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.

Tibetan sheep is a primitive Chinese breed valued for its excellent edible quality and high nutritional value. Despite this, limited research has explore d

As a source of non-protein nitrogen, ammonium chloride (NH₄Cl) is widely utilized in ruminant diets to reduce feed costs. However, the impact of its supplementation level on the flavor of sheep meat remains unclear, despite the known influence of fat on meat flavor. This study aimed to investigate the effects of dietary NH₄Cl supplementation levels on the lipidome and flavor compounds of subcutaneous adipose tissue in Tibetan sheep, providing a scientific basis for dietary optimization in Tibetan sheep farming. Eighty 2-month-old early-weaned Tibetan lambs were selected and randomly allocated into four groups, fed diets supplemented with 0% (N0 group), 1.49% (N1 group), 2.24% (N2 group), and 3.01% (N3 group) NH₄Cl for an experimental period of 105 days. The study conducted histomorphological observations, lipidomics analysis, and determination of flavor compounds. The results showed that NH₄Cl supplementation significantly reduced (p < 0.05) the contents of various unsaturated fatty acids and n-3 polyunsaturated fatty acids (n-3 PUFA) in the subcutaneous adipose tissue of Tibetan sheep. Specifically, the total saturated fatty acid (total SFA) content in the N3 group was significantly higher than that in the other groups, while the total monounsaturated fatty acid (total MUFA) content was significantly lower than that in the N1 and N2 groups (p < 0.05). The absolute contents of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and the sum of triglycerides (TGs) and diglycerides (DGs) in the N3 group were significantly higher (p < 0.05) than those in the other groups. Regarding flavor compounds, the contents of ketone aroma compounds, such as 2-propanone and 2-butanone monomer, were significantly higher (p < 0.05) in the N0 group than in the other groups. The ammonia content in the N1 and N3 groups was significantly higher (p < 0.05) than that in the N0 and N2 groups, while the allyl sulfide content in the N2 group was significantly higher (p < 0.05) than that in the other groups. Correlation analysis revealed that the majority of TG and DG differential lipids were significantly positively correlated with allyl sulfide, and most differential lipids belonging to the PC, PE, and hexosylceramide (Hex1Cer) classes were significantly positively correlated with ammonia (|r| ≥ 0.80, p < 0.01). Conversely, PC (16:0_18:3) exhibited significant negative correlations with multiple beneficial aroma compounds (|r| ≥ 0.80, p < 0.01). The study indicates that dietary NH₄Cl supplementation levels exceeding 2.24% are associated with alterations in lipid metabolism and reduced synthesis of unsaturated fatty acids and beneficial flavor compounds, such as 2-propanone and 2-butanone, in subcutaneous adipose tissue. This is also associated with the abnormal accumulation of phospholipids and ceramides, which correlate strongly with elevated ammonia concentrations in adipose tissue and the generation of oxidation products such as propanal, potentially compromising meat flavor quality.

Castration is a vital technical practice in Tibetan sheep farming on the Qinghai-Tibet Plateau. It reduces fighting among rams, making it easier to manage the herd while they are grazing. However, the impact of castration on the quality of Tibetan sheep meat and muscle metabolites is unclear at present. On this basis, this study examined differences in meat quality and metabolites between castrated (BTC) and non-castrated (BTN) Black Tibetan sheep using targeted and non-targeted metabolomics. Compared with the BTN group, the meat from the BTC group showed reduced drip loss and increased cooking loss, as well as higher levels of elasticity, chewiness and cohesiveness (P < 0.05). The levels of 11 amino acids, total amino acids, total umami amino acids, 23 fatty acids, SFA, PUFA and MUFA were significantly higher in the BTC group than in the BTN group (P < 0.05). A total of 34 differentially abundant metabolites were identified between the two groups, with uric acid, vitamin C, malate, glutamine and oleic acid being all upregulated in BTC. Purine metabolism, metabolic pathways, bile secretion, the phosphotransferase system, glyoxylate and dicarboxylate metabolism, pyrimidine metabolism, and ABC transporters were the key metabolic pathways associated with meat quality in the castrated group. In conclusion, there are certain differences in meat quality and muscle metabolites between BTC and BTN. Castration can affect meat quality characteristics to a certain extent.