Subcutaneous vaccination of chickens with a live, avirulent Pasteurella multocida, Vaccine

The immunogenic responses to various routes of vaccination of broiler-type chickens to the Clemson University strain of Pasteurella multocida were evaluated. Broilers were vaccinated at 9 or 10 weeks of age using the oral (drinking water), palatine cleft, ocular, or subcutaneous injection routes. All birds were challenged at 11 or 12 weeks of age with virulent X-73 strain of P. multocida by the palatine cleft method. The degree of efficacy of the various vaccination routes differed among three experiments. Nevertheless, the subcutaneous route produced the greatest degree of protection in all experiments and in two experiments differences were highly significant (P less than .01). Protection levels as high as 95% and 97.5% were attained in broilers vaccinated subcutaneously and no undesirable lesions or cheesy masses formed under the skin in the back of the necks of broilers.