These are conditions in which there are excess amounts of bone due to failure of normal osteoclastic activity. There are various disease conditions in which there is production of increased amounts of bone including callus during fracture repair and exostoses associated with chronic arthritis. This occurs in larger breeds of dog and is probably a manifestation of a similar condition in puppies of other breeds in which it has been termed Moller-Barlow's disease or infantile scurvy . The cause is not known but suggestions include excessive or inappropriate supplementation with minerals and vitamins. Recent evidence suggests that some metaphyseal lesions may be a result of canine distemper infection.
Epiphyseal cartilage is normal and calcifies in the normal way.
Osteoid produced is abnormal and is not normally mineralised, the calcified cartilage appearing prominent on radiographs. This is a proliferative disease of limb bones usually associated with chronic disease elsewhere in the body, normally in the chest. The pathogenesis is unclear but seems to be related to changes brought about via the autonomic nervous system. This may occur in cats fed excess liver and is associated with the formation of exostoses, particularly on the cervical vertebrae, in the region of ligament and tendon attachment. This is a disease of farm animals grazing contaminated pastures around certain industrial sites.