Effect of parity on periparturient neutrophil function in dairy cows.

Impairment of periparturient neutrophil function in dairy cows has been described. This may contribute to increased susceptibility of cows to bacterial infections during the periparturient period. Susceptibility to many complications of the postpartum period is influenced by parity. The aim of this experiment was to determine whether parity influenced periparturient neutrophil function in Holstein cows. Cows (n = 46, of which 26 were calving for the first, second or third time, and 20 were of more advanced parity) were sampled during the last prepartum week, the first postpartum week, 3 weeks postpartum and 6 weeks postpartum. Neutrophils were isolated by centrifugation and hypotonic lysis of erythrocytes. Neutrophil superoxide anion production was determined by the superoxide dismutase inhibitable reduction of ferricytochrome c, and stimulus-induced shape change was determined at 0, 30, 60 and 120 s after exposure to zymosan activated bovine plasma. Superoxide anion production was significantly depressed in the first postpartum week in all cows. At this time, superoxide anion production was significantly lower in cows in their fourth or greater lactation than in cows in the first three lactations. Neutrophil shape change responsiveness was also influenced by parity; immediately prepartum, the shape change responsiveness differed between groups at 120 s after application of the stimulus, and during the first postpartum week shape change responsiveness was less in cows of advanced parity at 30, 60 and 120 s after application of the stimulus. We concluded that cows in the fourth or greater lactation suffered more profound periparturient impairment of neutrophil function than younger cows and that this may be a factor mediating their increased susceptibility to some postpartum complications.