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 investigated the effects of the dietary protein level and rumen-protected methionine and lysine (RPML) on the growth performance, rumen fermentation, and serum indexes of yaks. Thirty-six male yaks were randomly assigned to a two by three factorial experiment with two protein levels, 15.05% and 16.51%, and three RPML levels: 0% RPML; 0.05% RPMet and 0.15% RPLys; and 0.1% RPMet and 0.3% RPLys. The trial lasted for sixty days. The results showed that the low-protein diet increased the DMI and feed conversion ratio of yaks. The diet supplemented with RPML increased the activities of IGF1 and INS and nutrient digestibility. The high-protein diet decreased the rumen butyrate concentration and increased the rumen isovalerate concentration. The low-protein diet supplemented with RPML increased the rumen pH and the concentrations of total volatile fatty acids, butyrate and NH₃-N; the high-protein diet supplemented with a high level of RPML decreased the rumen pH and the concentrations of isobutyrate, isovalerate, propionate and NH₃-N. The low-protein diet supplemented with RPML increased the total antioxidant capacity and glutathione peroxidase activity, along with the concentrations of malondialdehyde and amino acids such as aspartic acid, lysine, cysteine, etc. In conclusion, a low-protein diet supplemented with RPML is beneficial for rumen and body health, physiological response, and metabolic status in yaks.

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 aimed to investigate the effects of dietary guanidinoacetic acid (GAA) supplementation on yak physiology by evaluating growth performance, serum biochemical indices and plasm metabolomic profiles to elucidate the underlying regulatory mechanisms. Twenty-four male yaks (4–5 years; 249.38 ± 11.69 kg BW) were randomly allocated to three dietary treatments (n = 8): CON (basal diet), GAA1 (basal diet + 0.055% GAA), and GAA2 (basal diet + 0.11% GAA), with 55:45 of concentrate:roughage (DM basis). After a 10-day adaptation period, the feeding trial lasted 90 days. Body weights were measured on days 0 and 90 for growth performance evaluation, with blood samples collected on the final day for separation into serum and plasma to assess serum metabolic and antioxidant parameters and for plasma metabolomic profiling. The result showed that growth performance parameters displayed a positive trend, with average daily gain (ADG) showing marginal improvement (p = 0.072). Serum biochemical analysis revealed that dietary supplementation of GAA had no effect on serum biochemical parameters while tendency decreased GSH-Px activity (p = 0.087). Non-targeted metabolomics identified 39–121 differentially abundant metabolites in plasma across treatment groups. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis of these metabolites revealed pathways such as tryptophan metabolism, glycerophospholipid metabolism, and arginine metabolism. Among the differentially abundant metabolites, N(omega)-Hydroxyarginine and tryptophan metabolites such as 5-hydroxytryptophan and serotonin were specifically highlighted. In conclusion, dietary supplementation of GAA in yaks has been confirmed to improve ADG, with a 0.11% supplementation level being more effective, and this may be associated with GAA enhancing amino acid metabolism, particularly arginine and tryptophan metabolism.