Conventional radiography has traditionally been employed for investigations of skeletal disease of captive elephants.1 However, it is predominantly cortical bone which is assessed by standard radiography, and quantitative assessment of bone is only possible when pathology is advanced.2 A precise and relatively non-invasive method of quantitatively assessing bone, in isolation or as a compliment to standard radiography, would have positive health and welfare implications for elephants because skeletal disease is prevalent in both extant species in captivity.3 The advent of biochemical markers of bone metabolism represents a watershed in non-invasive diagnostics of normal bone homeostasis and pathology in humans and animals alike.4 These markers are classified as markers of formation and resorption and are comprised of enzymes expressed by osteoblasts or osteoclasts, or organic compounds released during the synthesis or resorption of bone matrix.5
In this study, two human enzyme immunoassays (METRA™ Osteocalcin EIA kit, METRA™ BAP EIA kit, Quidel Corporation, San Diego, CA) and one radioimmunoassay (UniQ™ ICTP RIA, Orion Diagnostica, Espoo, Finland) were validated and used to measure osteocalcin (OC), bone alkaline phosphatase (BAP), and the C-terminal telopeptide domain of type I collagen (ICTP), respectively, three biochemical markers of bone in serum procured from a small sample population (n=12) of captive Asian elephants (Elephas maximus) of various ages from three European zoos. Serum from four adult females sampled on seven days consecutively were also analyzed to assess the existence and magnitude of the intra-individual, day-to-day variability of these markers.
Excellent cross-reactivity was found to exist between assay antibodies and elephant’s marker antigens. Significant inverse correlations were found between the age of the animals and concentrations of all three markers. Strong significant-positive correlations were also noted between serum concentrations of all three markers. No statistically significant intra-individual variability was found over seven days in the population of adult females for any of the markers assessed. The results suggest a promising role for biochemical markers of bone turnover in monitoring skeletal growth and bone disease in captive Asian elephants.
The authors wish to thank Willem Schaftenaar, DVM, and Andreas Knieriem, DVM, of Rotterdam and Hannover Zoological Gardens, respectively, whose co-operation and provision of vital samples were imperative to the completion of this research. In addition, sincere thanks go to Professor David Church, and the Department of Clinical Studies, Royal Veterinary College, London, for financial support of this study.
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