Effects Of Diets With Different Energy To Nitrogen Ratios On Rumen Microbial Protein Production And Methane Emissions Of Beef Cattle

The purpose of this research was to study the effects of diets with different energy to nitrogen ratios on rumen microbial proteins and methane emissions in beef cattle,through comprehensively evaluating nutritional values of five feedstuffs,so as to provide a theoretical basis for the formulation of ruminant diets and the regulation of methane emissions.This research consists of three parts,and the details are as follows.ExperimentⅠ:Evaluating the nutritional value of five feedstuffsThe aim of this experiment was to evaluate the nutritional value of five feed materials for beef cattle,using Cornell Net Carbohydrate and Protein System（CNCPS 6.0）and NRC（2001）models.Corn,soybean meal,germ meal,cottonseed meal and rapeseed meal were selected.According to the CNCPS model,their nutritional compositions were determined and the carbohydrate（CHO）and protein（CP）components were analyzed.Meanwhile,the digestible nutrients and energy values were calculated by the NRC（2001）model.The results showed that:1)The content of CHO and total digestible nutrients(TDN_1X)in corn was extremely significantly higher than that of other four feedstuffs（P<0.01）.The content of non-biodegradable carbohydrates（CC）and non-biodegradable proteins（PC）in corn was the lowest（P<0.01）.2)The contents of rapidly degraded carbohydrates（CA）,slowly degraded carbohydrates（CB2）,and moderately degraded true protein（PB2）in soybean meal were higher,and its nutritional value was better than other feedstuffs.3)The rapid degradation of true protein（PA）content in the embryo meal was the highest.4)Cottonseed meal has high CC and PB2content and its nutritional value was relatively low.5)Rapeseed meal had the highest CC,PC content,and the lowest TDN_1X（P<0.01）content.ExperimentⅡ:Rumen degradation characteristics and in vitro gas production characteristics of five feedstuffsThe purpose of the experiment was to study the rumen degradation characteristics and in vitro gas production characteristics of five feedstuffs by using nylon bag method and in vitro gas production method,and to evaluate the nutritional value of five feedstuffs.Three grassland red cattle fitted with permanent rumen fistula were selected to evaluate the rate of the degradation of dry matter（DM）,CP,neutral detergent fiber（NDF）and organic matter（OM）for corn,soybean meal,germ meal,cottonseed meal and rapeseed meal,using the nylon bag method,as well as using in vitro gas production method to determinate pH,concentration of ammonia nitrogen（NH₃-N）,the content of MCP,CH₄ and carbon dioxide（CO₂）production after 12 h.The results showed that:1)The effective degradation rates of DM,CP and OM in the germ meal were the highest,while the effective degradation rates and nutritional values of each component in rapeseed meal were the lowest.2)The MCP content in rapeseed meal was the highest.The content of NH₃-N in soybean meal was the highest.3)CH₄ in germ meal and corn emissions was the highest,and CO₂ production in soybean meal,germ meal and cottonseed meal had no significant differences.ExperimentⅢ:In vitro gas production characteristics of diets with different energy to nitrogen ratiosThe purpose of this experiment was to study the characteristics of gas production by using in vitro gas production method.The experiment adopted the Latin square design,and five groups of experimental diets with different energy to nitrogen ratios（RDN:FOM）were prepared,and then the pH value,NH₃-N concentration,MCP content,volatile fatty acid（VFA）,CH₄ and CO₂ production were determined by in vitro gas production method after 12 h fermentation.The results showed that:1)The MCP content of RDN:FOM 27.08 g/kg was significantly higher than that of the other four groups（P<0.05）.The MCP content in group18.29 g/kg was the lowest.2)The content of NH₃-N of 18.29 g/kg group was significantly lower than that of the 34.26 g/kg group（P<0.01）.3)Gas production of CH₄ of 18.29 g/kg group was significantly lower than that in the other four groups（P<0.05）,and the gas production of CO₂ of the 27.08 g/kg group was significantly higher than that of the groups of 18.29 g/kg and 34.26g/kg（P<0.05）.Besides,there was no significant difference in gas production of CO₂ among these groups except 27.08 g/kg group（P>0.05）.4)There was no significant difference in VFA among the five groups.