Nanoparticles of Selenium with Stronger Physiological Effects presence of stress, etc. [42]. Another conclusion that has been obtained about the effect of selenium on blood cells is increasing the number of the cells (WBCs and neutrophils) and maintaining them in a high level for a longer period of time, so that nano-selenium has affected more severely than sodium selenite. The cause is the role of selenium as an anti oxidant and its ability to take care of body cells against antioxidative damages [27]. The researchers know selenium deficiency is an effective factor on the reduction of the lymphocyte reproductive potency and mention that the importing receptor of transferrin (which is effective in the reproduction of lymphocytes) will be reduced in the animals having selenium deficiency [43]. So, the researchers believe that selenium deficiency results in the weakness of immunity system by preventing the lymphocytes reproduction [30]. What should be noted here is that in all of the mentioned researches, selenium has played a role as an additive factor in increasing the lymphocyte reproduction, but according to the results of the present research, the number of lymphocytes has been decreased until the 20th day of responding nano-selenium and sodium selenite. To analyze this event, the role of neutrophils as the first defensive barrier of the body should be noted. An external material can activate specified immunity system when it passes through the intrinsic immunity barrier and is given to specified immunity system as an antigen, therefore not increasing the number of lymphocytes in the present study can be related to significant increase in the number of neutrophils and not encountering of the lymphocytes with any kind of stimulant factor. In addition, although there are potential advantages of nano-Se in living tissue, there are potential disadvantages of nano-Se also. Conclusions Based on all the information mentioned regarding the role of selenium, we can say that these materials can be important factors in increasing the resistance and the defensive ability of the intrinsic immunity in sheep. A selenium nanoparticle is more effective on the counts, survival duration, and the activity of neutrophils and increases them. The increase in TBARS value is longer and more severe when caused by sodium selenite than nano-selenium, which shows the better antioxidative effects of selenium nanoparticles. Since, in sheep, selenium nanoparticles were found to be less toxic and more bioactive than selenite, their use in feed instead of other forms of the element may be recommended. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. 307 References 1. 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