The rumen microbiota contributed to the development of mastitis induced by subclinical ketosis.

BACKGROUND: Mastitis is a serious disease which affects animal husbandry, particularly in cow breeding. The etiology of mastitis is complex and its pathological mechanism is not yet fully understood. Our previous research in clinical investigation has revealed that subclinical ketosis can increase the number of somatic cell counts (SCC) in milk, although the underlying mechanism remains unclear. Recent studies have further confirmed the significant role of mastitis. RESULTS: In this study, we aimed to examine the SCC, rumen microbiota, and metabolites in the milkmen of cows with subclinical ketosis. Additionally, we conducted a rumen microbiota transplant into mice to investigate the potential association between rumen microbiota disturbance and mastitis induced by subclinical ketosis in dairy cows. The study has found that cows with subclinical ketosis have a higher SCC in their milk compared to healthy cows. Additionally, there were significant differences in the rumen microbiota and the level of volatile fatty acid (VFA) between cows with subclinical ketosis and healthy cows. Moreover, transplanting the rumen microbiota from subclinical ketosis and mastitis cows into mice can induce mammary inflammation and liver function damage than transplanting the rumen flora from healthy dairy cows. CONCLUSIONS: In addition to the infection of mammary gland by pathogenic microorganisms, there is also an endogenous therapeutic pathway mediated by rumen microbiota. Targeted rumen microbiota modulation may be an effective way to prevent and control mastitis in dairy cows.

Gut/rumen-mammary gland axis in mastitis: Gut/rumen microbiota-mediated "gastroenterogenic mastitis".

BACKGROUND: Mastitis is an inflammatory response in the mammary gland that results in huge economic losses in the breeding industry. The aetiology of mastitis is complex, and the pathogenesis has not been fully elucidated. It is commonly believed that mastitis is induced by pathogen infection of the mammary gland and induces a local inflammatory response. However, in the clinic, mastitis is often comorbid or secondary to gastric disease, and local control effects targeting the mammary gland are limited. In addition, recent studies have found that the gut/rumen microbiota contributes to the development of mastitis and proposed the gut/rumen-mammary gland axis. Combined with studies indicating that gut/rumen microbiota disturbance can damage the gut mucosa barrier, gut/rumen bacteria and their metabolites can migrate to distal extraintestinal organs. It is believed that the occurrence of mastitis is related not only to the infection of the mammary gland by external pathogenic microorganisms but also to a gastroenterogennic pathogenic pathway. AIM OF REVIEW: We propose the pathological concept of "gastroenterogennic mastitis" and believe that the gut/rumen-mammary gland axis-mediated pathway is the pathological mechanism of "gastroenterogennic mastitis". KEY SCIENTIFIC CONCEPTS OF REVIEW: To clarify the concept of "gastroenterogennic mastitis" by summarizing reports on the effect of the gut/rumen microbiota on mastitis and the gut/rumen-mammary gland axis-mediated pathway to provide a research basis and direction for further understanding and solving the pathogenesis and difficulties encountered in the prevention of mastitis.

Gut dysbiosis induces the development of mastitis through a reduction in host anti-inflammatory enzyme activity by endotoxemia.

BACKGROUND: Mounting experimental evidence has shown that the gut microbiota plays a significant role in the pathogenesis of mastitis, and clinical investigations have found that the occurrence of mastitis is correlated with ruminal dysbiosis. However, the underlying mechanism by which the ruminal microbiota participates in the development of mastitis remains unknown. RESULTS: In the present study, we found that cows with clinical mastitis had marked systemic inflammation, which was associated with significant ruminal dysbiosis, especially enriched Proteobacteria in the rumen. Ruminal microbiota transplantation from mastitis cows (M-RMT) to mice induced mastitis symptoms in recipient mice along with increased mammary proinflammatory signature activation of the TLR4-cGAS-STING-NF-κB/NLRP3 pathways. M-RMT also induced mucosal inflammation and impaired intestinal barrier integrity, leading to increased endotoxemia and systemic inflammation. Moreover, we showed that M-RMT mirrored ruminal microbiota disruption in the gut of recipient mice, as evidenced by enriched Proteobacteria and similar bacterial functions, which were correlated with most proinflammatory parameters and serum lipopolysaccharide (LPS) levels in mice. Recurrent low-grade LPS treatment mirrored gut dysbiosis-induced endotoxemia and caused severe mastitis in mice. Furthermore, we found that gut dysbiosis-derived LPS reduced host alkaline phosphatase activity by activating neuraminidase (Neu), which facilitates low-grade LPS exposure and E. coli-induced mastitis in mice. Conversely, treatment with calf intestinal alkaline phosphatase or the Neu inhibitor zanamivir alleviated low-grade LPS exposure and E. coli-induced mastitis in mice. CONCLUSIONS: Our results suggest that ruminal dysbiosis-derived low-grade endotoxemia can cause mastitis and aggravate pathogen-induced mastitis by impairing host anti-inflammatory enzymes, which implies that regulating the ruminal or gut microbiota to prevent low-grade systemic inflammation is a potential strategy for mastitis intervention. Video Abstract.

Commensal cow Roseburia reduces gut-dysbiosis-induced mastitis through inhibiting bacterial translocation by producing butyrate in mice.

The precise mechanism by which gut dysbiosis contributes to the pathogenesis of extraintestinal diseases and how commensal microbes mediate these processes remain unclear. Here, we show that cows with mastitis had marked gut dysbiosis, characterized by the enrichment of opportunistic pathogenic Escherichia_Shigella and the depletion of commensal Roseburia. Fecal microbiota transplantation from donor cows with mastitis (M-FMT) to recipient mice significantly caused mastitis and changed the gut and mammary microbiota in mice. Notably, M-FMT facilitated the translocation of pathobiont from the gut into the mammary gland, and the depletion of Enterobacteriaceae alleviated M-FMT-induced mastitis in mice. In contrast, commensal Roseburia intestinalis improved M-FMT-induced mastitis and microbial dysbiosis in the gut and mammary gland and limited bacterial translocation by producing butyrate, which was associated with inflammatory signaling inhibition and barrier repair. Our research suggests that commensal Roseburia alleviates gut-dysbiosis-induced mastitis, although further studies in dairy cows and humans are needed.

The Role of Rumen Microbiota and Its Metabolites in Subacute Ruminal Acidosis (SARA)-Induced Inflammatory Diseases of Ruminants.

Subacute ruminal acidosis (SARA) is a common metabolic disease in ruminants. In the early stage of SARA, ruminants do not exhibit obvious clinical symptoms. However, SARA often leads to local inflammatory diseases such as laminitis, mastitis, endometritis and hepatitis. The mechanism by which SARA leads to inflammatory diseases is largely unknown. The gut microbiota is the totality of bacteria, viruses and fungi inhabiting the gastrointestinal tract. Studies have found that the gut microbiota is not only crucial to gastrointestinal health but also involved in a variety of disease processes, including metabolic diseases, autoimmune diseases, tumors and inflammatory diseases. Studies have shown that intestinal bacteria and their metabolites can migrate to extraintestinal distal organs, such as the lung, liver and brain, through endogenous pathways, leading to related diseases. Combined with the literature, we believe that the dysbiosis of the rumen microbiota, the destruction of the rumen barrier and the dysbiosis of liver function in the pathogenesis of SARA lead to the entry of rumen bacteria and/or metabolites into the body through blood or lymphatic circulation and place the body in the "chronic low-grade" inflammatory state. Meanwhile, rumen bacteria and/or their metabolites can also migrate to the mammary gland, uterus and other organs, leading to the occurrence of related inflammatory diseases. The aim of this review is to describe the mechanism by which SARA causes inflammatory diseases to obtain a more comprehensive and profound understanding of SARA and its related inflammatory diseases. Meanwhile, it is also of great significance for the joint prevention and control of diseases.

Changes in the rumen microbiota community in ketosis cows during propylene glycol treatment.

Ketosis, a common metabolic disorder in dairy cattle, occurs during early lactation and leads to higher concentrations of non-esterified fatty acids (NEFAs) and ß-hydroxybutyrate (BHBA), and is generally believed to be caused by excessive negative energy balance (NEB). Propylene glycol (PG), a gluconeogenic precursor, has been proved to promote gluconeogenesis and alleviate NEB. Oral administration of PG is widely considered one of the most effective therapeutic options for treating ketosis. Thus, in this study, we assessed the effects of PG on rumen microbiota via 16S rDNA analysis. The results show that one dose (500 mL) of PG treatment could rapidly reduce the blood BHBA level in ketosis cows by increasing the level and proportion of propionate in the rumen. Meanwhile, PG also had certain effects on the rumen bacterial community. Compared with before treatment, the relative abundances of Prevotella, Succinivibrionaceae_UCG-001 and Prevotellaceae_UCG-001 increased significantly, while those of Christensenellaceae_R-7_group, Butyrivibrio and Saccharofermentans significantly decreased. LEfSe analysis revealed that after PG treatment, only Rikenellaceae_RC9_gut_group was enriched in the rumen fluid at the genus level. In conclusion, the present study indicates that ketosis is accompanied by alterations in the rumen microbiota community. PG treatment changes the composition of rumen microbiota to a healthier state and contributes to rapid recovery from ketosis. These results support the usage of PG for treating such metabolic diseases that challenge high-yield cows due to their minimized cost and maximized safety without any adverse events.

Formononetin Protects LPS-Induced Mastitis Through Suppressing Inflammation and Enhancing Blood-Milk Barrier Integrity via AhR-Induced Src Inactivation.

Formononetin (FOR), a natural flavonoid derived from Radix Astragali, has been reported to have anti-inflammatory and anti-oxidative effects. However, its protective mechanism against mastitis is still unknown. Nuclear factor kappa-B (NF-κB) signaling pathway plays an important role in inflammation, especially mastitis. Aryl hydrocarbon receptor (AhR) is involved in inflammatory regulation and defense against diseases. We investigated the protective effect of FOR on LPS-induced mastitis in mice and the effect of Ahr and NF-κB signaling pathways on the development of mastitis. In this study, mastitis model was induced by LPS injection through the nipple duct. Protective effect of FOR on LPS-induced mastitis was assessed by FOR pretreatment. The protective mechanism of FOR against mastitis was further investigated using LPS stimulation on mouse mammary epithelial cells EpH4-Ev. The results showed that LPS-induced mammary histological injury was inhibited by FOR. FOR significantly inhibited LPS-induced MPO activity. FOR administration enhanced the integrity of blood-milk barrier. In vitro and in vivo experiments showed that FOR inhibited LPS-induced NF-κB signaling pathway activation and the production of inflammatory factors TNF-α and IL-1ß. Moreover, FOR increased the expression of tight junction protein and enhanced blood-milk barrier integrity. LPS activated AhR and Src expression. But FOR induced significant increase in AhR inhibited Src phosphorylation to exert anti-inflammatory effects. In addition, AhR antagonist CH223191 reversed the inhibition of FOR on Src expression. And the inhibition of FOR on NF-κB activation and inflammatory cytokine production were reversed by AhR antagonist CH223191. In conclusion, FOR had protective effects against LPS-induced mastitis via suppressing inflammation and enhancing blood-milk barrier integrity via AhR-induced Src inactivation.