Vitamin A (with β-carotene)
What it does
Vitamin A is needed for skin and mucous membranes, for vision and for immune defence. It does not enter the horse as a finished vitamin but as β-carotene from green plant material — the body builds it from there.
Why it matters
Mucous membranes are the first border against pathogens, and their renewal depends on this vitamin. As long as fresh green is on the menu, the ration covers this item by itself.
When it becomes critical
The months the horse spends mostly stabled are the critical stretch: stored hay loses much of its β-carotene, so a gap can open across weeks — showing up as brittle horn, dry membranes and infections that come more often. In the other direction, preformed vitamin A turns toxic at high doses; as a standing dose, 1000 IU per kilogram of body weight per day marks the ceiling. With pure β-carotene that risk does not arise.
How much a horse needs
Maintenance: about 15,900 IU a day for a 500 kg horse; for breeding mares and foals the figure is considerably higher. If a breeding mare gets no β-carotene from her forage, it can be supplemented – then at least 200 mg a day.
Needed for vision, skin, mucous membranes and the immune defences. Grass and good hay supply plenty of the precursor — vitamin A is the case in which supplementing turns into too much sooner than into too little.
Cited values
| Type | Value | Unit / context |
|---|---|---|
| Requirement | 150 | IU/kg metabolic body mass per day (maintenance) |
| Requirement | 225 | IU/kg metabolic body mass per day (work) |
| Requirement | 300 | IU/kg metabolic body mass per day (pregnant) |
| Requirement | 300 | IU/kg metabolic body mass per day (lactating) |
| Requirement | 300 | IU/kg metabolic body mass per day (growth) |
| Tolerance limit | 16000 | IU/kg feed DM |
| Maximum per meal | 1000 | IU per kg body mass per day (do not exceed in the long term — poisoning: rough hair, ataxia, depression) |
Careful when comparing: the requirement is given **per day**, the upper limit **per kilogram of feed dry matter**. These are different reference bases and cannot be compared directly. The upper limit is also not a target — it is the amount at which harm begins.
A maximum per meal applies per meal and per kilo of horse — not per kilo of feed. Two small meals can add up to more while each stays below the limit.
“Metabolic body mass” is a calculated figure, not a weight: body weight to the power of 0.75. For 600 kg that is about 121 — the requirement is multiplied by that figure, not by 600. That is why the number looks small even though it isn't.