Decreased Baseline Fecal Glucocorticoid Concentrations Associated with Skin and Oral Lesions in Black Rhinoceros (Diceros bicornis)

Abstract

Ulcerative lesions are a health concern for managed black rhinoceros (Diceros bicornis) populations. To examine possible relationships between ex situ variables and adrenal activity with the presence of lesions, facility and socioenvironmental surveys of 25:20 (male:female) black rhinos at 18 zoos were conducted, and fecal samples were collected twice weekly for 1 yr for glucocorticoid metabolite analyses. During the collection period, 5.1 rhinos exhibited skin lesions, 1.0 had oral lesions, and 1.0 had both. All of the rhinos with lesions recovered, except the one with both oral and skin lesions, which died shortly after the end of the study. In general, there were no relationships (P > 0.05) between ex situ variables, or rhino behavior indices, and lesion onset. There also were no differences (P > 0.05) in fecal glucocorticoid variability (+/- SEM) between rhinos with (coefficients of variation [CV] = 57.1 +/- 7.2 ng/g) and without (53.8 +/- 2.3 ng/g) lesions, or in overall mean (+/- SEM) glucocorticoid metabolite concentrations between rhinos with (45.1 +/- 4.0 ng/g) and without (34.6 +/- 2.8 ng/g) lesions. However, baseline mean (+/- SEM) glucocorticoid metabolite concentrations were lower (P < 0.05) in rhinos with lesions (n = 5.1, baseline mean = 29.9 +/- 3.3 ng/g, range: 24.3-84.9 ng/g) than without (n = 19.19 baseline mean = 40.0 +/- 2.4 ng/g, range: 19.4-50.8 ng/g). For a male rhino that developed lesions during the study, the mean glucocorticoid concentrations were lower (P < 0.01) when lesions were present (n = 12, overall = 30.1 +/- 2.4 ng/g, baseline = 28.7 +/- 2.2 ng/g) than prior to lesion onset (n = 75, overall = 36.5 +/- 1.0 ng/g, baseline 35.3 +/- 0.8 ng/g). These results suggest that ulcerative lesions may be associated with changes in adrenal activity, although it is not clear if this is a cause or effect of disease.