Abstract
Degenerative osteoarthritis, similar to that seen in mammals, including man, was observed in the fifth to seventh thoracic vertebral bodies of 58 two-year-old laying hens. Main gross lesions were roughening of the articular surface, narrowing or focal thickening of the articular cartilage, chondrophytes at the margins of the joints, and a decrease in length from the dorsal to ventral edge of the epiphyseal vertebral body. Histopathological changes consisted of degeneration of the matrix with an appearance of collagen fibers, erosion or ulceration, proliferation of chondrocytes, and cleft-like fractures in the articular cartilage, and necrosis and eburnation in the subchondral bone. The degenerative changes with an appearance of collagen fibers in the cartilage matrix were regarded as the initial lesions. The pathogenesis of this disorder was not clarified, however, as in mammals the anatomical characteristics of the thoracic vertebrae, the rearing environments, an anomaly of the chemical constituents of the cartilage with increased age and mechanical stress such as weightiness should be taken into consideration as the important factors.
