Michael Jones, DVM, DABVP
Vitamin A plays a crucial role in the health of avian species. It is necessary for vision, immune function, normal function of secretory tissues and growth and differentiation of epithelial cells within the respiratory tract and small intestine.3-7 Chronically low dietary vitamin A usually results in respiratory tract disease, poor feather quality and poor growth. Squamous metaplasia of epithelium within the oropharynx, choanal, sinuses, gastrointestinal tract, urogenital tract and uropygial gland and hyperkeratosis of the feet and gout may also occur.3-5 Susceptibility of birds to sinus infections in conjunction with a deficiency of vitamin A appears to be associated with blunting of the papillae of the choanal slit, which suggest inadequate differentiation of the lining of epithelial tissue lining the sinuses.
Minimum vitamin A requirements have been elucidated for various poultry and waterfowl species; however, the exact dietary requirements necessary for maintenance or toxicity in companion avian species is not known.8 Most likely the cause of hypovitaminosis A in psittacine species is the feeding of a seed based diet. Seed mixtures commonly fed to companion birds have concentrations <30 µg/kg and birds maintained on these diets often develop signs of hypovitaminosis.8
Clinical signs include white plaques, abscesses or focal kertinaceous granulomas in the oropharynx, blunting of chaoanal papillae, nasal discharge, periorbital swelling, dyspnea, polyuria, polydipsia, poor feather quality, feather picking and anorexia.5 Diagnosis is usually based upon dietary history, physical examination and cytology of the respiratory tract.
Converting the bird to a good quality pelleted diet is crucial to correcting dietary deficiencies. Immediate treatment of problems associated with vitamin A deficiency consists of the removal of plaques or abscesses, appropriate antimicrobial therapy, and supplementation of vitamin A both parenterally (maximum 20,000 IU/kg IM)9 (Aquasol A, AstroZeneca LP, Wilmington, DE) and orally as needed. Estimates of the requirements of vitamin A for maintenance is 600 µg/kg or below.8 However, be careful not to over-supplement with vitamin A as the range between deficiency and excess is very narrow compared to other vitamins.8 Many vitamin A supplements that are commercially available prescribe levels of supplementation those results in high levels of vitamin a equivalent to 7,500-30,000 µg/kg in the diet. Additionally, some commercially available pelleted diets are over formulated with vitamin A levels between 1,500-6,000µg/kg diet.8 Koutsos et al demonstrated dietary concentrations = 3,000 µg vitamin A/kg of diet can cause toxicity.8 Signs of vitamin A toxicity include poor feathering, pancreatitis, multifocal accumulation of lymphocytes within the duodenal lamina propria, hyperexcitability and exaggerated vocalizations.8 Converting the bird to a good quality pelleted diet is also crucial to correcting dietary deficiencies.
Excerpt from the article How I diagnose and manage nutritional disease in birds - Michael Jones, DVM, DABVP
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