Its easier for me just to quote Merck then try and explain in my own words:
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< =title6>Treatment and Control:>>
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< =para2>There is no specific treatment for selenium toxicosis. Eliminating the source and exposure and symptomatic and supportive care of the animal should be started as soon as possible. Addition of substances that antagonize or inhibit the toxic effects of selenium in the diet may help reduce the risk of selenium toxicosis. A high protein diet, linseed oil meal, sulfur, arsenic, silver, copper, cadmium, and mercury have reduced selenium toxicity in laboratory animals, but their use under field conditions is limited. Addition of arsenic salt at 0.00375% to enhance biliary excretion of selenium or use of a high-protein diet to bind free selenium may help reduce incidence of selenium poisoning in cattle.>>>
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< =para2>Soil and forages should be tested regularly in high-selenium areas.>>>Chronic Selenium Toxicosis - The Merck Veterinary Manual >>>
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Let me know if you have any other questions
Good Luck &
Best Fishes