Effects of granulocyte colony-stimulating factor administration to periparturient cows on neutrophils and bacterial shedding.

Administration of recombinant bovine granulocyte colony stimulatory factor to periparturient dairy cows was evaluated as a method to prevent periparturient immunosuppression. Eleven of 21 cows were experimentally infected with Staphylococcus aureus in one mammary quarter prior to the study. Cows were randomly assigned to four groups in a 2 x 2 factorial design to evaluate the effects of placebo or recombinant bovine granulocyte colony stimulatory factor administration on chronic, subclinically infected and uninfected cows during the periparturient period. Blood neutrophils were isolated and evaluated for phagocytic activities 5 wk before expected parturition through 7 wk postpartum. Administration of recombinant bovine granulocyte colony stimulatory factor (5 micrograms/kg body weight or placebo subcutaneously beginning 14 d prepartum through 10 d post-partum) resulted in a prepartum and postpartum leukocytosis of 35,600/microliters and 53,500/microliters, respectively. This was attributed to a mature neutrophilia of 24,010/microliters during prepartum and 38,080/microliters during postpartum treatment periods (pretreatment baseline = 2330/microliters). Mononuclear cell counts averaged 7610/microliters during prepartum and 9830/microliters during postpartum treatment periods (baseline = 3450/microliters). Neutrophil random and directed migration were reduced during recombinant bovine granulocyte colony stimulatory factor treatment compared with placebo or baseline levels. Ingestion of bacteria and cytotoxicity by neutrophils was increased during recombinant bovine granulocyte colony stimulatory factor therapy compared with placebo or baseline levels. Shedding of S. aureus in lacteal secretions was unaffected by recombinant bovine granulocyte colony stimulatory factor treatment. In summary, administration of recombinant bovine granulocyte colony stimulatory factor increased the number and functional activity of neutrophils and prevented some aspects of periparturient immunosuppression in dairy cows.