What is vitamin A?
Vitamin A is actually a group of fat-soluble retinoids with similar biological activity. Vitamin A plays a role in:
- Epithelial cell growth and repair maintaining the integrity of respiratory, urinary, and intestinal tracts
- Immune function
- Bone growth
- Vision, particularly night vision
- Feather color (carotene is incorporated into some pink, red, and yellow feathers) (Fig 1)
What are dietary sources of vitamin A?
High levels of vitamin A are found in foods of animal origin in the form of retinyl esters. Liver, fat, fish liver oils, and egg yolk are particularly good sources of vitamin A. Some plants and insects are also good sources of carotenoids. The dietary carotenoids found in dark, leafy greens and yellow and orange vegetables contain important precursors of vitamin A (download Table 1 Vitamin A content of selected raw vegetables and fruit).
What are the dietary requirements for vitamin A in the parrot?
Vitamin A requirements are not specifically known in the parrot. Diets containing 2000 IU vitamin A/kg were sufficient for maintenance in the cockatiel (Nymphicus hollandicus), however cockatiels developed no signs of deficiency (except possibly immune dysfunction) when vitamin A was withheld for 8 months.
What clinical signs are associated with vitamin A deficiency or toxicity?
All-seed diets are deficient in vitamin A. In cockatiels, clinical signs do not develop until deficiency is prolonged and severe (liver vitamin A < 50 IU/g). Hypovitaminosis A may lead to:
- Squamous metaplasia or hyperkeratinization of mucous epithelial cells lining the respiratory tract, oropharynx and salivary glands, esophagus, cloaca, ureters and collecting ducts, bursa of Fabricius, vagina, conjunctiva
- Non-specific signs of illness: anorexia, ruffled feathers, poor condition
- Poor feather condition
- Immunodeficiency due to impairment of T lymphocyte function and keratinization of the bursa
- Decreased egg and sperm production, poorly formed eggshells, early embryonic death
- Neurologic signs
- Night blindness (disruption of rod function)
- Xerophthalmia or “dry eye”
- Decreased amount and volume of vocalizations
Adult cockatiels may be more susceptible to toxicity than deficiency. The signs of vitamin A toxicity may be similar to signs of deficiency and include hyperkeratinization leading to problems such as conjunctivitis and enteritis. Additional signs of toxicity may include disruption of long bone growth plates resulting in bone deformity, fractures, and slow growth.
Table 1. Vitamin A content of selected raw vegetables and fruit
Download Table 1 (PDF)