Growth inhibition of Escherichia coli and Klebsiella pneumoniae during involution of the bovine mammary gland: relation to secretion composition.

Mammary secretions from 12 Holstein dairy cows were collected to evaluate growth inhibition of Escherichia coli and Klebsiella pneumoniae during involution and during physiologic transitions of the mammary gland. Mammary secretions obtained during late lactation poorly inhibited growth of E coli and K pneumoniae. However, as involution progressed, mammary secretions increasingly inhibited growth of both coliform mastitis pathogens. Greatest inhibition of E coli and K pneumoniae growth was observed when mammary glands were fully involuted. Growth inhibition remained high until 7 days before parturition, and then it decreased significantly (P less than 0.05) to that observed during late lactation. Inhibition of coliform mastitis pathogen growth was associated with high concentrations of lactoferrin and immunoglobulin G, decreased citrate concentration, and a low citrate to lactoferrin molar ratio. These data suggested that differences in susceptibility or resistance to new intramammary infection with coliform mastitis pathogens during the nonlactating period may be attributable, in part, to marked changes in mammary secretion composition that develop during physiologic transitions of the mammary gland. Resistance of the fully involuted mammary gland to coliform infection may be associated with high concentrations of natural protective factors.