Abstract
Bovine Respiratory Disease (BRD) complex remains the leading cause of morbidity, mortality, and economic loss in intensive beef feedlot operations worldwide. Despite widespread use of commercial multivalent vaccines, field efficacy is frequently challenged by herd-specific antigenic variation and suboptimal cross-protection against circulating field strains of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. This randomized controlled field trial evaluated the efficacy of a farm-specific autogenous bacterin-toxoid vaccine compared with a conventional commercial bacterin-toxoid in mitigating BRD incidence and severity. A cohort of 800 newly arrived crossbred steer calves (mean initial body weight: 242 ± 14 kg) was randomly allocated to receive either an autogenous bacterin-toxoid formulation (AV; n = 400) or a standard commercial vaccine (CV; n = 400) upon arrival, with booster doses administered on day 14. Over a 60-day feeding trial, calves receiving the autogenous preparation exhibited a significantly lower cumulative BRD incidence (14.2% vs. 24.8%; p < 0.001) and a reduced treatment relapse rate (12.3% vs. 28.3%; p = 0.018). Furthermore, the AV cohort demonstrated a 34.6% reduction in total therapeutic antimicrobial usage and achieved a higher average daily gain across the receiving phase (1.38 kg/day vs. 1.26 kg/day; p = 0.012). Post-slaughter thoracic evaluations revealed significantly lower macroscopic lung lesion consolidation scores in autogenous-vaccinated steers. These findings indicate that integrating herd-specific autogenous bacterin-toxoids into arrival processing regimens provides superior immunoprotection against local pathogenic isolates, presenting a viable intervention for improving animal welfare and advancing antimicrobial stewardship in intensive beef production systems.
