166. Bovine Defensin Expression in Nasal Mucosal Secretions of Calves Challenged with Bovine Respiratory Disease: A Preliminary Analysis

Abstract Bovine respiratory disease (BRD) presents substantial economic costs and risks to animal health in the U.S. beef cattle industry. The diversity in BRD-causing pathogens along with antibiotic overuse and resistance remains a significant challenge. Defensins are innate, antimicrobial proteins with potent immunoregulatory functions associated with the innate immune response and adaptive immunity activation. There are two primary defensin classes including α- and β-defensins. The α-defensins are highly concentrated in the granules of neutrophils or Paneth cells in the small intestine, while β-defensins are secreted by mucosal cells found in the eye, skin, oral mucosa, urogenital and respiratory tract. This preliminary study investigated β-defensin presence in nasal mucosal secretions. Understanding defensin’s biological activity against pathogens may provide a more effective strategy for mitigating BRD at the microbial level. Therefore, the objectives of this study were to 1) identify β-defensin expression in bovine mucosal secretions and 2) compare differential defensin expression in healthy and BRD-challenged calves. Nasal swabs were collected from healthy calves (n = 6) and calves exhibiting BRD symptoms (n = 6) including nasal discharge, heavy panting, and a body temperature at or above 39 °C. The initial defensins measured included DFEB401, 402, 403, 404, and 405. Defensin gene expression was determined by qPCR using 2-ΔΔCt method. The means were compared by Student T test and significance was set at P < 0.05. Calves infected with BRD demonstrated a defensin-associated immune response as indicated by DFEB403, 404, and 405 upregulation compared to healthy calves (P < 0.05). An inverse response was observed in healthy calves, with DFEB402 being the only defensin with upregulated expression (P < 0.05). The DFEB401 defensin was also observed, however its expression was not significantly different between healthy and BRD-challenged calves. These findings warrant further investigation. The preliminary results demonstrate that not only are β-defensins expressed in bovine nasal mucosal secretions but are also differentially expressed during BRD pathogen exposure. Therefore, identifying which defensins are upregulated during specific BRD pathogen presence, could be used as biomarkers to select calves with enhanced immune systems genetically predisposed to combating BRD-causing pathogens and reduce antibiotic use.