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Nutrition and immunomodulation Part 2
Nutrition and immunomodulation
A receptor for 1,25-dihydroxy vitamin D3 is present in peripheral mococytes. Vitamin D3 is necessary for the differentiation of pro-monocytes to macrophages and the proper phagocityc and cytotoxic activity of the marophages. CMI decreased significantly in broiler chicks fe diets without any supplemental vitamin D3.
Tocopherol and selenium
The immune system stimulated by infection or vaccination-especially under stress conditions-is prone to damage by peroxides and superoxides. Vitamin E and selenium protect the immune system under this situation. Vitamin E also enhances humoral immunity by favourably altering the proliferation and ratio of T-helper cells. Selenium in glutathione peroxidase together with vitamin E acts as an antioxidant and reduces the concentration of free radical in cells. Vitamin E and selenium play important roles in lymphocyte blastogenesi. Deficiency of these nutrients reduces the phagocytic activity of the macrophages.
The NCR recommendation for vitamin E (at 20mg/kg) is way below the level of 300mg/Kg that has been shown to increase the immune response and decrease mortality to E.coli, newcastle disease, infectious bursal disease and coccidiosis. Increasing vitamin E supplementation to 250mg/Kg was reported to prevent a drop in egg production in layer exposed to heat stress. The benefical role of higher levels (up to 300mg/kg) of vitamin E on immunity is mediated through increasing the maturation of T-cells. The same high level of vitamin E reduced the lymphoid organ levels of prostaglandins, which cause suppression of CMI, and thus improved antibody production. Both humoral and CMI response in immunised chicken increased significantly with supplemental vitamin E alone (200 vs 80mg/kg) or in combination with selenium (300mg/kg vitamin E and 1mg/kg selenium). Supplementation of vitamin E (0.03%) in a breeder diet or by injection (2.5-30.0mg/egg) to fertile eggs was reported to increase the immune response of chicks. Similiarly, incorporation of vitamin Ein oil adjuvant vaccines (Newcastle disease and infectious bursal disease) included more rapid and higher antibody titres than controls.
The synthesis of vitamin C in inadequate in newly hatched chickens and in adult birds subjected to severe stress. Vitamin C enhance both humoral (SRBC and Newcastle disease) and CMI responses and increases the resistance of birs to E.coli, Mycobacteirum avium, Newcastle disease, infectious bursal disease, Marek’s disease etc. Vitamin C, through its antioxidant properties, maintains the stability of leukocyte membranes. It is also essential for the optimum functioning of neutrophils/granulocyte and thereby, it enhances the phagocytic activity of the neutrophils. Vitamin C protects birds under heat stress by reducing the synthesis of glucocorticoids. The immune suppression caused by corticosterone and thermal stress was minimised by vitamin C supplementation (0.1%) in chickens. Variaton in the beneficial effects of vitamin C supplementation has been attributed to the poor stability of the vitamin in some forms under poor but practical storage conditions.
Vitamin B complex
B-complex vitamins play an important role in intermediate cell metabolism as co-factors for several enzymes involved in various metabolic reactions. Among the B-complex vitamins, vitamin B6 is has been widely studied for its effect on immunity. It is important in the development and maintenance of lymphoid tissue. Deficiency of vitamin B6 (0.95 and 1.48mg/kg) reduced the antibody response to SRBC and the production of IgG and IgM. Under conditions of heat stress, the adminstration of vitamin B2, B6 and B12 has had positive effect of chicken immunity.
Certain minerals play an important role in immunomodulation through their effect on osmoregulation and by acting as co-factors and enxymatic catalysts and also by optimising hormone function. Dietary concentrations of sodium (Na), chloride (Cl), zinc (Zn), Copper (Cu), Iron (Fe), manganese (Mn), selenium (Se) and Cobalt (Co) have all been shown to influence immune response. Generally, the inorganic forms of the minerals are less well absorbed than the organic/chelated form. Therefore, a higher immune response has been observed when chelated minerals are supplemented in the diet.
Sodium and chloried
Na and Cl in additon to potassium (K) play a key role in maintaining osmotic balance in extra and intra cellular fluids. During salt dificiency, chickens retain Na and Cl in the plasma, constituents, which may result in decreased immune response in birds fed low Na and K diets. Gengerally, antibody titres increased with higher levels of Na (0.14%) or Cl (0.21%) in the diet. The humoral response decreased with less than 0.14% Na and 0.17% Cl. Supplementary salt (NaCl; 0.25, 0.50 and 0.75%) improved antibody titres against SRBC. However, excessive levels of Cl (0.25 and 0.36%) reduced the antibody response even at a higher Na level in the diet (0.24 or 0.40%). Increasing Cl as an immunomodulator under conditions of heat stress should be used only with great care.
The role of Zn on immunity is mediated through increasing the thymocyte and perpheral T-cell count; the activity of natural killer cells (NKC) and neutrophils; macrophage production and antibody production; production of interferon; and reducing viral penetration. Zn is also required for the proper functioning of thymulin, which is involved in lymphocyte development, and metalloenzymes, e.g. DNA and RNA polymerases. Deficiency of Zn impairs interleukin-2 production, which plays a role in CMI, as well as through its role in maintaining the integrity of the lymphoid organs and T-cell function. A Zn deficiency in a breeder diet decreases antibody titres to SRBC in their offspring. Conversely, the antibody response increased significantly in the progeny was Zn was supplemented in the breeder diet (38-160mg/kg). A few studies have indicated no significant benefits of supplementing Zn up to 220mg/kg diet of breeders on humoral immunity or CMI. The concentration of Zn and other trace minerals in the basal diets used in the trials.
Supplementation of Zn in the form of a methionine chelate to a breeder diet was more beneficial in the development of immune system organs and increasing antibody titres to SRBC and CMI in the progeny and specific antigens, e.g Salmonella enteritidis, E.coli, in the parents.
Mn plays an important role in the development, repair and maintenance of epithelial tissues. Mn dependent super oxide dismutase (SODM), present in the mitochondria, inactivates free radicals produced whitin the cell. Organic forms of this mineral hel to reduce the incidence of cellulitis and increase the antibody response to infectious bursal disease, infectious bronchitis and Newcastle disease virus in breeders.
During the acute phase pf an immune response, liver cells produce and secrete APP, which gives protection to birds against infection. Ceruloplasmin is one significant APP in chickens, and it needs Cu as a co-factor. Ceruloplasmin protects the bird by removing the free radicals produced during phagocytosis. Thus, the Cu requirement increases during infection. Cu and Zn dependent SODM in the cytosol inactivates the free radicals. Generally, the requirement for Cu by chicks is higher when they are experiencing an acute phase response than when they are healthy. To increase bird health and well being, additional levels of Cu (125-250mg/kg) can be supplemented to the diet. Cupric chloride is more effective in enhancing intestinal health and acting as an atnimicrobial agent against E.coli and salmonella than copper sulphate. Providing Cu in a chelated form with amino acid is said to offer promise.
The role of Fe in immunity can be appreciated by the sudden fall in Fe concentratrin in the serum during the arly phase of infection. Fe supplementation has been shown to increase the batericidal activity of the macrophages in the liver and spleen of affected chicks. The survival rate increased in chicks inoculated with salmonella gallinarum with additional supplementation of 100mg/kg Fe in diets containing 200mg/kg Fe.
The beneficial effects of cobalt on immunity have been attributed to it positive effects on protein synthesis and the fucntion of the lymphoid organs. Supplementary feeding of 0.1 or 0.5mcg/kg bodyweight enhanced the host defence function against infection or Newcastle disease vaccination in broiler chickens. (Project Directorate on poultry)