Short chain fatty acids (SCFA), are a crucial form of nutrition for digestion and assimilation of grass for ruminants including the yaks. Gut microbiota degrades chyme, produces SCFA and influences its proportion. Here, we investigated the fecal microbiota and SCFA concentration in wild yak (Bos mutus) and domestic yak (Bos grunniens). We hypothesize that yaks’ gut microbiota influence concentration of SCFA and in that way increase the assimilation of nutrients from the grass. Microbes and SCFA concentration of yaks were processed and measured by 16S rDNA and Gas Chromatography-Mass Spectrometry respectively. The results show that the yak fecal microbes are mainly composed of Firmicutes(66.47%, 68.38%)(wild yak and domestic yak respectively, the same below), Bacteroidetes(26.00%, 26.16%) and Proteobacteria(3.48%, 1.52%) at the phylum level. Furthermore, Ruminococcaceae(55.18%, 58.48%), Bacteroidaceae(8.75%, 9.59%) and Lachnospiraceae(7.57%, 6.14%) at the family level; the domestic yak has the similar mainly composition with wild yak. SCFA concentration (including acetic acid, propionic acid, i-butyric acid, n-butyric acid and n-valeric acid) in wild yaks’ feces are significantly higher than in domestic yak (P<0.01). Spearman correlation relationship analysis shows that there is strong positive correlation between Porphyromonadaceae, Bacteroidaceae, Paraprevotellaceae, Rikenellaceae, Erysipelotrichaceae and SCFA concentration in wild yaks (r>0.4, P<0.05). However, there only has weak positive correlation in domestic yak’s microbes. Our result suggests that the digestion of grass in wild yaks is more efficient than in domestic yaks.

短链脂肪酸（SCFA）是反刍动物吸收饲草、饲料中营养物质的重要形式。肠道菌群能够降解食物生成SCFA并影响其比例。本文通过16S rDNA测序和气相色谱质谱联用仪，分别测定了野牦牛（Bos mutus）和家牦牛（Bos grunniens）粪便菌群组成及SCFA含量，通过比较分析两种牦牛肠道菌群与SCFA的关系，筛选出野牦牛肠道中与SCFA高浓度有正相关关系的菌群。结果显示，野牦牛粪便菌群主要的门有厚壁菌门（Firmicutes）（66.47%）、拟杆菌门（Bacteroidetes）（26.00%）和变形菌门（Proteobacteria）（3.48%），主要的科有瘤胃球菌科（Ruminococcaceae）（55.18%）、拟杆菌科（Bacteroidaceae）（8.75%）和毛螺菌科（Lachnospiraceae）（7.57%），家牦牛的菌群结构和组成与野牦牛相似。野牦牛粪便中SCFA以乙酸和丙酸为主，乙酸、丙酸、异丁酸、正丁酸和正戊酸的含量均显著高于家牦牛（P<0.01）。Spearman相关分析显示，野牦牛粪便菌群中紫单胞菌科（Porphyromonadaceae）、拟杆菌科（Bacteroidaceae）、普雷沃氏菌科（Paraprevotellaceae）、理研菌科（Rikenellaceae）和韦荣球菌科（Erysipelotrichaceae）与SCFA具有较强相关性（r>0.4），而家牦牛仅有弱相关性（r<0.3）。说明牦牛后肠道具有丰富的能够促进SCFA生成的益生菌群，进而提高食物的转化效率。