经过长期的自然选择和进化，使牦牛对青藏高原极端环境和冷季营养胁迫具有极强的适应能力。申请人通过近几年的研究发现，牦牛较本地黄牛具有较低的瘤胃甲烷排放特征，但其确切机制尚未阐明。本项目拟以黄牛为对照，通过生理生态和比较宏基因组学结合的方法从瘤胃甲烷排放、微生物群落结构、基因功能和代谢途径四个层次系统探讨：1）牦牛瘤胃甲烷生成的生理代谢特征；2）牦牛瘤胃微生物群落结构、不同微生物与产甲烷菌的协作关系及代谢途径；3）挖掘甲烷生成及纤维降解过程中的关键基因，分析其结构和功能；4）利用质子核磁共振，筛选与甲烷生成相关瘤胃代谢小分子物质，建立与差异微生物群落间的关联。以期初步揭示牦牛适应高寒营养胁迫的瘤胃微生物代谢和甲烷生成的微生态学机制，丰富极端环境下反刍动物生理生态和营养适应方面的基础理论，为提高牦牛生产和抑制反刍动物甲烷排放提供技术支撑。

Performance of yaks (Bos grunniens) is significantly affected by seasonal changes and they have adapted by displaying a circannual rhythm to better adapt to the harsh grasslands conditions. Our previous research demonstrated that yaks, compared to indigenous cattle (Bos taurus), seem to possess an N preserving metabolism, and produce little methane. The animal grazes exclusively on grasses, straw, and lichens, the rumen also harbor a unique microbiome for efficient conversion of fibrous materials, yet the metabolic diversity and physiological potential of these microbial communities are only beginning to be revealed. With advances in sequencing technologies, large-scale genomic surveys of microbial communities (metagenomics) are becoming routine, making deciphering the genetic and functional ‘differences that make a difference’ within and among microbial habitats increasingly feasible. However, for the yak, it remains elusive whether the traits of 'energy saving' or less methane production are common occurrence co-evolved with a unique rumen microbial ecosystem, or whether it is restricted to certain environment, e.g. native grazing. Therefore, it is worthwhile to compare rumen microbiome and methanogenesis from “energy-saving” animal (yak) and normal animal (cattle) in determining if the changes in the microbiota can be directly linked to the reduced methane emissions.. The goal is to quantify methane emissions from yak and cattle fed the same diet and identify the dominant organisms and pathways involved in hydrogenotrophy in the yak rumen, with the broader aim of understanding how these processes are able to predominate over methanogenesis. Nine domestic cattle and nine domesticated yaks are subjected to measurements of methane output using the sulfur hexafluoride tracer gas technique, nutrient intake and in vitro digestibilities. The experimental animals fed a mixed diet of oat hay and highland barley in ratio of 7:3 on a dry matter (DM) basis (ad libitum). Rumen microbial diversity was investigated by comparative metagenomics combined with of 16S rRNA gene sequences from rumen digesta samples.The libraries for microbial genomic DNA in the two animal groups are constructed and sequenced by Illumina sequencing, comparative metagenomic analysis common rumen microbiomes as well as those variables among them. Our hypothesis is that as an ‘energy saving’ animal, the yak rumen harbor a unique microbiome predominate over methanogenesis and is a heritable and repeatable trait.