[Osteochondrosis syndrome and arthropathia deformans as the cause of habitual and stationary luxatio incompleta of the sixth thoracic vertebra in laying hens with paralysis].

151 laying hens were kept in two experiments until the age of 610 or 786 days in floor pens, large cages with flat wire floor or small cages having inclined wire floor bottoms of 8 or 15 degrees. Paralysis was observed in 24 of the 151 hens. There was no relationship between the incidence of paralysis and the different housing systems. Fractures of the vertebral column or decreased stability of the skeleton were not observed. But in all of the 24 hens the paralysis was the result of the compressed spinal cord. The cause of the compression was the luxatio incompleta of the 6th thoracic vertebra. Different degrees of arthropathia deformans were observed in the diarthrotic vertebral joints of all the hens of the two experiments. The arthrotic lesions were accompanied by deformed articular surfaces. The destroyed and deformed articular surfaces were the cause of the instability of the 6th thoracic vertebra with spondylolisthesis or luxatio incompleta. The hypothesis, that the arthrotic lesions developed during the growing period of the hens, was supported by histological findings of disturbed growth of the epiphyseal cartilage. Overstressing of the epiphyseal cartilage was the causative agent of the arthrotic lesions in the vertebral joints. In this way the lesions are very similar to the osteochondrosis syndrome in broiler chickens and fast growing mammals.