Avian tibial dyschondroplasia: The interaction of genetic selection and dietary 1,25 ‐dihydroxycholecalciferol

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Abstract
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). Assessment was by examination with a portable Lixiscope to identify lesions in live birds, gross pathology and histopathology. Eighty broilers in 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% incidence. The chicks in the high‐TD line, when fed on a diet supplemented with 5 μg or with 10 μg 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 showed accumulations of transitional chondrocytes, supporting the hypothesis that a failure of chondrocyte differentiation is the cause of dyschondroplasia. This hypothesis is further supported by studies which indicate 1,25‐dihydroxycholecalciferol has a major role in chondrocyte differentiation.