Immune responses in poultry can be influenced by genetic background, nutrition, environment and management, or any combination of the above. Chicken heterophils are the first line of defense that can launch a series of intra- and extracellular antimicrobial mechanisms. Salmonella enterica serovar Enteritidis (SE) is a causative agent of a bacterial foodborne illness, commonly occurring after consumption of contaminated eggs and meat. In 2008, SE affected 3 out of 100,000 U.S. inhabitants on average and it is now receiving increased public awareness. The limited scope of current knowledge about basis for the difference in heterophil responses during and after exposure to immunomodulators prompted the study of heterophil defense mechanisms against Salmonella enterica serovar Enteritidis (SE) infection in three genetically distinct chicken lines (Leghorn, broiler and Fayoumi) supplemented with dietary immunomodulators (β-glucan, ascorbic acid and corticosterone).

We hypothesize that heterophil function in three genetic chicken lines during exposure to dietary immunomodulators and challenge with SE will be significantly different. To test the hypothesis, we have isolated blood heterophils from three diverse chicken genetic lines; [outbred broiler and two highly inbred layer lines (Leghorn and Fayoumi)] that were fed diet supplemented with immunomodulators (β-glucan, ascorbic acid and cortisol) and challenged with SE. We used heterophil extracellular trap release (HETs, phagocytosis, bacterial killing and oxidative burst to determine heterophil function differences from different treatment groups.

The emphasis of this dissertation was on the role of genetic background and dietary immunomodulators on chicken heterophil function in order to prevent and control SE colonization and shedding, using selected breeds of chickens. First, the baseline heterophil function was monitored in vitro using oxidative burst, phagocytosis and bacterial killing to study intracellular killing mechanisms. Additionally, HETs-DNA release has been for the first time described in avian species and used to explore a potential role of extracellular heterophil killing. We compared the responses of different chicken lines with dietary immunomodulatory effects when exposed to SE challenge. In vivo heterophil function and bacterial clearance by bacterial cultures were evaluated in both challenged and non challenged chickens.

The responses of chicken heterophils to dietary immunomodulators and SE challenge were significantly influenced by genetic background, and dietary immunomodulators have significant effect on heterophil function in both non-challenged and challenged chickens. Increased SE clearance in challenged birds that were fed with supplemented diet was also observed. This dissertation provides evidence of the significant role of the genetic background of chicken innate immune system and it's responses to dietary immunomodulation and disease challenge. The results of the studies presented in this dissertation support the use of dietary immunomodulators to manipulate heterophil function in chickens from the same genetic background. The modification of the immune system of chickens with targeted genetic selection and diet supplementation in production settings can lead to improved SE (disease) resistance and reduced risk of food borne illnesses.