Distribution of inflammation and association between active and chronic alterations within the endometrium of dairy cows

Objectives of this study were twofold: (i) to assess the association between polymorphonuclear (PMN) counts and chronic alterations within the bovine endometrium and (ii) to determine the distribution of inflammation throughout the endometrium of clinically healthy dairy cows. Holstein-Friesian cows (n = 32) from a single dairy farm were selected for this experiment. Before slaughtering, a complete reproductive examination was performed to discard any type of clinical disease. After slaughtering, reproductive tracts were collected, and the endometrium was sampled at 8 pre-defined locations. At each location, endometrial biopsies (EBs) and cytology (CY) samples were harvested. Histopathology samples were stained with haematoxylin-eosin (EB-HE) and naphthol-AS-D-chloroacetate-esterase (EB-naphthol), while CY samples were stained with Wright-Giemsa. In the EB-HE samples, parameters assessed were epithelium height, mononuclear cells infiltration, lymphocytic aggregates, periglandular fibrosis, angiosclerosis and haemorrhage. In EB-naphthol and CY slides, PMNs counts were evaluated. Binomial logistic regression was used to assess the association between the number of PMNs present in both the EB-naphthol and CY samples and alterations identified in the EB-HE samples and to analyse the distribution of the histopathological alterations (EB-HE). A Poisson mixed-effect model was used to analyse the distribution of PMNs within the endometrium. A significant positive association was found between the PMN counts and the mononuclear cells infiltration. The presence of erythrocytes was associated with higher odds to detect PMNs in the stratum compactum. Significantly, higher infiltration of PMNs and mononuclear cells were detected in the uterine body and the right horn region. Concluding, CY is a technique that allows the evaluation of PMN counts and therefore only evaluates active inflammation. A complete assessment of endometrial health can only be obtained using EB. To optimize the sensitivity to diagnose endometrial inflammation in cows, adjacencies of the corpus uteri should be considered as the preferred region to harvest samples.