Intermittent ultraviolet B exposure increases plasma 25-hydroxyvitamin D3 in blue-tongued skinks (Tiliqua scincoides)

Objective: Ultraviolet B (UVB) guidelines for husbandry and therapeutic exposure remain limited for reptiles. We aimed to determine whether intermittent UVB exposure can elevate and maintain plasma 25-hydroxyvitamin D3 (25-OHD3) concentrations in blue-tongued skinks (Tiliqua scincoides). Methods: A prospective, randomized experimental study was conducted using 11 subadult skinks. Six skinks received 2 hours of UVB exposure every 3 days for 30 days, while 5 controls received none. Subsequently, the control skinks received 2 hours of UVB every 7 days for 28 days. Plasma 25-OHD3 concentrations were measured at baseline and post-UVB using chemiluminescent immunoassay. Results: Both regimens significantly increased 25-OHD3 in a dose-dependent manner. Two-hour exposures every 3 days elevated median concentrations from 17 [13.8 to 25] to 587.5 [303.3 to 750] nmol/L, while 7-day exposures increased concentrations from 23 [17.5 to 27] to 51 [42 to 222.5] nmol/L, even with a change to new bulbs. Conclusions: Intermittent 2-hour UVB at 3- or 7-day intervals significantly elevated 25-OHD3 concentrations, demonstrating that UVB can be administered as a therapeutic dose tailored to species-specific requirements. More research is needed to determine species-specific 25-OHD3 reference intervals. Clinical Relevance: Periodic UVB dosing may offer a sufficient alternative to continuous daily exposure for maintaining vitamin D3 concentrations in captive blue-tongued skinks; this practical approach supports routine management while reducing the risk of prolonged artificial UVB-related concerns.