Influence of Involution on Intramammary Phagocytic Defense Mechanisms

¹ Milk Secretion and Mastitis Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
² Department of Animal Sciences, University of Maryland, College Park 20742-2311

Mammary secretions (n = 34 cows) and mammary phagocytes (n = 18 cows) were collected throughout the nonlactating (dry) period to determine changes in intramammary phagocytic defense mechanisms. Mammary secretions were evaluated for their ability to support phagocytosis of Staphylococcus aureus by neutrophils from donor cows and mammary phagocytes for phagocytic and chemiluminescence activity.

Ability of secretions to support phagocytosis decreased with advancing length of the dry period, This effect was more pronounced when dry cow secretions constituted 50% of the phagocytic mixture. Phagocytic activity of mammary phagocytes decreased with advancing dry period when autologous secretion was used in the incubation mixture. With homologous secretion, the percentage of phagocytosis increased 5 to 6 d after drying off compared with before drying off and then gradually decreased throughout the remainder of the dry period. Chemiluminescence activity (log₁₀ counts per minute) of mammary phagocytes was lower during the dry period and decreased with advancing dry period.

Results indicated diminishing ability of secretions to support phagocytosis and diminished phagocytic and bactericidal mechanisms during the dry period.

Key Words: chemiluminescence • mammary gland • phagocytosis

Submitted on September 20, 1991
Accepted on February 26, 1992