Effects of parturition and lactation on blood and milk cell concentrations, corticosteroids, and neutrophil phagocytosis in the cow.

Blood differential leukocytes, erythrocytes, milk somatic cells, and neutrophil phagocytosis in 14 Holstein-Friesian cows were measured at 2-day intervals for 2 weeks before parturition, on the day of parturition, on postpartum days 1,2,5,10,15, and 30, and at monthly intervals throughout lactation. Circulating corticosteroids were measured in 6 cows on days -6, -4, -2, on the day of parturition, and on days +1, +2, +5, +10, +15, +30, and +60. Circulating neutrophils on day -2 on the day of parturition, on days 2, 10, and 15 averaged 3,363, 5,889, 3,085, 4,116, and 3,558/mm, respectively. The increase in neutrophils at parturition was accompanined by an increase in corticosteroids (2.7, 9.0, 11.1, 6.1, and 5.4 ng/ml of blood plasma on days -4 and -2, on the day of parturition, and on days +1 and +2, respectively). The phagocytic ability of circulating neutrophils was determined by incubating yeast cells with whole blood (30 minutes, 37 C) and microscopically counting yeast cells per neutrophil. Mean yeast cells per neutrophil decreased (P less than 0.01) during the 2nd week after parturition (7.4, 6.5, 6.6, and 7.2 on days +2, +10, +15, and +30, respectively). But this decrease was compensated for by an increase in circulating neutrophils during the same period.