The demand for economic benefits has led to an increase in the proportion of high-concentrate (HC) feed in the ruminant diet, resulting in an increased incidence of subacute ruminal acidosis (SARA). During SARA, a high concentration of lipopolysaccharide (LPS) translocated in the rumen induces a systemic inflammatory response. Inflammatory diseases, such as endometritis and mastitis, are often associated with SARA; however, in sheep, the mechanism of the effect of SARA on the endometrium has rarely been reported. Therefore, the aim of this study was to investigate, for the first time, the influence of LPS translocation on endometrial tight junctions (TJs) during SARA in sheep. The results showed that LPS and TNFα levels in the ruminal fluid, serum, and endometrial tissue supernatant during SARA increased, transcription levels of TLR4, NFκB, and TNFα in the endometrium increased, the protein expression level of claudin-1 in the endometrium increased, and the protein expression level of occludin decreased. 17β-estradiol (E₂) inhibits claudin-1 protein expression and promotes occludin expression, and progesterone (P₄) promotes claudin-1 protein expression and inhibits occludin protein expression. E₂ and P₄ regulate claudin-1 and occludin protein expression through their receptor pathways. Here, we found that LPS hindered the regulatory effect of E₂ and P₄ on endometrial TJs by inhibiting their receptor expression. The results of this study indicate that HC feeding can cause SARA-induced LPS translocation in sheep, increase susceptibility to systemic inflammation, induce the endometrial inflammatory response, and cause endometrial epithelial TJ damage directly and/or by obstructing E₂ and P₄ function. LPS translocation caused by SARA has also been suggested to induce an endometrial inflammatory response, resulting in endometrial epithelial barrier damage and physiological dysfunction, which seriously affects ruminant production. Therefore, this study provides new evidence that SARA is a potential factor that induces systemic inflammation in ruminants. It provides theoretical support for research on the prevention of endometritis in ruminants.

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.

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.

Yaks are an ideal model for investigating mammalian adaptation to high-altitude hypoxia; however, the underlying adaptive mechanisms remain unclear. Therefore, this study aimed to investigate the mechanisms underlying yak adaptation to high altitudes, focusing on the role of the PINK1/Parkin pathway. In particular, we established normoxic and hypoxic models of yak skeletal muscle satellite cells (SMSCs). In addition, we examined the relationship between PINK1/Parkin-mediated mitophagy and the activities of key enzymes involved in mitochondrial energy metabolism. At the tissue level, an increase in altitude significantly decreased p62 expression and upregulated LC3B-II expression. Notably, mitophagy levels and the expression of PINK1 and Parkin in the skeletal muscle, lungs, and myocardial tissues increased with altitude. At the cellular level, hypoxia markedly elevated the expression of PINK1 and Parkin proteins in SMSCs, induced the conversion of LC3-I to LC3-II, decreased p62 accumulation, significantly increased the number of autolysosomes, and enhanced autophagic flux. Hypoxia altered mitochondrial electron transport chain function, resulting in compensatory elevation of key enzyme activities in the mitochondrial respiratory chain. However, 3-methyladenine (3-MA) treatment reversed these hypoxia-induced changes. In conclusion, yak SMSCs sustain mitochondrial functional homeostasis under hypoxia via PINK1/Parkin-mediated mitophagy, effectively managing hypoxic stress.

Premature ovarian failure, resulting from the premature activation of follicles in animals, has been linked to excessive levels of 5α-dihydrotestosterone (DHT). Additionally, melatonin has been demonstrated to be autonomously synthesized and secreted by sheep follicles. However, it remains unclear whether melatonin can counteract excessive DHT in sheep ovaries to support normal follicular development. Here, we investigated the effects of DHT and melatonin on early folliculogenesis in ovine ovaries. Ovarian cortices (~2×2 mm) and secondary follicles (280–360 μm) were cultured for 4 days with high-dose DHT (10⁻⁷ M) and/or melatonin (10⁻⁹ M). H&E staining, TUNEL assay, Western blotting, and RT-qPCR were used to examine the underlying mechanisms. DHT increased the number and diameter of secondary follicles (p < 0.05), but also induced granulosa cell apoptosis, which melatonin alleviated. Mechanistically, DHT upregulated cleaved caspase-3 and caspase-3 expression in granulosa cells, whereas co-treatment with melatonin reduced the Bcl-2/Bax ratio. Using the MT1 inhibitor Luzindole, melatonin was shown to suppress DHT-stimulated granulosa cell proliferation via MT1-mediated Akt phosphorylation, thereby counteracting the DHT-induced decline in follicular reserve. This study elucidates the pathogenic mechanism of DHT-triggered premature ovarian insufficiency and validates the melatonin-mediated protective regulation of follicular development, which provides a theoretical basis for the improvement and protection of reproductive function in reserve breeding ewes.