PSV-A-4 - Novel Method to Identify Cattle Predisposed to Severe Cases of Bovine Respiratory Disease

Abstract: Respiratory disease in several species can range from subclinical infection to acute death. Bovine respiratory disease (BRD) remains the greatest economic challenge facing the beef industry. Histones are core proteins in chromosomal structure that, when released extracellularly, are cytotoxic and could contribute to exacerbated tissue necrosis during infection. Work in our laboratory demonstrated cattle suffering severe cases of BRD had limited capacity to protect against the cytotoxic effects of extracellular histones, however, the protective mechanism(s) remain unknown. Literature suggests components of the complement system interact with extracellular histones, but the effects on cytotoxic activity of histones is unclear. The objective of the current experiment was to evaluate protective capacity against extracellular histones and complement activity in feedlot heifers and subsequent disease outcomes. Serum samples were collected from 118 heifer calves (BW 229 ± 2.4 kg) at feedlot arrival and evaluated for protective capacity against histone toxicity employing an extracellular histone toxicity assay; and complement activity using a 50% hemolytic complement screening assay. Animals were retrospectively assigned to groups consisting of: calves not requiring treatment with antibiotics for BRD (NT; n = 80) or calves that died from BRD within 1 wk of entering the feedlot (DA; n = 9). Serum from DA animals was less (P < 0.001) protective than NT animals against histone toxicity. Complement activity of DA animals was reduced (P < 0.05) compared to NT animals. Using a ratio of both assays under stringent selection points, the positive predictive value was 75%, and negative predictive value was 94%. Results indicate that cattle predisposed to severe cases of respiratory have impaired complement activity presumably contributing to impaired protective capacity against histone toxicity. Analyzing these functional pathways may provide a novel selection tool against cattle predisposed to severe cases of BRD.