Selenium (Se) is an essential trace mineral that is critical for antioxidant defense, thyroid function, immune health and reproductive performance. Selenium is located in the active center of glutathione peroxidase (GPx) and helps protect cells from oxidative damage. It works synergistically with Vitamin E; both prevent lipid peroxidation. However, selenium has a narrow therapeutic window; excess intake can be as dangerous as deficiency.
| Chemical Symbol | Se |
| Resource Type | Trace Mineral (Essential) |
| Function | Antioxidant (GPx) / Thyroid / Immune / Reproductive |
| Dog Need | 0.35 mg/kg DM (AAFCO min.) |
| Cat Needs | 0.30 mg/kg DM (AAFCO min.) |
| Safe Upper Limit | Dog: 2 mg/kg DM, Cat: 2 mg/kg DM (NRC) |
| Common Form | Sodium selenite, selenium yeast (organic) |
| Discussion Level | medium |
Selenium is an essential and clinically important trace mineral. It is indispensable for antioxidant defense and normal thyroid function. The organic form, such as selenium yeast, generally has higher bioavailability than inorganic forms like sodium selenite. Careful dosing is important because of selenium's narrow therapeutic window.
Why Added?
- Antioxidant: Cofactor of the enzyme glutathione peroxidase (GPx) — neutralizes hydrogen peroxide and lipid peroxides
- Thyroid function: Type I deiodinase enzyme is selenium dependent (T4 → T3 conversion)
- Immune support: Increases NK cell activity and antibody production
- Vitamin E synergy: Both prevent lipid peroxidation by different mechanisms
Selenosis (Selenium Toxicity)
selenium The therapeutic window is very narrow. Chronic excessive intake (>2 mg/kg DM) selenosis may cause: hair/feather loss, nail deformation, GI symptoms, neurological findings and liver damage. Acute selenium poisoning can be fatal. Additional selenium supplementation should never be given without veterinary supervision. The amount of selenium in food is safe within the limits of AAFCO/NRC.
Frequently Asked Questions
What is the difference between organic selenium and inorganic selenium?
Inorganic selenium (sodium selenite) is cheap and common but has lower bioavailability and can be toxic in narrow doses. Organic selenium (selenium yeast — selenomethionine) has higher bioavailability, can be stored in tissues and is safer. Organic selenium form is preferred in premium foods.
Related VetKriter Tools
Bibliography
- NRC (National Research Council). (2006). Nutrient Requirements of Dogs and Cats. National Academies Press.
- AAFCO (Association of American Feed Control Officials). (2024). Official Publication.
- Todd, S.E. et al. (2012). Selenium supplementation in dogs and cats. New Zealand Veterinary Journal, 60(6), 334-340.