Effect of infectious stunting syndrome on the immunocompetence of broilers

Immune responses and liveweights of broilers affected with the stunting syndrome (group C) were compared with those of unaffected birds from the same premises (group B) and normal control broilers of the same genetic origin (group A). Measurements of cell-mediated immunity were made using the phytohaemagglutinin (PHA) intradermal test and those of humoral immunity by antibody response to sheep red blood cells. Weekly observations were made of birds aged from two to eight weeks. Throughout the investigation the weekly mean weight of affected birds was very significantly lighter (P less than 0.001) than that of unaffected and control birds. From the second to the sixth week, wing web PHA reactions in group C were very significantly less than those in groups B or A (P less than 0.001), and during the seventh and eighth week wattle PHA reactions were significantly less in group C than those in group B (P less than 0.02). No significant differences were detected between the three groups in humoral immunity; the complete, IgG and IgM, antibody levels being closely similar. The significance and possible practical applications of these findings are discussed.