THE VITAMIN D STATUS OF ASIAN ELEPHANTS (ELEPHAS MAXIMUS) MANAGED IN A NORTHERN TEMPERATE CLIMATE

Short communication: Metabolic synthesis of vitamin D2 by the gut microbiome

The origin of vitamin D2 in herbivorous animals was investigated in vivo in sheep and in bovine as well as mouse gastrointestinal tracts. A high concentration of 25-hydroxyvitamin D2 in blood plasma of sheep both in summer and winter appeared to be incompatible with the undetectable level of vitamin D2 in the pasture on which the sheep were grazing. Studies with bovine rumen contents from a cow grazing the same pasture as the sheep, demonstrated an increased concentration of vitamin D2 on anaerobic incubation in a 'Rusitec' artificial rumen, which was further enhanced when cellulose powder was added as a fermentation substrate. The colon contents of mice that were fed from weaning on a vitamin D-free diet were found to contain vitamin D2. The results of these comparative studies in 3 animal species indicated that vitamin D2 was being generated by microbial anaerobic metabolism in the gastrointestinal tract.

SERUM VITAMIN D AND SELECTED BIOMARKERS OF CALCIUM HOMEOSTASIS IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS) MANAGED AT A LOW LATITUDE

An understanding of species-specific vitamin D metabolism and its role in calcium homeostasis is essential for correct diet formulation and development of husbandry protocols for managed nondomestic species. This study documented serum vitamin D metabolites and other analytes involved in calcium homeostasis in Asian elephants (Elephas maximus) managed at a latitude similar to their wild natural habitat. Serum values for 33 elephants managed at a low latitude were measured in the peak of summer, revealing low vitamin D2 (25(OH)D2 2.3 ± 0.6 ng/ ml and 24,25(OH)2D2 2.17 ± 0.52 ng/ml) and nondetectable vitamin D3. Serum minerals (calcium, phosphorus, magnesium), ionized calcium, and parathyroid hormone were within normal reported ranges. In comparison with previously reported values in elephants managed at a high latitude, 25(OH)D2 (P < 0.001), 24,25(OH)2D2 (P = 0.001), and magnesium (P = 0.013) were significantly lower, and parathyroid hormone was significantly higher (P < 0.001). The lack of D3 production during ample sun exposure at a low latitude suggests that Asian elephants are incapable of cutaneous photobiosynthesis of vitamin D, and that low serum D2 is normal for this species.

EXPERIMENTAL CHOLECALCIFEROL SUPPLEMENTATION IN A HERD OF MANAGED ASIAN ELEPHANTS (ELEPHAS MAXIMUS)

Vitamin D supplementation may pose a significant health risk in species where levels of deficiency, sufficiency, and toxicity have not been clearly established, and species-specific research on vitamin D supplementation should be performed. This study documented the effect of vitamin D supplementation on serum vitamin D metabolites and other analytes of Ca homeostasis in Asian elephants (Elephas maximus). Six adult Asian elephants received PO supplementation with cholecalciferol at 300 IU/kg of body weight (BW) once a week for 24 wk. Serum was analyzed every 4 wk for 25-hydroxyvitamin D₂/D₃ [25(OH)D]; 24,25-dihydroxyvitamin D₂/D₃ [24,25(OH)₂D]; 1,25-dihydroxyvitamin D [1,25(OH)₂D]; parathyroid hormone (PTH); total Ca; ionized Ca (iCa); P; and Mg. After the supplement was discontinued, serum 25(OH)D₂/D₃ was measured every 4 wk until levels returned to baseline. At the start of the study, the average serum 25(OH)D₃ was nondetectable (<1.5 ng/ml). With cholecalciferol supplementation, 25(OH)D₃ increased at an average rate of 2.26 ng/ml per month and reached an average concentration of 12.9 ± 3.46 ng/ml at 24 wk. Both 24,25(OH)₂D₃ and 1,25(OH)₂D increased over time with supplementation from an average of <1.5 to 12.9 ng/ml and from 9.67 to 36.4 pg/ml, respectively. PTH, iCa, Ca, P, and Mg remained within reported normal ranges throughout supplementation. After the supplement was discontinued, serum 25(OH)D₃ demonstrated a slow decline to baseline, taking an average of 48 wk. Elephants demonstrated significant individual variation in response to supplementation and subsequent return to baseline. Supplementation of Asian elephants with a weekly dose of 300 IU/kg BW cholecalciferol for 24 wk appears to be effective and safe. Additional clinical studies would be necessary to investigate the safety of other routes of administration, dosages, and duration of vitamin D supplementation, as well as associated health benefits.

VITAMIN D STATUS OF INDOOR-HOUSED HOFFMANN'S TWO-TOED SLOTHS (CHOLOEPUS HOFFMANNI): A PILOT STUDY

Disorders of calcium homeostasis have been reported with some frequency in two-toed sloths, yet little investigation has been performed on vitamin D and mineral metabolism in these species. This study evaluates biomarkers involved in vitamin D and calcium metabolism in a group of nine managed Hoffmann's two-toed sloths (Choloepus hoffmanni), correlated with diet analysis. Serum was analyzed for both vitamin D₂ and D₃ metabolites, minerals (calcium [Ca], phosphorus [P], and magnesium [Mg]), parathyroid hormone (PTH), and ionized calcium (iCa). The diet was analyzed for proximate nutrients, minerals and vitamins D₂ and D₃, and feed intake was estimated. Average values reported for D₃ metabolites, including 25(OH)D₃, 1,25(OH)₂D₃, and 24,25(OH)₂D₃, were 25.1 ng/ml, 52.23 pg/ml, and 7.65 ng/ml, respectively. Average PTH was 0.22 pmol/L while average iCa was 1.46 mmol/L. Values reported for Ca, P, Mg were within expected ranges. Dietary concentration of D₃ was 6.7 ng/g and the average daily intake per sloth was 113.7 IU/kg body weight. No detectable levels of vitamin D₂ metabolites 25(OH)D₂, 1,25(OH)₂D₂, or 24,25(OH)₂D₂ were found in the diet or serum. These data will serve as a starting point for future investigations into the vitamin D metabolism and calcium homeostasis of two-toed sloths to improve the health in managed settings.

Outside the Box: Working With Wildlife in Biocontainment

Research with captive wildlife in Animal Biosafety Level 2 (ABSL2) and 3 (ABSL3) facilities is becoming increasingly necessary as emerging and re-emerging diseases involving wildlife have increasing impacts on human, animal, and environmental health. Utilizing wildlife species in a research facility often requires outside the box thinking with specialized knowledge, practices, facilities, and equipment. The USGS National Wildlife Health Center (NWHC) houses an ABSL3 facility dedicated to understanding wildlife diseases and developing tools to mitigate their impacts on animal and human health. This review presents considerations for utilizing captive wildlife for infectious disease studies, including, husbandry, animal welfare, veterinary care, and biosafety. Examples are drawn from primary literature review and collective 40-year experience of the NWHC. Working with wildlife in ABSL2 and ABSL3 facilities differs from laboratory animals in that typical laboratory housing systems, husbandry practices, and biosafety practices are not designed for work with wildlife. This requires thoughtful adaptation of standard equipment and practices, invention of customized solutions and development of appropriate enrichment plans using the natural history of the species and the microbiological characteristics of introduced and native pathogens. Ultimately, this task requires critical risk assessment, understanding of the physical and psychological needs of diverse species, creativity, innovation, and flexibility. Finally, continual reassessment and improvement are imperative in this constantly changing specialty area of infectious disease and environmental hazard research.