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 B12, but deficiency is very unlikely in birds that eat a complete feed, live on litter or get some animal-based ingredients. B12 is made only by microbes, so plants are not a source. This guide explains where chickens get it, what deficiency looks like and when to involve a veterinarian.
Key Takeaways
- Vitamin B12 (cobalamin) contains cobalt and is made only by certain bacteria and archaea.
- Plants, including grass and leafy greens, are not a source of B12; animal products are.
- Complete feeds contain a vitamin premix; deficiencies usually come from leaving it out.
- Signs include poor growth and feathering, nervous disorders, anemia and, in breeders, poor hatchability.
- Fatty liver hemorrhagic syndrome in hens is linked to excess energy, not B12.
Correction: an earlier version of this article wrongly said grass and leafy greens contain significant B12, named fatty liver syndrome as a main sign of B12 deficiency, claimed effects on sperm and fertilization without support, and listed B12 levels in human foods as feeding advice.
What vitamin B12 is
Vitamin B12, or cobalamin, is the only vitamin that contains a metal, cobalt. Only certain bacteria and archaea can make it. Animals get it from animal-based foods or from microbes, which is why meat, fish and eggs contain it and plants do not. Chickens need only tiny amounts, so requirements are measured in thousandths of a milligram per kilogram of feed.
Where chickens get vitamin B12
- Complete feed: commercial feeds include a premix of vitamins and minerals. See our chicken feed guide.
- Gut bacteria: bacteria in the ceca produce B vitamins, including B12, but little of it is absorbed at that point in the gut.
- Litter: birds raised on litter pick up B12 from droppings (coprophagy).
- Animal-based ingredients: feeds or foods of animal origin supply B12.
Pasture helps but does not replace feed. Free-ranging chickens eat insects and seeds and a little grass, which they cannot properly digest, and pasture offers little feed value in late fall and winter.
The published requirement is tiny: 0.004 mg per kilogram of feed for laying hens and 0.009 mg per kilogram for young leghorn-type chicks (NRC 1994, reproduced in the Merck Veterinary Manual). The Merck Veterinary Manual calls B12 deficiency highly unlikely for birds on litter or fed animal-based ingredients, and notes that vitamin deficiencies most often result from leaving the vitamin premix out of the diet.
Signs of vitamin B12 deficiency
When deficiency does occur, usually on a home-mixed diet without a premix, the Merck Veterinary Manual describes:
- Reduced weight gain and feed intake in young birds.
- Poor feathering.
- Nervous disorders.
- Anemia and gizzard erosion.
- Fatty infiltration of the heart, liver and kidneys.
In breeding hens, hatchability drops markedly. Embryos show bleeding, fatty livers and a high rate of death in mid-incubation. Leg problems (perosis) can also appear, though these are likely linked to related methionine or choline shortages.
These signs overlap with many other problems, so a diagnosis should involve a veterinarian. Our guide to chicken diseases and symptoms can help you note what you see.
B12 and fatty liver: not the same thing
B12 deficiency can cause fat to build up in the liver, but it is not the cause of fatty liver hemorrhagic syndrome. That condition in laying hens is associated with eating more energy than needed, from any source, in birds that get little exercise. It mainly affects caged laying hens, which are often found dead without warning signs, with an enlarged, fragile, bleeding liver and a lot of abdominal fat. Affected hens can have a pale comb and wattles from blood loss, and flocks may lay fewer eggs.
What to do
- Check the feed: make sure the flock eats a complete feed for its age, not a home mix without a vitamin premix.
- If you mix your own feed, include a poultry vitamin and mineral premix; even organic feeds are allowed a synthetic premix for this reason.
- Keep treats and greens to what the birds eat in about 20 minutes so they do not dilute the feed.
- If birds show poor growth, poor feathering, weakness or poor hatch rates, talk to a veterinarian before adding supplements; treatment of a confirmed deficiency should follow veterinary advice.
Do not use greens or grass to fix a suspected B12 problem. Plants do not supply the vitamin, and too many greens and scraps dilute the complete feed that does.
Protein and B12 often come from the same animal-based ingredients; see our guide to protein for chickens.
FAQs
Do grass and leafy greens contain vitamin B12?
No. Vitamin B12 is made only by microbes and is found in animal products. Greens are a fine treat but not a B12 source.
Do chickens need B12 supplements?
Not if they eat a complete feed. Deficiency is highly unlikely in birds on litter or fed animal-based ingredients.
Can B12 deficiency cause anemia in chickens?
Yes. Anemia is one of the signs, along with poor growth, poor feathering, nervous disorders and gizzard erosion.
Is fatty liver in hens caused by B12 deficiency?
Usually not. Fatty liver hemorrhagic syndrome is linked to eating more energy than needed with little exercise. B12 deficiency can cause fatty infiltration of the liver, but that is a different problem.
Does B12 affect hatching eggs?
Yes. In breeding hens, B12 deficiency markedly reduces hatchability, with many embryos dying in mid-incubation.
Conclusion
Vitamin B12 matters for chickens, but a complete feed and normal living conditions cover it. If you mix your own feed, include a vitamin premix, and involve a veterinarian before treating suspected deficiency.
Sources
- Merck Veterinary Manual: Vitamin Deficiencies in Poultry
- Linus Pauling Institute (Oregon State University): Vitamin B12
- Merck Veterinary Manual: Nutritional Requirements of Poultry
- Extension Foundation (poultry.extension.org): Avian Digestive System
- Merck Veterinary Manual: Fatty Liver Hemorrhagic Syndrome in Poultry
- Oregon State University Extension (PNW 477): How to Feed Your Laying Hens
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.
