Vaccination of young turkeys against fowl cholera.

Turkey poults vaccinated at one day of age with commercial inactivated Pasteurella multocida (PM) bacterin responded with low titres of antibody (ab) as measured by ELISA, but had an acceptable degree of resistance when challenged with the X-73 strain of PM until 13 weeks of age. Turkeys vaccinated at 3 and/or 6 weeks of age responded with higher ab titres and were resistant to virulent challenge with PM. Turkey poults vaccinated at 3 and/or 6 weeks of age with a commercial live PM vaccine had a poor immune response and low resistance to virulent challenge. When live PM vaccine was given to turkey poults previously vaccinated with an oil-emulsion PM bacterin, the turkey poults were highly resistant to virulent challenge, although the booster vaccination did not always induce a significant increase in the ab titres. The ELISA test used did not appear to be adequate for evaluation of the degree of protection induced in turkey flocks vaccinated at a very young age.