Formaldehyde would probably prevent M. bovis from being pathogenic...by killing it.

http://www.cdc.gov/hicpac/disinfection_sterilization/7_0formaldehyde.html

"The aqueous solution is a bactericide, tuberculocide, fungicide, virucide and sporicide"

But during the preparation of vaccines for tuberculosis scientists do not use formalin(may be never tried). They usually follow different method, like growing the bacterium in low nutrients containing medium.