EFFECT OF INCREASED WEIGHT STRESS ON JOINT INTEGRITY, SYNOVIAL FLUID COMPOSITION AND CATHEPSIN B-LIKE ACTIVITY OF ARTICULAR CARTILAGE IN GROWING SWINE

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Abstract
Twenty crossbred gilts (20.5 kg) were individually penned in 1.2 × 1.5-m pens and fed ad libitum a 20% crude protein diet. An initial load of 15% of bodyweight was placed in shoulder bags on 50% of the animals and this ratio was maintained by weekly increases in load weight. Eight gilts from each treatment group were observed for 5 h on each of days 6, 11 and 16 to estimate the amount of time spent standing or walking. After 27 d the pigs were slaughtered. Elbow joints were examined grossly and histologically for osteochondrotic lesions. Lesions associated with a reduced proteoglycan staining occurred at the articular surface of the medial humeral condyle of 50% of the loaded animals but were not observed in the controls. Average daily gain, percent of time when pigs were standing, and elbow joint synovial fluid hyaluronate concentrations were 0.82 vs. 0.82 kg (P > 0.05), 12.8 vs. 17.0% (P > 0.05), and 2.42 vs. 2.58 mg mL−1 (P > 0.05) for loaded vs. control groups, respectively. Cathepsin B-like activity of humeral condylar cartilage was 2.25 and 2.56 μmoles of benzyloxycarbonyl-arginine-arginine-4 methoxy-2-naphthylamide hydrolyzed h−1 g dry cartilage−1 (P > 0.05) for the loaded and control groups, respectively. The results indicate that mild mechanical stress causes focal degeneration of humeral condylar cartilage which could predispose these animals to more severe osteoarthrosis and osteochondrosis at maturity. Key words: Swine, cartilage, cathepsin B, osteochondrosis, stress