Thesis submitted in accordance with the requirements of The Royal College of Veterinary Surgeons for the Diploma of Fellowship by Michael David Stanford.
August 2005
Abstract
Hypocalcaemia is a commonly presented pathological condition in the grey parrot (Psittacus e. erithacus) although rarely reported in other psittacine birds. Signs in the adult birds are neurological ranging from mild ataxia to seizures responding rapidly to treatment with calcium or vitamin . Captive bred grey parrot chicks suffering from calcium metabolism disorders present as juvenile osteodystrophy with characteristic bowing of the long bones and pathological fractures in severe cases. The condition is comparable to rickets in poultry. This 3 year longitudinal study reports the effects of husbandry changes on the plasma ionised calcium, 25 hydroxycholecalciferol and parathyroid hormone concentrations in two groups of 20 sexually mature healthy grey parrots.
The provision of a pellet diet with an increased vitamin and calcium content significantly increased the plasma concentration of ionised calcium and 25 hydroxycholecalciferol over a seed fed control group. The provision of 12 hours daily artificial ultraviolet radiation (UVB 315-285nm spectrum) significantly increased the plasma ionised calcium concentration independent of the diet fed. In the seed group plasma 25 hydroxycholecalciferol concentrations significantly increased after the provision of UVB radiation but not in the pellet group. In a separate study with South American parrots (Pionus spp.) UVB radiation did not have a significant effect on vitamin metabolism.
Blood samples were analysed from wild grey parrots recently caught in Guyana for the export pet trade. Serum ionised calcium concentrations were significantly lower in the wild birds than the captive main study group independent of the husbandry conditions employed. A significantly higher 25 hydroxycholecalciferol concentration was demonstrated in the pellet fed group over the wild grey parrots. The provision of UVB radiation resulted in significantly higher 25 hydroxycholecalciferol concentration independent of the diet fed over the wild greys.
Significantly reduced plasma ionised calcium and 25 hydroxycholecalciferol concentrations were demonstrated in 19 adult grey parrots with neurological signs. In 5 clinical cases of hypocalcaemia a significantly increased parathyroid hormone concentration was established suggesting that hypocalcaemia in grey parrots is due to nutritional secondary hyperparathyroidism. Comparative histological studies between tissues from grey parrot chicks with severe juvenile osteodystrophy and skeletally normal chicks demonstrated statistical differences between the groups. Histological changes were consistent with nutritional secondary hyperparathyroidism. Bone densitometry measurements demonstrated a statistically significant reduction in bone mineral density in osteodystrophic grey parrots compared with skeletally normal chicks. Progeny testing established that the provision of a pellet diet or UVB radiation would prevent radiographic evidence of juvenile osteodystrophy.
This study concludes that the provision of adequate dietary calcium and vitamin , plus UVB radiation are essential for the prevention of disorders of calcium metabolism in captive grey parrots.