Optimum replacement policies for the control of subclinical mastitis due to S.aureus in dairy cows

A dynamic program was used to establish the optimum replacement policy for dairy herds, taking into account subclinical mastitis caused by the bacteria Staphylococcus aureus. This particular pathogen is resistant to normal drug therapies and therefore culling is the major method of control. Methods are described to account for output losses due to yield loss and a reduction in milk price caused by extra somatic cells secreted into the milk by infected cows. Extra culling was justified in both infected and control herds in order to reduce the level of infection in the herd. The method described allows replacement policy to be treated as control expenditure rather than an output loss in the economic analysis of farm animal disease. This approach will become even more important as consumers demand an alternative to the prophylactic use of antibiotics in agriculture without compromising food quality and safety.