Effect of housing birds in cages or an aviary system on bone characteristics

Sixty-nine-week-old brown egg layers were either maintained in cages or moved to a litter-floored aviary system. After 10 or 20 d, birds were selected at random from within each environment, and their tibiae removed. After drying, bones were measured and then subject to various physical measurements of strength and elasticity. Bone ash and bone calcium content were also measured. Birds maintained in an aviary initially had stronger bones as measured by force (P < 0.05). After 20 d in an aviary, birds had stronger bones, as assessed by force, than their contemporaries maintained in cages. This same relationship was seen in measures of bone stress (P < 0.05). After 20 d in the aviary system, previously caged birds had bone ash values that were intermediate between birds held only in cages or the aviary (P > 0.05). Bone calcium content was not influenced by the bird's environment. It appears that the skeleton of caged birds can be affected by providing them with an environment that allows opportunity for increased static and dynamic loading of the bones.