Investigation of the effects of cricket ingestion on plasma uric acid concentration in inland bearded dragons (Pogona vitticeps)

Lily A. Parkinson Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706.

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Christoph Mans Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706.

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Abstract

OBJECTIVE

To determine whether plasma uric acid concentration in inland bearded dragons (Pogona vitticeps) was affected by recent ingestion of a meal of crickets.

ANIMALS

12 healthy adult inland bearded dragons.

PROCEDURES

Food was withheld for 48 hours prior to experiments. Animals (6/group) were randomly assigned to receive a meal of crickets (equivalent to 1% of the animal's body weight; 10 g/kg [4.5 g/lb]; treatment group) or have food withheld for an additional 48 hours (control group). Blood samples were collected for plasma uric acid measurement just before (time 0) and 4, 24, and 48 hours after feeding. Effects of feeding and time on the targeted measurement were assessed by repeated-measures ANOVA.

RESULTS

Mean plasma uric acid concentration for the treatment group was significantly increased from the time 0 value (2.5 ± 1.5 mg/dL) 24 hours following meal ingestion (6.5 ± 1.2 mg/dL), but not at the 4-hour time point, and returned to the time 0 value by the 48-hour time point. No significant changes in plasma uric acid concentration were detected for the control group.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested food should be withheld for ≥ 48 hours prior to blood collection if inland bearded dragons are used to establish reference intervals for plasma uric acid concentration or if feasible when obtaining samples from these animals for clinical evaluation. Veterinarians should consider the time from last meal consumption when interpreting plasma uric acid concentration for this species and potentially other terrestrial insectivorous and omnivorous lizards.

Abstract

OBJECTIVE

To determine whether plasma uric acid concentration in inland bearded dragons (Pogona vitticeps) was affected by recent ingestion of a meal of crickets.

ANIMALS

12 healthy adult inland bearded dragons.

PROCEDURES

Food was withheld for 48 hours prior to experiments. Animals (6/group) were randomly assigned to receive a meal of crickets (equivalent to 1% of the animal's body weight; 10 g/kg [4.5 g/lb]; treatment group) or have food withheld for an additional 48 hours (control group). Blood samples were collected for plasma uric acid measurement just before (time 0) and 4, 24, and 48 hours after feeding. Effects of feeding and time on the targeted measurement were assessed by repeated-measures ANOVA.

RESULTS

Mean plasma uric acid concentration for the treatment group was significantly increased from the time 0 value (2.5 ± 1.5 mg/dL) 24 hours following meal ingestion (6.5 ± 1.2 mg/dL), but not at the 4-hour time point, and returned to the time 0 value by the 48-hour time point. No significant changes in plasma uric acid concentration were detected for the control group.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested food should be withheld for ≥ 48 hours prior to blood collection if inland bearded dragons are used to establish reference intervals for plasma uric acid concentration or if feasible when obtaining samples from these animals for clinical evaluation. Veterinarians should consider the time from last meal consumption when interpreting plasma uric acid concentration for this species and potentially other terrestrial insectivorous and omnivorous lizards.

After feeding, animals expend extra energy to appropriately process ingesta and excrete waste.1 For this reason, fasting of human patients or food withholding for veterinary patients is currently recommended prior to most serum or plasma analyses. Animals cannot store amino acids as easily as lipids and carbohydrates, and amino acid breakdown products are often detected in the blood of animals prior to excretion.2 The form in which nitrogen is excreted can vary widely among species; land-based mammals usually produce urea, water-based turtles often produce ammonia or urea, and land-based reptiles and birds predominantly excrete uric acid.2 Results of several studies3–6 of penguins and falcons have indicated that blood uric acid concentration in these birds increases after food consumption. In addition, snakes and lizards that ingest small mammals (eg, rats and mice) whole were shown to develop significant postprandial increases in blood uric acid concentration.7,8

Considering the possible fluctuations in circulating uric acid concentration related to feeding cycles in avian and reptile species, the timing of blood collection to assess a patient's health status as well as the timing of blood collection for reference interval studies should be carefully considered. In some studies9,10 performed to provide values or establish reference intervals for plasma uric acid concentration in reptiles such as Gila monsters (Heloderma suspectum) and panther chameleons (Furcifer pardalis), food-withholding times for the enrolled animals were not reported. This makes it unclear whether recent meal ingestion could have contributed to variation in reported blood uric acid values and raises a question of when blood should be collected in relation to feeding to best compare results for a patient with these data. In studies11,12 that evaluated plasma biochemical variables in inland bearded dragons (Pogona vitticeps) and leopard geckos (Eublepharis macularius), food was withheld from animals for 24 hours prior to blood sample collection, but it is unclear whether this is an appropriate length of time to avoid postprandial confounding of variables for uricotelic reptiles.

To increase clinicians’ ability to detect pathological increases in circulating uric acid concentration, a better understanding of baseline (unfed state) and postprandial uric acid concentration in each species would ideally be available. Inland bearded dragons are a popular omnivorous uricotelic terrestrial lizard species for which uric acid dynamics have not been elucidated. The purpose of the study reported here was to assess the effects of recent ingestion of crickets (a commonly offered feeder insect for captive insectivorous and omnivorous reptiles) on plasma uric acid concentration in inland bearded dragons. The study hypothesis was that these values would increase ≤ 4 hours after the animals consumed a meal of crickets.

Materials and Methods

Animals

This study was approved by the University of Wisconsin-Madison School of Veterinary Medicine Institutional Animal Care and Use Committee. Twelve university-owned adult inland bearded dragons (7 males and 5 females; median age, 2 years [range, 1 to 4 years]; mean ± SD body weight, 0.28 ± 0.02 kg [0.62 ± 0.04 lb]) were enrolled in the study. The animals had been obtained from a commercial breeder for several unrelated studies and maintained with the same husbandry for ≥ 3 months prior to the start of the study. The animals were housed individually in glass tanks in a climate-controlled room with a 12hour light-and-dark cycle; UVB light was provided to each enclosure for 12 h/d, and temperature of the room was maintained between 25°C and 27°C (77°F and 81°F). This resulted in a temperature gradient from room temperature at one end of the tanks up to approximately 34°C (93°F) at the basking spot provided at the other end of the tanks. The animals were offered crickets (Acheta domestica), superworms (Zophobas morio), or mixed leafy greens once daily 6 d/wk on a rotating schedule (insects were offered every other day, and greens were offered on the remaining days). For additional nutrient supplementation, the insects were gut loaded before being fed to the study animals.a–c Fresh water was available in a bowl at all times, and all animals were placed in shallow warm water twice weekly for further hydration. A washout period of ≥ 4 weeks was established between inclusion in any previous studies and the start of the study reported here. All animals were deemed healthy on the basis of repeated physical examinations by a veterinarian; monitoring of food intake, fecal output, and body weight; and results of plasma biochemical testing prior to the study. In addition to routine monitoring and plasma uric acid measurements as described, the animals underwent physical examination daily during the study period.

Study design

Food was withheld from all bearded dragons for 48 hours at the start of the randomized, controlled, noncrossover study. Animals (6/group) were randomlyd assigned to receive a meal of crickets (10 g/kg [4.5 g/lb, an amount equivalent to 1% of body weight]; treatment group) or to have food withheld for an additional 48 hours (control group). Each animal was placed in a plastic container,e and the entire weighed cricket meal was placed on the far side of the enclosure. Water was available ad libitum throughout the study; however, no additional food was provided until the study ended.

Blood samples (0.2 mL) were collected from animals in both groups for plasma uric acid measurement at time 0 (just prior to feeding for the treatment group) and 4, 24, and 48 hours later. Blood was collected from the ventral tail vein with a 1-mL syringe and a 25-gauge needle and transferred into lithium heparin–containing tubes. Plasma uric acid concentration was determined with a commercial whole blood analyzerf marketed for testing of reptile samples.

Statistical analysis

Commercial softwareg was used to perform the data analysis. The data were tested for normality with the Shapiro-Wilk test and for equal variance with the Brown-Forsythe test. The data were assessed for the effects of feeding and time by repeated-measures 2-way ANOVA. The Holm-Sidak method was used for post hoc analysis. Values of P < 0.05 were considered significant. Data are reported as mean ± SD or SEM.

Results

Bearded dragons of the treatment group had significantly higher plasma uric acid concentration at the 24-hour time point (mean ± SD, 6.5 ± 1.2 mg/dL), compared with the 0-hour time point within the same group (2.5 ± 1.5 mg/dL; P < 0.001) and with the control group (2.6 ± 1.2 mg/dL; P = 0.005) at the 24-hour time point (Figure 1). For the treatment group, plasma uric acid concentrations at the 4-hour and 48hour time points were not significantly different from the time 0 concentration. For the control group, no changes in plasma uric acid concentration were detected among time points.

Figure 1—
Figure 1—

Mean ± SEM plasma uric acid concentration for 12 inland bearded dragons (Pogona vitticeps) that had food withheld for 48 hours and then received a meal of crickets (treatment group; white circles; n = 6) or had food withheld for an additional 48 hours (control group; black circles; 6). Water was available at all times. Venous blood sampling for all animals was performed just prior to feeding a meal of crickets (10 g/kg [4.5 g/lb]; equivalent to 1% of body weight) to the treatment group (time 0) and was repeated 4, 24, and 48 hours later. Measurement for the treatment group is significantly (P < 0.05) different from that for the control group at the same time point and from the time 0 measurement for the treatment group.

Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.933

Discussion

Historically, it has been accepted that reptiles do not experience a clinically relevant postprandial increase in blood uric acid concentration. This assumption is derived from information in previous studies13–16 that investigated postprandial blood uric acid concentration in reptiles. However, these studies13–16 were all performed for ureotelic aquatic species, such as Chinese soft-shelled turtles (Pelodiscus sinensis), green sea turtles (Chelonia mydas), and Kemp's ridley sea turtles (Lepidochelys kempii), or semiaquatic species, such as red-eared sliders (Trachemys scripta elegans) and American alligators (Alligator mississippiensis). The formation and proportion of excreted nitrogen waste products differ greatly between aquatic ureotelic reptiles (which predominantly excrete urea nitrogen) and terrestrial uricotelic species (which predominantly produce and excrete uric acid), and therefore, our finding that healthy inland bearded dragons had a significant increase in plasma uric acid concentration after being fed an amount of crickets equivalent to 1% of their body weight was in contrast to the previously described findings13–16 for other reptiles. However, one noncontrolled study7 of carnivorous lizards and snakes identified a significant postprandial increase in blood uric acid concentration after ingestion of mice equivalent to approximately 10% of the reptiles’ body weight, and in another noncontrolled study,8 snakes that were fed mice or rats also had a significant postprandial increase in blood uric acid concentration.

Mean plasma uric acid concentration in bearded dragons increased significantly by 24 hours, but not by 4 hours, after consumption of the described meal of crickets in the present study, with a return to the time 0 (unfed) value within 48 hours after consumption of the meal. This apparent peak was detected substantially later than has been found in previous studies of birds. In black-footed penguins (Spheniscus demersus) fed within a 2-hour window, blood uric acid concentration was found to peak ≤ 2 hours after feeding, and a decline was noted 4 to 6 hours after a meal.3 Peregrine falcons (Falco peregrinus) had peak blood uric acid concentration detected 8 hours after meal ingestion in another study.7 Reptiles appear to have a much later peak in circulating concentration of their principal nitrogen end products after a meal; in snakes, uric acid concentration peaked 2 days after ingestion of rats or mice,7,8 and in 2 carnivorous lizard species (Gila monsters and Savanna monitors [Varanus exanthematicus]), these values peaked 24 hours after ingestion of mice (an amount equivalent to approx 10% of reptiles’ body weight),7,8 similar to the results of the present study. In the aforementioned carnivorous snakes and lizards, blood uric acid concentration remained greater than preprandial concentration for at least 4 to 5 days.7,8 Chinese soft-shelled turtles had plasma urea concentration peak 24 hours after meal ingestion,15 similar to uric acid results for the bearded dragons in this study. American alligators had increased plasma ammonia concentration for at least 96 hours after meal consumption.15

As previously mentioned, studies11,12 that generated reference intervals for captive inland bearded dragons and provided plasma biochemical data for leopard geckos used animals that had had food withheld for 24 hours prior to blood sample collection. Data from the study reported here suggested that samples obtained after a 24-hour food-withholding period may have been collected during the postprandial peak of circulating uric acid concentration and therefore at a time not suitable for determination of baseline (unfed) reference values for this and potentially other biochemical variables in inland bearded dragons. This suggests additional studies are warranted to evaluate the effects of feeding and food-withholding times for other uricotelic insectivorous and omnivorous terrestrial reptiles. The application of reference intervals calculated from data obtained after an inadequate food-withholding period might prevent detection of abnormally high uric acid concentration attributable to pathological conditions in a reptile that has been anorexic prior to blood uric acid evaluation. Our results suggested that ≥ 48 hours would be a more suitable food-withholding period to establish a reference interval for circulating uric acid concentration in bearded dragons.

Although food withholding has also been reported to increase circulating uric acid concentration in some species,4 no significant increase in plasma uric acid values was found in the control group of bearded dragons that had food withheld for a total of 96 hours in the present study. Clearly, nitrogen end product metabolism is a very complex process for many species, and considering that plasma uric acid concentration is used clinically to assess kidney function in reptiles,17 working to better characterize this process in relation to food consumption intervals is necessary. Ideally, all reference intervals for nitrogen end products should be assessed in relation to the last meal consumed by the animals enrolled in a study.

Many other preanalytic factors, such as the characteristics of the meal ingested (eg, concentration of protein and amount consumed relative to the animal's body weight), body temperature, and season, should be further investigated to provide the best understanding of what condition animals used to establish an appropriate reference interval should be in and what other factors might influence blood uric acid values in reptile patients. The present study's inclusion of a small number of animals and investigation of only 1 type and quantity of food were important limitations. However, these results laid the groundwork for further investigations. Future studies should be pursued to elucidate an appropriate reference interval for plasma uric acid concentration in bearded dragons.

Acknowledgments

Funding for this study was provided in part by Abaxis Global Diagnostics.

The authors declare that there were no conflicts of interest.

Footnotes

a.

Orange Cube Cricket Diet, Fluker Farms, Port Allen, La.

b.

Hi-Calcium Cricket Diet, Fluker Farms, Port Allen, La.

c.

Cricket Quencher with Calcium, Fluker Farms, Port Allen, La.

d.

Microsoft Excel, Microsoft Corp, Redmond, Wash.

e.

N40 large mouse cage, Ancare Corp, Bellmore, NY.

f.

VetScan Avian/Reptile Profile Plus, Union City, Calif.

g.

SigmaPlot, version 13, Systat Software, San Jose, Calif.

References

  • 1. Secor SM. Specific dynamic action: a review of the postprandial metabolic response. J Comp Physiol B 2009;179:156.

  • 2. Singer MA. Dietary protein-induced changes in excretory function: a general animal design feature. Comp Biochem Physiol B Biochem Mol Biol 2003;136:785801.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3. Kolmstetter CM, Ramsay EC. Effects of feeding on plasma uric acid and urea concentrations in blackfooted penguins (Spheniscus demersus). J Avian Med Surg 2000;14:177179.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Alonso-Alvarez C, Ferrer M, Vinuela J, et al. Plasma chemistry of the chinstrap penguin Pygoscelis antarctica during fasting periods: a case of poor adaptation to food deprivation? Polar Biol 2003;26:1419.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5. Cray C, Stremme DW, Arheart KL. Postprandial biochemistry changes in penguins (Spheniscus demersus) including hyperuricemia. J Zoo Wildl Med 2010;41:325326.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6. Lumeij JT, Remple JD. Plasma urea, creatinine and uric acid concentrations in relation to feeding in peregrine falcons (Falco peregrinus). Avian Pathol 1991;20:7983.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Maixner JM, Ramsay EC, Arp LH. Effects of feeding on serum uric acid in captive reptiles. J Zoo Anim Med 1987;18:6265.

  • 8. Lam A, Halan M. Monitoring of physiological changes of uric acid concentration in the blood of snakes. Folia Vet 2017;61:5660.

  • 9. Cooper-Bailey K, Smith SA, Zimmerman K, et al. Hematology, leukocyte cytochemical analysis, plasma biochemistry, and plasma electrophoresis of wild-caught and captive-bred Gila monsters (Heloderma suspectum). Vet Clin Pathol 2011;40:316323.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10. Laube A, Pendl H, Clauss M, et al. Plasma biochemistry and hematology reference values of captive panther chameleons (Furcifer pardalis) with special emphasis on seasonality and gender differences. J Zoo Wildl Med 2016;47:743753.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11. Tamukai K, Takami Y, Akabane Y, et al. Plasma biochemical reference values in clinically healthy captive bearded dragons (Pogona vitticeps) and the effects of sex and season. Vet Clin Pathol 2011;40:368373.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12. Knotkova Z, Morici M, Oliveri M, et al. Blood profile in captive adult male leopard geckos (Eublepharis macularius). Vet Med (Praha) 2019;64:172177.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Anderson ET, Minter LJ, Clarke EO III, et al. The effects of feeding on hematological and plasma biochemical profiles in green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempii) sea turtles. Vet Med Int 2011;2011:890829.

    • Search Google Scholar
    • Export Citation
  • 14. Knotkova Z, Dorrestein GM, Jekl V, et al. Fasting and postprandial serum bile acid concentrations in 10 healthy female red-eared terrapins (Trachemys scripta elegans). Vet Rec 2008;163:510514.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15. Lee SM, Wong WP, Loong AM, et al. Postprandial increases in nitrogenous excretion and urea synthesis in the Chinese soft-shelled turtle, Pelodiscus sinensis. J Comp Physiol B 2007;177:1929.

    • Search Google Scholar
    • Export Citation
  • 16. Busk M, Overgaard J, Hicks JW, et al. Effects of feeding on arterial blood gases in the American alligator Alligator mississippiensis. J Exp Biol 2000;203:31173124.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17. Hernandez-Divers SJ, Martinez-Jimenez D, Bush S, et al. Effects of allopurinol on plasma uric acid levels in normouricaemic and hyperuricaemic green iguanas (Iguana iguana) (Erratum published in Vet Rec 2008;162:776). Vet Rec 2008;162:112115.

    • Search Google Scholar
    • Export Citation
  • Figure 1—

    Mean ± SEM plasma uric acid concentration for 12 inland bearded dragons (Pogona vitticeps) that had food withheld for 48 hours and then received a meal of crickets (treatment group; white circles; n = 6) or had food withheld for an additional 48 hours (control group; black circles; 6). Water was available at all times. Venous blood sampling for all animals was performed just prior to feeding a meal of crickets (10 g/kg [4.5 g/lb]; equivalent to 1% of body weight) to the treatment group (time 0) and was repeated 4, 24, and 48 hours later. Measurement for the treatment group is significantly (P < 0.05) different from that for the control group at the same time point and from the time 0 measurement for the treatment group.

  • 1. Secor SM. Specific dynamic action: a review of the postprandial metabolic response. J Comp Physiol B 2009;179:156.

  • 2. Singer MA. Dietary protein-induced changes in excretory function: a general animal design feature. Comp Biochem Physiol B Biochem Mol Biol 2003;136:785801.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3. Kolmstetter CM, Ramsay EC. Effects of feeding on plasma uric acid and urea concentrations in blackfooted penguins (Spheniscus demersus). J Avian Med Surg 2000;14:177179.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Alonso-Alvarez C, Ferrer M, Vinuela J, et al. Plasma chemistry of the chinstrap penguin Pygoscelis antarctica during fasting periods: a case of poor adaptation to food deprivation? Polar Biol 2003;26:1419.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5. Cray C, Stremme DW, Arheart KL. Postprandial biochemistry changes in penguins (Spheniscus demersus) including hyperuricemia. J Zoo Wildl Med 2010;41:325326.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6. Lumeij JT, Remple JD. Plasma urea, creatinine and uric acid concentrations in relation to feeding in peregrine falcons (Falco peregrinus). Avian Pathol 1991;20:7983.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Maixner JM, Ramsay EC, Arp LH. Effects of feeding on serum uric acid in captive reptiles. J Zoo Anim Med 1987;18:6265.

  • 8. Lam A, Halan M. Monitoring of physiological changes of uric acid concentration in the blood of snakes. Folia Vet 2017;61:5660.

  • 9. Cooper-Bailey K, Smith SA, Zimmerman K, et al. Hematology, leukocyte cytochemical analysis, plasma biochemistry, and plasma electrophoresis of wild-caught and captive-bred Gila monsters (Heloderma suspectum). Vet Clin Pathol 2011;40:316323.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10. Laube A, Pendl H, Clauss M, et al. Plasma biochemistry and hematology reference values of captive panther chameleons (Furcifer pardalis) with special emphasis on seasonality and gender differences. J Zoo Wildl Med 2016;47:743753.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11. Tamukai K, Takami Y, Akabane Y, et al. Plasma biochemical reference values in clinically healthy captive bearded dragons (Pogona vitticeps) and the effects of sex and season. Vet Clin Pathol 2011;40:368373.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12. Knotkova Z, Morici M, Oliveri M, et al. Blood profile in captive adult male leopard geckos (Eublepharis macularius). Vet Med (Praha) 2019;64:172177.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Anderson ET, Minter LJ, Clarke EO III, et al. The effects of feeding on hematological and plasma biochemical profiles in green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempii) sea turtles. Vet Med Int 2011;2011:890829.

    • Search Google Scholar
    • Export Citation
  • 14. Knotkova Z, Dorrestein GM, Jekl V, et al. Fasting and postprandial serum bile acid concentrations in 10 healthy female red-eared terrapins (Trachemys scripta elegans). Vet Rec 2008;163:510514.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15. Lee SM, Wong WP, Loong AM, et al. Postprandial increases in nitrogenous excretion and urea synthesis in the Chinese soft-shelled turtle, Pelodiscus sinensis. J Comp Physiol B 2007;177:1929.

    • Search Google Scholar
    • Export Citation
  • 16. Busk M, Overgaard J, Hicks JW, et al. Effects of feeding on arterial blood gases in the American alligator Alligator mississippiensis. J Exp Biol 2000;203:31173124.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17. Hernandez-Divers SJ, Martinez-Jimenez D, Bush S, et al. Effects of allopurinol on plasma uric acid levels in normouricaemic and hyperuricaemic green iguanas (Iguana iguana) (Erratum published in Vet Rec 2008;162:776). Vet Rec 2008;162:112115.

    • Search Google Scholar
    • Export Citation

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