Effects Of Chitosan On Growth Performance And Immune Function In Broilers And The Underlying Mechanisms

The present study was conducted to investigate the preparation of chitosan and study the effects of chitosan on the growth performance and immune function of broilers. The first experiment was about the preparation of chitosan with high degree of deacetylation (D.D.) in laboratory. The results showed that chitosan with above 85 % of D.D. could be prepared under the treatment conditions of 50% NaOH, 120℃ and more than 0.5 hours. Its molecular weight is 1.077 × 105 Da, and the other quantity technique indexes comes to the standards that some provinces and business enterprises draw up. The second experiment was conducted to study the effects of dietary chitosan (0, 0.02, 0.05, 0.10, 0.30 and 0.50%, respectively) and chlortetracycline (CTC, 50 mg/kg) on growth performance and immune functions in broilers. The results showed that the effects of chitosan on growth performance were related to the dose of chitosan added to the diet. ADG of broilers fed the diet supplemented with chitosan increased quadratically and their FCR decreased quadratically with increasing chitosan inclusion. At 0.05% level, chitosan gave the best ADG and FCR, but at 0.50% level, chitosan did not promote growth. There was no significant difference between the control and CTC treatment. Compared with the control and CTC, a diet containing 0.05 % chitosan tended to increase ADG of broilers. Along with the increment of the chitosan additive dose, various immunity parameters presented various degrees of linear or quadratic increasing tendency. A high level (0.50%) of chitosan raised obviously antibody titer of Newcastle disease in broilers. strengthenning the humoral immunity function. Phagocytic index, lymphocyte proliferation, spleen index and thymus index were also enhanced to some extent by dietary chitosan. In addition, on d 28, 0.05% dietary chitosan suppressed proliferation of E. coli in caecum ingesta of broilers compared with the control. and 0.05%~0.50% dietary chitosan improved proliferation of Lactobacill compared with CTC. The third experiment was conducted to study nutrient metabolism in broilers fed diets containing graded levels of chitosan. The results indicated that addition of 0.05% chitosan enhanced nitrogen retention and utilization efficiency compared with the control treatment, while apparent metabolisable energy was unaffected. In addition, addition of 0.50% chitosan decreased the metabolism rate of fat and calcium in diets. The fourth experiment was conducted to study alleviating action of chitosan on immune stress induced by LPS injection in broilers. The results indicated that dietary chitosan could, to some extent, inhibit declining of growth performance and rising of stress hormones in broilers injected LPS, and enhance lymphocyte proliferation, showing some degree of alleviating action on immune stress. The fifth experiment was conducted in vitro to study the effects of chitosan level (0, 40, 80, 160 and 320 u g/mL) on immune function and signal molecules of spleen lymphocyte in broilers. The results showed that along with the increment of the chitosan additive dose, lymphocyte proliferation and IL-2 bioactivity increased quadratically, and NO and iNOS production increased linearly or quadratically. In addition, chitosan influenced cAMP and cGMP production and the ratio of cAMP/cGMP. These results suggested that iramunomodulatory effects of chitosan on broilers were related to alteration of intracellular signal transduction.