comparison of two multivalent modified live viral/bacterial combination vaccines in feedlot calves at ultra-high risk of developing undifferentiated fever/bovine respiratory disease

Vaccine 1 (VAC1 group) and Vaccine 2 (VAC2 group) are com­mercially available vaccines labeled for the control of bovine respiratory disease (BRD) in beef cattle. There are limited data from large-scale commercial feedlot trials comparing VAC1 and VAC2 arrival processing vaccination pro­grams. The objective of this study was to evaluate the relative effects of VAC1 and VAC2 arrival processing vacci­nation programs on animal health, feedlot performance and carcass characteristic outcomes in feedlot calves at ultra-high risk of developing undifferentiated fever/BRD under large-scale commercial production conditions. Animals were randomly allocated at feedlot arrival to 1 of 2 experimental groups: VAC1 or VAC2. Animals in the VAC1 group (6 multi-pen lots; 3,001 animals) received a bovine rhinotracheitis-virus diarrhea-parainfluenza 3-respiratory syncytial virus-Mannheimia hae­molytica-Pasteurella multocida vaccine per animal once at allocation. Animals in the VAC2 group (6 multi-pen lots; 3,005 animals) received a bovine rhinotracheitis-virus diarrhea-parainfluenza 3-respiratory syncytial virus vaccine with a Mannheimia haemolytica toxoid per animal once at allocation. Vaccines differed regarding viral strains, bacterial protection, means for providing bacterial immunity, and adjuvant use. Animals were housed by experi­mental group in commercial feedlot pens and followed from allocation until slaughter. Although histophilosis mortality was higher in the VAC1 group compared to the VAC2 group (P = 0.040), no statistical differences were detected in overall mor­tality or any of the other outcome variables (P ≥ 0.050). The relative cost effectiveness of each arrival processing vaccina­tion program in the study population is therefore dependent on relative program cost.