体外法研究硝酸钠调控水牛瘤胃甲烷生成对脂肪酸生物氢化途径的影响

本试验旨在研究硝酸钠调控水牛瘤胃甲烷生成对脂肪酸生物氢化途径的影响。选取3头体重约为（650±50）kg、安装永久性瘤胃瘘管的水牛作为瘤胃液供体动物，通过体外批次培养，设计发酵底物的精粗比为40：60，试验设4个组，每组5个重复，每组各添加0.25 mg/mL的α-亚麻酸，硝酸钠添加水平分别为0（对照）、1、2、3 mg/mL。分别培养3、6、9、12、24 h时测定产气量和甲烷产量，在培养24 h结束后测定体外发酵参数和脂肪酸含量。结果表明：①添加硝酸钠显著降低了瘤胃培养液24 h的总产气量、甲烷（CH₄）含量和甲烷/总产气量的比例（P<0.05），添加1、2和3 mg/mL硝酸钠后瘤胃液甲烷含量分别降低了89.62%、91.20%、91.75%。②添加硝酸钠组瘤胃培养液的pH和氨态氮（NH₃-N）含量显著高于对照组（P<0.05），添加1 mg/mL硝酸钠组微生物蛋白（MCP）含量也显著高于对照组（P<0.05），其他组别差异不显著（P>0.05）；添加硝酸钠组瘤胃液乙酸浓度差异不显著（P>0.05），但丙酸、丁酸、异丁酸、戊酸和异戊酸浓度显著低于对照组（P<0.05），乙酸/丙酸显著高于对照组（P<0.05），添加3 mg/mL硝酸钠组瘤胃液总挥发性脂肪酸（TVFA）含量显著低于对照组（P<0.05）。③添加1 mg/mL硝酸钠组瘤胃液C18：2 cis-9，trans-11、C18：2 trans-10，cis-12、C20：1、不饱和脂肪酸（UFA）含量及UFA/SFA显著高于其他组（P<0.05）；添加硝酸钠组瘤胃液C18：2n6c、C18：1n9t、C20：5n3（EPA）和C22：6n3（DHA）的含量均高于对照组，且1 mg/mL硝酸钠组含量最高，但差异不显著（P>0.05）；添加1 mg/mL硝酸钠组瘤胃液C18：3n3、C18：2n6c和C18：1n9c含量均高于对照组，差异不显著（P>0.05）。由此可见，体外添加硝酸钠显著降低了瘤胃液总产气量和甲烷含量，pH和NH₃-N含量显著升高，TVFA含量降低，通过显著减少丙酸含量而升高乙酸/丙酸；添加1 mg/mL硝酸钠可显著提高瘤胃液共轭亚油酸（CLA）和UFA含量，且在抑制甲烷产生的同时能够降低不饱和脂肪酸的生物氢化程度。

Effects of Sodium Nitrate on Methane Production and Fatty Acid Hydrogenation Process of Buffalo in vitro Fermentation

The objective of this study was to investigate the effects of sodium nitrate on methane production and fatty acid hydrogenation process of buffalo was studied by in vitro batch fermentation.Three buffaloes weighted (650±50) kg with permanent rumen fistula were selected as the donors of rumen fluid.The ratio of concentrate to forage of substrate was 40:60.Four groups (5 replicates in each group) were set up,each group was added with 0.25 mg/mL α-Linolenic acid,and the level of sodium nitrate was 0,1,2 and 3 mg/mL respectively.The gas production and methane production were measured at 3,6,9,12 and 24 h respectively,and the fermentation parameters and fatty acid content were measured at the end of 24 h respectively.The results showed that:① Adding sodium nitrate significantly reduced the total gas production,CH₄ content and the ratio of methane/total gas production in rumen culture medium for 24 hours (P<0.05).Adding 1,2 and 3 mg/mL sodium nitrate reduced the methane content by 89.62%,91.20% and 91.75% respectively.② The pH and NH₃-N content of rumen culture medium added with sodium nitrate were significantly higher than that of the control group (P<0.05),the MCP content of 1 mg/mL sodium nitrate was also significantly higher than that of the control group (P<0.05),and the difference of other groups was not significant (P>0.05);The difference of acetic acid concentration added with sodium nitrate was not significant (P>0.05),but the concentrations of propionic acid,butyric acid,isobutyric acid,valeric acid and isovaleric acid were significantly lower than that of the control group (P<0.05),the acetic acid/propionic acid was significantly higher than that of the control group (P<0.05),and the total volatile fatty acid added with 3 mg/mL sodium nitrate was significantly lower than that of the control group (P<0.05).③ The content of C18:2 cis-9,trans-11,C18:2 trans-10,cis-12,C20:1,UFA and UFA/SFA in the group with 1 mg/mL sodium nitrate was significantly higher than that in the other groups (P<0.05);the content of C18:2n6c,C18:1n9t,C20:5n3 (EPA) and C22:6n3 (DHA) in the group with 1 mg/mL sodium nitrate was the highest,but the difference was not significant (P>0.05).The contents of C18:3n3,C18:2n6c and C18:1n9c in sodium nitrate groups were higher than those in the control group (P>0.05).It could be seen that the addition of sodium nitrate in vitro significantly reduced the total gas production and methane content,increased the pH and NH₃-N content,decreased TVFA content,increased acetic acid/propionic acid by significantly reducing propionic acid content.The addition of 1 mg/mL sodium nitrate significantly increased the content of CLA and UFA in rumen fluid,and inhibited methane,it could reduce the hydrogenation degree of unsaturated fatty acids at the same time.