This experiment was conducted to investigate the effects of methionine analogues 2-hydroxy-4-methylthio butanoic acid isopropyl ester (HBMi) on growth performance, nutrient apparent digestibility, serum metabolite, serum free amino acids, and rumen fermentation parameters of yaks. Twenty-four male Maiwa yaks (252.79 ± 15.95 kg) were randomly allocated to four dietary treatments: basic diet (CON), or three HBMi (MetaSmart (MS); Adisseo Inc., Antony, France) supplementation treatments: MS1 (5 g), MS2 (10 g), and MS3 (15 g). The results showed that the increase in the supplemented MS levels linearly increased the average daily gain (p < 0.05), while the serum alkaline phosphatase activity and malondialdehyde content were increased when yaks were fed with 15 g/d MS (p < 0.05). The diet supplemented with MS linearly increased the percentages of glutamic acid and proline, and linearly or quadratically decreased the percentages of isoleucine, phenylalanine, and valine (p < 0.05). Furthermore, supplementation of 10 g/d and 15 g/d MS increased ruminal microbial crude protein (p < 0.05). The ratio of acetate to propionate in the MS2 group was lower than those in CON and MS1 groups (p < 0.05). In summary, a diet supplemented with 10 g/d MS could be an effective way to improve the growth performance of fattening yaks without negative effects.

This study aims to investigate the effect of methionine analogue 2-hydroxy-4-methylthiobutanoic acid isopropyl ester (HMBi) on the rumen microbial community, microbial carbohydrate-active enzymes (CAZy), and protein metabolism pathways in yak. Twenty-four male Maiwa yaks (252.79 ± 15.95 kg) were selected and randomly divided into groups that received the basal diet alone, or a diet supplemented with different amounts of HMBi (5 g, 10 g or 15 g). At the phylum level, the group receiving 5 g of HMBi showed a considerably higher relative abundance of Lentisphaerae than the other treatment groups (p < 0.05). The relative abundance of Actinobacteria decreased linearly with the increase in HMBi supplemental levels (p < 0.05). The relative abundance of Prevotella increased linearly with the increasing level of HMBi supplementation (p < 0.05). The relative abundance of Butyrivibrio linearly decreased (p < 0.05), and the relative abundance of Alistipes tended to linearly decrease (p = 0.084). The addition of HMBi had linear or quadratic effects on the relative abundance of CAZy enzymes and functional proteins in the rumen of yak (p < 0.05). Conclusively, these results indicated that feeding yaks a diet supplemented with HMBi is an excellent strategy to enhance carbohydrate breakdown, and improve rumen microbial structure and function.

This study objected to assess the effect of substituting ground corn (GC) with steam-flaked corn (SFC) at various ratios on growth performance, serum biochemistry, rumen fermentation, and microbiome in fattening yaks. Fifty male Maiwa yaks (196.43 ± 16.08 kg) were randomly assigned to five groups: SFC 0, SFC 25, SFC 50, SFC 75, and SFC 100, representing 0%, 25%, 50%, 75%, and 100% substitution of GC with SFC. Results showed that the dry-matter intake (DMI) in SFC 0 group was significantly lower than those in other treatment groups ( P < 0.05). Among the serum biochemical parameters, the triglyceride (TG) content in the SFC 100 group was significantly higher than other treatment groups ( P < 0.05), with a quadratically increase ( P < 0.05). Regarding rumen fermentation parameters, the propionate in the SFC 50 and SFC 100 groups was significantly higher than in the other groups ( P < 0.05). At the phylum level of the rumen microbiome, the replacing with SFC significantly increased the relative abundance of Planctomycetota , Bacteria , and Candidatus_Saccharibacteria ( P < 0.05). At the genus level, the replacing with SFC significantly increased the relative abundance of Paludibacteraceae and Bacteria ( P < 0.05). Among the CAZy enzymes in the rumen, the relative abundance of cellulase modules (CM) in the SFC 0 group was significantly higher than other groups ( P < 0.05). In conclusion, replacing 50% of GC with SFC may be an effective strategy to enhances growth performance in yak farming by improving rumen fermentation, microbiome composition, and carbohydrate-active enzymes. Highlights: The replacement of GC with SFC can optimize rumen fermentation of yaks. The replacement of GC with SFC in the diets affected the rumen microbiome of yaks. Metagenome profiled differences between CAZy enzymes and eggNOG functional proteins.