Single-cell RNA sequencing (scRNA-seq) is useful for exploring cell heterogeneity. For large animals, however, little is known regarding spermatogonial stem cell (SSC) self-renewal regulation, especially in dairy goats. In this study, we described a high-resolution scRNA-seq atlas derived from a dairy goat. We identified six somatic cell and five spermatogenic cell subtypes. During spermatogenesis, genes with significantly changed expression were mainly enriched in the Notch, TGF-β, and Hippo signaling pathways as well as the signaling pathway involved in the regulation of stem cell pluripotency. We detected and screened specific candidate marker genes ( TKTL1 and AES) for spermatogonia. Our study provides new insights into goat spermatogenesis and the development of testicular somatic cells.

Heat stress (HS) commonly occurring in summer has gradually become a factor threatening the reproductive performance of male dairy goats by reducing their fecundity. Despite the melatonin is applied to relieve HS, it is still unclear whether melatonin protects against reproductive damage induced by HS in dairy goats and how it works. The purpose of the present study is to evaluate the role of melatonin in alleviating HS-induced spermatogenesis dysfunction in male dairy goats and further explore its mechanism. HS impaired spermatogenesis, sperm formation in the testes, and sperm maturation in the epididymis of dairy goats, resulting in decreased sperm quality. Melatonin rescued the decrease of sperm quality induced by HS via decreasing inflammatory and oxidative stress levels in testicular tissue and enhancing intercellular barrier function within the testes. Amplicon-based microbiota analysis revealed that despite gut microbiota differences between melatonin-treated dairy goats and NC dairy goats to some extent, melatonin administration tends to return the gut microbiota of male dairy goats under HS to the levels of natural control dairy goats. To explore whether the protective role of melatonin in sperm quality is mediated by regulating gut microbiota, fecal microbiota of HS dairy goats with or without melatonin treatment were transferred to HS mice, respectively. We found HS mice that had received fecal bacteria of HS dairy goats experienced serious testicular injury and dyszoospermia, while this phenomenon was ameliorated in HS mice that had received fecal bacteria of dairy goats treated with melatonin, indicating melatonin alleviates HS-induced spermatogenic damage in a microbiota dependent manner. We further found that the testicular tissue of both HS dairy goats and mice transplanted with HS dairy goat feces produced large amounts of arachidonic acid (AA)-related metabolites, which were closely associated with semen quality. Consistently, supplementation with AA has been shown to elevate the levels of inflammation and oxidative stress in the testicular tissue of mice, disrupting intercellular connections and ultimately leading to spermatogenic disorders. This study has revealed that melatonin can effectively alleviate spermatogenic disorders in dairy goats caused by HS. This beneficial effect was primarily achieved through the modulation of gut microbiota, which subsequently inhibited the excessive synthesis of AA in testicular tissue. These discoveries are of great significance for preventing or improving the decline in male livestock reproductive performance caused by HS, enhancing the reproductive efficiency of elite male breeds, and ultimately improving the production efficiency of animal husbandry.

Current measures mainly focus on how melatonin reduces physiological heat stress in animals, but its effects on reproductive damage to male dairy goats have been neglected. This study aimed to determine the protective effect of melatonin on male reproduction during heat stress in dairy goats and to further explore its mechanisms. A natural heat stress model of Saanen dairy goats was used to assess testicular tissue damage 7 days after heat stress and to examine semen quality changes during a spermatogenic cycle. RNA-seq, Western blot, RT–qPCR, and immunofluorescence staining were used to explore the mechanism by which melatonin protects against heat stress-induced reproductive damage and to validate the results. The data suggested that melatonin significantly alleviated the heat stress-induced decrease in sperm quality, protected varicose tubule structure, reduced the levels of heat shock proteins and apoptotic proteins and protected the spermatocytes and round spermatozoa, which are mainly affected by heat stress. RNA-seq results suggest that melatonin inhibits the PI3K/AKT signaling pathway, reduces the level of p-AKT, and promotes elevated BCL-2. In addition, melatonin treatment could upregulate the gene expression of MT2 which was downregulated by heat stress and improve the change in extracellular matrix components and restore serum testosterone levels. Our results suggest that melatonin can protect against testicular and spermatogenic cell damage and improve semen quality in male dairy goats under heat stress. This study provides an important reference for subsequent studies on the molecular mechanisms of melatonin in protecting male reproductive processes under heat stress and using exogenous melatonin to prevent heat stress.

Alhagi-honey (AH) is a well-established traditional ethnic medicine with advantageous effects against diarrhea and headaches. We aimed to explore the preventive effect of AH on liver damage induced by heat stress (HS) and its underlying mechanism. HS models were established by thermostat, and mice were treated at 39 ℃ for 10 h, lasting for 7 days. Hematoxylin–eosin (H&E) staining and Periodic Acid-Schiff (PAS) staining were used for histological observation, and transmission electron microscopy (TEM) was used for ultrastructure examination of hepatocytes. Gut microbiota (GM) composition and liver metabolites were respectively analyzed by 16S rRNA sequencing and non-targeted metabolome sequencing. AH pretreatment alleviated liver damage caused by heat stress in mice. The main manifestation was that AH alleviated serum aspartate transferase (AST) and aspartate transaminase (ALT). It was found that AH improved symptoms of hepatocyte damage. In addition, the relative abundance of f_Rikenellaceae, g_Incertae_Sedis and s_Staphylococcus_Orisratti, g_Lachnoclostridium, g_GCA-900066575, and s_Alistipes_inops were modified by AH and these bacterial genera showed association with 6 metabolites (2- (3,4-dihydroxyphenyl) acetamide, 3-hydroxy-3-methylpentanedioic acid, PC (17:0/17:1), Y-L-Glutamy-L-glutamic acid, L-Isoleucine, 5-Methyluridine, 8,8-dimethyl-2-phenyl-4H,8H-pyrano [2, 3-h] chromen-4-one). The Pearson analysis also showed a strong correlation between these microbes and 2 risk indicators (AST and ALT) of liver damage. AH alleviated HS-induced liver damage by regulating liver metabolism and maintaining normal GM. It demonstrated that AH held potential as a prophylactic drug for the prevention of HS-induced liver damage.

Taurine is abundant in seminal plasma and is involved in redox balance, osmoregulation, and sperm membrane stability. However, its role in protecting dairy goat bucks against heat stress-associated declines in sperm quality remains unclear. In this study, eighteen Guanzhong dairy goat bucks were assigned to three groups: control (NC), field heat stress (HS), and HS with taurine supplementation (HS + Tau). Heat stress reduced seminal plasma taurine abundance and was associated with metabolic reprogramming, impaired sperm quality, disturbed redox homeostasis, and decreased LH and testosterone levels. Specifically, HS reduced sperm motility, viability, membrane integrity, and kinematic performance, increased sperm abnormalities, and shortened in vitro sperm survival time. Taurine supplementation alleviated these adverse changes and shifted the seminal plasma metabolome toward a more homeostatic profile. Metabolomic analysis indicated that HS was associated with the accumulation of long-chain acylcarnitines in seminal plasma. Complementary mouse and TM4 Sertoli cell experiments provided preliminary mechanistic support, suggesting that taurine may partially protect Sertoli cell tight-junction proteins, particularly ZO-1, under heat- and acylcarnitine-related stress, and may be associated with the modulation of p38/AKT signaling. Collectively, these findings suggest that taurine alleviates heat stress-induced declines in sperm quality in dairy goat bucks, at least in part, by modulating seminal plasma metabolism.