Effect of Age on Bone Structure Parameters in Laying Hens.

Changes in medullary and cortical bone structure with age remain unclear. Twenty Hy-Line W36 hens, 25 or 52 weeks of age, were euthanized, and both tibiae were collected when an egg was present in the magnum. Serial cross sections of the tibiae were stained with Alcian blue. The bones were scanned using micro-computed tomography. Trabecular width (Tb.Wi) was significantly higher (p < 0.05) in 25-week-old hens, whereas medullary bone tissue volume (TV) was significantly higher (p < 0.01) in 52-week-old hens. 25-week-old hens had significantly higher (p < 0.01) bone volume fraction (BVF = calcified tissue / TV). Moreover, the cortical bone parameters were significantly higher (TV and bone mineral content (BMC) at p < 0.05, and bone volume (BV) and BVF at p < 0.01) in younger hens. Open porosity and total porosity, which indicate less density, were significantly higher (p < 0.01) in older hens. Older hens showed significantly higher (p < 0.01) tibial diaphysis TV than younger hens. Younger hens had significantly higher (p < 0.01) BV, BVF and bone mineral density (BMD) of the tibial diaphysis. These findings reveal that reductions in medullary bone quality might be associated with age-related low estrogen levels and stimulation of osteoclastic bone resorption by parathyroid hormone. Cortical bone quality decreased with enlargement of the Haversian canals and loss of volume, with a longer egg-laying period leading to osteoporosis.