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

Abstract

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 D3 (5, 20, 125 and 250 µg 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 µg vitamin D3/kg, tibia ash was maximised with 125 µg vitamin D3/kg. A high incidence of tibial dyschondroplasia (TD) was decreased to very low levels with 125 µg vitamin D/kg. 3. At 42 d, performance and bone characteristics showed no response to vitamin D3 concentrations above 20 µg/kg. 4. Dietary vitamin A within the range 2·4 to 4·5 mg retinol/kg did not show any interaction with vitamin D3 status at either age. 5. In experiment 2, responses to vitamin D3 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 D3 concentrations up to 125 µg/kg but more was needed at less optimal concentrations of calcium and available phosphorus. TD incidence was minimised with 250 µg/kg. 6. This study shows that high dietary concentrations of vitamin D3 can prevent TD. It is concluded that the vitamin D3 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 µg/kg for cortical bone quality and up to 250 µg/kg for prevention of TD. The vitamin D3 requirement for cortical bone quality after 14 d is not higher than 20 µg/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 D3 concentrations in broiler starter diets may need to be reviewed.