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Simple Summary: Yaks are important for the economy and livelihood of local herders in the Tibetan Plateau and are their primary source of income. Traditionally, the production performance of ruminants is generally improved by increasing the proportion of concentrate feed in the diet. To the best of our knowledge, the optimal proportion of concentrate feed is limited in actual production and research of yak. This study fed three diets with different dietary forage-to-concentrate ratios (50:50, 65:35, and 80:20) to 36 male yaks (Bos grunniens). The changes in the distribution of fecal microorganisms were studied by 16S rRNA gene sequencing and liquid chromatography–mass spectrometry. We found that the dietary forage-to-concentrate ratio significantly impacted yak fecal microorganisms. As such, these studies help us understand the fecal microbiota of yaks, further provide more complete information on the requirements of yak diets in terms of concentrate-to-forage ratio and improve yak growth performance, and provide a theoretical basis for accurate housing of yaks. (1) Background: This study aimed to investigate the effects of different dietary concentrate to roughage ratios on growth performance and fecal microbiota composition of yaks by 16S rRNA gene sequencing. (2) Methods: In the present study, three diets with different dietary forage-to-concentrate ratios (50:50, 65:35, and 80:20) were fed to 36 housed male yaks. (3) Results: The result shows that Final BW, TWG, and ADG were higher in the C65 group than in the C50 and C80 groups, but the difference was not significant (p > 0.05). DMI in the C65 group was significantly higher than in the other two groups (p < 0.05). The DMI/ADG of the C65 group was lower than that of the other two groups, but the difference was insignificant (p > 0.05). At the phylum level, Firmicutes were the most abundant in the C65 group, and the relative abundance of Bacteroidetes was lower in the C65 group than in the other two groups. At the genus level, the relative abundances of Ruminococcaceae_UCG_005, Romboutsia, and Christensenellaceae_R-7 were higher in the C56 group than in the C50 and C80 groups. The relative abundance of Lachnospiraceae_NK3A20 and Rikenellaceaewas_RC9_gut is lower in the C65 group, but the difference was insignificant (p > 0.05). At KEGG level 2, the relative abundance of lipid metabolism and energy metabolism were lowest in the C50 group, and both showed higher relative abundance in the C65 group. (4) Conclusions: In conclusion, the structure of fecal microbiota was affected by different concentrate-to-forage ratios. We found that feeding diets with a concentrate-to-forage ratio of 65:35 improved yaks' growth and energy metabolism. [ABSTRACT FROM AUTHOR]

Many prediction equations are available for enteric methane (CH 4) emission in cattle; however, these are not suitable for yaks, as CH 4 emission differs between these species. To our knowledge, no equation has been generated for yaks and, consequently, the aim of this study, at least in part, is to fill this gap. Feed and energy intakes, dry matter digestibility, and CH 4 emissions were measured in 16 yak calves (8 males and 8 females) at 8, 12, and 16 months of age. Concentrate (C) and forage (F) were offered the calves at a ratio of 60:40. There was no difference (P = 0.92) in body mass (m b) between sexes, but there was a difference (P < 0.001) among ages. Significant differences (P < 0.001) were observed in the dry matter intake (DMI), organic matter intake (OMI), neutral detergent fiber intake (NDFI), acid detergent fiber intake (ADFI), gross energy intake (GEI), digestive energy intake (DEI), and metabolizable energy intake (MEI) among ages and between sexes. The CH 4 emission (g/d) and the energy equivalent of CH 4 emission (MJ/d) increased (P < 0.005) with increasing age, and they were higher (P < 0.005) in males than in females. There was no difference (P = 0.22) in CH 4 emission between sexes in g CH 4 /kg DMI. Using simple linear regressions, DMI, OMI, and NDFI each explained 49–50% of the variation in CH 4 emission; whereas, GEI explained 49% of the energy loss due to CH 4 emission. In multiple regressions, NDFI and either m b or ADFI explained 49–50% of the variation in CH 4 emission. It was concluded that CH 4 emission in yaks: (1) tended to be lower than emissions reported in the literature for cattle and Murrah buffalo calves fed diets of similar C:F ratios; and, (2) as in cattle, can be predicted by dry matter intake. • Prediction equations of enteric methane emission for yaks were generated. • Dry matter intake explained 50% of the variation in methane emission. • Methane emission was lower in yak than cattle and Murrah buffalo calves. • Methane emission for yaks was lower than predicted for ruminant of its mass. [ABSTRACT FROM AUTHOR]