A COMPARISON OF THE IMMUNE PERFORMANCE OF A 1991 COMMERCIAL BROILER WITH A 1957 RANDOM-BRED STRAIN WHEN FED TYPICAL 1957 AND 1991 BROILER DIETS

The general objective of the present study was to assess the contribut ion that changes in genetic selection and dietary regimen have made on the immune performance of broilers. Chicks were hatched from 1991 and 1957 strains and placed on diets thought to be typical of those fed d uring 1957 and 1991. Immune responses were measured as total, IgM, and IgG antibody production, macrophage, and natural killer (NK) cell fun ctions. Significant differences were observed between strains in antib ody production. For example, 1957 males fed 1957 diets had the highest total (P < .0001), IgM (P < .0016), and IgG (P < .015) anti-sheep red blood cell antibodies as compared with all other strain-diet-sex grou ps. Both strains behaved similarly in terms of inflammatory macrophage recruitment, substrate adherence potential, and in the phagocytosis o f sheep red blood cells. A greater percentage of the 1991 strain birds exhibited NK cell activity than all other groups. These studies sugge st that genetic selection towards enhanced performance traits has nega tively influenced the adaptive arm of the immune system (antibody prod uction) with little or no effect on the nonadaptive components (macrop hage and NK functions).