Analysis of biochemical markers of bone metabolism in Asian elephants (Elephas maximus).

Two human enzyme immunoassays (EIA) and one radioimmunoassay (RIA) were validated and used to measure osteocalcin (OC), bone alkaline phosphatase (BAP), and the cross-linked telopeptide domain of type I collagen (ICTP), in serum from Asian elephants (Elephas maximus). Sera from four adult females sampled on 7 consecutive days were also analyzed to assess the existence and magnitude of intraindividual day-to-day variability of the serum concentration of these markers. Sample dilution curves were parallel with assay standard curves, which demonstrated that excellent cross reactivity existed between assay antibodies and elephants marker antigens. Statistically significant inverse correlations were found between age and concentrations of all three markers: BAP, r = -0.862 (P < 0.01); OC, r = -0.788 (P < 0.002); and ICTP, r = -0.848 (P < 0.01). Strong positive correlations were found between BAP and OC (r = 0.797, P < 0.01), OC and ICTP (r = 0.860, P < 0.01), and between BAP and ICTP (r = 0.958, P < 0.01). No statistically significant intraindividual variability was found over 7 days in the four adult females for any of the markers assessed (OC: P = 0.089; ICTP: P = 0.642; BAP: P = 0.146; n=4 in each case). The overall coefficient of variability observed in this group of animals was 10.3%, 7.4%, and 5.5% for OC, BAP, and ICTP, respectively. These results suggest a potential role for biochemical markers of bone turnover in monitoring skeletal health and bone disease in Asian elephants.