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Locomotory system disorders, bone breakage and associated infections contribute to low productivity, premature culling, carcass condemnations, and mortality. Bone strength is determined not only by the volume of bone tissue and the microarchitectural organization, but also by the degree of mineralisation of the bone matrix.
Cross-sections of tibiae from young (A), adult (B) and aged (C) laying hens
Indicators of bone mineral status are bone density, bone mineral content, bone ash, and bone breaking strength. Bone mineral density (BMD) is highly correlated with bone rigidity (the ability to resist deformation) and strength (the ability to resist fracture). Various methods exist to assess leg fragility :
- the second moment of area is calculated according to bone’s geometrical resistance to bending.
- the limit of elasticity refers to the stress up to which the bone is deformed elastically
- the bending strength is the highest bending stress on the surface of the flexed bone
- the fracture stress is the bending stress at the point of fracture
- toughness represents the work needed to deform the bone up to its failure