Hypovitaminosis A has been suggested as a cause of morbidity in captive amphibian species. A study was designed to evaluate the efficacy of topical supplementation of vitamin A in 24 Houston toad hybrids (Bufo houstonensis x woodhousii). Group A (6.6 animals) was treated with 150 USP vitamin Aa topically on the ventrum, every 3–7 days for 21 treatments. Group B (6.6 animals) was treated with sterile saline. Blood retinol was measured at the start and end of the study. A liver biopsy was taken at the end of the study and analyzed for retinol concentration. Blood retinol levels decreased over time but there was no difference between groups. Average pre-treatment retinol was 46.26 μg/ml±64.13 μg/ml for both groups. Post-treatment retinol was 3.46 μg/ml±3.75 μg/ml in Group A and 4.51 μg/ml±4.93 μg/ml in Group B. No difference was seen between the groups in the liver retinol values (Group A: 3.74 μg/g±3.87 μg/g, Group B: 2.96 μg/g±3.89 μg/g).
These results suggest that topical absorption of vitamin A was not effective in this species and there was no correlation between the blood and the liver retinol values. Hepatic retinol values overall were very low compared to other amphibians, but more wild Houston toad samples are needed for comparison. A liver biopsy may be a viable alternative to euthanasia in toads weighing more than 35 grams.
More studies are underway to evaluate the efficacy of oral administration of Aquasol-A (Mayne Pharma, Paramus, NJ, USA) in this species.
a. Aquasol-A (Mayne Pharma, Paramus, NJ, USA).
The authors would like to thank the United States Fish and Wildlife Service for their financial support to the study and the Houston Zoo staff for help in this project.