A survey of the husbandry of captive tuatara (Sphenodon spp.) in relation to factors implicated in nutritional secondary hyperparathyroidism

Abstract

AIM: To examine selected aspects of the diet and husbandry of captive tuatara (Sphenodon spp.) in New Zealand, in order to develop recommendations on provision of ultraviolet B light and diet, to reduce the incidence of nutritional secondary hyper-parathyroidism (NSHP). METHODS: Information was collected from 18/20 institutions holding tuatara in New Zealand, on the numbers kept, dimensions and type of enclosures, and type of light sources used. Historical information on breeding activity and problems known to be associated with NSHP, and standardised measurements of levels of ultraviolet B light in enclosures were also recorded. Diet samples were collected (n=17) and analysed for Ca, P and vitamin D content. RESULTS: The intensity of ultraviolet B light was lower where there was a history of previous high, compared with medium or low, risk of NSHP for tuatara kept indoors (p>0.001). Light sources varied significantly in both output of ultraviolet B light (spectral irradiance) at the source, and fractional reduction in electromagnetic fluence with increasing distance from the source. The average exposure to ultraviolet B light of captive tuatara kept indoors was 26.44 (SE 4.29) µW/cm2, and there was significant variation between enclosures, with 4/14 (29%) institutes having no measurable ultraviolet B light present. For tuatara kept outdoors ultraviolet B light at ground level was influenced by weather conditions (p≤0.007), roofing material (p=0.004), and substrate shading (p=0.003). The Ca:P ratio of dietary samples was 2.3 (SE 1.9), but this included one extreme outlier (32.7). When the outlier was excluded, it was 0.53 (SE 0.16). The levels of vitamin D in the feed samples were below the minimum detectable level of the assay (<20 IU/100 g) for all but one sample (72 IU/100 g) that had been dusted with vitamin/mineral supplement prior to freezing. CONCLUSIONS AND CLINICAL RELEVANCE: The current diet and husbandry of captive tuatara in New Zealand predisposes the animals to NSHP. The ultraviolet B light emitted from commercial light sources dissipates rapidly with increasing distance from the source. Regular direct measurement of ultraviolet B light at substrate level is recommended for indoor enclosures, whereas tuatara kept outdoors should have access to an unshaded basking area through a wire-meshed roof. The Ca:P ratio and concentration of vitamin D of most common food items fed to tuatara is deficient, and reptile vitamin and mineral supplements should be provided by dusting or gut-loading insect food items.