体外法研究低蛋白条件下添加尿素和硝酸钠对瘤胃微生物的影响

Effects of Urea and Sodium Nitrate Supplementation to Low Protein Diet on in vitro Rumen Microbial

试验旨在研究低蛋白条件下添加尿素和硝酸钠对体外模拟瘤胃甲烷和氢气产量、瘤胃发酵特征和微生物蛋白合成的影响。采用单因素试验设计,对照组以低蛋白饲粮为发酵底物,尿素组为发酵底物中添加17 g/kg尿素,硝酸钠组为发酵底物中添加40 g/kg硝酸钠,使用无氮人工瘤胃缓冲液进行体外发酵,每个组包含6个重复,分3批次发酵。瘤胃液来自3只装有永久瘤胃瘘管的浏阳黑山羊,采用全自动体外模拟瘤胃发酵装置进行48 h的厌氧发酵。结果显示:添加尿素对底物体外干物质降解率(DMD)、总产气量、甲烷和氢气产量没有显著影响(P>0.05):添加硝酸钠显著降低DMD、总产气量和甲烷产量并显著提高氢气产量(P<0.05)。添加尿素显著提高体外发酵液中氨态氮(NH_(3)-N)和微生物蛋白浓度(P<0.05),但对总挥发性脂肪酸(TVFA)浓度、乙酸和丙酸的比例无显著影响(P>0.05);添加硝酸钠显著降低体外发酵液中氨态氮和总挥发性脂肪酸浓度以及乙酸和丁酸的比例(P<0.05),并显著提高微生物蛋白浓度和丙酸比例(P<0.05)。体外发酵模式下,低蛋白饲粮中添加尿素可促进微生物蛋白的合成,但对瘤胃发酵模式和甲烷生成无影响,而添加硝酸钠促使氢向丙酸合成和微生物蛋白合成途径迁移,进而减少甲烷生成。

This experiment studied the effects of urea and sodium nitrat supplementation on in vitro ruminal methanogenesis,fermentation,and microbial protein synthesis based on low-protein diet.Single factor design was used in the present study.The control group used low-protein diet as substrate(CP=8.3 g/kg),the urea group was added with 17 g/kg urea(CP=12.2 g/kg;DM basis),the sodium nitrate group was added with 40 g/kg sodium nitrate(CP=12.2 g/kg;DM basis).Nitrogen-free artificial rumen buffer was used for in vitro fermentation,each group contains 6 replicates,which were fermented in 3 batches.The rumen fluid was collected from 3 healthy adult ruminally cannulated Liuyang black goats.The fermentation was carried out for 48 hours in an automated in vitro batch incubation system.The results showed that the addition of urea had no significant effect on the dry matter degradation(DMD),total gas production,methane and hydrogen production(P>0.05),but the addition of sodium nitrate reduced DMD,total gas and methane production,and increased hydrogen production(P<0.05).The addition of urea increased the concentration of ammonia and microbial protein(P<0.05),but it had no effect on the total volatile fatty acid concentration and the molar percentage of acetate and propionate(P>0.05);while the addition of sodium nitrate reduced the concentration of ammonia and total volatile fatty acids and the molar percentage of acetate and butyrate(P<0.05),and increased the microbial protein concentration and the propionate percentage(P<0.05).In the in vitro fermentation condition,the addition of urea to the low-protein feed can promote the synthesis of microbial protein,but has no effect on the rumen fermentation pathway and methane production.The addition of sodium nitrate promotes the redirection of hydrogen to propionate and microbial protein synthesis,thereby reducing methane production.