Abstract
The effects of various treatments on the immune response of chickens to vaccine prepared from Pasteurella multocida strain P1059 were investigated. The treatments, given on or before the day of hatching, consisted of surgical bursectomy (SB), hormonal bursectomy (HB), surgical thymectomy (ST) and X-irradiation (X). In chickens subjected to SB, SBX or HB before vaccination, the production of agglutinin and immunoglobulin was impaired, but the production of resistance against challenge was not. In chickens subjected to ST or STX before vaccination, the production of agglutinin and immunoglobulin was unimpaired, but the production of resistance against challenge was diminished. Protection was therefore thymus-dependent.