This study hypothesized that combining oregano essential oil (OEO) and yeast cultures (YCs) would modulate rumen microbiota to promote gastrointestinal homeostasis and function. Twenty-four newborn, healthy, disease-free, crossbred Simmental male calves (birth weight ≥ 35 kg) were assigned to one of four treatments based on birth data. Treatments were as follows: (1) Control (CON), calves fed calf starter without additives; (2) OEO, calves fed calf starter containing 60 mg/kg body weight (BW) of OEO per day; (3) YCs, calves fed calf starter containing 45 mg/kg BW of YC per day; and (4) MIX, calves fed calf starter with OEO (60 mg/kg, BW) and YC (45 mg/kg, BW) combination. The experimental period lasted 70 days. Rumen fluid was collected on the final day, and 16S rRNA sequencing was performed to assess alterations in rumen microbiota. Calves fed MIX exhibited significantly greater microbial richness, species diversity, and lineage diversity (p < 0.05) compared with calves in the other groups. MIX-fed calves also showed changes (p < 0.05) in the relative abundance of certain rumen species, identified as through LEfSe analysis (LDA > 4, p < 0.05). These biomarkers included f_Rikenellaceae, g_Rikenellaceae_RC9_gut_group, g_Erysipelotrichaceae_UCG-002, c_Saccharimonadia, o_Saccharimonadales, f_Saccharimonadaceae, and g_Candidatus_Saccharimonas. Pathways enriched (p < 0.05) in MIX-fed calves involved nucleotide metabolism, lipid metabolism, glycan biosynthesis and metabolism, amino acid metabolism, terpenoids and polyketides metabolism, antimicrobial drug resistance, xenobiotic biodegradation and metabolism, antineoplastic drug resistance, and excretory system pathways. In conclusion, this study demonstrates that the OEO and YC combination enhances rumen microbial community modulation in calves more effectively than OEO or YCs fed individually or with the control diet.

Acetyl-CoA carboxylase beta (ACACB) is a functional candidate gene that impacts fat deposition. In the present study, we sequenced exon 37–intron 37, exon 46–intron 46, and intron 47 of yak ACACB using hybrid pool sequencing to search for variants and genotyped the gene in 593 Gannan yaks via Kompetitive allele-specific polymerase chain (KASP) reaction to determine the effect of ACACB variants on carcass and meat quality traits. Seven single nucleotide polymorphisms were detected in three regions. Eight effective haplotypes and ten diplotypes were constructed. Among them, a missense variation g.50421 A > G was identified in exon 37 of ACACB, resulting in an amino acid shift from serine to glycine. Correlation analysis revealed that this variation was associated with the cooking loss rate and yak carcass weight (p = 0.024 and 0.012, respectively). The presence of haplotypes H5 and H6 decreased Warner–Bratzler shear force (p = 0.049 and 0.006, respectively), whereas that of haplotypes H3 and H4 increased cooking loss rate and eye muscle area (p = 0.004 and 0.034, respectively). Moreover, the presence of haplotype H8 decreased the drip loss rate (p = 0.019). The presence of one and two copies of haplotypes H1 and H8 decreased the drip loss rate (p = 0.028 and 0.004, respectively). However, haplotype H1 did not decrease hot carcass weight (p = 0.011), whereas H3 increased the cooking loss rate (p = 0.007). The presence of one and two copies of haplotype H6 decreased Warner–Bratzler shear force (p = 0.014). The findings of the present study suggest that genetic variations in ACACB can be a preferable biomarker for improving yak meat quality.

Objective: Although yak meat is valued for its distinctive flavor profile, little is known about the mechanisms underlying flavor variation among different muscle types. This study aimed to systematically investigate the differences in flavor precursors, metabolic enzyme activities, gene expression profiles, and volatile flavor compounds among three muscles-longissimus thoracis (LT), triceps brachii (TB), and semimembranosus (SM) of the Tianzhu white yak, and to elucidate the underlying regulatory mechanisms.Methods: A comprehensive approach was employed, integrating targeted metabolomics, untargeted metabolomics, flavoromics, real-time quantitative polymerase chain reaction, and histochemical staining to compare the biochemical characteristics of the three muscles.Results: The results of volatile profiles and sensory evaluation demonstrated that the TB muscle exhibited more favorable flavor-related traits. The TB muscle was enriched in key flavor precursors, including glutamic acid, glutamine, arginine, and total free amino acid content (p<0.05). Concurrently, the expression levels of key lipogenic genes (FASN, ELOVL4, SREBP1) were significantly higher in the TB muscle (p<0.05). Flavoromics analysis further revealed that the TB muscle exhibited greater diversity and higher relative abundance of key volatile compounds, such as aldehydes, ketones, and alcohols (p<0.05). Sensory evaluation further indicated that the TB muscle exhibited stronger sweet and fruity flavors. Untargeted metabolomics and pathway enrichment analysis indicated that this profile was associated with enrichment of arginine and proline metabolism and unsaturated fatty acid biosynthesis.Conclusion: This study demonstrates that flavor enhancement in yak meat is associated with the coordinated upregulation of lipid synthesis genes, thereby promoting the accumulation of flavor precursors. This process provides sufficient substrates for the Maillard reaction and lipid oxidation, facilitating the generation of volatile flavor compounds. These findings provide a theoretical basis for yak meat quality evaluation and precision processing.

(1) Background: Hair growth can function as an indicator of an animal’s health and nutritional status, furnishing a valuable means for early diagnosis and timely modifications to management practices, and is influenced by hormones, the immune system, and the levels of minerals within the animal’s body. (2) Methods: In this study, a total of 81 yaks were selected and divided into three groups according to their ages (1–2 years, 3–4 years, 5–6 years), and the concentrations of melatonin, dihydrotestosterone, IgA, IgG, and IgM in their blood serum and the levels of Ca, Mg, Zn, Fe, and P in both their blood serum and hair were detected. (3) Results: The levels of melatonin and dihydrotestosterone in yaks aged 1–2 years were significantly higher than those of other age groups (p < 0.001). In addition, the concentration of melatonin in male yaks was markedly greater than that in female yaks (p < 0.05). When it came to immunoglobulins, the IgA level in 1–2-year-old yaks was strikingly higher than those in yaks aged 3–4 years and 5–6 years (p < 0.05). In terms of mineral elements, the concentrations of calcium, magnesium, zinc, and iron in the blood serum of 1–2-year-old and 5–6-year-old yaks were significantly elevated compared to those in 3–4-year-old yaks. However, there was no notable difference between the 1–2-year-old and 5–6-year-old groups. The correlation analysis showed that there was a significant correlation between DHT and the levels of melatonin and IgA in yaks. Additionally, a significant correlation was observed between IgA and IgG, as well as between IgA and the levels of Fe, Mg, and Ca. It is likely that they jointly regulate the hair growth and immune processes of yaks. (4) Conclusions: There are positive correlations among melatonin, dihydrotestosterone, and IgA in the blood serum and the content of Fe and Mg in the hair to varying degrees, implying these indicators may jointly regulate yak hair growth and immune status. These research findings provide data support for applied research into evaluating the overall health status of yaks through the growth status of hair or by measuring the mineral content in hair in a non-invasive way.

The molecular mechanisms underlying testicular development in the yak remain poorly understood. In this study, RNA sequencing was performed on testicular tissues from Tianzhu white yaks at three postnatal developmental stages: 0.5 (prepubertal), 2.5 (pubertal), and 4.5 (adult) years, with six animals in each group. Differential expression analysis was integrated with weighted gene co-expression network analysis (WGCNA) to characterize transcriptomic changes associated with testicular maturation. A total of 9646 differentially expressed genes (DEGs) were identified between the 0.5- and 2.5-year groups, whereas only 126 DEGs were detected between the 2.5- and 4.5-year groups, indicating that the transition to puberty represents the most dynamic phase of transcriptional reprogramming during testicular development. Functional enrichment analysis revealed that focal adhesion and extracellular matrix–receptor interaction were the most significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways, suggesting a potential role for extracellular matrix (ECM) remodeling in the establishment of the blood–testis barrier and testicular maturation. WGCNA identified seven age-associated co-expression modules. The turquoise module showed the strongest positive correlation with developmental stage and was significantly enriched for genes involved in spermatid differentiation and maturation, including SPATA6, SPMIP11, TNP1, and ODF1. Collectively, these findings provide a comprehensive transcriptomic characterization of yak testicular development.