Selenium toxicity in sheep grazing reclaimed phosphate mining sites

Area of Science:

• Environmental Toxicology
• Animal Science
• Geochemistry

Background:

• Phosphate mining in southeastern Idaho releases naturally occurring selenium (Se) into the environment.
• Elevated selenium concentrations in forage and water pose a health risk to grazing livestock, particularly sheep.
• Previous incidents of sheep mortality linked to selenium toxicosis necessitate further investigation in natural grazing settings.

Purpose of the Study:

• To monitor the health status of sheep exposed to elevated selenium levels in a natural grazing environment.
• To quantify selenium uptake and its effects on sheep physiology under controlled exposure conditions.
• To assess the risk of selenium toxicosis in sheep grazing on reclaimed mine lands.

Main Methods:

• A controlled study involving 72 Columbia x Suffolk sheep divided into control, low selenium (LoSe), and high selenium (HiSe) groups.
• Sheep were subjected to a baseline phase (normal Se), an exposure phase (reclaimed mine areas with elevated Se), and a depuration phase (normal Se).
• Whole blood, serum, and tissue selenium levels were monitored, alongside clinical signs, histopathology, and post-mortem examinations.

Main Results:

• The HiSe group exhibited peak mean whole blood and serum selenium levels of 1.32 ppm and 0.99 ppm, respectively.
• One sheep in the HiSe group died from diagnosed selenium toxicosis, with high tissue selenium concentrations.
• Other exposed sheep showed elevated tissue selenium, indicative of high or toxic exposure, even without overt clinical signs.

Conclusions:

• Grazing sheep in selenium-contaminated areas, such as reclaimed phosphate mines, can lead to selenium toxicosis.
• Elevated selenium levels in forage and water pose a significant risk to sheep health, potentially causing mortality.
• Further research is crucial to understand the toxicology of selenium in sheep within natural grazing environments.