Cage Layer Fatigue in Poultry

The term cage layer fatigue was initially used in North America (Couch, 1955) to describe a leg weakness in high producing hens housed in cages. Caged layer fatigue (CLF) seems to be an extreme consequence of loss of structural bone in the vertebrae that leads to spinal bone collapse and paralysis (Urist and Deutsch, 1960 Bell and Siller, 1962) which is and characterized by an inability to stand on their feet and fragile bones. It is mainly observed in young layer hens reared in batteries in the period of maximum egg-laying. 

High-producing laying hens maintained in cages sometimes show paralysis during and just after the period of peak egg production due to a fracture of the vertebrae that subsequently affects the spinal cord. Birds become lame and are reluctant to stand in the cage. The fracture is caused by an impaired calcium flux related to the high output of calcium in the eggshell. Because medullary bone reserves become depleted, the bird uses cortical bone as a source of calcium for the eggshell. Affected birds are invariably found on their sides in the back of the cage. At the time of initial paralysis, birds appear healthy and often have a shelled egg in the oviduct and an active ovary. Death occurs from starvation or dehydration because the birds cannot reach feed or water. Egg shells become thin.

Cage layer fatigue is easy to prevent through proper management practices. Affected birds will recover if moved to the floor. A high incidence of cage layer fatigue can be prevented by ensuring the normal weight-for-age of pullets at sexual maturity and by giving pullets a high calcium diet (minimum 4.0% Ca) for at least 7 days prior to first oviposition. Diets must provide adequate quantities of calcium and phosphorus to prevent deficiencies. However, feeding diets that contain >2.5% calcium during the growing period produces a high incidence of nephrosis, visceral gout, calcium urate deposits in the ureters, and sometimes high mortality, especially in the presence of infectious bronchitis virus. Eggshell strength and bone strength can both be improved by feeding ~50% of the dietary calcium supplement in the form of coarse limestone, with the remaining half as fine particle limestone. Offering the coarse supplement permits the birds to satisfy their requirements when they need it  most, or allows the coarse material to be retained in the gizzard where the calcium can be absorbed continuously. A readily assimilable calcium and/or calcium phosphate supplement is effective if started very soon after paralysis due to calcium deficiency develops. Adding a vitamin/electrolyte supplement to drinking water is recommended in any age bird suffering from this condition.