Noninfectious Skeletal Disorders in Breeders (Poultry)
Cage layer fatigue (see Hypocalcemia, Sudden Death, Osteoporosis, or Cage Layer Fatigue (Poultry)) describes a syndrome in which laying hens become paralyzed in their cages and have brittle bones. Layers 25–50 wk old are most severely affected. Osteopenia in cage layer fatigue is a consequence of osteoporosis, a deficiency in the quantity of normal fully mineralized structural bone, and osteomalacia, a reduction in bone density. The sternum is often deformed, and the ribs infolded at the junctions of the sternal and vertebral portions. Fractures occur in the long bones and vertebrae. Bone cortices are thin, and the medullary bone is osteomalacic. Parathyroid glands are hypertrophic and hyperplastic. This syndrome is due in part to a lack of exercise of hens held in cages and to selection for high egg production, but poor nutrition, with inadequate calcium, phosphorus, and/or vitamin D, exacerbates the condition. Although prevention of osteopenia in layers with nutritional management has not been successful, sources of calcium that enable the slow release of mineral, such as oyster shell, appear to give the best results to reduce development of osteopenia and improve eggshell quality.