8153

• UCREFRP Catalog Number: 8153
• Author: Jacobs, e. L. W.
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1989
• Copyright Material: YES

16 MAYLAND ET AL.
mon to much of the area, and named the problem alkali disease. Not until
1931 did researchers associate alkali disease with selenosis. Since then,
researchers have continued to characterize Se in soils and plants and its toxi-
cosis in animals. Early efforts succeeded in describing areas in the western
USA and Canada where Se accumulator plants contained concentrations of
50 to 500 mg Se/kg or higher (Rosenfeld & Beath, 1964; Fig. 2-1).
Research continued on soil, plant, and animal factors associated with
high Se levels, but by 1958, nutritional deficiencies of Se were noted in the
diets of many animals including grazing livestock (NAS-NRC, 1983). Areas
of the USA were then mapped where plants contained <0.1 mg Se/kg (Fig.
2-2) and where Se deficiency disorders were likely to occur in livestock and
poultry. In general, Se concentrations of 0.05 to 0.1 mg Se/kg diet and 5
to 15 mg Se/kg diet may be considered as critical levels of adequacy and
toxicity, respectively.
~ o
Fig. 2-l . Distribution of seleniferous vegetation in the western USA and Canada (adapted from
Rosenfeld & Beath, 1964). Each open dot represents the place of collection of a plant speci-
men containing 50-500 mg Se/kg; each solid dot represents specimens containing > 500 mg
Se/kg.