In recent years many exciting research results have indicated that
selen- ium, depending on its concentration, can influence mammalian
metabo- lism. It has been estimated that in selenium-deficient areas,
selenium or selenium-vitamin E combinations added to animal feed can
prevent an- nuallosses to beef and dairy cattle and sheep valued at 545
million dollars and poultry and swine losses valued at 82 million
dollars. Some animal diseases that can be prevented by a
selenium-supple- mented diet include liver necrosis, nutritional
muscular dystrophy, exu- dative diathesis, pancreatic degeneration,
mulberry heart disease, infer- tility, growth impairment, periodontal
disease, and encephalomalacia. Selenium intake levels are dependent on
the plant or animal feed con- centrations, which, in turn, are dependent
on the pH of the soil and the types of rocks from which the soils are
derived. At normal metabolic levels selenium possesses an antioxidant
affect manifested through glutathione peroxidase, and selenium also has
an ef- fect on cytochrome P-450 and heme metabolism. Comparisons are
made between metabolism of selenium and sulfur in plants, animals, and
hu- mans. At greater selenium intake levels acute poisoning occurs when
high-selenium-content (10,000 ppm Se) plants are consumed in large quan-
tities. The toxic reactions were first manifested in cavalry horses near
Fort Randall, Nebraska, in the 1860s.