Treatment with SA exacerbates mastitis in antibiotic-treated mice through the microbiota-gut-mammary axis by facilitating the growth of opportunistic pathogen and activating TLR4-NF-κB/NLRP3 signatures, while limitation of SA production, regulation of gut homeostasis by commensal microbes and targeted inhibition of opportunistic pathogen expansion attenuated gut dysbiosis-associated mastitis in mice. This evidence concerns the gene TLR4 and mastitis.