添加亚油酸条件下不同剂量硝酸钠对水牛瘤胃体外发酵脂肪酸组成及相关微生物数量的影响

为了探究添加亚油酸条件下不同剂量硝酸钠对水牛瘤胃体外发酵脂肪酸组成及相关微生物数量的影响，本试验选用3头装有永久性瘤胃瘘管的母水牛，以精粗比40∶60为底物进行瘤胃液体外发酵试验。试验组硝酸钠的浓度分别为1、2、3 mg·mL^-1，对照组不加硝酸钠，每组均添加0.25 mg·mL^-1的亚油酸，每组各5个重复。在体外培养3、6、9、12、24 h时测定产气量和甲烷产量，24 h结束培养，测定瘤胃体外发酵参数、脂肪酸含量及瘤胃微生物数量。结果表明：1）添加硝酸钠显著降低了总产气量和甲烷产量（P<0.05）；2）添加硝酸钠pH值和氨态氮（NH₃-N）含量显著升高（P<0.05），异丁酸和异戊酸含量显著降低（P<0.05），而对总挥发性脂肪酸（TVFA）含量无显著性影响（P>0.05）；3）添加1 mg·mL^-1硝酸钠，C18：2cis-9，trans-11、C18：2trans-10，cis-12含量和不饱和脂肪酸/饱和脂肪酸（UFA/SFA）显著高于其他组（P<0.05），且C20：5n3 （EPA）含量显著高于添加3 mg·mL^-1硝酸钠组（P<0.05），添加2 mg·mL^-1硝酸钠C22：6n3 （DHA）含量显著高于其他组（P<0.05）；4）添加硝酸钠组原虫数量显著低于对照组（P<0.05），添加2、3 mg·mL^-1硝酸钠产甲烷菌数量显著低于添加1 mg·mL^-1硝酸钠组（P<0.05），添加1 mg·mL^-1硝酸钠总细菌、真菌、溶纤维丁酸弧菌、蛋白分解丁酸弧菌、非典型丁酸弧菌、亨氏丁酸弧菌数量显著高于其他组（P<0.05）。由此可得，体外法添加1~3 mg·mL^-1硝酸钠和0.25 mg·mL^-1亚油酸在维持水牛TVFA含量不变的情况下显著降低了甲烷含量，且1 mg·mL^-1硝酸钠能促进亚油酸生成共轭亚油酸（CLA），优化脂肪酸组成，并能增加大多数瘤胃微生物的数量。

Effects of different doses of sodium nitrate on fatty acid composition and microbial population in in vitro simulation of buffalo rumen fermentation with added linoleic acid

This research explored the effects of different doses of sodium nitrate on the composition of fatty acids and the numbers of microorganisms in in vitro simulation of buffalo rumen fermentation with added linoleic acid. Three female buffaloes with permanent rumen fistula were used. The ratio of dietary concentrate to roughage was 40∶60. The experiment comprised five replicates of four experimental treatments： a blank control （CK） and addition of sodium nitrate at rates of 1， 2 or 3 mg·mL^-1， with 0.25 mg·mL^-1 linoleic acid added in each case. Gas and methane production were measured after 3， 6， 9， 12 and 24 h anaerobic incubation in vitro， and the fermentation parameters， fatty acid concentrations and numbers of rumen microorganisms were determined after 24 h incubation. It was found that adding sodium nitrate significantly reduced the total gas production and methane production （P<0.05）. Adding sodium nitrate also significantly increased the simulated rumen pH value and ammonia nitrogen （NH₃-N） concentration （P<0.05）， significantly reduced the contents of isobutyrate and isovaleriate （P<0.05）， but had no significant effects on the concentrations of total volatile fatty acids （TVFA） （P>0.05）. With the addition of 1 mg·mL^-1 sodium nitrate， the contents of C18：2cis-9， trans-11， C18：2trans-10， cis-12 and unsaturated/saturated fatty acid ratios were significantly higher than those in other groups （P<0.05）. The concentration of C20：5n3 （eicosapentaenoic acid） in the 1 mg·mL^-1 sodium nitrate group was significantly higher than that in the 3 mg·mL^-1 sodium nitrate group （P<0.05）， and the concentration of C22：6n3 （docosahexaenoic acid） with 2 mg·mL^-1 sodium nitrate added was significantly higher than that of other groups （P<0.05）. The number of protozoa in treatments with added sodium nitrate was significantly lower than for CK （P<0.05）. The number of methanogens in treatments with 2 and 3 mg·mL^-1 added sodium nitrate was significantly lower than in the 1 mg·mL^-1 sodium nitrate treatment （P<0.05）， and the numbers of bacteria， fungi， Butyrivibrio fibrisolvens， Butyrivibrio proteoclasticus， Atypical butyrivibrio， and Butyrivibrio hungatei in the 1 mg·mL^-1 sodium nitrate treatment were significantly higher than in other treatments （P<0.05）. In summary， the addition of 1-3 mg·mL^-1 sodium nitrate and 0.25 mg·mL^-1 linoleic acid in vitro significantly reduced methane generation while maintaining the TVFA concentration. Moreover， 1 mg·mL^-1 sodium nitrate promoted the formation of conjugated linoleic acid （CLA）， optimized fatty acid composition， and increased the numbers of most rumen microorganisms.