Selenium is essential for cattle, however too much selenium can be toxic. Selenium exists naturally in the soil, varying in concentration across different geographical regions.
Nearly all plants accumulate selenium from the soil; however some plants, known as selenium accumulators, require a large amount of selenium to grow. Their presence in the pasture is a good indicator that the selenium levels in the soil are high. However another danger is that certain times of the year or during particular environmental conditions, these selenium accumulating plants may appear appetizing to cattle. Through consuming these plants, cattle ingest varying elevated levels of selenium causing differing levels of toxicity. Cattle owners need to be mindful of the selenium concentration in their area, as otherwise they could easily and unknowingly be poisoning their herd. The different forms of selenium toxicity include acute and chronic toxic conditions.
- Acute (Blind staggers): Least common form. Occurs when a cow ingests a high dose of selenium over a short period of time (greater than 500 to 1000 ppm).
- Chronic (Alkali or bobtail disease): Most common form of selenium toxicity seen in cattle. Cattle must ingest a minimum of 3.3 mg/kg of body weight of Se daily.