Most nutritional research on various nutrient requirements for animals is carried out under strict sanitation and pathogen free state that can not be applicable in real field conditions. For this reason, the minimum nutrient requirements prescribed by various feeding standards (NRC, ARC, BIS) may not be relevant to on-farm conditions. The immune system must compete with production for nutrients. When the immune system is engaged in defense against a particular pathogen, its actual nutrients demand might be increased manifolds because of anabolic components of the immune system i.e. clonal proliferation of lymphocytes, production of immunoglobins, recruitment of new myloid cells, synthesis of mineral content enzymes and metallo-proteins, chaperones, hepatic secretion of acute phase proteins including complement components, thousands types of receptor proteins, transcription factors etc. Many effector mechanisms used by the immune system generate large amount of reactive oxygen intermediates. Nutrient antioxidants can successfully protect bio-molecules against damage from these reactive oxygen intermediates. For instance, vitamin E exerts its action on the immune system by lowering of the prostaglandin synthesis and by preventing the oxidation of PUFA in the cell membrane. Nutritional manipulation might affect not only the development of immune system but also the immune defense to pathogen.
