Polymorphonuclear neutrophil leukocyte function in clinical bovine patients and in cows with or without Staphylococcus aureus mastitis.

A fluorochrome microassay was used to investigate peripheral blood polymorphonuclear leukocyte (PMNL) function in cattle. Glass-adherent PMNL were reacted with Staphylococcus aureus preincubated in 20% bovine serum for 30, 60 and 90 min. Coverslips were stained with acridine orange (AO) followed by crystal violet to quench extracellular bacterial fluorescence. PMNL function was evaluated by counting the number of dead (stained red with AO) and live (stained green with AO) S. aureus contained within 100 PMNL. A phagocytic index was calculated as the average number of bacteria contained within PMNL. The percentage killing of S. aureus was calculated from the average proportion of S. aureus within PMNL that were dead. Six clinically normal Holstein calves, 3-4 months of age, were sampled on 6 consecutive days. PMNL phagocytosis and killing did not vary significantly (p greater than 0.05) among repeated samplings per calf. PMNL function increased with increasing time of incubation of PMNL with S. aureus. Means (+/- SD) for percentage killing were 46.7 +/- 13.1, 57.4 +/- 11.6, and 62.1 +/- 9.8% for 30, 60 and 90 min of reaction, respectively. Means (+/- SD) for the phagocytic index were 2.9 +/- 0.8, 3.6 +/- 1.0, and 4.2 +/- 1.1 bacteria/PMNL for 30, 60 and 90 min of reaction, respectively. PMNL function was determined in 30 normal cattle of various breeds, age and sex, and these values were pooled to provide normal values for PMNL function. When values for bovine clinical patients (n = 25) with various diagnoses were compared with normal values (defined by the mean +/- 2SD for the 30 normal cattle) for PMNL function, only one patient was observed to exhibit PMNL hypofunction. A cow with disseminated intravascular coagulation in association with peracute coliform mastitis exhibited decreased PMNL killing capacity. Abnormal PMNL function was uncommon in the hospital population studied. Peripheral blood PMNL function was evaluated in lactating Holstein cows with (n = 15) or without (n = 15) chronic subclinical S. aureus mastitis. There was no significant (p greater than 0.05) difference in PMNL function among these cows.