Vitamin A supports vision (especially night vision and adaptation to changing light), immune defense, skin and coat integrity, reproductive function, and proper growth in young horses. Horses efficiently convert beta-carotene from fresh green forage into retinol (active vitamin A), and they can store significant reserves in the liver — enough to last several months on stored hay before deficiency develops. Fresh pasture is loaded with beta-carotene, but levels drop dramatically once grass is cut and dried. Hay that has been stored for more than six months, or hay that was rain-damaged or sun-bleached, may have very low vitamin A activity.
A 500kg horse needs about 15,000 IU of vitamin A per day — easily provided by about one medium carrot (which delivers roughly 10,000 IU of beta-carotene) alongside normal hay. Fresh green pasture provides abundant beta-carotene. Horses on long-stored hay without pasture access may need supplementation, which most commercial feeds and vitamin-mineral supplements provide.
0.0% of daily nutrient intake
Vitamin A makes up 0.0% of your horse's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Night blindness or difficulty adjusting to dim light, tearing or weepy eyes, increased susceptibility to respiratory and skin infections, poor coat condition, reproductive failure in mares, and poor growth in foals. Deficiency develops slowly due to liver storage reserves.
Vitamin A toxicity is possible from over-supplementation with synthetic vitamin A (retinol), causing bone fragility, skin peeling, and liver damage. Beta-carotene from food sources is self-regulating — the body reduces conversion when stores are full. Do not supplement both a vitamin A product and a feed already fortified with vitamin A without checking total intake.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 15000 | 30000 | IU | For a 500kg horse. Fresh pasture easily meets this. Hay-only diets may fall short after several months of storage as beta-carotene degrades. |
| Pregnant / Nursing | — | 22500 | 45000 | IU | Pregnant mares need more vitamin A for fetal development. Ensure fresh forage or supplementation, especially in late gestation. |
Source: NRC 2007
Vitamin A is fat-soluble and requires dietary fat for proper absorption. The natural fat content in forage (2-4%) is sufficient to support vitamin A uptake.
What this means: No special action needed — the natural fat in hay and pasture supports vitamin A absorption. This is one of many reasons a forage-based diet works as a complete nutritional system for horses.
