Vitamin B1
What it does
Thiamine, as vitamin B1 is also called, stands at the beginning of energy production from carbohydrates and is at the same time required for orderly nerve function.
Why it matters
The requirement grows with the carbohydrate share of the ration — the more starch and sugar, the more B1. With plenty of forage, feed and gut flora supply this item together.
When it becomes critical
It gets tight with very concentrate-heavy, fibre-poor rations and through substances that destroy B1 — found in mould, marsh horsetail and bracken. Signs of a gap are skittishness, uncoordinated movement and declining performance. A surplus via feed is harmless.
How much a horse needs
Maintenance is reckoned at 32 mg daily for 500 kg of live weight, which corresponds to 3–5 mg in each kilogram of dry matter. Heavy workloads sit at the upper end.
Needed for sugar metabolism in muscle and nerve cells. The horse normally covers its requirement itself: the microbes in the large intestine produce thiamine, and cereals and yeast provide more. It becomes scarce mainly under work — there the requirement doubles.
Cited values
| Type | Value | Unit / context |
|---|---|---|
| Requirement | 0.3 | mg/kg metabolic body mass per day (maintenance) |
| Requirement | 0.3 | mg/kg metabolic body mass per day (work, lower end) |
| Requirement | 0.6 | mg/kg metabolic body mass per day (work, upper end) |
| Requirement | 0.3 | mg/kg metabolic body mass per day (pregnant) |
| Requirement | 0.3 | mg/kg metabolic body mass per day (lactating) |
| Requirement | 0.3 | mg/kg metabolic body mass per day (growth) |
| Requirement | 3 | mg/kg feed dry matter (lower end, different basis) |
| Requirement | 5 | mg/kg feed dry matter (upper end; for high-performance horses 4-5) |
“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.
Possible deficiency signs
- Rare, because the feed usually supplies plenty and the gut flora produces more.
- It becomes significant when the gut flora is disturbed: after diarrhoea, with mouldy hay, with low-fibre rations, after a sudden change of feed or under medication that inhibits gut bacteria.
- ⚠️ B vitamins — apart from B12 — are hardly stored in the body. That is why a gap in supply shows through faster than with the fat-soluble vitamins.
- Take care with bracken and marsh horsetail in the hay: both contain a substance that destroys thiamine.
- The signs of a general B vitamin deficiency are non-specific — poor performance, variable appetite, reluctance to eat, changes in blood and skin, sometimes nervous symptoms.