Nutritional osteodystrophy in South American birds of prey

ABSTRACT: Nutritional osteodystrophy is a metabolic bone disease characterized by increased bone resorption and replacement by fibrous connective tissue, resulting from a diet with excess phosphorus or deficient in calcium or vitamin D. In this retrospective study, we describe the clinical and pathological findings from six raptor chicks with metabolic bone disease. Included are a southern caracara (Caracara plancus), a black vulture (Coragyps atratus), three barn owls (Tyto furcata) and a Stygian owl (Asio stygius) presenting poor development, prostration, locomotor disorders and deformed bones. All birds were free-living orphaned juveniles that were rescued and fed by lay keepers, who inadvertently provided inadequate diets in the form of boneless meat or homemade food. During the clinical care, birds were supplemented with oral and/or parenteral calcium and given supportive treatment. The birds died spontaneously or were euthanized due to poor prognosis. At necropsy, birds revealed poor body condition, skeletal deformities, soft bones with multiple fractures, and enlarged parathyroid glands. At histopathology, bones of all birds presented thin bone trabeculae surrounded by numerous osteoclasts or plump osteoblasts, with diffuse replacement by fibrous connective tissue. Additionally, parathyroid glands were hyperplastic and hypertrophied. The diagnosis of secondary osteodystrophy of nutritional origin was determined based on clinical and pathological data and a history of apparent unbalanced calcium food supply. The aim of this study was to gather information on the pathological aspects of fibrous osteodystrophy in different species of neotropical birds of prey and to review the condition with emphasis on wild birds. The results obtained reinforce the need for adequate feeding of these species in captivity.