Changes in penetrability of bovine papillary duct to endotoxin after milking

The relative penetrability of bovine papillary ducts was assayed using frequency of inflammatory response to implantation of Escherichia coli endotoxin at a depth of 3 mm. Penetrability immediately after machine milking, compared with penetrability after delays of 10 to 480 minutes, indicated a decrease in frequency of penetrability to a minimum at 2 hours after milking, a decrease of about 75%. Four and 8 hours after milking, frequency of penetrability increased to about 55% of that measured immediately after milking.