Fluxion and regulation of selenium in soil, plants, and animals in grassland grazing system

The trace element selenium has various biological functions and is essential for animal health. There is considerable transference of substances in the grassland grazing system and, therefore, selenium circulates through the soil into plants and animals. This review summarized the recent research studies on various aspects of the circulation of selenium including its content, distribution, and functions in soil, plants, and animals. In addition, we analyzed the cyclic characteristics of selenium in the grassland grazing system. The results showed that the content of selenium in soil, plants, and animals was 0.1~2.0, 0.05~1.50, and 0.02~0.05 mg·kg-1, respectively. The circulation of selenium in the soil, plants, and animals is affected by numerous factors and has exhibited considerable differences and instability, which has led to consistent deficiencies in its intake by grazing animals. The implementation of a reasonable grazing system would efficiently increase the circular flow of selenium by initiating appropriate fertilization methods and reseeding selenium-enriched forage. We believe these strategies would relieve or resolve the current situation where grazing livestock consistently show deficient selenium levels.