Selenium in soils and crops, its deficiencies in livestock and humans: Implications for management

Selenium (Se) content in soils varies greatly depending upon the parent rock, weathering and texture. In general, total soil Se of 0.1 to 0.6 mg kg(-1) is considered deficient. Selenium deficiency regions in New Zealand, Denmark and the Atlantic Region of Canada contain 0.1 to 0.6 mg Se kg(-1) in the soil. Soil acidity is an important factor resulting in decreased Se availability to crops. Selenium concentration in plants can range from 0.005 mg kg(-1) in deficient crops to about 5500 mg kg(-1) in Se accumulators on seleniferous soils. Among crops, brassicas and legumes, particularly soybeans, contain higher Se than other crops. Selenium is an essential mineral for livestock as well as for humans, but its essentiality for the growth of Se accumulators or non-accumulators has so far not been demonstrated. Feed crops containing more than 0.1 mg Se kg(-1) will protect livestock from Se deficiency disorders. Inadequate Se in animal rations can cause White Muscle Disease in calves, sheep and goat; Exudative Diathesis in poultry and Mulberry Heart Disease in pigs. Selenium deficiency can be prevented by Se injections to females at late gestation and/or to the young stock shortly after birth. In humans, lack of Se has been linked to several kinds of cancer, heart disease and other chronic and life threatening conditions. Oral Se therapy has been reported to produce significant decreases in lung, prostate and colorectal cancer in a recently published study. It has also been shown to help prevent cardiomyopathy in young children in China. Pills containing Se alone or in combination with vitamins and/or minerals, are available in several countries as a human supplement. Eating Se enriched foods and animal products and/or Se pills may protect humans from pathology associated with Se deficiency. Selenium fertilization of crops is now permitted in New Zealand, Finland and to a limited extent in China and Canada.