The Effect of UV-B Lighting

[timotian]

 

 

Vitamin D tightly regulates calcium metabolism in birds as in mammals; it decreases renal clearance and increases intestinal absorption of calcium. The metabolism of vitamin D is closely controlled by parathyroid hormone secreted from the parathyroid glands in response to low serum ionized calcium concentrations.

 

 

 

 

Birds acquire vitamin D3 from a combination of endogenous synthesis and dietary supply. The natural synthesis of vitamin D3 begins with the conversion of cholesterol to 7-dehydrocholesterol by isomerization. This reaction occurs in the featherless epithelial cells of the bird’s skin and requires radiation in the 285-315nm wavelength (ultraviolet [uV]-B) spectrum. Poultry have been shown to have 30 times more provitamin D on the featherless skin of the legs compared with the back, indicating the importance of this area for vitamin D metabolism. Only small amounts of provitamin D were found in preen gland oils in the same study. Poultry do not have a dietary requirement for vitamin D if they are supplied with adequate UV-B radiation.

 

 

If vitamin D3 is supplied in the diet, it can be absorbed with 60-70% efficiency in birds. Vitamin D can be toxic, causing soft fluorescent tubes tissue calcification and renal failure if fed to excess. Some species of psittacine birds, Harrison’s High such as macaws, seem more susceptible than others to clinical signs of vitamin D toxicosis. To prevent toxicity, dietary vitamin D is supplied as the inactive precursor, cholecalciferol, which requires metabolism by a two-stage hydroxylation to become biologically active. Failure to provide adequate light in the UV-B spectrum to poultry while feeding diets with low calcium or vitamin D3 content will lead to a breakdown in vitamin D metabolism and, subsequently, clinical signs of hypocalcemia. Rickets is a common abnormality in commercial poultry reared with inadequate calcium, vitamin D3 or light in the UV-B range. In commercial poultry flocks, the incidence of skeletal abnormalities is 1.72%. Hypocalcemic birds also show poor reproductive performance. In most situations with commercial poultry, there is a compromise between the amount of dietary vitamin D3 administered (on the basis of economy and toxicity) and UV light supplementation provided for adequate vitamin D metabolism. Hypocalcemia in captivity is a well-recognized syndrome in African grey parrots (Psittacus erithacus),

 

although its etiology is still unconfirmed. Affected adult birds present clinically with a variety of neurological signs, ranging from slight ataxia to seizures, which respond to calcium or vitamin D3 therapy. In juvenile grey parrots, osteodystrophy is a common presenting clinical sign, Radiographs of affected birds will show curvature of the long bones.

 

Histopathology of the parathyroid glands and bone from osteodystrophic juvenile grey parrots suggests a diagnosis of nutritional secondary hyperparathyroidism. Although hypocalcemia is reported in other psittacine birds, it appears to be most prevalent in African grey parrots. It is possible that the syndrome could be due to either primary hypoparathyroidism or hyperparathyroidism secondary to inadequate husbandry. Captive grey parrots are usually fed seed-based diets containing low levels of calcium and vitamin D3 with high levels of phosphorus. This would be expected to lead to a secondary nutritional hyperparathyroidism but does not explain why grey parrots are more susceptible to hypocalcemia than other captive parrot species. These birds are indigenous to West Africa and live in open forest with low shade where they are exposed to high levels of UV light. South American species live below a dense tree canopy, which reduces their exposure to UV-B radiation.

 

 

In captivity, parrots are usually kept indoors with limited access to UV light. This might suggest that African grey parrots require more UV light supplementation than other psittacine birds and may explain the increased susceptibility of this breed to hypocalcemia. Initial studies have shown that the provision of adequate UV light might be important for behavioral responses and, in particular, mating rituals in companion psittacine birds. Over 68% of psittacine birds have UV-reflective and fluorescent plumage, the former of which has been shown to have a significant effect in the selection of a mate in budgerigars. Bulbs providing UV-B radiation have recently been marketed in aviculture circles to encourage improved breeding performance. However, the role of UV-B radiation in the control of vitamin D metabolism has not been researched in psittacine birds. The majority of captive reptiles require artificial lighting that emits radiation in the UV-B (315-285nm) spectrum. Failure to provide adequate lighting leads to inadequate calcium metabolism and subsequent metabolic bone disease, often with accompanying pathologic fractures. This condition may be difficult to treat, as the patient is often presented in an advanced clinical state, and animals usually succumb to secondary renal hyperparathyroidism. One might expect this to be the case as well in psittacine birds indigenous to countries with high UV light levels. However, artificial lighting has not traditionally been considered necessary for captive psittacine birds.

 

 

Michael Stanford, BVSc, MRCVS<br><br>Post edited by: timotian, at: 2009/05/17 07:37

[danmcq]

Thanks for posting this very informative article.

 

The statement "However, artificial lighting has not traditionally been considered necessary for captive psittacine birds."

 

This is sad but true. It good full spectrum lighting with both UVA and UVB of correct percentages of each of vitally important for birds that are kept in the house with no outside exposure, during winter months especially when temperatures and weather do not permit sufficient outdoors time for UVB absorption.

 

If people are feeding a pelleted diet formulated specifically for each species, they include the correct amounts of Vitamin D3 supplement. Otherwise, good indoor avian lighting is a must.