Syn: Selenium/vitamin E deficiency, white muscle disease, nutritional myopathy, 'muscular dystrophy'

This disease complex usually occurs as defined clinical and pathological syndromes which bear a several names. They are thought to have a nutritional pathogenesis involving a dietary deficiency of selenium and/or vitamin E.

Diagnosis

Specimens required

1. 10 ml of heparinised blood submitted chilled (not frozen) for glutathione peroxidase (GSHPx) activity, from at least 5 animals in the group.

   Selenium status can be measured directly by analysis of blood or tissue selenium levels, or indirectly by analysis of blood glutathione peroxidase levels. The latter, as in most enzyme tests, requires heparinized blood (EDTA is unsuitable). The correlation between glutathione peroxidase (GSHPx) activity and selenium levels is very high in non deficient animals. In deficient animals, this high mathematical correlation is not present, but of little diagnostic consequence, i.e. in deficient animals, both GSHPx and Se levels are low but there is not necessarily a close mathematical correlation between values.

2. Sections of affected and unaffected skeletal muscle and cardiac muscle, in buffered formalin for histopathology.
3. At least 2 ml of serum, free of cells and haemolysis, submitted frozen for serum enzymology and vitamin E analysis.
4. 20 g liver, submitted frozen and protected from light immediately following collection. (See Collection of specimens for biochemistry and Vitamin deficiency).

NB. Whenever possible, submit heparinised blood from 3-5 peer animals rather than tissues of dead cases

Interpretation of blood glutathione peroxidase (GSHPx) concentrations

The following values should be taken only as a guide:

Note that current blood concentrations of GSHPx reflect the selenium intake of the animal at the time the present circulating erythrocytes were formed. An 'average' time would be the half life of the erythrocyte for the species and age of animals to be examined (e.g. adult cattle approx. 80 days, adult sheep approx. 60 days, calves and lambs approx. 50 days).

The interpretation of selenium status and prognosis is further complicated by factors which include:

• Season (winter and summer peaks, autumn and spring troughs of Se availability).
• Soil type (acid soils < pH 5.5 have 50% reduction in Se availability to plants).
• Pasture type (legumes and other leafy plants lower in Se than grasses).
• Fertilizer history (competitive interaction from sulphur results in reduced selenium in pastures on superphosphate fertilized soils).
• Age of animals preruminant animals more prone to deficiency than ruminants.

For diagnosis of selenium deficiency in sheep, it is recommended that weaners be sampled after access to good feed (e.g. clover). Older sheep normally have lower levels. Diagnosis should be considered on a property basis.