Selenium (Se) deficiency is a widespread and seasonally chronic phenomenon observed in Tibetan sheep (Ovis aries) traditionally grazed on the Qinghai–Tibet Plateau (QTP). Effects of the dietary addition of Se-enriched yeast (SeY) on the bacterial community in sheep rumen and rumen fermentation were evaluated with the aim of gaining a better understanding of the rumen prokaryotic community. Twenty-four yearling Tibetan rams [initial average body weight (BW) of 31.0 ± 0.64 kg] were randomly divided into four treatment groups, namely, control (CK), low Se (L), medium Se (M), and high Se (H). Each group comprised six rams and was fed a basic diet of fresh forage cut from the alpine meadow, to which SeY was added at prescribed dose rates. This feed trial was conducted for over 35 days. On the final day, rumen fluid was collected using a transesophageal sampler for analyzing rumen pH, NH3-N content, volatile fatty acid (VFA) level, and the rumen microbial community. Our analyses showed that NH3-N, total VFA, and propionate concentrations in the M group were significantly higher than in the other groups (P < 0.05). Both the principal coordinates analysis (PCoA) and the analysis of similarities revealed that the bacterial population structure of rumen differed among the four groups. The predominant rumen bacterial phyla were found to be Bacteroidetes and Firmicutes, and the three dominant genera in all the samples across all treatments were Christensenellaceae R7 group, Rikenellaceae RC9 gut group, and Prevotella 1. The relative abundances of Prevotella 1, Rikenellaceae RC9 gut group, Ruminococcus 2, Lachnospiraceae XPB1014 group, Carnobacterium, and Hafnia-Obesumbacterium were found to differ significantly among the four treatment groups (P < 0.05). Moreover, Tax4fun metagenome estimation revealed that gene functions and metabolic pathways associated with carbohydrate and other amino acids were overexpressed in the rumen microbiota of SeY-supplemented sheep. To conclude, SeY significantly affects the abundance of rumen bacteria and ultimately affects the rumen microbial fermentation.

Domestic yak (Bos grunniens) have coexisted with plateau pika (Ochotona curzoniae) for thousands of and they play irreplaceable roles in shaping the structure and function of alpine meadow ecosystem. However, the mechanisms whereby the greenhouse gas (GHG) emissions change in response to the interactive effects between yak grazing and plateau pika burrowing remain unclear. In this study, we examined the response of ecosystem GHG emissions (CO 2 , CH 4 , and N 2 O flux) to yak grazing and pika burrowing in alpine meadow in Zoige County, China. The GHG emissions was measured with a static opaque chamber method. Our results revealed that CO 2 , CH 4 , N 2 O flux and CO 2 -eq were significantly influenced by yak grazing and pika burrowing independently, and in conjunction. Crucially, the relative importance of pika burrowing was higher than yak grazing on a pastoral scale. Specifically, high pika burrowing led to an increase of 440.29%, and 110.72% for CO 2 -eq relative to low pika burrowing under moderate and heavy yak grazing situations, respectively. The value of CO 2 -eq with low pika burrowing was negative, especially under light yak grazing conditions. Furthermore, we found that GHG emissions were sensitive to plant species richness, soil temperature, soil moisture, soil organic carbon, and soil microbial factors. Structural equation modeling indicated that pika burrowing can affect CO 2 -eq though altering soil temperature and belowground biomass under heavy yak grazing conditions and changing soil moisture and soil microbe under light yak grazing. The results of this study enrich our understanding of the role of small burrowing mammals in the carbon sequestration of alpine meadow. In the context of the carbon neutrality of alpine grassland ecosystem, small mammals' activities and their interactions with domestic livestock-induced changes in microtopography on GHG emissions should not be neglected.

Satisfying the animals feed demand from the forage supply by grasslands remains a major challenge in the grassland–livestock ecosystem. To provide an alternative forage sources, this study conducted two feeding trials in the summer of 2015 and 2016 to compare the nutritive value, digestibility and nutrients utilization of native pasture (NH) and oat forage (OT) fed to Tibetan sheep (Ovis aries). Twelve Tibetan sheep with a mean body weight of 39.11 ± 3.66 kg in 2015 and 27.97 ± 2.69 kg in 2016 were use in this study. The experiment was 2 (year: 2015 and 2016) by 2 (forage: NH and OT) factorial. Data on proximate analysis, fiber fraction and nutrients digestibility were collected and analyzed using general linear model. However, the crude protein (CP) and water‐soluble carbohydrates contents in OT were higher (P < .001) than those in NH by 7.81–8.93% and 46.40–47.05%, respectively. In contrast, the neutral detergent fiber (NDF) and acid detergent fiber contents were higher (P < .001) in NH by 14.28–15.78% and 15.62–18.00%, respectively. The dry matter digestibility coefficient in OT (0.82 in 2015 and 0.79 in 2016) was significantly higher than that in NH (0.68 in both years). In addition, the OT diet had higher (P < .001) organic matter, NDF and CP digestibilities. Animals fed OT retained significantly more nitrogen (2.66 g/day in 2015 and 1.93 g/day in 2016) than those fed NH (0.96 g/day in 2015 and 0.42 g/day in 2016). The digestible energy and metabolizable energy were higher (P < .001) in OT than in NH. Our data indicated that Tibetan sheep urinary N excretion increased by 0.726 g with increase of 1 g in the nitrogen intake. Conclusively, the OT had higher nutritive value than NH and could therefore use to satisfy livestock demand and reduce the grazing pressure on grasslands.