Vitamin K is the clotting vitamin — without it, even a small wound or internal bruise could lead to dangerous uncontrolled bleeding. It activates the proteins (clotting factors) that form blood clots and seal injuries, which is essential in a flock where pecking-order scuffles and minor injuries are routine. Vitamin K also plays a role in bone metabolism, helping direct calcium into bones and eggshells rather than soft tissues.
Chickens synthesize some Vitamin K through beneficial bacteria in their ceca (the paired pouches at the junction of the small and large intestine), but this internal production alone is often insufficient, especially in birds on antibiotics or those with disrupted gut flora from illness. Coccidiosis — one of the most common poultry diseases — damages the intestinal lining and worsens Vitamin K status both by impairing absorption and by destroying the gut bacteria that produce it. This is why blood in droppings during a coccidia outbreak can become life-threatening — the bird is losing blood while simultaneously losing its ability to clot.
Dark leafy greens are far and away the richest natural source of Vitamin K1 (phylloquinone). A flock with daily access to fresh greens or pasture rarely has Vitamin K problems. Confined flocks on an all-pellet diet without greens are more vulnerable.
About 0.5 to 1.0 mg per hen per day keeps clotting factors healthy. A few leaves of kale, spinach, or some broccoli florets provide this easily. If your birds free-range on grass, they are likely getting a good baseline. After any course of antibiotics, offer extra greens for a week to help rebuild the gut bacteria that produce Vitamin K internally.
0.0% of daily nutrient intake
Vitamin K makes up 0.0% of your chicken's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Prolonged bleeding from minor wounds, blood spots inside eggs, bruising under the skin visible when parting feathers, pale combs from blood loss, internal hemorrhaging that can be fatal in severe cases, worsened outcomes during coccidiosis outbreaks
Vitamin K from food sources is extremely safe and the body excretes what it does not need. Synthetic menadione (Vitamin K3), sometimes found in cheap feed supplements, can cause toxicity at high doses including liver damage. Natural Vitamin K1 from greens carries no such risk.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 0.5 | 1 | mg/day | Natural K1 from greens is preferable. Increase after antibiotic treatment to compensate for reduced bacterial synthesis in the ceca. |
Source: NRC Poultry 1994; general veterinary consensus
Vitamin K activates osteocalcin and matrix GLA protein, both of which are calcium-binding proteins that direct calcium to bones and teeth while keeping it out of soft tissues like arteries and kidneys. For laying hens cycling enormous amounts of calcium daily, Vitamin K ensures that calcium deposits where it is needed (shells and medullary bone) rather than accumulating in the kidneys or blood vessels. Vitamin K also activates the blood clotting factors that depend on calcium as a cofactor.
What this means: Include Vitamin K-rich greens like kale, spinach, and broccoli in your flock's regular treat rotation, especially for high-producing layers. The combination of calcium from oyster shell with Vitamin K from dark leafy greens creates a synergistic effect that maximizes shell quality while protecting soft tissues from inappropriate calcification.
