Modulation Of Immune Responses And The Underlying Mechanisms Of Dietary Conjugated Linoleic Acid In Broiler Chickens

Six trials were conducted to study the effects of dietary CLA on immune responses, anti-oxidation capability, lipid metabolism and meat quality of broiler chickens. Furthermore, lymphocyte signal transduction, eicosanoid metabolism and transcription factor mRNA gene expression were examined to discuss the mechanism of CLA on immune functions in broiler chickens.Trial 1 was used to study the effects of dietary CLA on growth performance, lipid metabolism, carcass composition and meat quality in broiler chicks. Growth performance and lipid metabolism were not affected by CLA. Proportions of breast muscle to live body weight were significantly (P<0.05) elevated in chicks fed 0.5, 1% CLA diets. Chicks fed 1% CLA diet had significantly increased (P<0.05) proportions of leg muscle to live body weight. Abdominal fat depositions were not different among treatments. Ratios of protein to fat in breast muscle were significantly (P<0.05) increased in chicks fed 1% CLA diet compared with chicks given control diet. Drip loss and malondialdehyde (MDA) content during cold storage were decreased in breast muscle from chicks fed 0.5 and 1% CLA diets.Trial 2 was conducted to assess the effects of CLA on antioxidant defense system in broiler chicks. After 42 days' CLA intake, the activities of total superoxide dismutase (T-SOD) in liver, serum and muscle were substantially (P<0.05) increased in chicks fed 1 % CLA diet. The activities of catalase in liver were significantly (P<0.05) higher in chicks fed 1% CLA diet compared with chicks fed control diet.Serum MDA levels were significantly (P<0.05) decreased in chicks fed CLA diets. Muscle MDA levels in chicks fed 0.5 and 1% CLA diets were significantly (P<0.05) lower than those fed control diet. For chicks exposed to endtoxin, 1 % dietary CLA supplementation remarkabley (P<0.05) prevented the increase of serum ceruplasmin and MDA. CLA partially prevented (P<0.10) the decrease of serum T-SOD activity. These results suggest that feeding CLA enhance the activities of antioxidant enzyme including SOD and catalase and may be beneficial for chicks to maintain health status.In trial 3, the effects of dietary CLA on immune response of broiler chicks were studied. Chicks fed 1% CLA diet produced more lysozyme at age of 21 d compared with the control group (P<0.05). Lymphocyte proliferation of peripheral blood to Con A were significantly enhanced and prostaglandin E₂ (PGE₂) production were decreased in chicks fed 1% CLA diet. Antibody production to Newcastle Disease Virus (NDV) was not affected by dietary CLA. Antibody titers to Brucella Abortus (BA) were significantly (P<0.05) higher in chicks fed 0.5 and 1% CLA diets compared with chicks fed control diet. Results indicated that CLA could be beneficial to innate and adaptive immune responses in chicks.Trial 4 was carried out to study the effects of dietary CLA on T cell subsets and intracellular signal transduction of peripheral blood lymphocyte. Chick fed CLA diets had significantly (P<0.05) enhancedproliferation responses to Concanavalin A (Con A) and interleukin-2 (IL-2) secretion. CLA significantly (P<0.05) increased pheripheral blood CD3⁺ and CD8⁺ T cells at age of 42 d. Free calcium concentrations was remarkably (P<0.05) increased by 1% CLA at age of 21 d. CLA (P<0.05)significantly enhanced calcium concentration at age of 42 d. Nitric oxide (NO) production in chicks fed 1% CLA diet were significantly (P<0.05) lowered at age of 42 d. Chicks fed 1% CLA diet had significantly (P<0.05) higher cyclic guanosine monophosphate (cGMP) at age of 21 d. At age of 42 d, CLA enhanced cGMP concentration and cyclic adenosine monophosphate (cAMP) concentration and ratios of cAMP/cGMP were significantly (P<0.05) decreased in chicks fed 1% CLA diet. The results showed that dietary CLA enhanced CD3⁺ and CD8⁺ T cells at age of 42 d. CLA enhanced lymphocyte proliferation and IL-2 secretion due to induction of cell free calcium and cGMP production.In trial 5, the effects of dietary CLA on spleen fatty acids composition, cyclooxygenase (COX) activities and PGE₂...