It is well known that both selenium (Se) and vitamin E are essential nutrients that should be in all horses’ diets. Vitamin E is a fat-soluble vitamin that plays a vital role in numerous metabolic processes, including regulating heart function, improving immune response, supporting reproduction, and maintaining hormone metabolism in the brain. It also assists in carbohydrate and creatine metabolism, as well as muscle metabolism and glycogen balance.
Selenium’s main function is to inhibit lipid (fat) oxidation in metabolic processes. It is a component of the enzyme glutathione peroxidase, which can be measured in the blood. When selenium combines with vitamin E, they work synergistically to protect the immune system by preventing the formation of free radicals that damage cells. This combination promotes antibody production and supports healthy heart and liver function, while aiding efficient tissue respiration. Selenium also supports pancreatic function and tissue elasticity.
In humans, selenium supplementation has shown promise in addressing arthritis, cardiovascular disease, male infertility, cataracts, AIDS, and high blood pressure. In horses, however, the key benefits of selenium and vitamin E supplementation include improved muscle function, delayed onset of tying up, and reduction of tissue damage caused by free radicals during exercise. This ultimately improves post-exercise recovery.
Selenium is an essential mineral, but its required amount is very specific—too much can result in toxicity. The National Research Council (NRC) has established the recommended selenium levels for various livestock, shown below.
| Species | Phase of Production | Se Requirement | Basis |
|---|---|---|---|
| Dairy | All | 0.30 | mg/kg DM |
| Beef | All | 0.10 | mg/kg DM |
| Horse | All | 0.10 | mg/kg DM |
| Poultry – Broilers | 0.15 | mg/kg | |
| Poultry – Layers | 0.05 – 0.15 | mg/kg | |
| Turkeys | 0.20 | mg/kg | |
| Ducks | 0.20 | mg/kg | |
| Japanese Quail | 0.20 | mg/kg | |
| Swine (3–10 kg body weight) | 0.30 | mg/kg | |
| Swine (10–20 kg body weight) | 0.25 | mg/kg | |
| Swine (20–120 kg body weight) | 0.15 | mg/kg | |
| Gestating/Lactating Sows & Boars | 0.15 | mg/kg |
The selenium content in natural feed ingredients is typically low and variable. The table below shows an example comparison of selenium levels in common feed ingredients in the United States and Canada.
| Ingredient | United States (ppm) | Canada (ppm) |
|---|---|---|
| Alfalfa | 0.01 – 2.00 | 0.02 – 0.27 |
| Barley | 0.05 – 0.50 | 0.02 – 0.99 |
| Bentonite | 1.00 – 20.00 | – |
| Blood meal | – | 0.50 – 1.20 |
| Brewers’ grains | 0.15 – 1.00 | 0.29 – 1.10 |
| Corn | 0.01 – 1.00 | 0.01 – 0.33 |
| Fish meal | 1.00 – 5.00 | 1.30 – 3.40 |
| Gluten meal | 0.10 – 1.50 | 0.20 – 0.57 |
| Oats | 0.01 – 1.00 | 0.01 – 1.10 |
| Rapeseed meal | – | 0.46 – 1.90 |
| Soybean meal | 0.06 – 1.00 | 0.04 – 0.78 |
| Wheat | 0.01 – 3.00 | 0.02 – 1.50 |
| Wheat middlings | 0.15 – 1.00 | 0.41 – 0.89 |
Source: Selenium from Nutrition (Revised Edition), National Academy Press.
Feed manufacturers producing complete feeds or supplements have several selenium sources to choose from, most commonly sodium selenite or sodium selenate. These salts are well absorbed through the digestive tract, whereas elemental selenium is not. Once absorbed, selenium is incorporated into the enzyme system glutathione peroxidase (GSH) in the form of selenocysteine, which is derived from the amino acid cysteine.
Liquid SeeVitE is a specialized formulation combining selenium (bound to the amino acid methionine to form organic selenomethionine) with vitamin E in a precise ratio. The water-based liquid dissolves the selenomethionine and emulsifies the fat-soluble vitamin E, allowing both nutrients to be rapidly absorbed in the small intestine.
When selenium is required in the body, the selenium-methionine bond breaks, releasing selenium for use (e.g., to form glutathione peroxidase). When not immediately needed, it remains in the methionine pool, creating two internal depots for selenium storage. This ensures selenium availability when required.
Excess selenium is eliminated primarily through urine, with smaller amounts excreted in faeces and through the lungs.
Studies in poultry and pigs comparing selenium sources found that selenium bound to methionine resulted in up to three times higher muscle selenium levels than sodium selenite or selenate. Additionally, selenium toxicity risk is lower when it is present in organic form.
Supplementation with organic selenium offers several key benefits:
Young animals deficient in selenium may develop nutritional muscular dystrophy or white muscle disease (vlekspiersiekte), along with reduced immune responses to disease or vaccination. These conditions highlight the importance of maintaining adequate selenium levels in muscle tissue. Other tissue damage-related conditions may also respond positively to Se and vitamin E supplementation, though not all are cured or prevented by these nutrients alone.
The only oral liquid organic form of selenium combined with vitamin E available in South Africa is Liquid SeeVitE.
