The Condition

Vitamin E and selenium have complementary, but independent roles in the protection of cells against the damaging effects of lipid peroxides and free radicals produced during normal metabolism. Tissues or cells which undergo rapid increases in oxidative metabolism, such as muscle (skeletal, cardiac or respiratory) and blood cells (e.g. erythrocytes, phagocytes and lymphocytes) are particularly susceptible to damage in the event of a deficiency in one or both of these antioxidants. The most commonly recognised condition of vitamin E/selenium deficiency is the myodegenerative syndrome most commonly referred to as white muscle disease (WMD) because of the pale appearance of the body muscles and heart. WMD most commonly occurs in animals up to 6 months of age and signs can vary widely from lambs with mild stiffness and discomfort (often mistaken for joint ill) to those that lie down and are unwilling to move, or even collapse when driven. Sometimes breathing difficulties may be observed when the muscles controlling breathing are involved (Suttle et al., 1991).

Adverse weather conditions and stress may affect the occurrence and/or severity of WMD (Greig and Hunter, 1980). It is also claimed that deficiencies in vitamin E and/or selenium can impair productivity through their effects on growth and/or reproduction (Kott et al., 1983). In the latter case, the overall effect is often reflected in poorer lambing rates (Mudd and Mackie, 1973). Selenium alone has been associated with ill thrift in lambs and with tooth and gum disease (Suttle et al., 1991).

Pregnant ewes which are severely deficient in vitamin E and/or selenium may produce stillborn progeny, or weakly lambs which only survive for a few days before dying of acute heart failure (Hamliri et al., 1990). Selenium and vitamin E deficiency have been implicated in the death of embryos in early pregnancy, although reports are conflicting (Niekerk et al., 1996; Suttle et al., 1991; UK, North of Scotland College of Agriculture, 1981; Vipond, 1984). Selenium deficiency may also impair the animal's immunity (Larsen et al., 1988; Reffett et al., 1988; Turner and Finch, 1990).

Vitamin E is synthesised by plants but not by animals. Grass normally contains adequate levels of vitamin E, but lush spring grass may contain high levels of polyunsaturated fatty acids (PUFAs). When eaten by the animal, these PUFAs are converted into the toxic peroxides referred to earlier (Suttle et al., 1991). Forage crops such as rape or kale are a good source of vitamin E, as is grass silage. Root crops are poor sources and many hays may also be low in vitamin E (Greig and Hunter, 1980). The maturity and storage of feed materials affect their vitamin E content. Cereals contain moderate levels of vitamin E, but the use of propionic acid or caustic soda to preserve moist grain rapidly destroys the vitamin (Bradley et al., 1986; Watson et al., 1988).

Selenium status in grazing crops is dependent on incorporation from soil, which in turn obtains most of its selenium from surrounding rocks. However, substantial areas of the United Kingdom, especially north-east Scotland and parts of south-east England, are selenium deficient (Anderson et al., 1979). Selenium levels in herbage are influenced by other constituents of the soil as well as by the chemicals applied to it. For example, the application of superphosphate fertilisers containing sulphates may reduce the uptake of selenium from the soil by plants, or may reduce its availability to the animal, or a combination of both.