Enhancing Herd Immunity: The Indirect Immune Effects of the M. bovis-BoHV-1 Combined Vaccine

Abstract

Bovine respiratory disease (BRD) is a complex illness driven by the interplay of various bacteria and viruses, often resulting in co-infection. It stands as one of the most significant and costly challenges in the cattle industry. The development of vaccines targeting BRD pathogens has garnered substantial attention, particularly for their ability to induce indirect immune protection in unvaccinated animals through the immune effects of vaccinated individuals. In this study, we comprehensively evaluated the indirect immune effect of our developed attenuated and marker Mycoplasma bovis-BoHV-1 combined vaccine. Our results demonstrated that the combined vaccine effectively activates the innate immune response in animals cohabitating with immunized individuals. This was evidenced by a significant increase in serum lysozyme levels, blood lymphocyte counts, and elevated cytokine levels. Furthermore, these cohabitating animals exhibited effective activation of the humoral immune response, as indicated by the elevated levels of specific antibodies against various pathogens. Notably, M. bovis serum ELISA antibodies and BoHV-1 neutralizing antibodies in all calves from the co-housing group turned positive by the second week, exceeding the threshold values of 41% and 1:8, respectively. In addition, serum levels of total IgA and IgG antibodies were significantly elevated compared to the blank control group. In conclusion, the attenuated and marker M. bovis-BoHV-1 combined vaccine we developed shows a notable indirect immune effect, which is essential for controlling the spread of infection and enhancing calf survival. This study greatly facilitated the sustainable growth of the cattle industry.