Vitamin K is essential for blood clotting and plays a role in bone metabolism. Horses obtain vitamin K from two sources: green forages (vitamin K1/phylloquinone) and synthesis by hindgut bacteria (vitamin K2/menaquinone). Between these two sources, dietary deficiency is essentially unheard of in healthy horses on a forage-based diet.
A 500kg horse's needs are fully met by normal hay consumption and hindgut bacterial synthesis — no specific intake target is established by the NRC because deficiency is so rare. Green leafy hay and fresh pasture are abundant sources. Supplementation is only needed if a horse has been exposed to dicoumarol toxicity from moldy sweet clover hay.
Excessive or prolonged bleeding from cuts or wounds, unexplained bruising, and blood in manure or urine. These signs are extremely rare from dietary causes and usually indicate poisoning (e.g., from moldy sweet clover containing dicoumarol) or severe liver disease.
Vitamin K from food and bacterial synthesis does not accumulate to toxic levels. Excess is not a concern from dietary sources.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 0 | 0 | mg | No NRC requirement established. Vitamin K is adequately synthesized by hindgut bacteria and provided by green forage. Supplementation is only needed in cases of dicoumarol toxicity from moldy sweet clover. |
Source: NRC 2007
