The high degree of commingling and accumulation of stressors during and after transport makes prevention of bovine respiratory disease (BRD) extremely challenging in the veal and dairy beef industry. Upon arrival, vaccination for agents involved in BRD is practically most achievable, but its efficacy under such conditions in dairy veal calves is unknown. Given the high prevalence of subclinical pneumonia in these settings, the primary objective of the present study was to determine the effect of 2 vaccination protocols administered upon arrival against bovine respiratory syncytial virus (BRSV), bovine parainfluenza type 3 virus (BPI-3), and Mannheimia haemolytica on clinical BRD and lung ultrasonographic findings in dairy veal calves. In addition, the effects of vaccination on average daily live weight gain and cold carcass weight were determined. In this randomized clinical trial, 443 male dairy calves were assigned to one of 3 groups: a negative, placebo-controlled group (n = 151), a vaccination group with 2 subcutaneous injections 4 wk apart with an inactivated vaccine containing BRSV, BPI-3, and M. haemolytica (parenteral [PE] group; n = 149) and a second vaccination group receiving an intranasal live-attenuated vaccine containing BRSV and BPI-3 and 2 subcutaneous vaccinations with the same inactivated vaccine as the PE vaccination group (intranasal-parenteral [IN-PE] group; n = 143). Clinical scoring and quick thoracic ultrasonography (qTUS) were performed on all calves on arrival (wk 0), at the peak of respiratory disease (outbreak; wk 1), at the end of the first antimicrobial group treatment (wk 3), and at a long-term evaluation point (wk 10). Culture and nanopore sequencing on nonendoscopic bronchoalveolar lavage (nBAL) samples were used to identify pathogens involved in the outbreak. Upon arrival, 15.1% of the calves had lung consolidation ≥1cm and incidence quickly rose to 42.8% during the outbreak. In both the PE and IN-PE group, the odds of pneumonia in wk 10 were reduced by 62% (odds ratio [OR] = 0.38; 95% confidence interval [CI] = 0.23-0.64) and 41% (OR = 0.59; 95% CI = 0.37-0.96), respectively. Short-term cure rate (50.3%), as determined immediately after the first group antimicrobial treatment, was not influenced by vaccination. In contrast, long-term cure rate, determined at wk 10, was affected by vaccination with higher cure in the PE group compared with the control group (69.4% vs. 51.2%; OR = 2.2; 95% CI = 1.1-5.0). Average daily gain in the first 10 wk of production was not affected by vaccination. Vaccination resulted in an increase in cold carcass weight of 3.5 and 4.3 kg in the PE (95% CI = -0.9-7.9) and IN-PE group (95% CI = -0.17-8.7), respectively. In conclusion, under the conditions of the present study, vaccination upon arrival resulted in a reduced prevalence of pneumonia at wk 10 of production, likely caused both by an improved cure rate of secondary infections and a reduced incidence of new cases between outbreak and long-term evaluation. The present protocol, using qTUS for pneumonia detection and nBAL diagnostics for pathogen identification adds a new dimension to randomized clinical trials on respiratory disease in calves.
Keywords: Mannheimia haemolytica; bovine respiratory disease; bovine respiratory syncytial virus; thoracic ultrasound; vaccination.
© 2023, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).