BILIRUBIN CONCENTRATIONS IN CLINICALLY HEALTHY AND DISEASED CAPTIVE WATERBUCK (KOBUS ELLIPSIPRYMNUS) AT THE SAN DIEGO ZOO SAFARI PARK.

Abstract

Captive waterbuck ( Kobus ellipsiprymnus ) that appear clinically healthy have been noted to have high serum bilirubin concentrations compared with other ruminants; however, questions remain about the physiologic factors affecting bilirubin concentration and its potential association with underlying disease and icteric serum or mucous membranes. Serum bilirubin concentrations of healthy and diseased waterbuck housed at the San Diego Zoo Safari Park from 1989 to 2012 were retrospectively analyzed to determine any link between icteric serum, total bilirubin concentration (tBili), and disease entities in this species. Total bilirubin and direct (dBili) bilirubin concentrations and the prevalence of icteric serum were compared by subspecies, age group, and health status; associations with complete blood count and biochemical results and clinical diagnosis were assessed. No significant differences were found in tBili or dBili between Ellipsen (n = 32) and Defassa (n = 29) subspecies or in juveniles (n = 22) versus adults (n = 39). Clinically healthy waterbuck (n = 40) had significantly higher tBili (mean ± 2SD, 7.9 ± 1.2 mg/dl; P < 0.001) and dBili (3.7 ± 1.0 mg/dl; P < 0.001) than did diseased waterbuck (n = 21; tBili: 4.9 ± 2.56 mg/dl; dBili: 2.2 ± 0.8 mg/dl). No waterbuck had icteric tissues on physical examination. Twelve (19.7%) waterbuck (six healthy, six diseased) had icteric serum. Few minor correlations were seen between tBili or dBili and clinical, laboratory, or necropsy evidence of disease, though an inverse correlation between dBili and blood glucose was noted. Of the 40 healthy animals, reference intervals were calculated for tBili (5.5-10.3 mg/dl), dBili (1.7-5.7 mg/dl), and indirect bilirubin (2.2-6.2 mg/dl). These results suggest healthy waterbuck have relatively high tBili and dBili compared with related species. Icteric serum may be seen in up to 15% of healthy animals in the absence of icteric tissues.