Vitamin K for Chickens: Role, Deficiency Signs & Causes

Health note: This guide is general information, not veterinary advice, and our writers are not veterinarians. If a bird is sick, injured or not improving, contact a poultry vet, and always follow product labels and your vet's instructions for any medication. How we write health content.

Chickens need vitamin K for normal blood clotting, and a complete commercial feed already supplies enough, so most backyard flocks never need a supplement. Deficiency is uncommon, but bleeding problems can also come from rat poison, some medications or coccidiosis. Here is what to know and when to call a veterinarian.

Key Takeaways

Vitamin K is needed to make blood-clotting proteins; the main sign of deficiency is impaired clotting and bleeding.
The published requirement is 0.5 mg per kg of feed for laying hens and young chicks; complete feeds include it in the vitamin premix.
Causes include diets without a vitamin premix, antimicrobials in feed, coccidiosis, sulfaquinoxaline and anticoagulant rat poisons.
Chickens on a complete feed do not need routine vitamin K supplements.
Unexplained bleeding or sudden deaths need a veterinarian.

Correction: an earlier version of this article gave an incorrect requirement attributed to unnamed experts, recommended weekly supplements, listed invented toxicity and deficiency signs, and claimed without support that vitamin K improves calcium absorption and immunity.

What vitamin K does

Vitamin K is a fat-soluble vitamin that chickens need to produce prothrombin and other blood-clotting proteins. Without enough of it, blood clots slowly and small injuries or internal damage can lead to serious bleeding. In deficient young chicks, blood prothrombin can fall to as little as 2% of normal.

It comes in natural forms, such as phylloquinone (vitamin K1) found in green leafy plants and menaquinones made by bacteria, and a synthetic form, menadione, which is what poultry feeds usually contain.

How much vitamin K chickens need

The National Research Council requirement, reproduced in the Merck Veterinary Manual, is 0.5 mg of vitamin K per kilogram of feed for laying hens and for young leghorn-type chicks. Commercial feeds include vitamin K in their vitamin premix, usually with a safety margin.

According to Merck, vitamin deficiencies in poultry are most often caused by leaving the vitamin premix out of the diet. That is a risk with home-mixed rations, not with a complete feed. Hens also pass vitamin K into their eggs, so chicks from hens on a poor diet can start life short of it; the Merck Veterinary Manual advises that breeder diets be well fortified. See our chicken feed guide for choosing one.

What causes vitamin K deficiency and bleeding

Diet: low vitamin K in the feed, or in the hen’s diet, which affects her chicks.
Less gut production: reduced bacterial synthesis in the intestine, including from antimicrobials in the feed.
Coccidiosis: intestinal damage from coccidiosis can lead to excessive bleeding.
Sulfaquinoxaline: this sulfonamide blocks vitamin K; at high feed levels it causes widespread hemorrhages.
Anticoagulant rat poisons: products such as warfarin block vitamin K and can cause sudden death with internal bleeding.

Keep rodent bait where chickens cannot reach it, and see our tips on keeping rats out of the coop.

Signs of vitamin K deficiency

The Merck Veterinary Manual describes impaired blood clotting as the major sign. Look for:

Bleeding under the skin or bruising on the breast, legs or wings.
Internal bleeding into the abdomen or on the intestine, which can be fatal.
Anemia (pale, weak birds) following blood loss.
Bleeding that does not stop from minor wounds; in deficient birds, clotting time can stretch from about 20 seconds to 5-6 minutes or longer.

Anticoagulant poisoning often shows up as sudden death with hemorrhages in the lungs, intestine or abdominal cavity.

What to do if you suspect a problem

Remove any possible source: rodent bait, a home-mixed feed without a premix, or medications added without veterinary advice.
Call a veterinarian. Sulfonamide-related bleeding usually responds to vitamin K, but dose and form should be decided by the vet.
If a bird dies with unexplained bleeding, ask the vet about a necropsy; a laboratory can test the liver for anticoagulant rodenticides.
Check that the whole flock is on a complete feed made for its age.

Greens, supplements and safety

Leafy greens such as kale, spinach and collards contain vitamin K1, and they make a fine treat. Greens also help keep egg yolks a deep orange color. Keep all treats and greens to what the flock can eat in about 20 minutes so they do not dilute the balanced feed.

There is no known toxicity from high intakes of natural vitamin K1 or K2. The synthetic form, menadione, can be harmful at high doses in some species, so do not add extra vitamin K products unless a veterinarian recommends it.

FAQs

Do chickens need a vitamin K supplement?

Not if they eat a complete feed, which already contains vitamin K. Supplements are for diagnosed problems under veterinary direction.

What happens if a chicken eats rat poison?

Anticoagulant rat poisons block vitamin K and cause internal bleeding, often seen as sudden death. Contact a veterinarian right away if you suspect exposure.

Can chickens get too much vitamin K?

No toxicity is known for natural vitamin K1 or K2. The synthetic form, menadione, can be harmful at high doses, so follow label or veterinary directions.

Can coccidiosis cause bleeding problems?

Yes. The intestinal damage from coccidiosis can lead to excessive bleeding, and it is listed among the causes of vitamin K problems in poultry. Coccidiosis needs its own treatment.

Why might newly hatched chicks bleed easily?

Chicks depend partly on vitamin K passed into the egg by the hen, so chicks from hens on a poor diet can be deficient. Breeder hens should eat a well-fortified feed.

Conclusion

Vitamin K keeps chickens’ blood clotting normally, and a complete feed provides what they need. Real bleeding problems usually point to rat poison, certain drugs, coccidiosis or a feed without a vitamin premix, so call a veterinarian instead of reaching for a supplement.

Sources

Checked September 2026. Labels change, so always read the label on the product you buy. See our editorial policy for how we research health articles.