Response of two lines of turkeys to challenge with Pasteurella multocida

Two lines of turkeys were challenged with Pasteurella multocida during three trials. The two lines were 1) a randombred control line (RBC1), and 2) a subline (E) of Line RBC1 selected for increased egg production. Each trial differed as to the age at which poults were challenged. In Trial 1, unvaccinated birds were subcutaneously inoculated with P. multocida at 6 wk of age. In Trial 2, poults vaccinated (on the back of the neck) at 7 and 9 wk of age with .5 mL of P. multocida bacterin and unvaccinated poults were challenged at 11 wk of age. Trial 3 was similar to Trial 2, except that poults were vaccinated at 8 and 10 wk of age and challenged at 12 wk of age. Line E had significantly (P less than .05) higher mortality than Line RBC1 (66.7 vs. 31.8%) in Trial 1. In Trials 2 and 3, unvaccinated birds of Line E had higher mortality than unvaccinated birds of Line RBC1; however, differences between lines were not significant in either trial. Significantly lower levels of mortality were observed for vaccinated poults than for unvaccinated poults in the second and third trials, where birds were vaccinated and challenged at older ages.