Inflammation is the body's response to injury and is characterized by pain, swelling, redness, and heat. Eicosanoids are lipid mediators of inflammation. Leukotrienes (LT) are 20-carbon eicosanoids produced from arachidonic acid (AA), an n-6 fatty acid (FA), and eicosapentaenoic acid (EPA), an n-3 FA. LT produced from AA are proinflammatory (LTB₄) and those produced from EPA (LTB₅) are less inflammatory. Two experiments were conducted. The objective of the first experiment was to optimize the assay conditions for LT production by platelets from chickens, and neutrophils from horses and dogs. Optimal production of LT from equine and canine neutrophils and chicken platelets was characterized in terms of incubation time (2.5, 5, 10, 15 or 20 minutes), temperature (25 or 37°C), and calcium ionophore A23187 concentration (0.1, 1, 10 or 20 μM). In all species, incubation at 37°C resulted in optimal LTB₄ production compared to 25°C (p≤0.05). Production of LTB₄ was maximum when neutrophils were stimulated with 20 μM calcium ionophore A23187 in all species (p≤0.05). Incubation times greater than 2.5 minutes did not further increase LTB₄ production in chickens and horses; in dogs, incubation for 2.5 and 10 minutes resulted in the highest concentrations of LTB₄ (p≤0.05). These results indicate that platelets from chickens, and neutrophils from horses and dogs, are capable of producing LTB₄; optimum conditions for LTB₄ production are similar in all three species. In the second study, the effect of feeding diets that differed in n-6 and n-3 FA ratios to breeder hens was investigated with regard to changes in composition of immune tissue, alteration of delayed-type-hypersensitivity (DTH) response, and LT production by platelets. Chicks hatched to hens fed these diets were also studied with regard to fatty acid composition of immune tissues and LT production by platelets at various stages of growth (7, 14, 21 days). A total of 72 breeder hens were randomly divided into three groups (n=24) and fed diets supplemented with either 3.0% (by weight) sunflower oil (SF0; rich in n-6 FA; Diet I), a mixture of 1.5% SF0 and 1.5% fish oil (Diet II), or 3.0% fish oil (FO; rich in n-3 FA; Diet III). Production of LTB₄ and LTB₅ by platelets stimulated with calcium ionophore A23187 were assessed by RP-HPLC. The hens fed Diet I synthesized 43.9 ± 2.5 ng of LTB₄ per 5x10⁶ cells compared to 13.3 ± 0.9 ng of LTB₄ from hens fed Diet II (p≤0.05). However, no LTB₄ was produced by hens fed Diet III. Production of LTB₅ by platelets of hens fed Diet III was 36.7 ± 4.9 ng compared to 47.4 ± 5.7 ng of LTB₅ from hens fed Diet II. No LTB₅ was produced by hens fed Diet I. The DTH reaction was smaller at 48 hrs post injection of bovine serum albumin in hens fed the 3% FO Diet III (p≤0.05). Fatty acid composition spleen and platelets in hens reflected the fatty acid composition of diets consumed by them (p≤0.05). Hatched chicks from hens fed Diet I produced significantly less LTB₄ at 14 days (p≤0.05) compared to 7- and 21-day-old chicks, which were not different from each other. Chicks from hens fed Diet II produced more LTB₄ at 21 days (p≤0.05) compared chicks from hens fed Diet III produced more LTB₄ at 7 and 21 days (p≤0.05) compared to 14-day-old chicks. There were no significant differences in LTB₅ production from chicks hatched to hens fed Diet III at 7 and 14 days of growth. By 21 days of growth, chicks hatched to hens fed Diet III showed decreased production of LTB₅ compared to 7- and 14-day-old chicks. The spleen and bursa tissue fatty acid composition in chicks at 7 and 14 days of age were similar to the maternal diet fatty acid composition, however, there were no significant differences in platelet fatty acid composition between the groups at different stages of growth. These results indicate that the type of fat in diets fed to breeder hens may alter the inflammatory response in hatched chicks, which could lead to less mortality and increased production performance in poultry. / Graduation date: 2005