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.