Differences In Rumen Fermentation Characteristics And Microbial Community Among The Different Breeds Of Beef Cattle

China is a predominant beef production and consumption country in the world,but the inadequate supply of beef cattle is a serious problem.The yak,cattle-yak and Holstein bull can be used as the supplements of beef cattle resources,but their differences in production performance,nutrient utilization and rumen microbial community have not been studied.Therefore,in order to provide theoretical basis for feeding different breeds of beef cattle,this experiment was performed to investigate the differences in fermentation characteristics,CH₄ production,and the rumen bacterial and methanogenic community among Maiwa yak,China Holstein steer and cattle-yaks（Tibetan yellow cattle×Maiwa yak）in vivo and in vitro.Trial 1,comparing the rumen fermentation characteristics and CH₄ emission among different breeds of beef cattleFifteen healthy steers（24-month-old）,including 5 Maiwa yaks,5 Chinese Holstein steers and 5 cattle-yaks,were selected as the ruminal fluid donor.All the animals were fed with the same diet for 42 days,then on d 43,the ruminal fluid was collected from all animals2 h before morning feeding for in vitro fermentation of diet.The GP,fermentation parameters,the yield of CH₄,H₂ and CO₂ were analyzed and compared.The main results showed as follows:（1）The slowly fermentation fraction gas production and potential gas production of cattle-yak group were significantly higher than those of Maiwa yak group and Chinese Holstein steer group（P（27）0.05）,while the rapidly fermentation fraction gas production and gas production rate of Maiwa yak group and Chinese Holstein steer group were significantly higher than those of cattle-yak group（P（27）0.05）.（2）The p H value of each group was in the normal range.The concentration of NH₃-N showed a trend of decreasing first and then increasing.The concentration of NH₃-N was highest at 48 h and 72 h and the highest MCP concentration was observed in the Maiwa yak group（P（27）0.05）.The concentration of VFA in each group gradually increased in the first 48h.The concentration of acetate and butyrate continued to increase from 48 to 72 h only in the Maiwa yak group.The concentration of acetate,propionate,butyrate and TVFA were highest in Maiwa yak group（P（27）0.05）.The acetate/propionate in Maiwa yak group and cattle-yak group was significantly lower than that in Chinese Holstein steer group during3～48 h（P（27）0.05）.（3）The H₂ production of the cattle-yak group was highest during 48～72 h（P（27）0.05）.The CO₂ yield of the Maiwa yak and the Chinese Holstein steer group during 3～24 h was higher than cattle-yak group,while the CO₂ yield of cattle-yak group was significantly higher than Maiwa Yak group at 48 h（P（27）0.05）.The CH₄ yield of the Chinese Holstein steer group was highest before 48 h（except for the 6th hour）（P（27）0.05）,while the CH₄ yield of the cattle-yak group was significantly higher than Maiwa yak group at 48 h（P（27）0.05）.（4）The acetate molar ratio was positively correlated with CH₄ yield during 3～24 h（P（27）0.05）.The CH₄ production was negatively correlated with propionate molar ratio,but an opposite relationship was found between the CH₄ production and acetate/propionate at 9 h and 24 h.The CO₂yield was positively correlated with CH₄ yield during 3～72 h（except for the 12th hour）（P（27）0.05）.Trial 2,comparing the production performance,nutrients apparent digestibility and rumen microbiome among different breeds of beef cattleOn the basis of trial 1,we compared the differences of performance and nutrients apparent digestibility among different breeds of beef cattle.Moreover,by 16S r RNA Amplicon Sequencing and Quantitative Real-time PCR to compare the differences of rumen microbiomes among these breeds,we explored the main microbiomes that affect rumen fermentation and methane production among different breeds of beef cattle.The results showed as follows:（1）The ADG and DMI were significantly higher of Chinese Holstein steer than Maiwa yak and cattle-yak（P（27）0.05）,while DMI/IBW were similar among three breeds（P>0.05）.The ADFD of Maiwa yak were significantly higher than that of cattle-yak（P（27）0.05）.（2）The Observed species、Chao1 and Shannon indices of rumen bacteria and methanogens were different among Maiwa yak,Chinese Holstein steer and cattle-yak（P（27）0.05）.The Principal coordinate analysis（PCo A）revealed that the structure of rumen bacteria and methanogens were different among the three groups,indicating that the diversity of rumen bacteria and methanogens was distinct among different breeds.（3）The relative abundance of carbohydrate-degrading bacteria（unclassified F082）,protein-degrading bacteria（Prevotellaceae UCG-003）and butyrate-producing bacteria（Oscillospira）were highest in Maiwa yak（P（27）0.05）.The fiber-degrading bacteria（Succiniclasticum,unclassified Muribaculaceae and p-1088-a5 gut group）and protein-degrading bacteria（Prevotellaceae UCG-004）relative abundance were highest in Chinese Holstein steer（P（27）0.05）.While the succinate-producing bacteria（Fibrobacter）were highest in cattle-yak（P（27）0.05）.Moreover,the fungi quantity was highest in Maiwa yak（P（27）0.05）.（4）The relative abundance of the H₂-utilizing methanogens Methanobrevibacter sp.YE315 were significantly higher in Maiwa yak than cattle-yak,besides,the abundance of Methanobrevibacter millerae were highest in Maiwa yak（P（27）0.05）.The relative abundance of the H₂-utilizing methanogens（Methanobrevibacter sp.G16）were highest in cattle-yak（P（27）0.05）and the composition of rumen methanogens in Maiwa yak and cattle-yak were more similar.However,the H₂-utilizing methanogens（Methanobrevibacter boviskoreani JH1）and methylotrophic methanogens（Methanosphaera sp.ISO3-F5）were highest in Chinese Holstein steer（P（27）0.05）.In conclusion,under the same feeding conditions,the production performance,nutrients apparent digestibility,rumen fermentation characteristics and rumen microbial composition were distinct among different breeds of beef cattle.The ADG and DMI were highest of China Holstein steer,while DMI/IBW were similar among three breeds.The fiber digestibility of Maiwa yak was higher than cattle-yak.The Maiwa yak had highest relative abundance of fiber and protein-utilizing bacteria.Additionally,the Maiwa yak exhibited a propionate fermentation mode,and the MCP and VFA content in rumen were highest.Meanwhile,the H₂-utilizing methanogens of Maiwa yak were highest,subsequently,Maiwa yak produced lower H₂ and CH₄ yield.The rumen fermentation in Chinese Holstein steers was acetate mode,and the composition of rumen bacteria was conducive to digest carbohydrates and proteins in the ration.Moreover,the H₂-utilizing methanogens and methylotrophic methanogens in Chinese Holstein steers were most abundant,which were beneficial for the production of CO₂ and CH₄ in vitro fermentation.Similar to Maiwa yak,the rumen fermentation of cattle-yak was propionate mode.However,compared to Maiwa yak and Chinese Holstein steers,the relative abundance of succinate-producing bacteria in the rumen of cattle-yak were highest as well as the H₂yield in vitro fermentation,but the MCP content was lowest.