Globally, mastitis is still the costliest disease to the dairy industry. Losses include decreased milk production, discarded milk, treatment costs, and cows culled due to chronic mastitis. While a few infections can occur from a systemic infection, most mastitis arises from pathogens ascending the teat canal. The barrier defenses of the teat canal are part of the local immune system; however, the systemic immune system is involved in responses to infections within the mammary gland. The goal of the immune response in the infected quarter is twofold: to minimize inflammation and to remove the pathogen.