Ruminal dysbiosis-induced mastitis: new insight into the pathogenesis of mastitis.

Mastitis is one of the most significant diseases affecting the development of the dairy industry and has traditionally been associated with pathogenic infections. However, emerging evidence highlights that ruminal microbial homeostasis also plays a crucial role in the pathogenesis of mastitis. Specifically, cows with mastitis exhibit reduced alpha diversity and altered microbial composition in the rumen. Inducing ruminal dysbiosis through a high-concentrate diet has been shown to trigger mastitis in cows, and transplantation of ruminal microbiota from mastitis-affected cows to recipient mice can induce mastitis in mice. Mechanistically, ruminal dysbiosis increases gastrointestinal inflammation and compromises the integrity of the gastrointestinal barrier, thereby facilitating the translocation of harmful bacterial components, metabolites, and pathobionts into the bloodstream. This disruption impairs blood-milk barrier function, leading to systemic inflammation and the development of mastitis. In this review, we summarize recent advances in understanding how ruminal dysbiosis induces mastitis and explore potential prevention and control strategies targeting the modulation of ruminal microbiota.