Variation among cows in the ability of milk to support phagocytosis and in the ability of polymorphonuclear leukocytes to phagocytose Staphylococcus aureus.

Marked variation existed among cows in the ability of their milk to support phagocytosis and in the ability of polymorphonuclear leukocytes isolated from their milk to phagocytose Staphylococcus aureus. Furthermore, milk samples that supported a low degree of phagocytosis were generally obtained from cows that had a greater occurrence of clinical mastitis per lactation (r = 0.41). Results from this study suggest that variation in the phagocytic defense mechanism of the bovine mammary gland could contribute to the difference in susceptibility to infection by mastitis pathogens.