Diagnosis and management of intramammary infection caused by staphylococcus aureus for dairy cows and herds

Intra-mammary infection due to the Gram-positive bacterium Staphylococcus aureus remains the most common cause of contagious mastitis for the majority of UK dairy herds and often results in persistent subclinical infections. Classically, infection has been well controlled by the Five Point Plan, although recent evidence shows that some strains of S. aureus may behave differently in terms of epidemiology. It is important that isolation of this organism from individual cases and bulk tank samples does not automatically trigger a herd diagnosis of a contagious mastitis without evidence for a contagious disease pattern from somatic cell count and clinical mastitis data analysis. Systematic analysis of clinical mastitis and in somatic cell count data is required to understand the impact of this major pathogen in the herd; of particular use is the rate of new infection in lactation, the relationship between the proportion of cows infected and those chronically infected and the apparent rate of cure across the dry period. This paper reviews diagnosis for infected cows and herds, treatment of infected cows and control priorities for infected herds.