Intravascular granulocyte kinetics in developing calves.

Intravascular granulocyte kinetic values of normal developing calves were determined, using the chromium radioisotope 51Cr as the cell label. A total of 15 kinetic trials were conducted in the calves at 8 to 365 days of age. The clearance of labeled granylocytes from the circulation was an exponential function. The kinetic data from the oldest group of calves (7 experiments on 5 calves, 180 days of age and older) were remarkably similar to those reported for persons. Mean total blood granulocyte pool was 6.34 times 10-8 granulocytes/kg of body weight, of which 45.6% was in the circulating granulocyte pool. Mean clearance half-life (T1/2) was 8.9 hours, and mean granulocyte turnover rate was 12.44 times 10-8 granulocytes/kg of body weight/day. In the oldest calf group, there was significant correlation between the blood granulocyte count and the total blood granulocyte pool size. There was also significant correlation between the total blood granulocyte pool size and the clearance half-life. The youngest group of calves (4 experiments on 4 calves, 8 to 16 days of age) had significantly larger total blood granulocyte pool and shorter intravascular half-life than did the oldest group. These factors combined to yield a markedly greater granulocyte turnover rate of 39.91 times 10-8 granulocytes/kg of body weight/day in the youngest group of calves. Calves of an intermediate age group (70 to 127 days) had kinetic which were intermediate between those of the youngest and oldest groups of calves.