Selenium in Beef Cattle Nutrition

Selenium is an essential trace mineral required for reproductive efficiency, immune function, and muscle health in cattle. Despite its importance, selenium concentrations in Manitoba forages are generally low, and routine analysis is uncommon due to high testing costs.
 
1. Importance of Selenium
Adequate selenium is critical for:
  • Reproductive performance
    • Prevents irregular heats, early embryonic loss
  • Prevention of retained placenta
  • Immune system function
    • Low selenium increases susceptibility to mastitis and metritis
  • Muscle integrity
    • Prevents white muscle disease in calves
Selenium works closely with vitamin E as part of the antioxidant system responsible for reducing cellular damage.
 
2. Selenium Toxicity
Selenium can be toxic when consumed in excessive amounts.
Acute Toxicity
  • Occurs when livestock consume selenium accumulator plants
  • These plants may contain 100–9,000 mg/kg selenium
  • Leads to rapid death
Chronic Toxicity
  • Long-term intake around 5 mg/kg can cause poisoning
  • Symptoms may include hair loss, hoof deformities, and reduced feed intake
Because the margin between deficiency and toxicity is narrow, supplementation must be carefully controlled.
 
3. Selenium Status in Manitoba
  • Manitoba is recognized as a “low to deficient” selenium region
  • Most soils and forages do not provide adequate selenium for beef cattle
  • Routine forage analysis is not commonly performed due to high laboratory costs
  • As a result, commercial mineral supplements remain the primary selenium source in most beef operations
 
4. Supplementation Considerations
  • Use a balanced mineral supplement containing selenium (often 0.6–3 mg/kg depending on format and regulations)
  • Selenium can be provided as:
    • Sodium selenite or sodium selenate (inorganic forms)
    • Organic forms (e.g., selenium yeast), which are often more bioavailable
  • Ensure livestock do not have access to selenium‑accumulator plants in high‑risk areas
  • Monitor intake when using free‑choice mineral to avoid both under- and over-supplementation