Vitamin A is crucial for a healthy immune system, healthy feathers and skin as well as vision health. Plants don’t contain active vitamin A; they contain vitamin precursors in the form of carotenoid plant pigments with carotene being the most important of the pro-vitamin A compounds which the body converts into vitamin A.
The liver stores a majority of the vitamin A in the body with the preferential storage form being retinyl palmitate. Additional stores are in the kidneys, adrenals, blood, and lungs. When vitamin A is required by the body it is mobilized from the liver.
Sources of vitamin A are typically the foods that are orange in color like sweet potato, carrot, pumpkin, cantaloup, mango, and passion fruit. You might be surprised though that vitamin A also found in cherries and watermelon as well as kale, broccoli, and Oak Leaf Lettuce.
Some avian species like Eclectus and certain Amazons respond better to higher levels of vitamin A in their diet. The increased need for vitamin A in Amazons is often linked to increased immunity to viral disease (poxvirus).
Increased dietary cartenoids do not contribute to potential vitamin A toxicity because they're not converted into retinol unless there is a metabolic need for vitamin A; at excessive levels they may result in a temporary yellow pigmentation of the skin and fat.
Hypovitaminosis A (low vitamin A) can cause abnormal changes in the tissues forming the outer layer within the oropharynx, choana, sinuses, GI tract, urogenital and reproductive tracts, and uropygial gland as well as abnormal thickening of the outer layer or skin on the feet. All-seed diets and even diets that are a mixture of half seeds and half pellets are deficient in vitamin A.
Clinical signs of low vitamin A are nasal discharge, sneezing, periorbital swelling, conjunctivitis, labored breathing, polyuria, excessive thirst, poor feather quality, feather picking, and anorexia. White plaques (hyperkeratosis) may develop in and around the mouth, eyes, and sinuses. In vitamin A deficient birds, yellow, orange, and red feather colors are much duller and the green plumage (made of yellow carotenoid and blue caused by scattered light) is affected too.
Treatment involves providing a balanced diet of fresh fruits, vegetables, and pulses/legumes (peas and beans), and working with your Avian Vet to identify and treat any secondary infections or symptoms resulting from the deficiency. Providing a balanced diet is only part of the challenge ... making sure your bird EATS it is the other challenge. For this reason it’s recommended that you provide a good quality pellet for the balanced vitamins and minerals that many parrots lack.