Fluctuation of neutrophil counts around parturition in Holstein dairy cows with and without retained placenta

Retained placenta (RP) is often diagnosed in high-yielding dairy cows and can negatively affect reproductive performances. The objective of the present study was to investigate the hematological and biochemical profile of cows with RP before and immediately after parturition, with particular emphasis on neutrophil counts, since a previous study demonstrated the presence of peripheral neutropenia in dairy cows with RP sampled a few days after parturition. Results from 12 Holstein cows affected by RP and from 17 clinically healthy controls sampled one week pre-partum, within 12 h after calving and between 48 and 72 h after parturition were compared between groups and over time. Compared with controls, cows with RP had lower lymphocyte counts before parturition, lower leukocyte and neutrophil counts at parturition, lower monocyte counts at all times, and higher β-hydroxybutyrate before and after parturition. Erythroid and biochemical parameters were similar over time in both groups, whereas RP cows did not show the increase of neutrophil counts that occurs in controls at parturition. Hence, the finding of a lower neutrophil count in a routinely hemogram performed at parturition could be used as an alarm signal suggesting to monitor the affected animals. Moreover, although the underlying pathogenetic mechanism should be better investigated, the present study describes for the first time the association between altered blood leukocyte concentrations at parturition in RP compared to control cows.