Immunologic response to turkey poults of various ages to an avirulent Pasteurella multocida vaccine in the drinking water.

Fowl cholera has been reported in turkey poults in South Carolina between 5 and 6 weeks of age. An experiment was conducted to determine the earliest age that poults could be vaccinated with the Clemson University Pasteurella multocida strain (using the drinking water route) that would result in an effective immunity at 5 to 6 weeks of age. In group of vaccinates challenged with a virulent P. multocida (P-1059 strain) at 5 weeks of age, none were infected in groups vaccinated at either 20 days or at 25 days, 1 of 10 vaccinated at 15 days, 3 of 10 vaccinated at 10 days, 6 of 10 vaccinated at 5 days, and 8 of 10 became infected of those vaccinated at 1 day of age. Eight of 10 of each of 2 group of nonvaccinates developed evidence of infection. In groups of vaccinated challenged at 12 weeks of age, 2 of 10 turkeys became infected that had been vaccinated at 25 days of age, 4 of 10 that had been vaccinated at 20 days, 8 of 10 vaccinated at 15 days, 8 of 10 vaccinated at 10 days, 8 of 9 vaccinated at 5 days, and 8 of 9 became infected of those vaccinated at 1 day of age. All 10 of one group of nonvaccinates and all 9 of a second group developed evidence of infection. These results suggest, under the conditions of this experiment, the turkey poults vaccinated at 35 days of age and poults vaccinated at 20 days of age experienced an excellent immunological respone by 5 weeks of age. This response was less evident but, for the most part, still present, at 12 weeks of age.