Abstract
Urinalysis of 26 okapis in four European zoos revealed glucosuria in 58%. Mainly, animals from the age of four onwards are glucosuric without any difference in urinary specific gravity between non-glucosuric and glucosuric animals. Diabetes mellitus is not the cause4 and neither is Fanconi syndrome,1 as animals have normal values for urinary specific gravity, phosphatemia, and kalemia and do not show any clinical symptoms. Benign renal disease, which is a genetic disease, seems very unlikely as there is practically no inbreeding in the zoo population. Retrospective analysis of longevity of animals born and raised semi-wild in the station of Epulu (Democratic Republic of Congo) with a natural diet restricted to leaves only and then imported into SSP (Species Survival Plan) and EEP (European Endangered Species Programme) institutions, revealed a significant difference between animals that had been living in Epulu for only their first two years and those that stayed longer in Epulu. Considering the importance of diet in the anatomic and physiologic development of the young ruminant stomach,7 we changed our previous diet (i.e., fruit, vegetables, concentrates, lucerne hay) to a diet with less easily digestible carbohydrates (i.e., no fruit, addition of unmolassed beet pulp and leaves). Urinary glucose/creatinine ratio decreased over time in two adult females. More analyses of the natural diet (leaves) are necessary to adjust the diet of our okapis even more.
Material and Methods
From May 1999 until March 2008 urinalyses of 26 okapis in four European zoos (Antwerp, Cologne, London, Marwell) were performed on midstream urine samples. A mechanical fluid densitometer (urinometer, 1.000–1.060) was used to determine the specific gravity (SG) in 116 samples of eight okapis in Antwerp. Glucose and creatinine were quantitatively determined in 87 samples of nine okapis in Antwerp using dry biochemistry (Kodak, Johnson and Johnson) and the ratios calculated to reduce the influence of urine volume.3 In August 2006 a drastic diet change was carried out which was gradually implemented during the following six months. Unmolassed beet pulp and dried leaves of six different species were introduced; fruit was omitted and only small amounts of vegetables low in sugar and starch (i.e., celery, chicory, savoy cabbage, endives) remained. Two adult glucosuric females could be followed regularly whilst receiving this new diet and the glucose/creatinine ratio was calculated in a total of 11 and 28 urine samples respectively, during a 19 month observation period. One calf was confronted with the changed diet during its early preweaning period and 13 urine samples were analyzed during the 16-month follow-up. One subadult animal changed to the new diet at an age of 22 months and follow-up lasted for 7.5 months, during which 11 urine samples could be analyzed.
The Okapi International Studbook provided information on dates and places of birth and death of all okapis. Longevity (disregarding young animals that died within six months after birth) was calculated with the confirmed ages of all animals in Epulu (Democratic Republic of Congo) from 1940 till 2001 (n=34) and from 1975 till 2005 in SSP (n=25) and EEP (n=52).
Discussion and Conclusion
One of the causes of glucosuria is diabetes mellitus, which does not appear to be the cause in okapis, since Fleming et al.4 observed that glucosuric animals have normal serum levels of insulin, glucose, and fructosamine.
Pathologic renal disease with dysfunction of the proximal tubules (Fanconi syndrome) also leads to glucosuria with low specific gravity, hypophosphatemia, and hypokalemia and clinical illness.1 The okapis in our collection never showed hypophosphatemia nor hypokalemia, and urinalyses of four glucosuric and four non-glucosuric animals demonstrated a normal specific gravity comparable to that in cows, sheep, and goats (SG=1.015–1.045)3 with no statistical difference between glucosuric and non-glucosuric animals. A total of 116 urine samples of eight okapis revealed a mean SG of 1.020 (SD=0.007), of which 74 glucosuric samples had a mean SG of 1.020 (SD=0.005) and 42 non-glucosuric samples had a mean SG of 1.019 (SD=0.008).
Benign renal disease is known in humans as a genetic disease with glucosuria in the absence of hyperglycemia, the incidence in the United States is estimated at 0.16–6.3%.2 With 47% glucosuric animals in the SSP okapi population and practically no inbreeding,4 benign renal disease seems highly unlikely. In the EEP okapis there is no inbreeding of any significance either9 and still 58% of examined animals were glucosuric with no difference between gender, but very significant difference considering the ages. It seems that most (92%) of the adult animals from four years of age onwards are glucosuric, with an odds ratio of 40.0 and a relative risk of 8.80.
In Epulu station (Democratic Republic of Congo), all okapis are non-glucosuric and receive only a natural diet of 23 kg leaves of diverse plant species.4 On the contrary, in zoos a substitute diet has been developed with only small amounts of leaves. This significant difference may, therefore, bear an influence on their age. The mean longevity of 11 years is identical for animals born in the two captive populations (SSP, SD = five years; EEP, SD = six years), but significantly different from the mean longevity of 16 years (SD = eight years) for those born in Epulu. Further analysis revealed a significant positive correlation (r=0.41; p<0.05)8 between the number of years spent in Epulu and longevity of animals that were imported from Epulu and died in SSP and EEP (n=34). All SSP animals (n=11) spent their first three years in Epulu and had the same longevity as those EEP animals (n=14) that also spent three years in Epulu. Yet, those EEP okapis that spent only their first two years of life in Epulu (n=9) died at a significantly (p<0.01) lower age than animals that came later in the EEP (n=14).
Langer7 describes the ontogenic development in the true four-chambered ruminants (cervids, giraffids, antilocaprids, and bovids). The postnatal anatomic development is directly affected by the nature of the food. The epithelial development of the ruminal wall is influenced by constituents of the gastric content. The cooperation between internal ontogenetic and external trophic influences is necessary to form a functioning adult organ.
In true ruminants, the nature of the food items ingested early in life is very important for normal morphologic and functional development.7 In the wild only fresh young shoots are eaten (like in Epulu station) and okapis prefer leaves which are low in fiber content.5 In zoos this is totally different, as a diet purely consisting of leaves is hardly feasible. On dry matter base, the former Antwerp diet consisted of vegetables (2%), fruit (5.5%), pellets (13.5%), and lucerne hay (79%). The fibre analysis of this diet corresponds with the natural leaves diet but also contains high amounts of easily digestible carbohydrates. Implementing research results,6 major improvements have been obtained in order to adapt the diet better to a natural fermentation with rapid passage through the rumen. The new diet in Antwerp consists of vegetables (0.3%), fruit (0%), pellets (11%), leaves (14%), unmolassed beet pulp (17%), and lucerne hay (58%), which has the same comparable amount of fibres but much lower amounts of sugars and starch (i.e., a decrease of approximately 260 g per day). Two adult okapis showed a decrease of the glucose/creatinine ratio over time with a negative correlation r=-0.62 (p<0.001) and r=-0.58 (p>0.05), respectively. One young calf had no detectable amounts of urinary glucose, except on two occasions (ratios of 1.19 and 1.21 at the ages of 13.5 and 14 months, respectively) during its 16-month follow-up. One subadult remained non-glucosuric during the whole observation period.
In order to provide still more proof for adapting our diet there is a need for more profound analyses of the natural plants in Epulu, including easily digestible carbohydrates and secondary compounds.
Literature Cited
1. Deinhofer M. Paradoxic glucosuria (Fanconi syndrome) in a bull. Vet Rec. 1996;138:395–396.
2. Feld LG. Renal glucosuria. www.emedicine.com. Accessed 2006.
3. Finco DR. Kidney function. In: Kaneko JJ, ed. Clinical Biochemistry of Domestic Animals. 4th ed. San Diego, CA: Academic Press Inc; 1989;496–542.
4. Fleming GJ, Citino SB, Petric A. Glucosuria in captive okapi (Okapia johnstoni). J Zoo Wildl Med. 2006;37:472–476.
5. Hart JA, Dierenfeld E, Shurter S. Preference, intake, and digestion of natural diets by captive okapi. Draft paper, 1989.
6. Hummel JK-H. Ernährung und Nahrungsaufnahmeverhalten des Okapis (Okapia johnstoni) in Zoologischen Gärten. Inaugural-Dissertation, Köln, Germany. 2003;1–175.
7. Langer P. Ontogenic development. In: Gustav Fischer Verlag. The mammalian herbivore stomach. Comparative Anatomy, Function, and Evolution. Stuttgart, Germany. 1988;78–95.
8. Petrie A, Watson P. Statistics for Veterinary and Animal Science. 2nd ed. Oxford, UK: Blackwell Publishing; 2006.
9. Vercammen F, De Deken R, Brandt J. The effect of dietary sugar content on glucosuria in a female okapi (Okapia johnstoni). In: Proceedings from the Joint Nutr Symp. Antwerp, Belgium: 2002:124.