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The mammary gland is a complex organ that provides neonatal offspring with milk for nourishment and disease resistance. Specific and innate immune factors associated with mammary gland tissues and secretion also play a vital role in protecting the gland from infectious disease. Through genetic selection and technological advances in milk removal, the bovine mammary gland yields for more milk than is needed to nourish the newborn calf. This excess is the basis of the dairy industry. Factors associated with the intense management of dairy cattle can profoundly affect mammary gland immunity and the ability of the host to resist mastitis. Technological advances in immunology have led to the availability of new research tools that can facilitate the study of mammary gland immunity and disease pathogenesis. In recent years, considerable research effort has focused on enhancing the natural defense mechanisms of the mammary gland during periods of heightened susceptibility to disease. This paper provides a comprehensive overview of mammary gland immunity with special emphasis on the bovine system. The underlying mechanisms of disease susceptibility and development of potential immunoregulatory strategies to control mastitis are discussed.

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Dairy cattle are susceptible to increased incidence and severity of disease during the periparturient period. Increased health disorders have been associated with alterations in bovine immune mechanisms. Many different aspects of the bovine immune system change during the periparturient period, but uncontrolled inflammation is a dominant factor in several economically important disorders such as metritis and mastitis. In human medicine, the metabolic syndrome is known to trigger several key events that can initiate and promote uncontrolled systemic inflammation. Altered lipid metabolism, increased circulating concentrations of non-esterified fatty acids and oxidative stress are significant contributing factors to systemic inflammation and the development of inflammatory-based diseases in humans. Dairy cows undergo similar metabolic adaptations during the onset of lactation, and it was postulated that some of these physiological events may negatively impact the magnitude and duration of inflammation. This review will discuss how certain types of fatty acids may promote uncontrolled inflammation either directly or through metabolism into potent lipid mediators. The relationship of increased lipid metabolism and oxidative stress to inflammatory dysfunction will be reviewed as well. Understanding more about the underlying cause of periparturient health disorders may facilitate the design of nutritional regimens that will meet the energy requirements of cows during early lactation and reduce the susceptibility to disease as a function of compromised inflammatory responses.