Assessment of hemolytic and bactericidal complement activities in normal and mastitic bovine milk

Bactericidal and hemolytic complement activities were investigated in 51 quarter milk samples of 13 cows in late lactation. Hemolytic activity was in all of the samples but one, after accounting for whey inhibitory activity. Mean hemolytic activity and inhibitory activities were .18 and .34 complement hemolytic units. Inflammation, in relation to infection status, increased hemolytic titers and heat-labile bactericidal activities of milk. Correlation coefficient was .76 between albumin content of milk serum and hemolytic titer of samples from infected quarters. Normal milk decreased bactericidal titer of bovine serum against a serum-sensitive Escherichia coli strain. When compared to veronal buffer saline solution, milk did not accelerate decay of hemolytic activity over 7-h incubation at 39 degrees C. Taken together, these results suggest that the adverse effect of milk on both hemolytic and bactericidal activities of complement is limited and might be of significance essentially before full establishment of the inflammatory reaction to bacterial invaders.