Chickens need 13 essential vitamins to stay healthy: four fat-soluble vitamins (A, D, E, and K) and nine water-soluble B vitamins (B12, biotin, folic acid, niacin, pantothenic acid, pyridoxine, riboflavin, and thiamin). Chickens can manufacture their own vitamin C, so it’s not a dietary requirement. Most commercial feeds are formulated to cover these bases, but understanding what each vitamin does helps you spot deficiencies early and make smarter feeding choices.
Fat-Soluble Vitamins: A, D, E, and K
Fat-soluble vitamins dissolve in fat and can be stored in the body, which means chickens build up reserves over time. That storage ability is a double-edged sword: it buffers against short-term gaps in the diet, but it also means oversupplementation can lead to toxic buildup.
Vitamin A
Vitamin A supports vision, respiratory health, and the lining of the digestive tract. A deficiency shows up first in the eyes: watery eyes, swollen membranes, and in severe cases, a buildup of cheesy material around the eyes that can lead to blindness. The respiratory system takes a hit too, with white or yellowish nodules forming in the throat and esophagus. Young chicks are especially vulnerable. Commercial broiler feeds typically include 10,000 to 15,000 IU of vitamin A per kilogram of feed, while laying hen feeds run 8,000 to 13,000 IU/kg.
Vitamin D
Vitamin D controls how chickens absorb and use calcium. For laying hens, this is critical: the hen’s body pulls about 40% of the calcium in each eggshell from a special bone reservoir called medullary bone, and vitamin D regulates that entire process. Without enough of it, eggshells thin out, bones weaken, and chicks develop rickets. The active form of vitamin D triggers the proteins that transport calcium in the intestines and the shell gland. Most layer feeds include vitamin D3 at around 2,800 IU/kg or higher. Pastured birds that spend plenty of time in sunlight synthesize vitamin D through their skin, making deficiency far less likely for free-range flocks.
Vitamin E
Vitamin E works closely with the mineral selenium to protect cells from damage. When both are lacking, chickens can develop a cluster of serious conditions: fluid leaking under the skin (exudative diathesis), brain tissue damage, pancreatic deterioration, and muscular dystrophy. Vitamin E also plays a role in immune function. Starter feeds for young broilers average about 46,000 IU per ton of feed, while breeder feeds run even higher at roughly 61,000 IU per ton, reflecting the greater demands of reproduction.
Vitamin K
Vitamin K is essential for blood clotting. Deficient birds bruise easily and can bleed out from minor injuries. Green forages are a natural source, and most commercial feeds include supplemental vitamin K as well.
B Vitamins and Their Roles
The B vitamins are water-soluble, meaning chickens can’t store them the way they store fat-soluble vitamins. They need a steady daily supply through feed or forage. B vitamins drive energy metabolism, nervous system function, and growth.
Riboflavin (B2) is one of the most important to watch. Deficient chicks grow poorly, develop diarrhea, and lose the ability to straighten their legs at the hock joint. Their toes curl inward progressively until the chicks end up walking on their hocks. This “curled-toe paralysis” can kill chicks by the third week of life. On examination, the sciatic nerves of affected birds are visibly swollen. Starter feeds typically supply around 7.7 grams of riboflavin per ton of feed.
Niacin supports skin health and digestion. Deficiency causes inflammation of the mouth and tongue, poor feathering, and bowed legs in ducks and turkeys (which are more sensitive than chickens). Thiamin (B1) is critical for nervous system function, and deficiency leads to a characteristic “stargazing” posture where the head tilts backward. Folic acid supports feather development and red blood cell formation, while B12 is necessary for growth and hatchability. Pantothenic acid deficiency causes crusty sores around the beak and eyes, and biotin deficiency leads to foot pad lesions and poor hatchability in breeders.
How Requirements Change With Age
Vitamin needs are not the same across a chicken’s life. Young chicks in the starter phase (roughly days 1 through 14) need the highest vitamin concentrations in their feed to support rapid growth and developing organ systems. As broilers move through grower, finisher, and withdrawal phases, the supplementation levels step down across the board. For example, vitamin A drops from about 8.4 million IU per ton in starter feed to around 5.2 million IU per ton in the withdrawal phase.
Breeder birds buck this downward trend. Their vitamin requirements are the highest of any category, exceeding even starter levels for every single vitamin. This makes sense: breeding hens must transfer vitamins into the egg to sustain embryo development. Breeder feeds average around 9.6 million IU of vitamin A, 3.9 million IU of vitamin D, and 61,000 IU of vitamin E per ton, along with elevated levels of all B vitamins. Folic acid and biotin are roughly double the starter levels in breeder rations.
Natural Sources From Pasture and Forage
Free-range and pastured chickens can get a surprising amount of their vitamins from the environment. Green forages are rich in all the fat-soluble vitamins except D, and pastured birds get their vitamin D from sunlight. Leafy greens like kale, alfalfa, and clovers are particularly valuable. Kale was historically grown specifically as poultry food on many farms, and alfalfa provides highly bioavailable calcium alongside its vitamins.
Pasture vegetation supplies ample riboflavin, folic acid, and B6. The B vitamins that are harder to find in plants, specifically niacin, thiamin, and B12, come from animal sources. Chickens on healthy pasture hunt insects, worms, spiders, and other invertebrates that provide these nutrients. Insects deliver roughly four times more usable protein and energy per unit of weight compared to standard feed rations, and they carry B12 that plant-based diets lack entirely.
For winter months or when pasture access is limited, traditional poultry keepers fed root vegetables like mangels (a large livestock beet) and carrots, along with cabbage and sprouted grains like oats or wheat. These keep the vitamin supply going when fresh forage isn’t available.
Risks of Oversupplementation
Because fat-soluble vitamins accumulate in the body, it’s possible to give too much. Excess vitamin A causes poor appetite, reduced growth, and changes to skin and mucous membranes. Excess vitamin D is potentially more dangerous: it forces excessive calcium into the bloodstream, which can calcify soft tissues like the kidneys and arteries, leading to irreversible organ damage. Growth slows, appetite disappears, and in severe cases the bird dies.
Water-soluble B vitamins carry much less toxicity risk because excess amounts are excreted rather than stored. The practical takeaway: if you’re using a quality commercial feed formulated for your birds’ life stage, additional fat-soluble vitamin supplements are rarely necessary and can do more harm than good. Supplementing B vitamins or offering natural forage carries far less risk of overdoing it.
Matching Feed to Your Flock
The simplest way to meet your chickens’ vitamin needs is to use a commercial feed matched to their life stage: starter for chicks, grower for adolescent birds, layer for hens in production, and breeder feed for birds producing hatching eggs. These formulations are designed with the declining or escalating vitamin profiles that each stage demands.
If you mix your own feed, a poultry-specific vitamin premix is essential. Grains alone do not supply adequate levels of most vitamins, particularly A, D, riboflavin, and B12. Pastured flocks have an advantage because forage and insects fill many gaps, but even pastured birds benefit from a balanced base feed, especially during winter or in climates with limited sunlight.