Microbiome of Bovine Milk and Factors Influencing Its Composition

The bovine milk microbiome is a complex and dynamic microbial ecosystem, comprising both commensal and pathogenic bacteria. Its composition is shaped by endogenous factors, including udder physiology, lactation stage, and health status, particularly mastitis, as well as by exogenous factors, such as housing conditions, farm infrastructure, milking practices, and post-milking processing. Mastitis not only alters milk quality but also induces persistent dysbiosis that may persist even after clinical recovery, highlighting the need for continuous microbiome monitoring to ensure milk safety. Advances in molecular and metagenomic techniques have enabled the detection of microbial taxa that are difficult to identify using traditional culture-based methods. However, challenges remain due to low microbial biomass, reagent contamination, and the inability to distinguish live from dead bacteria, all of which complicate accurate characterization. Environmental contamination from skin, air, and equipment, along with microbial shifts during transport, storage, pasteurization, and product separation, further modulate microbial communities. While mastitis-related changes in milk microbiota have been extensively studied, the effects of other bovine diseases and systemic health conditions remain largely unexplored, constituting a critical knowledge gap. Understanding the factors that shape milk microbial communities is essential for ensuring dairy product safety, optimizing herd management, and developing microbiome-based innovations in milk production.