Subclinical endometritis (SCE) has a severe negative effect on reproductive performance of dairy cows. Different studies have shown a wide variety of cut points for the polymorphonuclear neutrophilic leukocyte (PMNL) percentage to define SCE and differing sampling times. Possible risk factors for SCE, such as low body condition score, hyperketonemia, and increased haptoglobin concentrations have been demonstrated. The aim of this study was to determine the relationship between bacterial findings in the uterus and PMNL in the early postpartum period and to compare 2 classification schemes for the diagnosis of SCE. Cytological and bacteriological samples from the uterus were taken from 149 cows at 2 consecutive times postpartum [10±1 and 24±1d in milk (DIM)] and additionally, 131 cows were sampled at 21 to 27 DIM. For sample collection, the cytobrush technique was used and vaginal discharge was examined by vaginoscopy. Polymorphonuclear neutrophilic leukocyte cut points were set at 5, 10, and 18%. Cows positive with α-hemolytic streptococci at 10±1 DIM had significant higher PMNL percentages at 21 to 27 DIM and greater median days to pregnancy (193.5d) than cows not infected (123.0d). Cows with Trueperella pyogenes at 10±1 DIM had higher odds (5.2) of having more than 18% PMNL at 21 to 27 DIM compared with cows without infection. Escherichia coli had no effect on the prevalence of SCE regardless of the cut point. Primiparous cows with more than 18% PMNL had greater median days to pregnancy (144.5 d) than cows with less than 5% (80.0d) or cows between 5 and 18% PMNL (68.0d). Cows between 5 and 18% PMNL or 10 and 18% PMNL showed the best reproductive performance. The results demonstrate that an early infection with α-hemolytic streptococci increased the PMNL percentage 2wk later and that 18% PMNL at 21 to 27 DIM was a predictive cut point for primiparous cows to diagnose animals with or without SCE.
