Selenium is one of the indispensable trace elements in animal production. In particular, mammals, the main way of selenium intake is feed, but the poisoning dose of selenium and its nutritional dose is very close to a slight inadvertent lead to selenium poisoning. The introduction of nano-selenium will solve this problem. 1 Comparison of various selenium sources 1.1 Inorganic selenium and organic selenium Inorganic selenium selenate is usually added to poultry diets, but due to its high toxicity, it has caused inconvenience to production and use. On the one hand, inorganic selenium is absorbed through the intestinal wall in a passive diffusion way and then enters into the liver, and then converted into biological selenium, which has low bioavailability. At the same time, a large amount of inorganic selenium that has not been utilized is discharged into the environment, causing serious environmental pollution. On the other hand, the use dose of inorganic selenium is difficult to grasp. Animals, especially young animals, are more sensitive to selenium and easily cause poisoning. There are many types of organic selenium on the market today, including selenium amino acids and yeast selenium. Compared with inorganic selenium, organic selenium has less toxicity and is easy to use in feed. Organic selenium is absorbed by the body through the intestinal wall through an active transport mechanism. Its absorption rate is higher than inorganic selenium, which can reduce the amount of feed in the feed and reduce the environmental pollution of selenium. However, organic selenium is not as strong as inorganic selenium, and the subchronic toxicity doses are close to each other. At the same time, the organic selenium production process is complex, the production cost is high, and there are few reports on actual production. 1.2 Nano-selenium Nano is a unit of length, one-billionth of lm. Nanotechnology refers to a comprehensive technology system for the preparation and research of substances at the nanoscale. Studies have confirmed that when the micro-particles enter the nanometer scale, many new properties emerge in their physical properties such as light, heat, electricity, and magnetism. After nano-treatment of feed additives, due to the large specific surface of the nano-system, the bond state is seriously mismatched, many active centers appear, surface steps and roughness increase, and the surface appears non-chemical equilibrium, which can lead to the nature-specificity of feed additives. Change, thus revealing many unique changes. Due to the change of selenium scale, this makes nano-selenium has stronger advantages of low toxicity and high efficiency compared with other forms of selenium. In terms of acute toxicity, inorganic selenium is 15 mg/kg, and sodium selenium is 113 mg/kg. In terms of chronic toxicity, when the content of inorganic selenium or organic selenium in the feed is between 4 and 5 mg/kg, the body weight and cirrhosis of the rats can be reduced, but the above phenomenon will not occur when the nano-selenium and selenium content is 6 mg/kg. Nano-selenium is the selenium supplement that has been found to have the lowest acute toxicity (Zhang Jinsong, Gao Xueyun et al. 2001). Compared with other selenium sources, nano-selenium has the following features: 1.2.l High biological activity studies show that compared with standard reference materials, nano-selenium has high biological efficacy. 1.2.2 High-safety nano-selenium is the safest sun preparation reported at home and abroad. Its toxicity to mice is 1/7 to 1/10 of the selenium standard reference substance, which is the lowest known acute toxicity. Selenium preparations. 1.2.3 High immunomodulators Nano-selenium can significantly stimulate the body's cells, body fluids, and non-specific immune functions, thereby improving the body's ability to prevent disease and disease. Experiments show that nano-selenium can sensitively improve the immune function of mice. Zhang Lide (2002) proposed that the use of nano-composite technology can greatly improve the efficacy of seaweed polyester sulfate combined with nano-selenium, greatly improving the efficiency of anti-virus. 1.2.4 High Anti-oxidation Nano-selenium is a tiny unit formed by tens of thousands of selenium compounds. It has a stronger ability to resist oxidation and scavenge free radicals, and it can well inhibit free radicals and protect cells from damage. It was shown that the efficiency of scavenging hydroxyl radicals by nano-selenium was 5 times that of inorganic selenium and 2.5 times that of organic selenium. 1.2.5 High Absorption Rate As nano-selenium has a very fine particle size, it is easily absorbed by the animal's gastrointestinal tract and can be used to a greater extent. 2 Preliminary application experiments of nano-selenium in animal production show that nano-selenium has many advantages and it is completely feasible for animal production. 2.1 The stability of nano-selenium is made into nano-sized particles selenium for easy storage, transportation and use. 2.2 Cost Factors Nano-selenium is a trace additive, but because of its high absorption rate, utilization rate, and high biological activity, it is determined that it has very little addition in practical applications. With the development of nanotechnology, the manufacturing process is becoming more and more advanced and mass production, and its manufacturing cost will be reduced. 2.3 Health Factors Existing tests have shown that the selenium content in rats fed with nano-selenium is higher than that fed with other selenium sources. Since selenium also has a very important role in the human body, it is possible to use nano-selenium to produce animal products that have health effects such as selenium-enriched meat. 2.4 Safety Factors Nano-selenium has less environmental pollution. For a long time, people have been investigating the selenium chemical form with high efficiency and low toxicity. The study focused on the preparation of nano-selenium from the physical form of selenium, and broadened the way for people to search for low toxicity and high selenium. The numerous characteristics and advantages of nano-selenium will enable its wide application in animal production.