Immune mechanisms of the bovine udder: an overview.

Understanding basic defenses of the udder is instrumental in developing measures to prevent mastitis. The teat canal is the first defense against pathogens, providing a physical barrier and antimicrobial substances. When bacteria breach the teat canal, milk leukocytes provide a second defense by ingesting pathogens. Intramammary devices have been used experimentally to increase leukocyte numbers and to enhance destruction of bacteria. Milk antibodies opsonize and lyse bacteria, neutralize toxins, and prevent adhesion to tissue. Vaccinating cows against mastitis generally has been unsuccessful; however, immunization is useful in controlling specific bacterial strains. Antibody-producing plasma cells preferentially accumulate in internal teat end tissues. Because bacteria contact these tissues to reach milk-producing areas of the udder, an immunostimulant to enhance locally the protective nature of plasma cells may decrease the occurrence of infection.