CHANGES IN SWINE KNEE ARTICULAR CARTILAGE DURING GROWTH

Twenty-five crossbred boars reared under normal conditions were serially slaughtered at the age of 3 days, and 5, 10, 20 and 30 wk. Five boars were slaughtered at each age and morphological, histochemical and biochemical age-related changes in femoral condylar articular cartilage were studied. No osteochondrotic joints were found in pigs 10 wk of age or younger, while 7 of the 10 boars slaughtered at 20 and 30 wk of age were osteochondrotic. Cartilage thickness increased (P < 0.05) until the age of 5 wk and decreased (P < 0.05) thereafter. Cell density decreased (P < 0.05) as age advanced. Age-associated changes found in the chemical composition of the cartilage were an increase in the concentration of dry matter and hydroxyproline and a decrease in the concentration of glycosaminoglycans (GAG) including chondroitin sulfate (ChS), keratan sulfate and hyaluronic acid. The proportions of soluble proteoglycan and 4-sulfated disaccharide from the ChS fraction decreased (P < 0.05) while the proportion of 6-sulfated disaccharide from ChS increased (P < 0.05). Osteochondrosis was observed as a disturbed endochondral ossification, and softening and fracture of the cartilage. The former was accompanied by a loss of intercellular GAG and cell necrosis, and the latter by local losses of GAG and cells. Osteochondrotic cartilage also contained higher proportions of soluble proteoglycan and 6-sulfated disaccharide, and lower proportions of 4-sulfated disaccharide than did the visually normal cartilage.