Immunological Mechanisms, Cellular Processes, and Hindgut Interactions in the Development of Liver Abscesses in Cattle: A Molecular and Cellular Analysis

Liver abscesses are a major health concern in feedlot cattle, often linked to dietary practices and microbial translocation due to compromised epithelial barriers. This thesis explores the immunological, molecular, and epithelial mechanisms involved in liver abscess formation, with the overarching goal of advancing preventive strategies and reducing reliance on prophylactic antimicrobials. In Chapter I, a comprehensive literature review contextualizes the roles of Fusobacterium necrophorum, Trueperella pyogenes, and Salmonella enterica in liver abscess pathogenesis, highlighting epithelial dysfunction, bacterial virulence, and host immune responses. Chapter II presents a transcriptomic analysis of hepatic tissues from experimentally challenged Holstein steers, revealing distinct gene expression profiles in animals that developed abscesses versus those that resisted infection. Findings point to an association between liver abscess development and upregulation of inflammatory and fibrotic pathways, while resistance was linked to immunometabolic balance. Chapter III details the development and validation of a protocol for isolating and culturing primary bovine gastrointestinal epithelial cells (PBGIECs), confirming epithelial identity through gene expression of key markers (CDH1, CLDN4, TJP1, KRT8, KRT18) across different segments (rumen, ileum, jejunum, colon) and stages (tissue, post-isolation, post-culture). Variations observed suggest segment-specific gene sensitivity and emphasize the influence of in vitro conditions, including cell passage number and tissue dissociation. Collectively, this work provides novel insights into host-pathogen interactions, epithelial biology, and hepatic responses in liver abscess development, offering a foundation for future research on bovine health management and antimicrobial alternatives.