carbohydrates,but also 38%,-9%and 22%of hexose energy is lost when it convert into acetate,propionate and butyrate,respectively.Moreover,between 2%and 12%of feed energy is lost in the form of CH₄.Energy is important for animal productivity and health.The objective of this study was to manipulate ruminal carbohydrate metabolic to produce more propionate and less CH₄.This study contained rumen microbial regulation and biochemical regulation two parts,including five experiments as follow:PartⅠ,rumen microbial manipulation strategy.The manipulating hypothesis:selective inhibition of ruminal acetate-producing microbe would cause more substrate to be used to produce propionate by propionate-producing microbe.It would also compete with methanogens for hydrogen and reduce CH₄ emissions.The protozoa occupies about 50%of the total biomass of the rumen,and is the main acetate-producing microbe.The meta-analysis of Exp.1 was conducted to quantitatively summarize the temporal dynamics of methanogenesis,ruminal volatile fatty acid（VFA）profiles and dietary fiber digestibility in ruminants following the elimination of rumen protozoa（also termed defaunation）.A total of 49 studies from 22 publications were evaluated.The results revealed that defaunation reduced CH₄ production and shifted ruminal VFA profiles to consist of more propionate and less acetate and butyrate,but defaunation also reduced the total VFA concentration and dietary fiber digestibility.However,these effects were diminished,at different rates,with time during the first few weeks after defaunation;eventually,the acetate to propionate ratio（A:P）and CH₄ production were increased after 7and 11 wk of defaunation,respectively.Therefore,elimination of rumen protozoa adversely affected the energy supply of the host animals in a long run.Exp.2 aimed to examine the temporal（hourly within a day and daily over a long term）dynamics of CH₄ emissions,ruminal fermentation,and in situ alfalfa degradation in dairy goats during adaptation to monensin supplementation,which inhibits the ruminal protozoa and bacteria simultaneously.Six ruminally cannulated dairy goats were used in the self-control design before and after treatment.The experiment included a baseline period of 3wk followed by a treatment period of 8 wk with 32 mg monensin/d,and a washout period of 2wk.The confounding interferences caused by the changes of environmental temperature and feed intake were avoided by feeding restricted amount of ration and housing in environmental controlled chambers.The decreasing effects of monensin on CH₄ emissions,ruminal A:P and fiber degradability,and the suppressing extent showed largest after feed intake.However,those reductions faded with time,hours after feeding and days of treatment.The enhancing effects of monensin on propionate was relatively persistent.The changes of monensin on theαandβdiversity of ruminal microflora were gradually restored over time,but the structure was reshaped that the relative abundances of both amylolytic and cellulolytic bacteria gradually increased following monensin treatment.Therefore,monensin supplementation over long terms was more benefit for the energy supply of the host animalsPartⅡ,rumen biochemical manipulation strategy.The manipulating hypothesis:the ruminal propionate fermentation pathway can be stimulated by biochemical regulators,that more substrate is converted into propionate.Exp.3 was to study the stimulating-effects of bioactive substrates to propionate fermentation.This study quantitatively evaluated and compared the efficacies of six bioactive polysaccharides（Astragalus polysaccharide,Lycium barbarum polysaccharide and Lentinan polysaccharide）and oligosaccharides（xylooligosaccharide,fructooligosaccharide and chitooligosaccharide）（10 g/kg diet）with respect to carbohydrate fermentation using a rumen simulation technique.The results demonstrated that Astragalus polysaccharide,Lycium barbarum polysaccharide and xylooligosaccharide increased the relative abundances of the cellulolytic bacteria（R.albus,R.flavefaciens or B.fibrisolvens）,while only Lycium barbarum polysaccharide increased the dietary fiber degradation.Astragalus polysaccharide,Lycium barbarum polysaccharide and xylooligosaccharide also increased the VFA production,which was much higher than the conversion of itself.Therefore,bioactive polysaccharides and oligosaccharides supplementation at 1%level could stimulate rumen fermentation,but not specific on propionate fermentation.Exp.4 was to study the factors affecting the conversion of fumaric acid（FA,8%）to propionic acid in vitro from the biochemical and microbiological angles:restrictive coenzyme（10 ppm biotin）,hydrogen partial pressure（0.5%tannin）and the abundance of propionate-producing microbe（100 ppm monensin）.The results showed that adding biotin,tannin or monensin had no effect on VFA concentrations.The addition of FA increased the propionate concentration,while the actual conversion rate of FA to propionate was only54.7%.The conversion rate was increased by adding biotin（60.8%）or monensin（77%）,and was reduced by adding tannin（48.8%）.The conversion rate was the highest（80.6%）when simultaneously added biotin and monensin,while was the lowest（44.9%）when simultaneously added biotin and tannin.Therefore,hydrogen partial pressure is a factor limiting ruminal propionate fermentation,while biotin is not.Fumaric acid and monensin have a good synergistic effect in promoting ruminal propionate production.Exp.5 studied the dynamic and synergistic effects of methanogenesis inhibitor（nicorandil）and hydrogen receptor（FA）on carbohydrate metabolism in dairy goats.The experiment was designed with with a 2×2 factorial arrangement of treatments:FA（0 or 34g/d）and nicorandil（0 or 0.5 g/d）.24 first lactation dairy goats were randomly blocked into the 4 groups.The samples were collected at the 3,6,9 and 12 wk.The results showed that FA and nicorandil supplementation could persistently inhibit CH₄ emissions in dairy goats.The actual CH₄ reduction of FA was 3.5 times than that of FA playing as hydrogen acceptor,but it decreased to 1.3 times when FA was added with nicorandil.FA and nicorandil had no adverse effects on dietary digestibility.FA increased ruminal propionate proportion,but decreased the concentrations of glucose andβ-hydroxybutyric acid in the serum,and increased the activity of malate dehydrogenase and the total antioxidant capacity.Although nicorandil had no effect on rumen VFA profile,it increased the serum total antioxidant capacity,decreased triglyceride concentration,and tended to decrease glucose concentration.Therefore,FA could not only competitively utilize hydrogen with methanogenesis to enhance propionate,but also enhance the propionate producing pathway,and the responses to FA likely depend on ruminal capacity to metabolize FA.FA and nicorandil improve animal glycolysis and antioxidant capacity,and inhibit lipid mobilization.In conclusion,（1）inhibition of ruminal acetate-producing microbe could reduce CH₄emissions and enhance propionate fermentation,but the regulation effect decline with time.Based on the regulation effects and persistences on ruminal carbohydrate metabolism,the inhibition of ruminal acetate-producing protozoa and bacteria is superior to elimination of protozoa.（2）Substrate stimulation:bioactive polysaccharides and oligosaccharides supplementation at 1%level could stimulate rumen fermentation,but not specific on propionate fermentation.Intermediate metabolic factors:hydrogen partial pressure is a factor limiting ruminal propionate fermentation,while biotin is not.（3）FA could not only competitively utilize hydrogen with methanogenesis to enhance propionate,but also enhance the propionate producing pathway,and the responses to FA likely depend on ruminal capacity to metabolize FA.