Nodulation and folding at the costro-chondral junction of the ribs is a common consequence of osteoporosis in laying hens. Cransberg et al. (2001) used a 6-point scale to score rib deformity in cage-housed laying hens and found that 80% of the hens in their research flock were affected by 42 weeks of age, with about 30% having severe deformities. They thought that the rib deformity developed around 27 weeks of age because they noticed that hens with severe rib deformities had reduced body weight... and egg production between 27 and 31 weeks of age. Wilkins et al. (2004) demonstrated that keel palpation was a reliable means to identify healed keel bone breaks of laying hens, but used the method to investigate bone breakage from collision of free-flying hens with fixed structures in open housing systems rather than attempting to evaluate bone weakness. Caged laying hens often have keel deformities from healed breaks. These breaks are probably due to osteoporosis because the cage environment provides little opportunity for forceful impact with fixed structures.