Effect of cholecalciferol derivatives on the mechanical properties of chick bones.

Chicks were depleted of vitamin D, divided into groups, and treated daily with (a) cholecalciferol, (b) 1 alpha-hydroxycholecalciferol [1 alpha (OH)-D3], (c) 24R, 25-dihydroxycholecalciferol [24R,25-(OH)2D3], or (d) 1 alpha (OH)D3 and 24R,25(OH)2D3. Two additional groups of chicks were studied, one that was continuously depleted of vitamin D, and another that was continuously supplemented with the vitamin, since day 1. After killing, the tibiae were removed and tested for their mechanical properties. Bending load was applied to the midshaft, and the intrinsic properties of this site, its quantity and geometry were analyzed. From a mechanical point of view, the weakest bones found were of birds depleted of vitamin D, whereas the strongest were of those treated with 1 alpha (OH)D3. Only the bones of the 24R,25(OH)2D3-treated or the 1 alpha (OH)D3 and 24R,25(OH)2D3-treated groups of birds showed mechanical properties comparable to those obtained with vitamin D-replete chicks.