CHeSS has been designed to determine the prevalence of specific mastitis pathogens (Staph. aureus, Strep. agalactiae, and Mycoplasma bovis), and other infectious diseases (leukosis, leptospirosis, neosporosis, Johne’s disease and Salmonella Dublin) on dairy farms, based on bulk milk, individual and environmental samples. Subsequently, the control each of these infectious diseases will be investigated on a subset of infected farms, which will increase the understanding of farm-specific risk factors and control strategies for infectious diseases. By including a targeted control program, CHeSS not only monitors, but aims to actively reduce the prevalence of described infectious diseases.