In order to investigate the composition and differences in volatile organic compounds (VOCs) in yak and cattle-yak meat and determine the key metabolites and metabolic pathways related to flavor formation. In this study, the VOCs and non-volatile metabolites in Longissimus dorsi muscle of two groups of samples were detected and analyzed by gas chromatography–ion migration spectrometry (GC-IMS) and gas chromatography–mass spectrometry (GC-MS). The results showed that 31 VOCs were identified by GC-IMS, including 5 alcohols, 5 ketones, 5 esters, 3 aldehydes, 2 furans, 2 hydrocarbons, 1 amine, 1 acid, 1 thiazole, 1 pyrazine, and 5 others. Most of them were alcohols, ketones, esters, and aldehydes. A total of 75 non-volatile metabolites with significant differences were obtained by GC-MS screening, among which amino acid contents such as serine, glycine, phenylalanine, and aspartic acid were significantly up-regulated in cattle-yak, and glutamic acid and tyrosine were significantly up-regulated in yak. The non-volatile differential metabolites in the two groups were significantly enriched in the metabolic pathways of arginine biosynthesis and oxidative phosphorylation. By combining GC-IMS and GC-MS, this study comprehensively and intuitively reflected the differences in VOCs between yak and cattle-yak meat, and clarified the metabolomic reasons for the differences in VOCs, so as to provide a theoretical basis for meat quality improvement.

Spermatogenesis is a complex process that involves proliferation and differentiation of diploid male germ cells into haploid flagellated sperm and requires intricate interactions between testicular somatic cells and germ cells. The cellular heterogeneity of this process presents a challenge in analyzing the different cell types at various developmental stages. Single-cell RNA sequencing (scRNA-seq) provides a useful tool for exploring cellular heterogeneity. In this study, we performed a comprehensive and unbiased single-cell transcriptomic study of spermatogenesis in sexually mature 4-year-old yak using 10× Genomics scRNA-seq. Our scRNA-seq analysis identified six somatic cell types and various germ cells, including spermatogonial stem cells, spermatogonia, early-spermatocytes, late-spermatocytes, and spermatids in yak testis. Pseudo-timing analysis showed that Leydig and myoid cells originated from common progenitor cells in yaks. Moreover, functional enrichment analysis demonstrated that the top expressed genes in yak testicular somatic cells were significantly enriched in the cAMP signaling pathway, PI3K-Akt signaling pathway, MAPK signaling pathway, and ECM receptor interactions. Throughout the spermatogenesis process, genes related to spermatogenesis, cell differentiation, DNA binding, and ATP binding were expressed. Using immunohistochemical techniques, we identified candidate marker genes for spermatogonial stem cells and Sertoli cells. Our research provides new insights into yak spermatogenesis and the development of various types of cells in the testis, and presents more reliable marker proteins for in vitro culture and identification of yak spermatogonial stem cells in the later stage.

Progesterone (P4) can participate in the development of female mammalian antral follicles through nuclear receptor (PGR). In this experiment, the differences of P4 synthesis and PGR expression in different developmental stages of sheep antral follicles (large > 5mm, medium 2-5mm, small < 2mm) were detected by enzyme-linked immunosorbent assay, immunohistochemistry, qRT-PCR and Western blotting. Secondly, sheep follicular granulosa cells were cultured in vitro. The effects of different concentrations of FSH and LH on P4 synthesis and PGR expression were studied. The results showed that acute steroid regulatory protein (StAR), cholesterol side chain lyase (P450scc) and 3β Hydroxysteroid dehydrogenase (3β-HSD) and PGR were expressed in antral follicles, and with the development of antral follicles in sheep, StAR, P450scc and the expression of 3β-HSD and PGR increased significantly. In vitro experiments showed that FSH and LH alone or together treatment could regulate P4 secretion and PGR expression in sheep follicular granulosa cells to varying degrees, hint P4 and PGR by FSH and LH, and LH was the main factor. Our results supplement the effects of FSH and LH on the regulation of P4 synthesis during follicular development, which provides new data for further study of steroid synthesis and function in follicular development.

The aim of this study is to determine the effects of a high-concentrate diet on growth performance, serum biochemical indexes, and rumen microbiota in house-fed yaks. Sixteen male yaks (body weight, 151.73 ± 14.11 kg; 18 months) were randomly allocated into two dietary treatments: a group with a low level of concentrate (n = 8, LC, concentrate–forage = 40:60) and a group with a high level of concentrate (n = 8, HC, concentrate–forage = 60:40). We found that compared with the LC group, the average daily feed intake (ADFI), the average daily gain (ADG), and the serum albumin (ALB) concentration in the HC group were significantly increased (p < 0.05). The rumen bacterial compositions also differed significantly between the groups, as indicated by principal coordinate analysis (p < 0.05). Firmicutes and Bacteroidota were the main dominant phyla of rumen bacteria in yaks. Compared with the LC group, the relative abundance of Firmicutes in the HC group was significantly increased (p < 0.05) and the relative abundance of Bacteroidota was significantly decreased (p < 0.05). At the genus level, Rikenellaceae_RC9_gut_group, Succiniclasticum, Prevotella, Christensenellaceae_R-7_group, and NK4A214_group had the highest relative abundance. The relative abundance of Christensenellaceae_R-7_group in the HC group was significantly higher than that in the LC group (p < 0.05). The PICRUSt 2 results showed a significant enrichment in glycosaminoglycan degradation, apoptosis, and ECM–receptor interaction in HC relative to LC (p < 0.05). In conclusion, high-concentrate diets can enhance growth performance and alter the compositions and functions of ruminal bacterial communities in yaks.

Epididymis development is the basis of male reproduction and is a crucial site where sperm maturation occurs. In order to further understand the epididymal development of yak and how to regulate sperm maturation, we conducted a multi-omics analysis. We detected 2274 differential genes, 222 differential proteins and 117 co-expression genes in the cauda epididymis of yak before and after sexual maturity by RNA-seq and proteomics techniques, which included TGFBI, COL1A1, COL1A2, COL3A1, COL12A1, SULT2B1, KRT19, and NPC2. These high abundance genes are mainly related to cell growth, differentiation, adhesion and sperm maturation, and are mainly enriched via extracellular matrix receptor interaction, protein differentiation and absorption, and lysosome and estrogen signaling pathways. The abnormal expression of these genes may lead to the retardation of epididymal cauda development and abnormal sperm function in yak. In conclusion, through single and combined analysis, we provided a theoretical basis for the development of the yak epididymal cauda, sperm maturation, and screening of key genes involved in the regulation of male yak reproduction.

In mammals, the melatonin (Mel) concentration in the gastrointestinal tract is 400 times greater than in the pineal gland. However, the origin of Mel in the gastrointestinal tract and its role in reproductive regulation remains unclear. Therefore, we analyzed three potential Mel sources (feed, microorganisms, and the rumen wall) for their contribution to high Mel levels in the rumen and their biological effects. The feed contained high Mel concentrations, and Mel in rumen fluid and blood peaked two hours after feeding. Rumen microbial analysis showed a strong positive correlation between Mel and specific microbes, including Megasphaera, Butyrivibrio, Acetobacter, and Olsenella. In vitro experiments indicated that rumen microorganisms synthesized Mel from tryptophan. The rumen wall also contains key enzymes, AANAT and HIOMT, which catalyze Mel synthesis and membrane receptors MT1 and MT2 that mediate the function of Mel, suggesting that the rumen wall synthesizes Mel. Mel peaked in both rumen fluid and blood two hours after feeding. Feeding also altered blood levels of Mel, Gonadotropin-releasing hormone (GnRH), Luteinizing hormone (LH), Follicle-stimulating hormone (FSH), progesterone (P4), and Estradiol (E2), with a correlation between Mel and fluctuations in GnRH, LH, P4, and E2 levels. Our findings suggest that feed is the primary source of high Mel levels in the rumen and impacts reproductive hormone fluctuations. This study elucidates the origin of high rumen Mel concentrations and reveals that food intake affects the natural secretion of various hormones, offering a new perspective on food sources for regulating reproductive physiology.