Morphometric skeletal traits, femoral measurements, and bone mineral deposition in mice with agonistic selection for body conformation

Morphometric skeletal traits, femoral histomorphometry, and bone mineral deposition were investigated in two lines of mice (CBi+ and CBi-) divergently selected for body conformation (CBi+: high body weight, long tail; CBi-: low body weight, short tail) and in the unselected control line CBi. Linear morphometric measurements, absolute and relative skeletal weights, absolute and relative femoral weights, and total biomass sustained per unit of total or tail-less skeletal weight were increased in CBi+ mice in comparison with controls. This greater biomass implies a greater mechanical demand that is satisfied by a heavier skeleton. Looking specifically to the femur, CBi+ mice had heavier bones, both absolute and relative, with a greater diameter and a greater cortical thickness, resulting in a greater cortex/diameter ratio than controls. Although morphometric measurement and absolute skeletal weight were lower in CBI-l:han in CBL mice, the relative skeleton weight and the biomass sustained per unit of skeletal weight were not modified in the downward selection line when compared with controls. Therefore: CBi- mice did not exhibit a greater mechanical demand as CBi+ mice did. These results led us to consider at least three main aspects: bone length growth; cortical thickness/bone diameter ratio; and bone calcification. The long bones appeared to have a genetically determined predisposition tea achieve a given length, which, however, could be modified by artificial selection, Cortical thickness would be directly related to the biomass sustained, This variable increased in CBi+ mice, a genotype that supports a greater biomass than controls, and did not change in CBi- mice, which sustained. the same biomass as CBi, The pattern of mineral deposition did not accompany the functional demand because it was higher in CBi- than in CBi+; however, as artificial selection separately affected bone material quality and bone architectural design, these genotypes could express architectural modifications that override any change in bone material quality. (C) 1998 by Elsevier Science Inc. All rights reserved.