The effect of Escherichia coli endotoxin and culture filtrate on the dry bovine mammary gland.

The mammary glands of eight non-lactating dairy cows were infused with either endotoxin or the sterile culture filtrate in which Escherichia coli had been grown (CCF). Animals were necropsied at intervals up to 24 h after infusion. Only mild inflammation of the teat and lactiferous sinuses occurred after 4 h, subsiding gradually to 24 h. After mixing dry cow secretion with either endotoxin or CCF, an intense inflammatory response was produced on inoculation of quarters of a lactating cow; CCF also produced necrosis of the epithelium. Thus, dry gland secretions do not inhibit the effect of filtrate or endotoxin. It was concluded that the refractory nature of the gland to these toxins in the non-lactating animal is due to the changes which occur in the ductular epithelium during involution.