Circulating and endometrial polymorphonuclear leukocyte function dynamics in postpartum dairy cows with subclinical or clinical endometritis

We aimed to compare the circulating polymorphonuclear leukocyte (cPMN) and endometrial PMN (ePMN) viability and function dynam- ics in postpartum dairy cows with subclinical (SCE) or clinical endo- metritis (CE). To do so, blood samples from 38 Holstein cows were collected at −7, 9, 21 and 36 days relative to calving, and endometrial cytology samples from 32 Holstein cows were harvested at 9, 21 and 36 days postpartum. The uterine health status was assessed at 36 days postpartum, and cows were classified as healthy (absence of mucopurulent discharge and ≤5% ePMN), SCE (absence of mucopu - rulent discharge but >5% ePMN) or CE (mucopurulent discharge or worse and >5% ePMN). Viability and function parameters, phago- cytosis (PC), oxidative burst and intracellular proteolytic degrada- tion were evaluated via flow cytometry. Cows with CE had a lesser proportion of cPMN viability (84.5 ± 2.1%) and greater apoptosis (14.4 ± 2.0%) than healthy (92.4 ± 1.3 and 6.7 ± 1.3%, respectively) or SCE (95.3 ± 2.4 and 3.8 ± 2.3%, respectively) at 9 days postpartum. Interestingly, cPMN intracellular proteolytic degradation was lower (6.2 ± 0.1 MFI) in SCE than healthy (6.7 ± 0.08 MFI) or CE (6.8 ± 0.1 MFI) at d 9 postpartum. The proportion of necrotic ePMN was higher for healthy (49.6 ± 5.1%) than SCE (27.4 ± 7.3%) and CE (27.7 ± 7.3%) cows at 36 days postpartum. Also, at 36 days postpartum, the pro- portion of ePMN for PC was higher in CE (47.0 ± 8.6%) compared with healthy (18.4 ± 7.6%) cows, but it was not different than SCE (25.9 ± 8.7%). Results of the present study modestly suggest that cPMN viability and function at 9 days postpartum contribute to the pathogenesis of uterine disease. Remarkably, ePMN found in cows with SCE at 36 days postpartum is mostly viable, but dysfunctional.