The objective of this study was to investigate the effects of different dietary energy levels on serum concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1), as well as gene expression of their associated binding proteins and receptors in yak. Fifteen adult male yaks with BW of 276.1 ± 3.5 kg were allotted in three dietary groups and were fed with low (LE), medium (ME), and high energy (HE) level diet having different NEg of 5.5 MJ/kg, 6.2 MJ/kg, 6.9 MJ/kg, respectively. The effects of these treatments on ADG, BW, ADFI, and feed conversion ratio were significant (p < 0.05) throughout the experimental period. Serum GH concentration decreased (p < 0.05) with an increase in dietary energy level on d 30 and d 60. While IGF-1 concentration was higher (p < 0.05) in ME group, as compared to LE and HE groups on d 60. The expression level of growth hormone receptor (GHR) was decreased (p < 0.001) and IGF-1 was increased with the increase in the dietary energy level. The relative expression of insulin-like growth factor binding protein 3 (IGFBP-3) was higher (p < 0.001) in ME and HE groups, except the LE group. In conclusion, our findings provide a first insight into the combined effect of GH and IGF-1 in controlling the metabolism and productivity of yak. It also showed that medium energy level diet contributed to promote growth performance of yak during the cold season.

Resveratrol (RES) and β-Hydroxy-β-methyl butyric acid (HMB) have been shown to exert antioxidant, anti-inflammatory effect as well as influence intestinal microbiota composition in monogastric animal. However, the mechanism by which RES and HMB regulate duodenal function in ruminants remains unclear. In this study, the effects of RES and HMB on the development and health of the duodenum in Tibetan sheep were investigated. A total of 120 early weaned Tibetan rams with similar initial body weight (15.5 ± 0.14 kg) were selected and randomly allocated into 4 groups. Each group received a basal diet supplemented with 1.5 g RES/d (RES group), 1.25 g HMB/d (HMB group), 1.5 g RES/d plus 1.25 g HMB/d (RES_HMB group), and without any additives (CON group). The results showed that RES and HMB supplementation significantly increased (p < 0.05) the villus height and the ratio of villus height to crypt depth in the duodenum. Meanwhile, the concentrations of cellulase and trypsin were increased (p < 0.05) when RES and HMB were supplemented in the basal diet. The RES group exhibited higher (p < 0.05) levels of anti-inflammatory markers (IgG, IL-6, and IL-1β), while combined supplementation of RES and HMB promoted (p < 0.05) the duodenal antioxidant capacity, as indicated by increased levels of GSH-Px and T-AOC. Furthermore, the RES group was characterized by a higher relative abundance of Butyrivibrio, while the HMB group was characterized by a higher relative abundance of Aeromonas, Rummeliibacillus, UCG-002, Ralstonia and Stenotrophomonas (p < 0.05 and LDA > 3.5). Metabolomics analysis showed that differential metabolites were significantly enriched (p < 0.05) in the cyanoamino acid metabolism, biosynthesis of secondary metabolites, protein digestion and absorption and ABC transporters. These results indicated that RES and HMB can be used as feed additives to maintain intestinal health by enhancing duodenal development, promoting digestive enzyme secretion, and improving antioxidant and anti-inflammatory capacity in Tibetan sheep.

Background: Intramuscular fat (IMF) is a key determinant of meat sensory quality, but the effects of rumen-protected betaine (RPB) on IMF deposition in Tibetan sheep remain unclear. Methods: Sixty male, 3-month-old Tibetan lambs (Initial weight 17.72 ± 1.36 kg) were randomly assigned to a control (basal diet, n = 30) or RPB supplementation (basal diet supplemented with 0.08% RPB, n = 30) for 90 d. Results: Transcriptomic and lipidomic analyses revealed that RPB modulated glycerophospholipid metabolism-related genes (DGKI and AGPAT1) and altered lipid profiles, including PC (16:0/20:5) and PC (16:0/16:0). RPB increased T-AOC and SOD activities and decreased MDA content (p < 0.05). Intramuscular adipocyte area and diameter increased, while density decreased (p < 0.05). LC-MS/MS analysis showed that unsaturated fatty acids C14:1, C17:1, and C22:4 were significantly increased (p < 0.05). Muscle fiber density in the longissimus dorsi increased, whereas shear force, cooking loss, hardness, and chewiness were reduced (p < 0.05). MYH1, MYH2, and MYH7 expression were upregulated by 2.05-, 1.89-, and 2.73-fold, respectively. Conclusions: In summary, dietary RPB supplementation was associated with increased IMF deposition, which may contribute to improved meat quality, potentially through modulation of glycerophospholipid metabolism.

The parturition season of grazing Tibetan ewes spans from October to March, a period that exacerbates the adverse impacts of nutrient-deficient herbage on milk yield, body condition, and postpartum recovery. To alleviate the weight loss of ewes during the cold seasons, we provided concentrate supplements at four levels (dry matter (DM) basis), 260 g (C1), 440 g (C2), 520 g (C3), and 610 g (C4), alongside a basal diet of grazed pasture. A total of 96 multiparous Tibetan ewes (third parity, body weight: 45.17 ± 3.69 kg (body weight (BW) were enrolled within 12–18 h postpartum and randomly allocated to four dietary groups (n = 24 ewes per group). We measured growth performance, ruminal histomorphology, fermentation parameters, and digestive enzymes. A multi-omics technique (16S rRNA gene sequencing and RNA-seq) was employed to investigate the mechanisms underlying alterations in ruminal function. The results showed that increasing the concentrate level decreased body weight loss and increased average dry matter intake (p < 0.05). Rumen morphology was significantly altered: papilla width and muscle layer thickness were greatest in the C4 group, whereas submucosal thickness was highest in the C1 group (p < 0.05). Cellulase activity was lowest in the C1 group (p < 0.05). Papilla width of lactating Tibetan ewes in the C4 group was higher (p < 0.05) than that in the C1 and C3 groups. Concentrate supplementation altered ruminal microbiota composition and diversity. Each group exhibited a distinct microbial signature: the C1 group was characterized by Lachnospiraceae_XPB1014_group, Candidatus_Omnitrophus, Paenibacillus, and unclassified_Oligoflexaceae; the C2 group was enriched in Papillibacter, Anaerovibrio, V9D2013_group, and unclassified_Peptococcaceae; the C3 group was characterized by unclassified_Bacteroidales_RF16_group; and the C4 group was characterized by Ruminococcus, Pseudobutyrivibrio, and Mitsuokella (p < 0.05). Transcriptomic analysis identified differentially expressed genes (TRPA1, EPHB1, GATA3, C4, ABCG2, THBS4, and TNFRSF11B) that are predominantly involved in immune regulation, signal transduction, and nutrient digestion. The results of Spearman correlation analysis showed that Anaerovibrio was negatively correlated with propionate (r = −0.565, p < 0.05). However, it was positively correlated with the ratio of acetate and propionate (r = 0.579, p < 0.05). Moreover, Lachnospiraceae_XPB1014_group was negatively correlated with cellulase (r = −0.699, p < 0.05) and α-amylase (r = −0.514, p < 0.05). These findings suggest that the increasing concentrate supplementation alleviates body weight loss in lactating Tibetan sheep by orchestrating improvements in rumen histomorphology, digestive function, altering bacteria composition, and ruminal immune and modulating host epithelial gene expression.

Resveratrol (RES), a natural polyphenol, and β-hydroxy-β-methylbutyric acid (HMB), a key metabolite of leucine, are emerging as potent feed additives in animal production. This study investigated the individual and combined effects of dietary RES and HMB on gut microbiota, metabolic profiles, and meat quality in Tibetan sheep. A total of 120 two-month-old male lambs were randomly assigned to four experimental groups: control (C, basal diet, n = 6), RES (basal diet + 1.5 g/d RES, n = 6), HMB (basal diet + 1.25 g/d HMB, n = 6), and RES-HMB (basal diet + 1.5 g/d RES + 1.25 g/d HMB, n = 6), with 16S rDNA sequencing and LC-MS/MS analyses performed on rumen fluid and longissimus lumborum (LL). Meat quality improved significantly in all supplemented groups, the RES-HMB co-administration exhibited the most pronounced effects, suggesting a synergistic interaction. These improvements were linked to the activation of amino acid (AA) and unsaturated fatty acid biosynthesis pathways, leading to increased levels of AAs and polyunsaturated fatty acids (PUFAs). Concurrently, dietary RES and HMB supplementation enriched the relative abundance of beneficial gut microbiota, notably Christensenellaceae_R-7_group and Solibacillus, which further promoted the production of short-chain fatty acids, AAs, and PUFAs. The study highlights the role of rumen microbiota in regulating muscle metabolism and meat quality, offering a new scientific basis of strategies for using green feed additives in Tibetan sheep.

Introduction: Urea shows substantial potential as a cost-effective alternative to soybean meal in ruminant production. Given the critical role of subcutaneous adipose tissue (SAT) in meat quality, this study evaluated the effects of different dietary urea levels on the histomorphology, fatty acid composition, lipidomic profiles, and volatile flavour compounds of SAT in Tibetan sheep. Methods: Eighty female lambs (16.2 ± 1.01 kg, 2 months old) were randomly assigned to four dietary treatments supplemented with 0% (U0), 0.80% (U1), 1.19% (U2), and 1.61% (U3) urea. The 105-day trial comprised a 15-day adaptation period followed by a 90-day experimental period. Results: The results indicated that: high urea levels (U2 and U3) disrupted adipocyte integrity, resulting in disordered arrangement, cellular rupture, and a significant reduction in adipocyte diameter ( p < 0.05). Increasing dietary urea levels significantly decreased the concentrations of trans monounsaturated fatty acids (e.g., C16:1 T) and n-3 polyunsaturated fatty acids ( p < 0.05), while increasing the level of cis monounsaturated fatty acid C18:1n9c ( p < 0.05). Lipidomic analysis identified 48 differential lipid molecules (|log2Fold change| ≥ 2, adjusted p < 0.05), primar ily comprising glycerolipids (Triglycerides, Triglycerides) and glycerophospho lipids (phosphatidylcholine, phosphatidylethanolamine, Phosphatidylglycerol). Urea supplementation significantly influenced the volatile compounds profile ( p < 0.05); excessive urea (U3) led to ammonia accumulation and pungent off odors, whereas moderate supplementation imparted desirable milky and vanilla aromas. Discussion: In conclusion, dietary urea levels affected lipid metabolism and reduced trans-fatty acid content; excessive dietary urea disrupted cell structure, increased ammonia accumulation and reduced aroma-contributing substances in the SAT of Tibetan sheep.