INTERACTION BETWEEN DIETARY 1,25-DIHYDROXYCHOLECALCIFEROL AND CALCIUMAND EFFECTS OF MANAGEMENT ON THE OCCURRENCE OF TIBIAL DYSCHONDROPLASIA, LEG ABNORMALITIES AND PERFORMANCE IN BROILER-CHICKENS

1. Two experiments were performed to compare the relative effectivenes s of feeding 1,25-dihydroxycholecalciferol (1,25-DHCC) in minimising l eg abnormalities in broilers with other methods and to investigate int eractions between dietary 1,25-DHCC and calcium. 2. Adding 5 mu g 1,25 -DHCC/kg to a diet containing 12 g calcium/kg was more effective than early food restriction or meal feeding in preventing leg abnormalities but was found to cause a growth depression. 3. The second experiment, which had a factorial design, with diets containing 7.5, 10.0 and 12. 5 g calcium and 0, 2.0, 3.5 and 5.0 mu g 1,25-DHCC/kg, showed linear a nd quadratic interactions between these dietary factors. Diets with hi gher concentrations of both 1,25-DHCC and calcium resulted in growth d epression associated with hypercalcaemia. 4. The incidence of tibial d yschondroplasia (TD) at 3 weeks of age was highest with the basal diet containing 7.5 g calcium/kg and was markedly reduced by addition of 1 ,25-DHCC and/or calcium. The incidence was very low or non-existent wh en 1,25-DHCC was fed at 35 mu g/kg or greater. 5. Feeding 5 mu g/kg 1, 25-DHCC had no effect on plasma 1,25-DHCC concentrations, although at the higher dietary calcium contents plasma concentrations of 25-hydrox y- and 24,25-dihydroxy-cholecalciferol were lower in those birds fed 1 ,25-DHCC. 6. It is concluded that 1,25-DHCC is most effective in preve nting TD without accompanying growth depression when it is fed in conj unction with diets containing less than 10g calcium/kg.