Mastitis is recognized as one of the most costly diseases affecting dairy cows and a major cause of economic losses in the dairy industry worldwide. In South Africa, milk with more than 500000 somatic cells/mL is not approved for human consumption and therefore it cannot be sold. The effect of just a few cows with very high SCC on the bulk milk (tank) is so large that the entire milk from a tank can be penalised, although the vast majority of the cows have low cell counts. The SCC can be effectively controlled with antibiotic therapy, but this practice is currently not acceptable. There is a...