Dyschondroplasias, including osteochondrosis, in boars between 25 and 169 days of age: histologic changes.

Microscopic sections of physeal and articular-epiphyseal (A-E) cartilages from major limb bones of 60 boars between 25 and 169 days of age were examined. The objectives in this study were to determine the age of onset and pathogenesis of osteochondrosis, a defect of endochondral ossification. Lesions regarded as typical of osteochondrosis were associated with physes of pigs from 25 days of age, indicating an earlier age of onset than has generally been documented. Two morphologically distinct lesions were observed, but both had areas with increased depth of the zone of hypertrophying chondrocytes. Some lesions were repairing. With increasing age of the pigs, the number of involved physes increased in each of 6 different age groups up to 169 days. Lesions associated with physes were observed in boars younger than those with lesions associated with A-E complexes. A few pigs at, or older than, 53 days of age, had osteochondrosis-like lesions involving epiphyseal growth cartilages. However, a dyschondroplasia different from osteochondrosis and typified by chondrolysis was more frequently associated with A-E complexes of pigs at or greater than 79 days of age. The number of affected cartilages and sites with this type of lesion also increased with age. Although osteoarthrosis had not developed in any of the pigs, it is probable that chondrolytic areas were precursors of degenerative joint disease. To date, osteochondrosis has been used to encompass lesions involving physes and A-E complexes. However, in view of the findings in the present study, dyschondroplasia is the preferred term to be used generically and then qualified by morphologic description, since causations may be different.