Experimental hypophosphataemia in growing pigs: effects on endochondral ossification in comparison to osteochondrosis.

Hypophosphataemia was induced in growing pigs by dietary supplementation with aluminium hydroxide. The effect on endochondral ossification was studied morphologically in comparison with normophosphataemic pigs given aluminium phosphate or left untreated. The aim of the investigation was to elucidate further the role of nutritional factors in the pathogenesis of disturbed endochondral ossification, occurring in osteochondrosis. In all pigs, focal arrestment of endochondral ossification with subsequent cartilage retention in the epiphyseal or metaphyseal growth zones was seen. In normophosphataemic pigs, focal degenerative cartilage changes were associated with impairment of vascular penetration. The lesions had morphological characteristics of early osteochondrosis. In hypophosphataemic pigs, a more generalized disturbance, endochondral ossification, was seen with impaired vascular penetration and excessive deposition of osteoid in the primary spongiosa. Focal cartilage retentions were associated with necrotic changes in the primary spongiosa and not with cartilage degeneration. The lesions were similar to rickets and it was concluded that hypophosphataemia is not an aetiological factor in the development of osteochondrosis. The differentiation between the cartilage retention seen in early stages of osteochondrosis and rickets must be based on histological examination.

Effects of vitamin D and A, calcium, phosphorus, and protein on frequency and severity of osteochondrosis in pigs.

The generalized nature of osteochondrosis indicates that systemic factors, i.e. of nutritional or genetic origin, are of importance in etiology of osteochondrosis. Several experimental investigations are reported. On the basis of the morphologic findings it was considered possible that dietary factors such as hypovitaminosis D, hyper- or hypovitaminosis A, and low calcium or high protein intake could be of importance in etiology. The reason for this was that there were similarities between cartilage changes in osteochondrosis and those observed in various dietary imbalances in other domestic animals and in experiments with pigs. The effect of hyper- and hypovitaminosis A and hypovitaminosis D was studied in 23 pigs from 2 litters. In another experiment 32 pigs from 4 litters were fed rations with varying levels of calcium, phosphorus, and protein in the feed. Clinical examinations were made of these animals. Bone seeking fluorochromes were given prior to slaughter, and complete necropsy was performed, including macroscopic, radiologic, histologic and microradiographic techniques. Neither hypervitaminosis A, nor hypovitaminosis A and D had any noticeable effect on frequency and severity of osteochondrosis. A similar negative finding was made in the experiment with different intake of calcium and protein.