ngestion of S. aureus by PMN was significantly increased 1 week after calving in comparison with 1 week before calving and was normalised after 3 weeks ( Fig. 1). One week after calving, opsonized zymosan phagocytosis-induced CL was significantly reduced by 12% in first parity cows and by 18% in cows of parity greater than 1 when compared to 1 week before calving. The decrease of CL was more pronounced and lasted longer in cows in their second or greater lactation (results not shown). The average decrease in CL for all cows was 15% 1 week after parturition (Fig. 2). Between 1 and 5 weeks after calving, CL of PMN gradually increased but did not return to pre-calving values at the end of the observation period.