[Myopathies in a riding horse stable]

In this case report on myopathies in 6 saddle-horses, a combined dietary vitamin E and selenium deficiency is presumed. Other disorders, such as exertional myopathy ("Monday morning disease") due to excessive energy intake or ionophore intoxication could be excluded by calculating the energy supply or by a simple colour test. The selenium requirement of horses is estimated to 0.1-0.2 mg/kg dry matter (Meyer 1986). If natural feed compounds are low in selenium, adequate amounts of this trace element can be supplied by means of supplemental feeds, sodium selenite (20 mg/500 kg BW/week) or bruised linseed (cooked, 200-500 g/d). In horses tolerance of increased selenium intake is low. After oral administration of sodium selenite lethal dose was 3.3 mg/kg bodyweight. In feedstuffs selenium concentration must be below 5 mg/kg dry matter (Traub-Dargatz et al, 1986). The intake of vitamin E should be 0.25-1 mg/kg bodyweight. The requirements are influenced by feed compounds, especially the concentration of dietary unsaturated fatty acids, and the performance of the horses (Meyer 1986). Foals, pregnant or lactating mares, and racing horses have higher requirements. In acute disease vitamin E and selenium are given parenterally (5 mg Se/horse) or by oral application of sodium selenite (46% selenium, 20 mg/horse), in addition to symptomatical treatment.