High vitamin D3 requirements in broilers for bone quality and prevention of tibial dyschondroplasia and interactions with dietary calcium, available phosphorus and vitamin A

1. Two experiments were carried out to investigate responses in performance and bone compositional and structural characteristics in broilers fed diets containing 4 concentrations of vitamin D-3 (5, 20, 125 and 250 mg cholecalciferol/kg) at different concentrations of calcium, available phosphorus and vitamin A. 2. In experiment 1, body weight and tibia breaking strength were maximised at 14 d with 250 mg vitamin D-3/kg, tibia ash was maximised with 125 mg vitamin D-3/kg. A high incidence of tibial dyschondroplasia (TD) was decreased to very low levels with 125 mg vitamin D/kg. 3. At 42 d, performance and bone characteristics showed no response to vitamin D-3 concentrations above 20 mg/kg. 4. Dietary vitamin A within the range 2.4 to 4.5 mg retinol/kg did not show any interaction with vitamin D-3 status at either age. 5. In experiment 2, responses to vitamin D-3 were strongly influenced by dietary calcium/available phosphorus. With 13 g calcium and 5 g available phosphorus/kg, performance and bone characteristics responded to vitamin D-3 concentrations up to 125 mg/kg but more was needed at less optimal concentrations of calcium and available phosphorus. TD incidence was minimised with 250 mg/kg. 6. This study shows that high dietary concentrations of vitamin D-3 can prevent TD. It is concluded that the vitamin D-3 requirement of broilers up to 14 d of age at optimal dietary calcium and available phosphorus concentrations may be in the range 35 to 50 mg/kg for cortical bone quality and up to 250 mg/kg for prevention of TD. The vitamin D-3 requirement for cortical bone quality after 14 d is not higher than 20 mg/kg. These requirements are much higher than earlier estimates and may be related to higher calcium requirements of modern broiler genotypes. Current regulations limiting maximum vitamin D-3 concentrations in broiler starter diets may need to be reviewed.