Correlation of Physiological Metabolism and Rumen Microbes in Ruminants

In complex digestion and metabolism of rumen, rumen microbes play a decisive role. Currently, the relationship between rumen microbial system and rumen metabolism has not been understood comprehensively, which will be reviewed in the paper, with particular focus on digestion and metabolism of bacteria, fungi and protozoa in the rumen of ruminants.

The release and catabolism of ferulic acid in plant cell wall by rumen microbes:A review

Ferulic acid(FA)is one of the most abundant hydroxycinnamic acids in the plant world,especially in the cell wall of grain bran,in comparison with forage and crop residues.Previous studies noted that FA was mainly linked with arabinoxylans and lignin in plant cell walls in ester and ether covalent forms.After forages were ingested by ruminant animals or encountered rumen microbial fermentation in vitro,these cross-linkages form physical and chemical barriers to protect cell-wall carbohydrates from microbial attack and enzymatic hydrolysis.Additionally,increasing studies noted that FA presented some toxic effect on microbial growth in the rumen.In recent decades,many studies have addressed the relationships of ester and/or ether-linked FA with rumen nutrient digestibility,and there is still some controversy whether these linkages could be used as a predicator of forage digestibility in ruminants.The authors in this review summarized the possible relationships between ester and/or ether-linked FA and fiber digestion in ruminants.Rumen microbes,especially bacteria and fungi,were found capable of breaking down the ester linkages within plant cell walls by secreting feruloyl and p-coumaroyl esterase,resulting in the release of free FA and improvement of cell wall digestibility.The increasing evidence noted that these esterases secreted by rumen microbes presented synergistic effects with xylanase and cellulase to effectively hydrolyze forage cell walls.Some released FA were absorbed through the rumen wall directly and entered into blood circulation and presented antioxidant effects on host animals.The others were partially catabolized into volatile fatty acids by rumen microbes,and the possible catabolic pathways discussed.To better understand plant cell wall degradation in the rumen,the metabolic fate of FA along with lignin decomposition mechanisms are needed to be explored via future microbial isolation and incubation studies with aims to maximize dietary fiber intake and enhance fiber digestion in ruminant animals.

Effects of Limiting Amino Acids on Rumen Fermentation and Microbial Community In vitro

Three goats fitted with cannula were used to provide rumen liquor to investigate the effects of limiting amino acids on rumen fermentation and microbial community in vitro. The removal method was used in the current experiments. Treatments are total essential amino acid （TEAA）, His-removal, Lys-removal, Met-removal, and branch chain amino acid （BCAA）- removal. Results indicated that, pH-value ranged between 5.9 and 6.8, with the highest mean value for the group with BCAA-removal （6.54） in the culture. Concentration of NH3-N ranged between 10.99 to 30.51 mg 100 mL^-1, with the group of TEAA recording the highest average NH3-N concentration （17.85 mg 100 mL^-1）. Yields of microbial protein and limiting degree on microbial growth varied with treatments （P 〈 0.01）, and the lowest accrued in treatment with BCAA-removal （0.1389, 0.1772, and 0.3161 mg mL^-1 for bacteria, protozoa, and mixed microbes, respectively）, compared to the group with TEAA, microbial production of mixed microbes decreased by 44.52%. As for micro-flora, protozoa to bacteria ratio was the lowest for the group with Lys-removal （89.12%）, while the highest for the group with BCAA-removal （127.60%） （P 〈 0.01）. Furthermore, PCR-SSCP analysis revealed that, microbial profile subjected to substrates within bacteria and protozoa groups. It was therefore concluded that, dietary amino acid influenced both rumen fermentation and microbial characteristics.

The effects of the unsaturated degree of long-chain fatty acids on the rumen microbial protein content and the activities of transaminases and dehydrogenase in vitro

This study investigated the effects of the degree of unsaturation（unsaturity） of long-chain fatty acids on microbial protein content and the activities of transaminases and dehydrogenase in vitro using goat rumen fluid as the cultural medium.Six types of fatty acids,stearic acid（C18：0,group A,control group）,oleic acid（C18：1,n-9,group B）,linoleic acid（C18：2,n-6,group C）,α-linolenic acid（C18：3,n-3,group D）,arachidonic acid（C20：4,n-6,group E）,and eicosapentaenoic acid（C20：5,n-3,group F）,were tested,and the inclusion ratio of each fatty acid was 3%（w/w） in total of culture substrate.Samples were taken at 0,3,6,9,12,18 and 24 h,respectively,during culture for analyses.Compared with stearic acid,linoleic acid,a-linolenic acid,and arachidonic acid increased the bacterial protein content,while oleic acid and eicosapentaenoic acid had no significant effects;the protozoal protein content was reduced for all the unsaturated fatty acids,and the magnitude of the reduction appeared to be associated with the degree of unsaturity of fatty acids.The total microbial protein content was dominantly accounted by the protozoal protein content（about 4-9 folds of the bacterial protein）,and only increased by linoleic acid,but reduced by oleic acid,arachidonic acid and eicosapentaenoic acid.There were no significant effects in the activities of both glutamic oxaloacetic transaminase（GOT） and glutamic-pyruvic transaminase（GPT） for all the other fatty acids,except for arachidonic acid which enhanced GOT activity and oleic acid which enhanced GPT activity.The total dehydrogenase activity was positively correlated with the degree of unsaturation of fatty acids.In conclusion,the inclusion of 3%of long-chain unsaturated fatty acids increased bacterial protein content,whereas reduced protozoal protein content and enhanced dehydrogenase activity.The fatty acids with more than three double bonds had detrimental effects on the microbial protein content.This work demonstrates for the first time the effect rule of the unsaturation degree of long-chain fatty acids on the rumen microbial protein in vitro.

Grassland-based ruminant farming systems in China: Potential, challenges and a way forward

With an increasing demand for high-quality,eco-friendly food products and growing concerns over ecological conservation,the development of ecology-based alternatives for ruminant production in China is urgently needed.This review discusses the capabilities for integrating grassland grazing into existing livestock farming systems to meet the contemporary human needs for high-quality foods and ecologically stable environments.Additionally,this review provides a critical analysis of the challenges and future directions associated with grassland-based ruminant farming systems.Integrating nutritional manipulation with grazing manipulation is critical for improving the productivity of grassland-based ecosystems and natural ecological functions.Biodiversity is the primary determinant of grassland ecosystem functions,while the composition and function of rumen microbiomes determine ruminant production performance.Future studies should focus on the following aspects:1)how livestock grazing regulates grassland biodiversity and the mechanisms of grassland biodiversity maintenance,offering an important scientific basis for guiding grazing manipulation practices,including grazing intensity,livestock types,and grazing management practices;to 2)characterize the microbial ecology within the rumen of grazing ruminants to offer clarified instruction for the nutritional manipulation of grazing ruminants.Our recommendation includes creating a transdisciplinary system that integrates ecology,animal nutrition,and animal behavior to develop grassland-based ruminant farming systems sustainably,thereby achieving high-quality animal production and environmentally sustainable goals.