Recent findings suggest that glucosuria is present in a number of clinically normal okapi in captive collections in the United States, Europe,7 and Japan. Preliminary urine glucose levels in captive U.S. okapi (n=10) at the White Oak Conservation Center (WOCC) were determined using glucose Chemstrips (Roche Diagnostics Corp., Indianapolis, IN; range: undetectable–1000 mg/dl) and compared to glucose levels of okapi (n=10), held captive in situ in Epulu, Democratic Republic of the Congo. Captive U.S. okapi had urine glucose levels ranging from undetectable to 1000 mg/dl of glucose, which was in contrast to the in situ okapi, none of which had detectable urine glucose. Additional urine samples on captive U.S. okapi (n=10) were then obtained and glucose concentrations were determined using Chemstrips and quantitatively determined using an automated chemistry analyzer and comparing results against urine creatinine levels to minimize the effects of concentrated urine samples. Of the 10 samples, three were negative using both Chemstrip and automated analysis, and the remaining seven okapi were positive using automated analysis (27–868 mg/dl) compared with the appropriate ranges of the Chemstrip. Urine glucose/creatinine ratios on positive samples appear to be elevated, ranging between 1 and 20, (<1 assumed to be normal). This is comparable to work completed in Belgium where urine glucose/creatinine ratios on a single okapi ranged between 6.32 and 13.56.7
Serum was collected from two U.S. captive okapi during annual exams for additional testing of glucose, insulin, and fructosamine. Insulin levels of <2 µIU/ml appear to be normal when compared to insulin levels of cattle (0–5 µIU/ml),5 however, corresponding glucose was normal to high-normal (99–180 mg/dl; normal = 115±21 mg/dl). Serum fructosamine concentrations were comparable (362 and 221 µmol/L) to concentrations reported in horses (257±60 µmol/L) and for half-bred zebu calves: (215–232 µmol/L).2,6
Diet may play a role in the incidence of glucosuria, as the Epulu okapi are fed only a natural browse diet of over 60 species of plant, whereas both the European and U.S. okapi are fed produce, though less produce is fed in the United States.7 Certain specialized feeders, such as the ‘concentrate selectors’ (e.g., royal antelope, Neotragus pygmaeus; moose, Alces canadensis) may be able to bypass the rumen with higher quality food, such as fruits, allowing the direct utilization of glucose. This may result in a transient serum glucose increase,3,4 which may explain the higher serum glucose concentration. If this is the case, it is possible that the glucose renal threshold (100–140 mg/dl for ruminants) could be reached and excess glucose may be excreted in the urine.1 Currently, the glucose renal threshold for okapi is unknown. Other possible etiologies, such as renal insufficiency and renal tubular problems, might be considered. Additional testing including verification of insulin and fructosamine levels, renal glucose threshold, and fractional excretion also would prove useful information. It is recommended a urine dipstick test along with quantitative laboratory analysis of urine for glucose and creatinine, and electrolyte levels should be carried out to build a database of normals for captive okapi.
1. Carlson GP. Clinical chemistry tests; urinalysis. In: Smith BP, ed. Large Animal Internal Medicine. Philadelphia PA: Mosby Co; 1990:41.
2. Coppo JA. Evolution of fructosaminaemia and glucaemia during the growth of unweaned and early weaned half-bred zebu calves. Vet Res Communications. 2001;25:449–459.
3. Hoffmann RR. Evolutionary steps of ecophysiological specialization and adaptation of ruminants: a comparative view of their digestive system. Oecologia. 1989;78:443–447.
4. Hoffmann RR, Nygren K. Morphophysiological specialization and adaptation of the moose digestive system. Alces. 1992;(s1):91–100.
5. Kaneko JJ. Clinical Biochemistry of Domestic Animals. 4th ed. San Diego, CA: Academic Press; 1989.
6. Murphy D, Reid SW, Graham PA, Love S. Fructosamine measurement in ponies: validation and response following experimental cyathostome infection. Res Vet Sci. 1997;63(2):113–118.
7. Vercammen F, De Deken R, Brandt J. The effect of dietary sugar content on glucosuria in a female okapi (Okapi johnstoni). In: Proceedings from the Joint Nutrition Symposium. 21–25 August 2002; Antwerp, Belgium. Abstract 124.