ABSTRACT
The acquisition of milk requires harvesting an animal product on a daily basis, sometimes three or more times a day. In its natural state, milk has a very short shelf life, so it is thus processed into a myriad of products (e.g. cream, butter, yogurt, cheese, etc.), both to extend its shelf life and to diversify the products available to the consumer. The need for these products to be consistent in quality and to maximise their shelf life means that tight controls are placed on the levels of allowable bacterial contamination and somatic cell count (SCC) that are deemed acceptable in milk destined for human consumption. In order to achieve these targets – particularly SCC levels – both clinical and subclinical mastitis (often caused by bacterial intramammary infections) must be kept under control. This has historically meant the use of antimicrobials (AMs), both to treat clinical cases of mastitis during lactation and to treat existing and prevent new infections at the end of lactation, usually termed ‘dry cow therapy’. Whilst this is still normal practice today in much of the world, for reasons which will be discussed later in this chapter, established practices are now being challenged, and will need to change in the future.
