Conference PaperPDF Available

Vitamin A in Reptiles

  • Mandai Wildlife Group
Vitamin A Balance in Reptiles
Shangzhe Xie1, BSc/BVMS, MVS (Conservation Medicine); Ji Zhen Low2, BSc/BVMS
1School of Animal and Veterinary Sciences, The University of Adelaide, Adelaide,
SA, Australia; 2St. Bernards Road Veterinary Clinic, Magill, SA, Australia
Vitamin A is often implicated in diseases of reptiles, especially aquatic
chelonians, and diseases such as palpebral oedema and aural abscesses are
thought to be associated with hypovitaminosis A due to poor diet and
husbandry (Brown et al. 2004; Boyer 2006). At the other end of the spectrum,
hypervitaminosis A, sometimes as a result of overzealous treatment of
suspected hypovitaminosis A, can result in dry patches of skin and generalized
sloughing of the epithelium.
Vitamin A has been shown to serve crucial biological functions in animals,
including reptiles. One of these functions is as a visual pigment in
photoreceptors (rods and cones) and this has been measured in reptilian
species including Pseudemys scripta, Chelonia mydas (Liebman, Granda
1971), Podarcis sicula, and Anolis carolinensis (Provenico et al. 1992). Vitamin A
also encourages the formation of mucus-secreting cells at the expense of
keratinized cells to synthesise glycoproteins (Moore 1957), that is, it acts as a
hormone regulating epidermal growth (Vershinin 1999). This effect becomes
obvious when there is insufficient vitamin A, resulting in hyperkeratosis (Moore
In captivity, hypovitaminosis A is most commonly caused by a lack of dietary
intake of preformed vitamin A. Insects are poor sources of preformed vitamin A,
that is, retinoids, because invertebrates in general do not convert carotenoids to
retinol (Moore 1957) and the majority of retinoids are found in the insects' eyes
(Finke 2003). Whole vertebrate prey, in general, contain sufficient preformed
vitamin A in their livers (Douglas et al. 1994), which may explain why there are
less reports of hypovitaminosis A in reptiles consuming such prey (e.g., snakes).
Some reptiles may be able to convert carotenoids to retinol, and Dierenfeld et al.
(2002) quoted unpublished information from Ferguson GW, that suggested that
Panther chameleons (Furcifer pardalis) might be one such species. Ferguson et al.
(1996) quoted unpublished information from Talent LG, suggesting that
insectivorous lizards can utilize beta carotene to overcome vitamin A deficiency,
but more definitive information does not seem to be available. Another study
involving juvenile green iguanas (Iguana iguana) found that polar xanthophyll,
not beta-carotene, was selectively accumulated by iguanas fed different
carotenoids after 56 days of carotenoid deficiency (Raila et al. 2002), indicating
that in some reptilian species, there may not even be absorption/digestion of
dietary carotenoids. In this study, there was also no change found in plasma
retinol levels after carotenoids were fed to the iguanas (Raila et al. 2002).
Environmental contamination with organochlorine compounds and
subsequent chronic exposure to these compounds is a possible cause of
hypovitaminosis A in wild reptiles (Holladay et al. 2001; Brown et al. 2004;
Sleeman et al. 2008). A study of aural abscesses in wild box turtles (Terapine
carolina) reported mucosal hyperplasia and squamous metaplasia of the
conjunctiva, pharynx, trachea, and auditory tubes, and that there was a
nonsignificant trend of decreased serum and hepatic vitamin A levels in the
turtles (Holladay et al. 2001). Brown et al. (2008) found that the histopathologic
changes were more severe in box turtles with aural abscesses and sometimes
involved bacterial infections. Sleeman et al. (2008) went one step further to
assign scores to the histopathologic changes and found that these scores were
positively correlated with o,p-DDT and vitamin A levels but no correlation with
total hepatic organochlorine compound concentrations. The positive correlation
between pathologic scores and vitamin A levels were unexpected, but possibly
explained by the initial increase in vitamin A levels as organochlorine
concentration increased (Sleeman et al. 2008). Laboratory-based studies may
produce more convincing results linking hypovitaminosis A to aural abscesses
but none have been reported to date.
Diagnoses of hypovitaminosis A are currently made on the basis of a dietary
history indicating a lack of preformed vitamin A intake; clinical signs of
hyperkeratosis, usually involving the eyelids, and general signs of lethargy,
anorexia, weight loss, and nasal/ocular discharge; and response to treatment
with vitamin A supplementation (Boyer 2006). A more definitive diagnosis
involving vitamin A assays of liver or blood is usually not possible for several
reasons. It may not be cost-effective and a liver biopsy would place the patient at
risk. On the other hand, although a blood sample is relatively easy to collect, a
vitamin A assay of the blood sample may not yield a meaningful result. This is
because retinol-binding proteins in blood tend to maintain blood levels of
vitamin A at fairly stable levels unless liver stores are severely depleted or in
cases of hypervitaminosis A (Schweigert et al. 1991).
A lack of preformed vitamin A intake does not always mean that the reptile will
suffer from hypovitaminosis A. There is generally no food intake at all during
hibernation of reptiles in the wild, and komodo dragons (Varanus komodoensis)
have been shown to still have large amounts of hepatic vitamin A despite not
eating for six months (Jensen, With 1939). This might indicate that a prolonged
period of poor diet and husbandry might be required to produce clinical
hypovitaminosis A. There are also a number of other causes of the more specific
signs of hyperkeratosis of the eyelids, such as foreign bodies and bacterial
infections (Lawton 2006). Furthermore, vitamin A supplementation is seldom
initiated without other improvements in diet and husbandry and other
treatments such as ophthalmic antibiotic ointments are often prescribed, and it
is very difficult to attribute resolution of clinical signs to vitamin A
supplementation alone. However, there have been instances where dramatic
improvement was reported after discontinuation of other treatments and single
doses of vitamin A injections (Boyer 2006), and these are probably the cases
where a response to treatment can be used to retrospectively diagnose
hypovitaminosis A.
Vitamin A appears to be a much maligned vitamin in reptilian diseases, but it has
been acquitted before, as illustrated by the following example. Vitamin A
deficiency has been implicated in upper respiratory tract diseases (URTD) of
desert tortoises previously (Fowler 1980), but it has since been proven that
serum and liver vitamin A levels are not significantly different in healthy desert
tortoises and desert tortoises with URTD (Jacobson et al. 1991). Mycoplasma spp.
and Pasteurella spp. are now the new suspects in this case (Jacobson et al. 1991).
This paper may have raised more questions than answers, but maybe the
point to take home is that thinking more critically about common diagnoses and
treatments of reptilian diseases may lead to new studies and discoveries that
are important in expanding the field of reptilian medicine. Very little additional
information has become available since Elkan and Zwart (1967) published their
comprehensive description of the clinical and histological changes in terrapins
with suspected hypovitaminosis A. More research, especially prospective,
laboratory-based controlled studies definitively linking hypovitaminosis A to the
clinical signs that are thought to be associated with hypovitaminosis A are
required to further the understanding of a relatively common syndrome in wild
and captive reptiles.
1. Boyer TH. Hypovitaminosis A and hypervitaminosis A. In: Mader DR, ed. Reptile Medicine and
Surgery. 2nd ed. St. Louis, MO: SaundersElsevier; 2006.
2. Brown JD, Richard JM, Robertson J, et al. Pathology of aural abscesses in free-living eastern box
turtles (Terrapene carolina carolina). Journal of Wildlife Diseases. 2004;40:704712.
3. Dierenfield ES, Norkus EB, Carroll K, Ferguson GW. Carotenoids, vitamin A, and vitamin E
concentrations during egg development in panther chameleons (Furcifer pardalis). Zoo Biology.
4. Douglas TC, Pennino M, Dierenfeld ES. Vitamins E and A, and proximate composition of whole
mice and rats used as feed. Comparative Biochemistry and Physiology. 1994;107A:419424.
5. Elkan E, Zwart P. The ocular disease of young terrapins caused by vitamin A
deficiency. Pathologia Veterinaria. 1967;4:201222.
6. Ferguson GW, Jones JR, Gehrmann WH, et al. Indoor husbandry of the panther
chameleon Chamaeleo [Furcifer] pardalis: effects of dietary vitamins A and D and ultraviolet
irradiation on pathology and life-history traits. Zoo Biology. 1996;15:279299.
7. Finke MD. Gut loading to enhance the nutrient content of insects as food for reptiles: a
mathematical approach. Zoo Biology. 2003;22:147162.
8. Fowler ME. Comparison of respiratory infection and hypovitaminosis A in desert tortoises. In:
Montali RJ, Migaki G, eds. Comparative Pathology of Zoo Animals. Washington DC: Smithsonian
Institute; 1980.
9. Holladay SD, Wolf JC, Smith SA, et al. Aural abscesses in wild-caught box turtles (Terapene
carolina): possible role of organochlorine-induced hypovitaminosis A. Ecotoxicology and
Environmental Safety. 2001;48:99106.
10. Jacobson ER, Gaskin JM, Brown MB, et al. Chronic upper respiratory tract disease of free
ranging desert tortoises (Xerobates agassizii). Journal of Wildlife Diseases. 1991;27:296361.
11. Jensen HB, With TK. Vitamin A and carotenoids in the liver of mammals, birds, reptiles and
man, with particular regard to the intensity of the ultraviolet absorption and the Carr-Price
reaction of vitamin A.Biochemical Journal. 1939;33:17711786.
12. Lawton MPC. Reptilian opthalmology. In: Mader DR, ed. Reptile Medicine and Surgery. 2nd ed.
St. Louis, MO: Saunders Elsevier; 2006.
13. Liebman PA, Granda AM. Microspectrophotometric measurements of visual pigments in two
species of turtle, Psedemys scripta and Chelonia nydas. Vision Research. 1971;11:105114.
14. Moore T. Vitamin A. New York, NY: Elsevier Publishing Company; 1957.
15. Provencio I, Loew ER, Foster R G, 1992. Vitamin A2-Based Visual Pigments in Fully Terrestrial
Vertebrates. Vision Research. 1992;32:22012208.
16. Sleeman JM, Brown J, Steffen D, et al. Relationships among aural abscesses, organochlorine
compounds, and vitamin a in free-ranging eastern box turtles (Terrapene carolina
carolina). Journal of Wildlife Diseases. 2008;44:922929.
17. Raila J, Shuhmacher A, Gropp J, Schweigert FJ. Selective absorption of carotenoids in the
common green iguana (Iguana iguana). Comparative Biochemistry and Physiology Part A.
18. Schweigert FJ, Uehlein- Harrell S, Hegel GV, Wiesner H. Vitamin A (retinol and retinyl esters), α-
tocopherol and lipid levels in plasma of captive wild mammals and birds. Journal of Veterinary
Medicine Series A. 1991;38:3542.
19. Vershinin A. Biological functions of carotenoids - diversity and evolution. BioFactors.
(click the speaker's name to view other papers and abstracts submitted by this
Ji Zhen Low, BSc/BVMS
St. Bernards Road Veterinary Clinic
Magill, SA, Australia
Shangzhe Xie, BSc/BVMS, MVS (Conservation Medicine)
School of Animal and Veterinary Sciences
The University of Adelaide
Adelaide, SA, Australia
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
Seventeen desert tortoises, Xerobates agassizii, with upper respiratory tract disease were examined; thirteen were euthanatized for necropsy. Four normal control desert tortoises from a clinically healthy population were similarly evaluated. Hemoglobin and phosphorus values were significantly (P less than or equal to 0.05) lower and serum sodium, urea, SGOT, and cholesterol values were significantly higher in ill tortoises compared to controls. No significant differences in concentrations of serum or liver vitamins A and E were found between the two groups. While no significant differences were found for concentrations of lead, copper, cadmium, and selenium, the livers of ill tortoises had higher concentrations of mercury and iron. Lesions were found consistently in the upper respiratory tract (URT) of ill tortoises. In all ill tortoises dense infiltrates of lymphocytes and histiocytes obscured the mucosal epithelium and underlying glands. The mucosal epithelium was variably dysplastic, hyperplastic, and occasionally ulcerated. Electron microscopic studies revealed small (350 to 900 nm), pleomorphic organisms resembling Mycoplasma sp., in close association with the surface epithelium of the URT of ill tortoises. Pasteurella testudinis was cultured from the nasal cavity of all ill tortoises and one of four control tortoises. A Mycoplasma sp. was cultured from the nasal passageways of four ill tortoises and was ultrastructurally similar to the pleomorphic organism present on the mucosa in tissue section.
Insects are known to be poor sources of preformed vitamin A, leading to the speculation that insectivorous species, including reptiles, may be able to convert carotenoid precursors to meet dietary requirements for this nutrient. This study was conducted to indirectly evaluate carotenoid and vitamin A metabolism in the panther chameleon (Furcifer pardalis). Eggs were obtained from females in Madagascar that were yolked either early or later in the breeding season, and carotenoid (α- and β-carotene, cryptoxanthin, lutein/zeaxanthin, and lycopene), vitamin A, and vitamin E concentrations were measured in egg contents in early, middle, or late embryonic development. An overall trend of decreased nutrient concentration as eggs matured (from egg period 1 (yolks) to egg period 3 (embryos)) was seen within both clutch groups. The season of clutch deposition was a significant influence on egg weight, α-carotene, and lutein/zeaxanthin concentrations, but on no other nutrients. Chameleon yolks contained considerably higher levels of carotenoids than levels previously reported from two viviparous lizard species, and β-carotene concentrations were of the same magnitude as reported in grazing tortoises. β-Carotene and β-cryptoxanthin were the predominant carotenoids in yolk and embryos, comprising about 95% of total carotenoids detected. Measurable concentrations of retinol at all stages of egg development in the chameleons suggests effective conversion from carotenoid precursors, with concentrations similar to those measured in other lizard eggs. Information from eggs obtained in native habitats may provide baseline data on nutrient interactions to improve and optimize captive dietary management; preliminary data suggest that micronutrient environments may vary over the protracted breeding season, with possible implications for embryo health and survival. Zoo Biol 21:295–303, 2002. © 2002 Wiley-Liss, Inc.
To assess the importance of diet and light for indoor maintenance, hatchling panther chameleons were reared for 1 year on crickets fed diets that differed in vitamin concentrations and in different light environments. Dietary transfer of vitamins from the cricket diet to the lizards via the crickets was quantified, as was UV irradiance. There was a statistically significant dietary enhancement of growth by both vitamins on males. UV-A irradiation significantly suppressed growth of females. Low vitamin A shortened life span and resulted in a number of gross and histological pathologies. Hepatocellular lipidosis, indicating a possible toxicosis, occurred with all diets and light treatments. Higher vitamin A resulted in mild soft-tissue mineralization, and high vitamin D shortened the life span of females. Low vitamin A drastically reduced reproduction in both sexes. The intermediate levels of dietary vitamins resulted in the best production of viable eggs by females. However, without high UV-B irradiation, all viable eggs died at term and contained different vitamin levels than hatching eggs from wild-caught females. Baseline levels of egg calcium are given for hatching eggs from wild-caught females. Modifications in current husbandry procedures are recommended. © 1996 Wiley-Liss, Inc.
A variety of commercially raised insects are fed to insectivorous reptiles, but information concerning appropriate diets used to feed these insects is limited. In the present study, house crickets (Acheta domesticus adults and nymphs), mealworms (Tenebrio molitor larvae), and silkworms (Bombyx mori larvae) were fed diets containing graded levels of calcium (Ca) and/or vitamin A–nutrients that are low or absent in most insects. Diets and insects were analyzed for moisture, Ca, phosphorus (P), and vitamin A. For adult crickets and cricket nymphs, body Ca and vitamin A concentrations increased in a linear fashion with increasing levels of dietary Ca or vitamin A. Ca concentrations of silkworms also increased in a linear fashion with increasing levels of dietary Ca. For mealworms, body Ca and vitamin A concentrations increased in a nonlinear fashion with increasing levels of dietary Ca or vitamin A. These regression equations, in conjunction with insect nutrient composition, allow for the calculation of the optimum nutrient concentration for gut-loading diets. Final recommendations were based on National Research Council (NRC) requirements for rats, adjustments for the energy content of the insects, and nutrient overages as appropriate. Gut-loading diets for crickets (adults and nymphs) should be supplemented to contain the following nutrients, respectively: Ca (51 and 32 g/kg), vitamin A (8,310 and 5,270 µg retinol/kg), vitamin D (300 and 190 µg cholecalciferol/kg), vitamin E (140 and 140 mg RRR-α-tocopherol/kg), thiamin (31 and 21 mg/kg), and pyridoxine (20 and 10 mg/kg). Gut-loading diets for mealworms should be supplemented to contain the following nutrients: Ca (90 g/kg), iron (51 mg/kg), manganese (31 mg/kg), vitamin A (13,310 µg retinol/kg), vitamin D (460 µg cholecalciferol/kg), vitamin E (660 mg RRR-α-tocopherol/kg), thiamin (5 mg/kg), vitamin B12 (650 µg/kg), and methionine (29 g/kg). Gut-loading diets for silkworms should be supplemented to contain the following nutrients: Ca (23 g/kg), iodine (0.7 mg/kg), vitamin D (140 µg cholecalciferol/kg), vitamin E (70 mg RRR-α-tocopherol/kg), and vitamin B12 (226 µg/kg).
Carotenoids first emerged in archaebacteria as lipids reinforcing cell membranes. To serve this function their long molecules have extremely rigid backbone due to the linear chain of usually 10 to 11 conjugated C=C bonds in trans-configuration — the length corresponding the thickness of hydrophobic zone of membrane which they penetrate as “molecular rivets”. Carotenoids retain their membrane-reinforcing function in some fungi and animals. The general structure of carotenoid molecule, originally having evolved for mechanical functions in membranes, possess a number of other properties that were later used for independent functions. The most striking fact is that these properties proved to fit some new functions to perfection. — The polyene chain of 9—11 double bonds absorbs light precisely in the gap of chlorophyll absorption — function as accessory light-harvesting pigments in all plants; — Unique arrangement of electronic levels owing to the by polyene chain structure makes carotenoids the only natural compounds capable of excitation energy transfer both (i) from carotenoid excited state to chlorophyll in the light-harvesting complex and (ii) from triplet chlorophyll or singlet oxygen to carotenoid in photosynthetic reaction centers — protection of RC from photodamage. The linear system of conjugated C=C bonds provides high reducing potential of carotenoid molecules making them potent antioxidants in lipid formations. Still, there is a lack of evidence of the chemical antioxidant function of carotenoids, especially in higher organisms; most data demonstrate an antioxidant ability rather than a function. Carotenoids have many other independent biological functions, including: specific coloration patterns in plants and animals, screening from excessive light and spectral filtering, defense of egg proteins from proteases in some invertebrates; the direct carotenoid derivative — retinal — acts as visual pigment in all animals and as chromophore in bacteriorhodopsin photosynthesis, retinoic acid in animals and abscisic acid in plants serve as hormones. All these functions utilize various properties (mechanical, electronic, stereospecific) of a single structure evolved in bacteria for a single membrane-reinforcing function, thus demonstrating an example of pure evolutionary preadaptation. One of the practical conclusions that can be reached by reviewing uniquely diverse properties and functions of carotenoids is that, when considering possible mechanisms of their effects in organisms (e.g., anticarcinogenic action), all their functional traits should be taken into account.
Aural abscesses are a common health problem in free-ranging eastern box turtles (Terrapene carolina carolina), and they have been associated with high body burdens of organochlorine (OC) compounds, which are known disruptors of vitamin A. The objective of this study was to determine if the presence of pathologic lesions in box turtles were correlated with increased and decreased levels of hepatic OC compounds and vitamin A, respectively. A graded scale for the pathologic changes observed in tissue samples collected from abscessed and nonabscessed box turtles over a 2-yr period (2003-04) was developed, and the levels of OC compounds and vitamin A in livers collected from the same turtles were determined through chemical analysis. Sixty-eight turtles (40 with aural abscesses and 28 without) were included in the study. Relationships between variables were analyzed using Spearman's Rank Correlation Test, where P</=0.05 was considered significant. Twenty-seven different OC compounds were identified. Mean+/-standard deviation (SD) total OC compound level for all turtles was 0.35+/-0.83 ppm (range 0-5.81 ppm), and mean+/-SD vitamin A level was 72.8+/-98.6 ppm (range 0-535.7 ppm). There was no correlation between pathologic score and total hepatic OC compound concentration (r = -0.18, P = 0.16). However, pathologic score was positively correlated with o,p'-DDT (r = 0.25, P = 0.05). Vitamin A was positively correlated with pathologic score (r = 0.32, P = 0.01), which was contrary to the expected result. There was no linear correlation between vitamin A and total hepatic OC compound concentration (r = -0.04, P = 0.75). However, a nonlinear regression provided a significant fit (r(2) = 0.12, P = 0.02), indicating an initial increase in vitamin A as the OC compound burden increased, followed by a decline as OC compound levels increased further. The hepatic OC compound residue concentrations in these box turtles were lower compared to levels found in freshwater aquatic turtles but similar to levels in other terrestrial reptile species. This study provides mixed results in support of a role of OC compounds, presumably of environmental origin, in the etiology of aural abscesses in free-ranging box turtles.
As part of a broad study of the ocular and extraocular photoreceptors of reptiles, we have used high performance liquid chromatography (HPLC) to identify the retinoids present in whole eye extracts of the arboreal lizard Anolis carolinensis and the non-arboreal ruin lizard Podarcis sicula. Unexpectedly, only vitamin A2-derived chromophore was detected in Anolis, while a mixture of vitamin A1- and vitamin A2-derived chromophores was detected in Podarcis. These are the first examples of fully terrestrial vertebrates using vitamin A2-derived chromophore for visual pigment generation. Furthermore, microspectrophotometric (MSP) data for Anolis show a class of photoreceptor having a visual pigment with maximum absorbance at about 625 nm, some 40 nm further into the red than has been found in any terrestrial vertebrate examined to date.
Vitamin A (retinol and retinyl esters), vitamin E and lipids were determined in a wide variety of wild mammals and birds held in captivity. In mammals plasma levels of vitamin A were generally below 500 ng/ml and those of vitamin E were highly variable (0.1-2 micrograms/ml). In primates, vitamin E levels were 3 to 8 micrograms/ml. Whereas in Marsupialia, Chiroptera, primates, Rodentia, Proboscidea, Sirenia, Perissodactyla and Artiodactyla only retinol was found, retinyl esters (basically retinol palmitate/oleate) represented 10 to 50% of the total plasma vitamin A in some birds of the order Ciconiiformes and Falconiformes. Retinol levels in birds were higher compared to mammals (500-2,000 ng/ml). The same was true for lipids as well as for vitamin E levels (1-26 micrograms/ml) in the plasma of birds.