Effects of vaccination and interventions on nasal microbiome and BRD-associated pathogens in calves

Vaccination is a widely adopted measure to prevent diseases, but the process of immunization can induce a substantial stress response. This study aimed to investigate the impact of a combined <i>Mycoplasma bovis</i>-BoHV-1 vaccine on the upper respiratory tract microbiome and BRD-associated pathogens in calves, as well as to evaluate the effects of potential interventions. The results showed that the percentage of <i>Pasteurella</i> species in the upper respiratory tract was elevated in calves after vaccination without intervention, and <i>Pasteurella multocida</i> was activated and proliferated. Interestingly, none of the three interventions (Sodium selenite-vitamin E, Astragalus polysaccharide and Ceftiofur sodium) affected antibody production after immunization. The administration of sodium selenite-vitamin E and astragalus polysaccharide reduced serum levels of cortisol and malondialdehyde, increased glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), and alleviated the proliferation of <i>Pasteurella multocida</i>. Furthermore, the use of ceftiofur sodium almost completely inhibited the proliferation of <i>Pasteurella multocida</i> induced by immune stress. These findings provide a reference for mitigating the negative impacts associated with vaccination and highlight the potential benefits of using targeted nutritional and antimicrobial interventions to optimize immune responses and maintain a stable respiratory microbiome in calves.