Immunity to Mycoplasma bovis infections of the respiratory tract of calves

Calves were inoculated intramuscularly with formalin killed Mycoplasma bovis with adjuvant and after 14 days intratracheally with killed organisms without adjuvant. Seven days later they were challenged intratracheally and 21 days after challenge they were found to have significantly fewer M bovis in their lungs than control calves. Two intramuscular or two intratracheal inoculations of killed M bovis were not found to induce resistance but immunity could be stimulated by three subcutaneous inoculations of inactivated mycoplasmas with adjuvant. Immunity was correlated with antibody detectable in lung washings by the single radial haemolysis technique. Combined intramuscular and intratracheal administration of killed M bovis induced a better antibody response in lung washings than two intramuscular or two intratracheal inoculations. Antibody was also detected in lung washings from calves inoculated three times subcutaneously but in this case it was thought to be derived from serum. The antibody detected in lung washings by single radial haemolysis was found to be IgG by radioimmunoassay.