# Measuring the Rise and Fall of Plasma 25-Hydroxyvitamin D Concentrations in Blue-Tongued Skinks (Tiliqua scincoides) Following Ultraviolet B Exposure and Withdrawal

## TL;DR

Blue-tongued skinks need UVB light to raise their vitamin D levels, and even short UVB exposure helps maintain these levels for months.

## Contribution

This study provides the first empirical evidence that blue-tongued skinks require UVB exposure to synthesize sufficient vitamin D.

## Key findings

- UVB exposure significantly increases plasma 25-OHD concentrations in blue-tongued skinks.
- Shorter UVB exposure (2 hours/day) still provides a significant and sustained increase in vitamin D levels.
- Dietary vitamin D alone is insufficient to maintain adequate plasma 25-OHD concentrations.

## Abstract

Blue-tongued skinks (Tiliqua scincoides) are popular pet reptiles, but there is limited evidence-based information about their care. For example, the method they use to obtain vitamin D—a nutrient vital to reptile health—is still unknown. This study investigated whether these skinks can meet their vitamin D needs through diet alone or require ultraviolet B (UVB) exposure. Skinks were raised on a wet cat food containing vitamin D, then exposed to UVB light for either 12 or 2 h/day for 4 weeks. The baseline vitamin D concentrations were low; however, UVB exposure dramatically increased these values. After the UVB lighting was removed, vitamin D concentrations decreased for the 12-hour and 2-hour groups, requiring more than 7 and 4 months for the values to return to baseline, respectively. These results indicate that blue-tongued skinks can utilize UVB light to synthesize vitamin D.

Species-specific husbandry guidelines remain limited for blue-tongued skinks (Tiliqua scincoides), especially in relation to ultraviolet B (UVB) lighting and vitamin D requirements. This study aimed to determine whether UVB exposure is necessary for these skinks and how long 25-hydroxyvitamin D (25-OHD) concentrations persist after UVB withdrawal. Eleven adult skinks who had been fed with wet cat food were exposed to 12 or 2 h of UVB per day for four weeks. Plasma 25-OHD concentrations were very low at the baseline, and significantly increased post-UVB in both groups (p < 0.01), with the 12-hour group increasing from baseline concentrations of 18.5 [12.8–20.5] nmol/L to 820 [730–1251.3] nmol/L and the 2-hour group increasing from baseline concentrations of 22 [15.5–22] nmol/L to 635 [401–892.5] nmol/L. Following the discontinuation of UVB exposure, 25-OHD gradually declined and was not significantly different from baseline concentrations at 7 and 4 months for the 12-hour and 2-hour groups, respectively. Dietary vitamin D3 (2.5 IU/g as dry matter basis), provided through wet cat food alone, appeared insufficient to support sustained plasma 25-OHD concentrations. These findings strongly suggest that blue-tongued skinks rely on UVB exposure to increase their 25-OHD concentrations. Moreover, the shorter 2-hour exposure provided a significant rise in 25-OHD concentrations and remained above baseline for 4 months, suggesting the shorter exposure can benefit these animals, while potentially reducing secondary risks associated with UVB exposure.