| Abstract: | Unvaccinated laying breeder hens and semen-producing toms were susceptible to the CU strain of Pasteurella multocida and highly susceptible to a virulent strain of P. multocida. Laying breeders vaccinated with CU strain when environmental temperatures were low ceased egg production during the first week after vaccination and had 29% mortality, whereas those vaccinated when temperatures were moderate had only a 25% decrease in egg production and 17% mortality. Comparable nonlaying breeders vaccinated during moderate temperatures did not die. Although few semen-producing toms died postvaccination and the quantity and quality of semen was not affected, 21.7% developed torticollis. Laying breeders were protected against CU vaccine and challenge with virulent P. multocida if vaccinated every 4 weeks beginning when 7 weeks old. Potential breeders vaccinated before laying with combinations of 3 vaccinations via drinking water, wing-web puncture, or inoculation into the air spaces of the head through the auditory tube were protected against challenge after the onset of laying. However, vaccination via wing-web puncture at 25 weeks of age resulted in abscesses that failed to resolve. The combination of vaccinations most effective in protecting laying breeders was vaccination in the drinking water at 7 and 11 weeks and inoculation into the air spaces of the head at 15 weeks. |
