Use of dietary Ca and P and photon absorptiometry to predict mechanical properties of bone in swine

Photjon absorptiometry provides a noninvasive method to determine bone mineral content (BMC) in patients, yet the relationship of BMC and mechanical properties of bone has not been established. To establish the relationship between mechanical properties of bone and BMC, the third metatarsal bones (MT) from 72 growing pigs (23.4 +- 2.5 kg) were collected after either 5, 10 or 15 weeks (T1, T2 and T3) of being fed 1 of 9 treatments. A central composite response surface design was utilized to provide a range of Ca (0.4 to 1.2%) and P (0.4 to 1.2%) levels. Using photon absorptiometry, BMC was predicted from four scans on the midshaft of excised bone, mechanical tests (3-point flexure test) were made and the bone was ashed. BMC can predict force (r2 = 0.89) and ash (r2 = 0.97);however, interactions with Ca, P and T were detected. Stress was not predicted reliably with BMC (r2 = 0.43), ash (r2 = 0.40) or dietary Ca and P (r2 = 0.41)