Effects of vitamin D3 supplementation and UVb exposure on the growth and plasma concentration of vitamin D3 metabolites in juvenile bearded dragons (Pogona vitticeps)

The effectiveness of dietary vitamin D3 and UVb exposure on plasma vitamin D metabolites in growing bearded dragons (Pogona vitticeps) was studied. A total of 84 (40 males and 44 females) newly hatched bearded dragons were allocated to six levels of oral vitamin D3 supplementation (0 to 400%) or six UVb exposure times (2 to 12 h). At 3 and 6 months of age, blood samples were obtained from each animal and analysed for 25(OH)D3 and 1,25(OH)2D3. At 3 months of age, plasma concentrations of 25(OH)D3 did not increase with increasing vitamin D3 supplementation unlike the 1,25(OH)2D3. At 6 months of age, plasma concentrations of both 25(OH)D3 and 1,25(OH)2D3 increased with increasing vitamin D3 supplementation. Plasma concentrations in UVb-exposed animals were 18 times higher for 25(OH)D3 (178.4 ± 9.0 vs. 9.9 ± 1.3 nmol/L) and 5.3 times higher for 1,25(OH)2D3 (1.205 ± 0.100 vs. 0.229 ± 0.025 nmol/L) than in vitamin D3 supplemented animals at 6 months of age. This study shows that 2 h of UVb exposure enables adequate physiological concentrations of plasma vitamin D metabolites to be maintained in growing bearded dragons. Oral supplementation of vitamin D3 is ineffective in raising plasma concentrations of 25(OH)D3 and 1,25(OH)2D3 to concentrations observed in UVb-exposed animals.