Single-dose Pasteurella multocida and Histophilus somni autogenous vaccines administered at induction significantly improved feedlot cattle performance and profitability in Australia.

Background: Bovine respiratory disease (BRD) is the most economically important disease affecting feedlot cattle. While viral pathogens are initiating agents, bacterial coinfections exacerbate disease severity. Vaccines for Pasteurella multocida and Histophilus somni are not commercially available in Australia.

Methods: This trial evaluated the efficacy of a single-dose autogenous vaccine targeting P. multocida and H. somni, administered intramuscularly at induction, on carcase characteristics, feed conversion efficiency and health performance in feedlot cattle.

Results: Vaccinated cattle showed a 6.20% lower prevalence of subclinical BRD than controls (16.50% vs. 22.70%), corresponding to a 27.31% lower likelihood of subclinical BRD with vaccination. Vaccinated cattle exhibited improved performance, with a 2.86% increase in average daily gain, a 0.50% increase in hot standard carcase weight, a 0.81% increase in loin eye muscle area and a 2.68% increase in dry matter intake compared with controls. Vaccinated cattle showed lower odds of lung consolidation compared with controls (odds ratio [OR] = 0.73), indicating a 27.00% reduction in the likelihood of consolidation. Similarly, vaccinated cattle showed a 35.50% reduction in pleurisy scores relative to controls (OR = 0.65). Despite slightly higher feedlot costs, vaccinated cattle achieved a higher total end value and higher gross profit margins with a cost-benefit ratio of 6.95.

Conclusions: Given the overall reduced BRD incidence during the study period, the observed results may be influenced by pathogen prevalence, vaccine dosage, timing, route of administration and environmental factors. While the single-dose vaccine improved subclinical disease outcomes and growth performance, further studies, including a two-dose vaccine trial, are required to assess the full potential of the anamnestic immune response.