Effect Of Dietary NDF Level On Growth Proformance,Methane Emission And Cecal Archaeal Diversity

Due to the smaller size and lower methane production in rabbit,the methane emission had been ignored.This experiment was conducted to investigate the effect of dietary NDF level on the growth performance,nutrition utilization,caecum fermentation,methane emission and cecal archaea community of growing New Zealand White rabbits.One hundred and twenty rabbits were weaned at 35d±2 and allocated into four treatments in accordance with body weight,each treatment had 5replicates and each replicate had 6 rabbits.The diet of the four treatments had similar energy and nitrogen level and also similar fiber composition pattern,but different NDF levels.The NDF level of the four treatments were 21%,25%,29%and 33%,respectively.The growth trial lasted 7 d for adaptation,and 56 d for test.The results were showed as following:?1?The growth performance of rabbits was significantly affected by dietary NDF level?P<0.05?.The ADFI and ADG were significantly decreased with decreasing of dietary NDF level?P<0.05?.According to the results of the regression analysis,there is a significant quadratic relationship between dietary NDF level?x,%?and the daily gain weight?y,g/d?:y=y=-0.051x²+3.0503x-14.332,R²=0.976,P=0.023;When the dietary NDF level was 29.85%,the daily gain weight had maximum value was31.27g/d.?2?TP,ALB and ALP in serum were significantly decreased with decreasing of dietary NDF level?P<0.05?.There were no significant difference on the TC,HDL-C,LDL-C and AST in serum among all treatments?P>0.05?.?3?The digestibility of CP was significantly increased and the digestibility of ADF and NDF were decreased with increasing of dietary NDF level?P<0.05?.The digestibility of CF was significantly higher in 25%group compared with other groups.?4?The villous height in duodenum,jejunum and ileum were significantly decreased with the decreasing of dietary NDF level?P<0.05?.The crept depth in duodenum was significantly increased?P<0.05?,but the crept depth in ileum was decreased with decreasing of dietary NDF level?P<0.05?.?5?CH₄ energy,ME/GE and ME/DE were significantly decreased?P<0.05?but UN was increased with the decreasing of dietary NDF level?P<0.05?.RN/IN and RN/DN were also significantly decreased when dietary NDF level decreased?P<0.05?.Methane emission was significantly decreased with decreasing of dietary NDF level?P<0.05?,the value of rabbit in four treatments were 0.12,0.11,0.09 and 0.05L/d or0.79,0.76,0.59 and 0.33 L/kg DMI,respectively.The regression analysis found that the methane emission?L/d?was a significant quadratic relationship with dietary NDF,ADF and CF intake?P<0.05?,Methane regressed to NDFI,ADFI and CFI were CH4?L/d?=-0.001[ADFI?g/d?]²+0.031 ADFI?g/d?-0.354?R²=0.998,P=0.046?,CH4?L/d?=-0.0002[NDFI?g/d?]²+0.02 NDFI?g/d?-0.375?R²=0.998,P=0.045?,CH4?L/d?=-0.008[CFI?g/d?]²+0.0385 CFI?g/d?-0.3228?R²=0.998,P=0.045?,respectively??6?Cecal NH₃-N concentration were significantly decreased with decreasing of dietary NDF level?P<0.05?.Decreased of dietary level had no effect on cecal pH,MCP and total VFA concentration?P>0.05?,but the molar proportion of acetic acid?%total VFA?was significantly decreased?P<0.05?and the molar proportion of butyric acid was significantly increased?P<0.05?with decreasing of dietary NDF level.?7?The abundance and composition of the archaea community in cecal content were significantly affected by dietary NDF level?P<0.05?.At phyla level,the relative abundance of Thaumarchaeota was significantly increased?P<0.05?but the relative abundance of Euryarchaeota was decreased with decreasing of dietary NDF level?P<0.05?.At genera level,the relative abundance of Candidatus Nitrososphaera was increased and the relative abundance of Methanobrevibacter and Methanosphaera were decreased with decreasing of dietary NDF level?P<0.05?.In summary,reduce the NDF level of the dietary could decrease the relative ahundance of Methanobrevibacter and Methanosphaera,change the cecal fermentation pattern,and reduce methane emissions,but it would inhibit the development of intestine,decrease the digestibility of fibre,reduce the efficiency of energy and nitrogen,ultimately affected the growth performance of rabbits.Under the condition of experiment,tabken the growth performance as reference standard,the suitable NDF level of the rabbit dietary was 29%.