Effects of recombinant granulocyte colony-stimulating factor on Staphylococcus aureus mastitis in lactating dairy cows.

The in vivo effects of recombinant human granulocyte colony-stimulating factor on blood and milk leukocytes in dairy cows was examined. A 2-fold increase in peripheral white blood cell counts was observed by d 5 of treatment and peaked on d 12 with values 3-fold those of controls. Counts remained elevated above pretreatment values during the treatment period, then returned to normal by d 23 of the trial. Differential white blood cell counts demonstrated that neutrophils predominated (73.8%) in treated cows versus controls (22.1%) during the treatment period. Immediately prior to experimental challenge with Staphylococcus aureus, milk SCC were 582 x 10(3) and 261 x 10(3)/ml, and percentages milk neutrophils were 64.4 and 45.3, respectively, in treated and control cows. After challenge, a 46.7% reduction in new infections was observed in quarters of treated cows compared with controls. Recombinant human granulocyte colony-stimulating factor was a granulopoietic growth and differentiation factor in the cow, and the resulting leukocytosis into the mammary gland may have been protective against experimental bacterial challenge.