Immunity to Pasteurella multocida in Protein-Deficient Chickens

Abstract

Studies were conducted to determine the effects of dietary protein restriction on the humoral immunity (HI) and cell-mediated immunity (CMT) of chickens. New Hampshire chickens were separated into two dietaiy treatment groups: basal, containing 3,200 kcal/kg and 21% protein; or protein restricted (PR), containing 3,200 kcal/kg and 7% protein. In studies involving HI, half of the birds in each dietary treatment were vaccinated against fowl cholera at 4 and 8 wk of age. Blood samples were collected weekly beginning at 4 wk of age. Overall, unvaccinated birds had lower titers than vaccinated birds and PR groups generally showed lower titers than basal groups. All birds were challenged by palatine cleft inoculation of live, virulent Strain X-73 of Pasteurella multocida. The vaccinated PR group survived live challenge as well as the vaccinated basal group, but all unvaccinated birds died as a result of the challenge, regardless of antibody titer.In studies involving CMI, half of the birds in each dietary treatment were vaccinated at 5 wk of age. At 2 to 3 wk postvaccination, representative birds from each treatment were bled for total and differential blood counts. Also, birds were sacrificed and spleen cells collected. Cells were cultured in Roswell Park Memorial Institute (RPMI) medium with phytohemagglutinin-M (PHA-M), sonicated P. multocida (X-73), or RPMI only. The PR birds had significantly decreased numbers of lymphocytes, as well as an overall decrease in total white blood cell counts. Within dietary treatments, vaccinated birds tended to have higher numbers of white blood cells, but (he differences were only significant for the PR groups in Experiment 4. The PR diet suppressed proliferation of splenic cells stimulated with PHA-M, and vaccination significantly increased lymphocyte proliferation in response to sonicated P. multocida, Strain X-73.