A global perspective of selenium deficiency and toxicity

Authors: Davis, Thomas - Zane; Panter, Kip; HALL, JEFFERY - Utah Veterinary Diagnostics Laboratory

Submitted to: International Symposium on Poisonous Plants
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2015
Publication Date: 6/5/2015
Citation: Davis, T.Z., Panter, K.E., Hall, J.O. 2015. A global perspective of selenium deficiency and toxicity. International Symposium on Poisonous Plants. 9:17-24.

Interpretive Summary: Selenium is an essential nutrient that is needed for the activity of many enzymes. However it has a very narrow range between deficiency and toxicity. When consumed in excess it can cause acute or chronic toxicosis depending upon the dose and duration of exposure. Selenium deficiency can cause metabolic diseases such as “white muscle disease” in calves and lambs and in humans it can cause a cardiomyopathy known as “Keshan disease” or an endemic osteoarthropathy disease known as Kashin-Beck disease. Most forages contain between 0.1 and 1 ppm selenium but in the some areas selenium-accumulator plants can accumulate up to 14,000 ppm selenium. Forages that contain greater than 5 ppm selenium pose a risk to livestock. The likelihood of an animal being poisoned is dependent upon the species and age of the animal in addition to the form and amount of selenium injected or ingested. Diagnosis is made by considering clinical signs and exposure history and can be confirmed by determining selenium concentration in serum, whole blood, or hair. Southeastern Idaho contains areas that have very high concentrations of selenium in the soil and forages. At times animals are poisoned after ingesting high selenium-containing forages. The data shown in this chapter describes three cases, 1) an acute poisoning case in sheep, 2) an acute poisoning case in cattle and, 3) a chronic poisoning case in horses. In conclusion, there are many rangelands throughout the world which contain forages with elevated concentrations of selenium which can cause acute or chronic selenosis in livestock and potentially in wildlife. Caution should be taken to prohibit livestock from grazing in selenium contaminated areas.

Technical Abstract: Selenium is an essential nutrient that has a relatively narrow margin between ingested amounts that cause deficiency and toxicosis. Both selenium deficiency and toxicosis occur in several regions in many countries throughout the world and result in substantial losses to the livestock industry. Selenium deficiency which results in white muscle disease and reproductive deficiency in livestock is common in areas where selenium concentrations in forages are very low. Selenium toxicosis is less common than selenium deficiency. Selenium toxicoses can be a result of either acute or chronic exposure, however, they have very different clinical signs and impact. Selenium toxicosis normally result from one of three types of exposure history: 1, grazing animals which ingest forages with elevated selenium concentrations on seleniferous soils; 2, toxicity from environmental contamination from drain water, reclaimed soils from mining, or fly ash; and 3, accidental overdoses by injection of supplemental selenium or by misformulation of feed mixes. Selenium doses that cause toxicosis depend on the chemical form of selenium, in addition to species, age, and selenium status of the animal ingesting the dose. Selenium deficiency and toxicosis have caused extensive financial losses in the livestock industry and have been extensively researched. However, recent research results demonstrate that there remains a significant amount of knowledge that needs to be discovered in order to fully understand both the beneficial roles and negative impacts of selenium.