Microbial communities and tight junction protein expression in the gastrointestinal tract of feedlot cattle.

The gastrointestinal tract (GIT) of cattle plays a vital role in nutrient absorption, immune function, and microbial homeostasis. While the importance of the GIT microbiome and epithelial barrier integrity has been increasingly recognized, the typical composition of microbial communities and the expression of tight junction proteins (TJPs) in feedlot cattle remains poorly characterized. We investigated microbial community structure and TJP expression at three GIT sites: the rumen (RU), small intestine (SI), and large intestine (LI) in 21 finish-fed feedlot steers sourced from 21 commercial feedyards in the Texas Panhandle. Samples of luminal contents and GIT tissue were collected from each region, as well as feces and liver abscess material. Microbial communities were characterized using 16S rRNA gene sequencing. TJP gene expression was quantified by RT-qPCR using synthetic standards, and protein expression was evaluated by immunohistochemistry (IHC) with both computer-generated and pathologist-generated scoring. Microbial community structures varied primarily by GIT region rather than by individual animals raised at different locations. Nine bacterial families were identified as core microbiome members, with Lachnospiraceae being the most abundant across the GIT. TJP gene expression varied considerably by site, with RU having significantly lower Claudin 1, Claudin 2, and E-Cadherin expression than the SI and LI. IHC results paralleled qPCR findings, with region-specific patterns of protein localization and intensity. Computerized and pathologist-generated H-scores showed moderate agreement but differed notably between epithelial and lamina propria regions. This study provides a comprehensive baseline of microbial and host factors associated with gut health in a uniquely diverse population of feedlot cattle. The identification of regional microbial communities and distinct TJP expression patterns offers foundational insights into gastrointestinal physiology and barrier function. This work establishes baseline data to support future investigations into the relationships among microbial ecology, epithelial barrier function, and cattle health and productivity.