Mastitis is one of the most common diseases affecting dairy cattle, causing huge annual financial losses to the dairy industry. Antibiotics are usually administered to treat this infectious and occasionally fatal disease of the mammary glands. Treatment results can vary greatly within and among farms, and treatment failure is sometimes blamed on antimicrobial resistance (AMR). AMR occurs when strains of bacteria become resistant to antibiotic medicines, rendering them ineffective in treating or preventing infections. A new project by researchers at the Faculty of Veterinary Science at the University of Pretoria (UP), funded by Milk SA, the statutory body of the milk industry, tackles some of the big unanswered questions regarding treatment failure at South African dairies. Led by Dr Martin van der Leek, from the Department of Production Animal Studies, the project on 'Resistance to available antibiotics in lactating cows with mastitis' looks at treatment failure caused by AMR and mastitis caused by other factors.