# Characterization of early-stage lesions and investigation on the role of mucosal trauma in hemorrhagic bowel syndrome in cattle

## TL;DR

This study investigates early-stage lesions in hemorrhagic bowel syndrome in cattle and explores whether mucosal trauma contributes to the condition.

## Contribution

The study provides the first detailed characterization of early-stage HBS lesions and experimentally supports the role of mucosal trauma in their development.

## Key findings

- Early-stage HBS lesions show degeneration of LMM smooth muscle cells at the ultrastructural level.
- Experimentally induced lesions closely resemble naturally occurring early-stage HBS lesions.
- No specific bacterium was associated with the development of early-stage HBS lesions.

## Abstract

Hemorrhagic bowel syndrome (HBS) is characterized by a dissecting intramucosal hematoma at the small bowel, causing obstruction and severe hemorrhage in dairy cattle. Recent investigation revealed the presence of early-stage lesions in cows affected by HBS. These are presumed to be the initial stage of the hematoma, as both share unique dissection of the lamina muscularis mucosae (LMM) as histological hallmark. Early-stage lesions of HBS have not been characterized in greater detail, and neither has the hypothesis of mucosal abrasion as etiology been explored. Therefore, the first objective of the present study was to characterize the morphology of early-stage lesions, by gross examination, histochemistry, immunohistochemistry and transmission electron microscopy. The second objective was to determine the effect of mucosal abrasion to the small intestine in an ex vivo model. A total of 86 early-stage lesions from 10 cows with HBS were characterized. No underlying alterations at the LMM were evident which could explain their occurrence. However, degeneration at the ultrastructural level of the LMM smooth muscle cells was present in 3 of 4 lesions, it is however unclear whether this is primary or secondary. Bacteriological examination did not reveal any association with a specific bacterium. Experimental-induced and early-stage lesions were gross and histologically evaluated and scored in three cows with HBS and seven controls. Experimentally induced lesions in both affected cows and controls, were histologically very similar to the naturally occurring early-stage lesions. Altogether, the results are suggestive for mucosal trauma to play a role in the pathogenesis of HBS.