AVIAN TIBIAL DYSCHONDROPLASIA - THE INTERACTION OF GENETIC SELECTION AND DIETARY 1,25-DIHYDROXYCHOLECALCIFEROL

The effects of dietary 1,25-dihydroxycholecalciferol on the incidence and severity of tibial dyschondroplasia (TD) were assessed in broiler fowl selected for TD (high-TD line) and against TD (low-TD line). Asse ssment was by examination with a portable Lixiscope to identify lesion s in live birds, gross pathology and histopathology. Eighty broilers i n four groups of 20 were examined. When fed on standard diets the low- TD line had a 15% incidence whereas the high-TD line had a 63% inciden ce. The chicks in the high-TD line, when fed on a diet supplemented wi th 5 mug or with 10 mug 1,25-dihydroxycholecalciferol/kg diet, showed a marked reduction in the incidence of TD, to 21% and 0% respectively. The growth plate in the proximal tibiotarsi of the high-TD line showe d accumulations of transitional chondrocytes, supporting the hypothesi s that a failure of chondrocyte differentiation is the cause of dyscho ndroplasia. This hypothesis is further supported by studies which indi cate 1,25-dihydroxycholecalciferol has a major role in chondrocyte dif ferentiation.