Effects of diet on total calcium, vitamin D and parathyroid hormone in falcons

Wild falcons feed almost exclusively on whole prey, typically catching smaller birds in flight. Captive raptors are generally fed whole prey diets, such as chicks, rats and quail, but falconers often supplement this diet with small amounts of deboned, lean muscle such as beef, rabbit or horse meat for variety, convenience or to reduce costs. The effects of this alteration are undetermined, but cases of metabolic bone disease due to failure of calcium homeostasis have been seen in the authors' clinics in raptors where the diet fed has been predominantly muscle with little or no whole prey provided. This study aimed to assess the effects of adding 10 per cent lean meat to the diet of captive falcons to calcium, Vitamin D3 and parathyroid hormone (PTH) levels. Whole prey diets have a calcium : phosphorous ratio of 1.5:1 (Bird and Ho 1976). Meat without bone has similar total calcium levels of 0.02–0.03 per cent of dry matter (Ullrey 2003), but has a calcium : phosphorous ratio of 1:20 (Macwhirter 2009), leading to an effective decrease in available calcium due to reduced intestinal uptake. As a result, feeding whole meat diets can lead to nutritional secondary hyperparathyroidism. Circulating calcium levels decline leading to increased PTH secretion and resorption of mineral from bone. Ongoing dietary imbalance leads to failure of replacement of depleted bone stores and continued demineralisation. Deviation of long bones and multiple folding fractures are common findings in raptors fed exclusively on red meat diets. Metabolic bone …