Bone lesions in clinically normal and in lame pigs

Abstract

A pathological study was made of the femur, rib and sternum of 76 clinically normal Yorkshire × Landrace pigs weighing 2·8 to 100·0 kg (10 days to 6 months of age) and on 26 lame Yorkshire × Landrace weighing 134·9 to 149·1 kg (9 months). Locomotor dysfunction of the hind legs occurred in all animals 6 months old or more and progressed with increase in age. In clinically normal pigs, unevenness of the width of the femoral growth plate was seen in pigs weighing 20 kg or more. Furthermore, the top of the great trochanter was lower than that of the femoral head, and the angle between the long axis of the femoral head and that of the great trochanter became gradually larger with increasing body weight. Histological changes in the femoral growth plate were characterized by necrosis of the cartilage in the area adjacent to the metaphysis or epiphysis, eosinophilic streaks, loosening of the cartilage matrix, and oblique arrangement of chondrocytic columns. These changes were seen in the pigs weighing 2·8 kg or more. In the rib, changes in the growth plate were essentially similar to those in the femur. No appreciable changes were seen in the sternum. In the lame pigs, noteworthy gross changes were an abnormal high position of the top of the great trochanter in relation to the level of the femoral head and a markedly open angle between the long axis of the femoral head and that of the great trochanter. Although the nature of the histological changes in the femur is essentially the same as those of clinically normal pigs, the changes such as oblique arrangement of chondrocytic columns and loosening of the cartilage matrix were more marked than those of the clinically normal pigs. Loosening of the cartilage matrix and oblique arrangement of chondrocytic columns were found in the growth plate of the rib. Cracks, eosinophilic streaks and loosening of the cartilage matrix were also observed in the growth plate of the sternum.