Vaccination of chickens through the drinking water with a live, Pasteurella multocida, vaccine

Broiler-type chickens were vaccinated orally at several ages with various dilutions of the Clemson University (CU) strain of Pasteurella multocida vaccine and then challenged orally with virulent strain P-1059 or strain X-73 of P. multocida to determine the degree of protection produced by vaccination. When vaccinated at 8 and 12 weeks of age for 2 consecutive days with a 1:133 dilution of the vaccine and then challenged at 17 and 19 weeks of age with strain X-73 and P-1059 P. multocida, respectively, no significant levels of protection were elicited in the vaccinates. Significant levels of protection were elicited in the vaccinates for 2 consecutive days at 9 weeks and at 13 weeks with 1:133 and 1:50 dilutions of the vaccine respectively, and then challenged at 16 weeks with strain X-73 and at 20 weeks with strain P-1059. Broilers vaccinated at 12 and 16 weeks for 3 consecutive days and then challenged at 20 weeks with strain X-73 showed a highly significant level of protection upon challenge when compared to the controls.