Growth of gram-negative bacteria in dry cow secretion.

Gram-negative bacteria (n = 192) isolated from infected bovine mammary glands were tested for growth in a pooled source of dry cow secretion. Growth of Klebsiella pneumoniae in dry cow secretion was greater than growth of Escherichia coli and Klebsiella oxytoca. Escherichia coli originating during the early dry period exhibited greater growth in dry cow secretion than those originating around calving or during lactation. Klebsiella pneumoniae growth did not differ with time of origin of intramammary infection. Escherichia coli, K. oxytoca, and K. pneumoniae growth in a synthetic medium was reduced by apolactoferrin plus Ig. Growth reduction was greatest for E. coli. Citrate reversed growth inhibition. The inhibitory properties of dry cow secretion for E. coli may contribute to the low number of naturally occurring intramammary infections originating during the early part of the dry period. Inhibitory properties of dry cow secretion are partially explained by lactoferrin acting in conjunction with antibody to prevent iron acquisition by many gram-negative bacteria.