Repeat herd investigations into milk quality and mastitis concerns were performed on a 350 cow dairy herd throughout 2014. This farm originally experienced an acute spike in somatic cell count(> 700,000 cells/ml) and a high rate of clinical mastitis following the introduction of new animals to the herd. The original assessment included individual cow cultures for the entire herd and limited test day data analysis which revealed an alarming level of both clinical and subclinical Staphylococcus aureus infections. At least 60% of the cows were infected. The initial control strategy was to cull or dry off the highest cell count cows and screen freshening animals for Staphylococcus aureus and place them in a staph positive pen to be milked last to minimize the transmission between animals in the parlor. These measures reduced the bulk tank somatic cell count to an acceptable level (250,000 - 300,000 cells/ml), but a high prevalence of subclinical infections continues to plague the herd. Subsequent investigations revealed a failure of compliance and the continued presence of significant risk factors which prevent the herd from making progress towards eradication. Staphylococcus aureus continues to be transmitted throughout the herd, reducing both overall milk yield and milk quality, creating a significant negative economic impact. Introduction Staphylococcus aureus is a common contagious mastitis pathogen found throughout the world. Many strains exist, but the majority of Staph aureus strains are farm specific. Like most contagious pathogens, different strains of Staph aureus have different levels of virulence, likely contributing to the variability seen in the rate of transmission, incidence of clinical disease, and response to treatment cited in Staph aureus studies (Joo et al., 2001 ). It is widely accepted that the main reservoir of the Staph aureus is the udder of infected cows. The udder can be infected at any time and dry period and pre-parturient heifer infections are common. In fact, replacement heifers infected before parturition are considered to be a major source of Staphylococcus aureus introduction into a previously culture negative herd.