Also see Management of Reptiles.
Appropriate husbandry of reptiles is as important as providing adequate nutrients. Photoperiod, temperature, humidity, substrate, stress, and cage “furniture” can affect feeding behavior and thus nutrient intake. Temperature and humidity gradients within a reptile enclosure allow the animal to select warm, dry spots or cooler, moist areas. Competition for preferred sites and for feeding stations in an enclosure with multiple animals should also be assessed. Sufficient numbers of warm spots, UVB exposure (basking) spots, and feeding stations should be available for all animals within an enclosure. Visual barriers may be useful to decrease competition for preferred sites or food dishes.
Prey such as rabbits, rats, or mice for carnivorous or omnivorous reptiles should come from commercial breeding centers and be offered dead, not only for injury prevention to the reptile but also for the welfare of the offered prey. Although it is not common, prey have been known to attack predators and can inflict serious bites. Offering dead prey can also decrease the chance of injury to the predator caused by striking the walls of the enclosure in trying to capture prey. However, some reptiles may initially need the stimulation of live prey to eat, particularly if they are not adapted to captivity. The possibility of disease or parasite transmission from prey to predator also should be considered. Ideally, commercially raised, pathogen-free feeder prey should be offered if possible.
As shown in the table Composition of Animal Foods That May Be Offered to Reptiles, the Ca:P ratio of most food items offered to reptiles is inadequate and should be at least 1:1, with 2:1 preferred (1). Seventy-two hours before being fed to a reptile, insects should have a mineral supplement that contains at least 8–10% calcium added to their feed. By the time these insects are fed to a reptile, the percentage of calcium they contain will have increased from 0.01% to 0.5% on a dry-matter basis.
Vertebrate prey should be fed nutritionally complete diets appropriate for the species (eg, mouse diet, rabbit diet, rat diet, etc). The nutrient content of the prey depends directly on what it is fed (eg, mice raised on a vitamin A-deficient diet have decreased liver storage of this essential nutrient). Additionally, if frozen mice or rats are routinely used to feed carnivorous reptiles, freezer storage conditions should be optimal (eg, ≤ 6 months in duration and in thick plastic bags to retard deterioration, stored at −20°C). Methods of thawing that minimize water loss are also important. Because many carnivorous reptiles rely on their prey not only as nutrient sources but also as water sources, the hydration status of the prey is very important. Thawing should be done in a cooler at < 8°C. (For more information, see Nutrition in Raptors.)
Familiarity with the food habits of a species in the wild is essential if appropriate foods and nutrient levels are to be offered to captive counterparts. Common practice has been to offer two or more different types of prey species, because differences in nutrient content exist among different types of vertebrate and invertebrate prey. Decreased dependence on a single food or prey species is also desirable because some prey items may periodically be difficult to obtain. Dependence on a single prey item is frequently observed in snakes and may be unavoidable.
Many commercial diets for reptiles are marketed, including products for carnivorous, herbivorous, and omnivorous reptiles, in frozen, freeze-dried, canned, extruded, pelleted, or sausage forms. Acceptability may be better when commercial diets are offered to reptiles when they are young. Appropriately formulated manufactured diets for reptiles are a potentially simpler and more economical alternative to feeding fresh produce or live prey. However, some of these diets may not be formulated based on scientific studies, and frequently, little information concerning micronutrient concentrations is provided by the manufacturers. When selecting a commercial product, the buyer should obtain accurate information about product formulation and specific nutrient concentrations. Unfortunately, little controlled research has been conducted on nutrient requirements of reptiles, and claims of product superiority may not have a scientific justification. (See the table Composition of Animal Foods That May Be Offered to Reptiles.)
Composition of Animal Foods Commonly Offered to Reptiles
Food Item | Dry Matter, % | Protein, % | Fat, % | Energy, Kcal/g | Calcium, % | Phosphorus, % | Ca:P Ratio |
|---|---|---|---|---|---|---|---|
Mealworms (Tenebrio) | 42.2 | 52.8 | 35 | 6.53 | 0.06 | 0.53 | 0.11 |
Superworms (Zophobas) | 40.6 | 17.4 | 17.9 | — | 0.01 | 0.02 | 0.43 |
Locusts | 31.2 | 61.7 | 19.4 | — | 0.1 | 0.75 | 0.13 |
Crickets | 38.2 | 55.3 | 30.2 | — | 0.23 | 0.74 | 0.31 |
Earthworms | 22 | 49.9 | 5.8 | — | 0.59 | 0.85 | 0.69 |
Wax worms | 38.3 | 15.5 | 22.2 | — | 0.03 | 0.22 | 0.13 |
Chicken muscle | 25.6 | 20.5 | 4.3 | 1.21 | 0.01 | 0.2 | 0.05 |
Egg, whole | 25.2 | 12.3 | 10.9 | 1.47 | 0.05 | 0.22 | 0.02 |
Mice, 1–2 days old | — | — | — | — | 1.6 | 1.8 | 0.88 |
Mice, adult | — | 19.86 | 8.81 | 2.07 | 0.84 | 0.61 | 1.37 |
—, not available. | |||||||
Herbivorous reptile pellets should make up 25–50% of herbivorous reptile diets. Reptiles should be fed 1–4% of their body weight daily on a dry-matter basis. Vegetables with a low oxalate content should be fed to decrease the likelihood of kidney stone formation. Good-quality grass hay or a so-called herbal hay, which includes leaves, flowers, and herbs, should be fed. No more than 50% of the diet should consist of fresh greens, fruits, and vegetables, and fruit should be no more than 5%. In Europe, herbs and dandelions are also often fed to herbivorous reptiles. Fresh, clean water must be available at all times.
See the table Recommended Nutrient Concentrations for Reptiles.
Recommended Nutrient Concentrations for Reptiles
--------------------------Concentrationa-------------------------- | |||
|---|---|---|---|
Nutrientb | Carnivorous Reptiles | Omnivorous Reptiles | Herbivorous Reptiles |
Crude proteinc | 30–50% | 20–25% | 18–22% |
Fat | — | 3–6% | — |
Crude fiber | — | 20–35% | — |
Arginine | 1.0% | 1.8% | — |
Isoleucine | 0.5% | 1.3% | — |
Lysine | 0.8% | 1.5% | — |
Methionine | 0.4% | 0.4% | — |
Methionine + cysteine | 0.75% | 0.75% | — |
Threonine | 0.7% | 1.0% | — |
Tryptophan | 0.15% | 0.3% | — |
Linoleic acidd | 1.0% | 1.0% | — |
Calcium | 0.8–1.1% | 1.0–1.5% | 1.4–2.0% |
Phosphorus | 0.5–0.9% | 0.6–0.9% | 0.8–1.0% |
Potassium | 0.4–0.6% | 0.4–0.6% | — |
Sodium | 0.2% | 0.2% | — |
Magnesium | 0.04% | 0.2% | — |
Manganese | 5 ppm | 150 ppm | — |
Zinc | 50 ppm | 130 ppm | — |
Iron | 60–80 ppm | 200 ppm | — |
Copper | 5–8 ppm | 15 ppm | — |
Iodine | 0.3–0.6 ppm | 0.4 ppm | — |
Selenium | 0.3 ppm | 0.3 ppm | — |
Riboflavin | 2–4 ppm | 8 ppm | — |
Pantothenic acid | 10 ppm | 60 ppm | — |
Niacin | 10–40 ppm | 100 ppm | — |
Vitamin B12 | 0.020 ppm | 0.025 ppm | — |
Choline | 1,250–2,400 ppm | 3,500 ppm | — |
Biotin | 70–100 ppb | 400 ppb | — |
Folacin | 200–800 ppb | 6,000 ppb | — |
Thiaminee | 1–5 ppm | 5 ppm | — |
Pyridoxine | 1–4 ppm | 10 ppm | — |
Vitamin Af | 5,000–10,000 IU/kg | 15,000 IU/kg | — |
Cholecalciferol (vitamin D3)g | 500–1,000 IU/kg | 500–1,000 IU/kg | — |
Vitamin Eh | 200 IU/kg | 200 IU/kg | — |
Abbreviations: —, not available. | |||
Recommendations are based on information from Dennert C. Ernährung von Landschildkröten. 5th ed. Natur und Tier; 2021. | |||
a Nutrient concentrations are recommended minimums for carnivorous reptiles and averages for omnivorous reptiles. | |||
b Nutrient levels expressed on a dry-matter basis. | |||
c Taurine requirements have not been determined for reptiles (the requirement for cats is 400–500 mg of taurine/kg dry diet). | |||
d A dietary source of arachidonic acid at 200 mg/kg dry diet may be necessary. | |||
e Thiamine concentrations should be increased to 10–20 mg/kg if frozen, thawed fish constitute > 25% of the diet offered. | |||
f A source of preformed vitamin A may be required, because it is not known whether reptiles can convert carotenes to retinol (vitamin A), although it is likely that herbivorous reptiles can. | |||
g Requirements for vitamin D may be partially or totally satisfied by exposure to sunlight or appropriate sources of artificial UV light. These suggested concentrations are not sufficient to prevent clinical signs of vitamin D deficiency in green iguanas. | |||
h 300 IU/kg dry matter is advisable if the diet is high in fat, especially unsaturated fat, which can increase the body's need for vitamin E. | |||
Vitamin C synthesis has been reported in many reptile species. It has been suggested that ulcerative stomatitis in snakes and lizards may be associated with vitamin C deficiency, although there is no definitive supporting evidence. In controlled studies with garter snakes (Thamnophis sp) fed supplemental vitamin C, tissue levels and body stores remained stable, although synthesis by the snakes was decreased (2).
Although most reptiles excrete nitrogen primarily as uric acid, aquatic reptiles typically excrete excess nitrogen as urea or ammonia. The relative proportions of various nitrogenous wastes excreted by reptiles may depend on the amount and composition of feed, frequency of feeding, and state of hydration. The excessive precipitation of urate crystals in joints, kidneys, or other organs (gout) is a common condition in some species of captive reptiles. The etiology is not clear, but diets high in protein may predispose reptiles to uric acid accumulation, which can cause gout (3). Impaired renal function and dehydration have also been suggested as possible causes.
When poor-quality protein is fed (imbalanced in amino acids) or tissue is catabolized for energy, uric acid excretion increases. Although gout in some reptiles is associated with increased circulating levels of uric acid, postprandial transient increases in circulating uric acid may occur in some species and may confound the diagnosis of gout. Assuring an adequate state of hydration in a susceptible reptile may help prevent uric acid precipitation in joints and organs. Feeding diets low in protein to carnivorous reptiles is unwise, because they are adapted to feeding on high-protein prey.
Vitamin D and Ultraviolet Light for Reptiles
Most vertebrates can either absorb vitamin D from the diet or synthesize it in skin from 7-dehydrocholesterol using energy from UVB light of certain wavelengths (290–315 nm) in a temperature-dependent reaction. Thus, vitamin D is required in the diet only when endogenous synthesis is inadequate, such as when animals are not exposed to UV light of appropriate wavelengths.
Many captive basking species appear susceptible to rickets or osteomalacia (metabolic bone disease). Bone fractures, soft tissue mineralization, renal complications, and tetany can develop. Reptiles frequently show few premonitory clinical signs, although lethargy, inappetence, and reluctance to move are commonly reported. Serum calcium concentrations may not be diagnostically useful. Compared with total serum calcium, ionized calcium is generally a more accurate reflection of the reptile's physiologically active calcium status. Although blood levels of vitamin D can be measured, normal values for most species are not known. Supplementation with oral calcium and injectable vitamin D may provide some short-term relief. However, exposure to UV light, or lack of it, may be an important, yet often overlooked, factor in the differential diagnosis. Complicating the diagnosis may be soft tissue mineralization, observed radiographically or at necropsy.
In green iguanas, metastatic calcification may result not only from vitamin D toxicity. Iguanas with both fractured bones and extremely low or undetectable levels of circulating 25-hydroxycholecalciferol also had calcified soft tissues (4). The etiology of the metastatic calcification in these cases is not well understood and is contrary to conventional understanding of clinical signs of vitamin D deficiency and toxicity in domestic species. Dietary sources of vitamin D alone may not be sufficient to prevent rickets and osteomalacia in green iguanas. Diets with as much as 3,000 IU vitamin D3/kg did not prevent bone fractures and cortical thinning in green iguanas (5). Bulbs emitting UVB radiation and placed over the lizards at approximately 30–46 cm (12–18 inches) for 12 hours/day appeared to reverse clinical signs in the least severely affected lizards. Therefore, UVB exposure, rather than dietary vitamin D, may be critically important in the production of active vitamin D in the skin of green iguanas and in the subsequent prevention of bone fractures.
Because some lizards seek a warm spot to increase body temperature, placement of a heat bulb, usually incandescent, adjacent to a UVB bulb helps ensure adequate exposure to UVB light. Depending on latitude, exposure to unfiltered natural sunlight during warmer months and use of UVB bulbs during the rest of the year usually eliminate the risk of metabolic bone disease caused by insufficient absorption of calcium (due to vitamin D deficiency). It has been suggested that some reptiles can accumulate 25-hydroxycholecalciferol when exposed to UVB emission of bulbs, so UVB exposure every day is not necessary; however, because much is still unknown, daily exposure to UVB radiation is still recommended. Additionally, it is not clear yet how much exposure is needed to maintain adequate vitamin D levels and how much time can pass before another UVB exposure is needed.
Some lizard species may be unable to absorb sufficient dietary vitamin D3, although the reason is poorly understood. New World primates are believed to have exceptionally high dietary requirements for vitamin D, which may be related to lower numbers of vitamin D cellular receptors than are present in Old World primates. Similar metabolic differences may exist in some basking lizard species, although this has not been established. UVB bulbs are sold in pet stores, but label claims may not always be reliable.
Some feeder insects (eg, mealworms) contain a limited amount of vitamin D (6). However, it is doubtful that this limited vitamin D content would fulfill the vitamin D requirement of the feeding reptile. Therefore, regular vitamin D supplementation is advised for many reptile species.
UVB Lighting for Reptiles
Three types of UVB lighting are on the market: fluorescent tubes, compact fluorescent bulbs, and mercury vapor bulbs. Fluorescent tubes supply diffuse light with a low level of visible light. Heat radiation is low, and the UVB gradient is fairly uniform. The light from fluorescent tubes more or less resembles natural UVB in the shade of a sunny day spread over a relatively large area. Compact fluorescent bulbs provide a more intensive UVB gradient focused on a small area. These bulbs are characterized by fairly low-intensity visible light and little heat. Mercury vapor bulbs (vapor spot and narrow spots) produce an intensive UVB gradient on a smaller area, producing heat and an intense light.
Mercury vapor bulbs can become very hot. Reptiles must be provided with an area to escape the bulb's focus to prevent them from getting burned during UVB basking. When a UVB lamp is added to a terrarium, the emission of UVB drops with the square of the distance; this explains the low UVB exposure level by the time the UVB rays reach the reptile when the lamp is hung too high. Following manufacturer's directions regarding hanging height of the bulb and replacing the bulb as indicated are key to maximizing the benefits a reptile gets from these bulbs.
The UVB radiation emitted by these bulbs declines with use. In general, UVB bulbs should be replaced once a year. However, it is best to regularly measure the amount of UVB with commercially available meters used in the artificial sunlight industry. A “D3 yield index” compares the vitamin D3–producing ability of a bulb with that of the sun, and the results show that there can be huge differences between UVB lamps, despite manufacturers' claims that all emit high levels of UVB.
Tests with LED-emitting UVB lights show that the optimal wavelength for synthesizing provitamin D in the skin is 283–304 nm (7). Products using UVB LEDs are now on the market, and further research is needed on the effects of UVB LED light on reptiles and other animals such as birds, primates, and other mammal species. UVB LED bulbs are expensive, plus the amount of UVB they emit is high and potentially toxic if an animal is overexposed.
How long and how much UVB exposure is needed in reptiles is not exactly known for every species. For example, bearded dragons do not develop metabolic bone disease if they are exposed only a few times a week to UVB radiation for a limited time. Similar effects of UVB may also apply to other reptile species; more research is needed. In general, reptiles that need UVB radiation must be exposed to 30-120 minutes of UVB light each day when older types of bulbs (non–mercury vapor) are used. It is still unknown how much UVB radiation reptiles and other animals should be exposed to when modern LED UVB bulbs are used.
Enlisting the assistance of a specialist is advised, because there is no ideal UVB bulb yet that meets the needs of all species (see Environmental Lighting for Reptiles).
Prey in Nutrition of Reptiles
Many reptiles, as well as some birds and mammals, are fed prey. The prey can consist of different species of rodents, birds, insects, and larvae. Widespread analyses of the fed prey come from research publications and anecdotal literature. Many analyses are performed on single prey species, which means that most are not statistically validated; analysis techniques can also vary.
See the table Proximate Analysis of Whole Prey, a summary of the most important nutritional values of prey. More information (eg, on fatty acid, amino acid, and vitamin and mineral composition of several prey species) can be found on the Feedipedia website.
Proximate Analysis of Whole Prey
Species | Scientific Name | Dry Matter(% DM) | Crude Protein, % in DM | Crude Fat, % in DM | Ash, % in DM | Ca, % in DM | P, % in DM | Cu, mg/kg DM | Fe, mg/kg DM | Zn, mg/kg DM | Mn, mg/kg DM |
|---|---|---|---|---|---|---|---|---|---|---|---|
Rodents | |||||||||||
Rat, adult | Rattus norvegicus domestica | 29.8 (20.8–34.4) | 59.7 (56.1–62.8) | 26.5 (22.1–32.6) | 11.7 (9.8–14.8) | 2.8 (2.1–3.5) | 1.7 (1.5–1.9) | 4.5 | 58.9 | 43.3 | NA |
Rat, baby | 20.8 | 65 | 20.9 | NA | 1.7 | 1.1 | 27.5 | 171.5 | 106.7 | 5.2 | |
Rat, 11 weeks | 35.7 | 63.4 | 34.9 | 7.5 | 2.3 | NA | NA | NA | NA | NA | |
Mouse, adult | Mus musculus | 28.1 (18.2–35.6) | 54.9 (44.2–64.2) | 28.4 (17.0–46.5) | 9.6 (7.6–11.8) | 1.9 (1.2–3.0) | 1.5 (1.2–1.7) | 11.8 (6.7–19.2) | 139.4 (34.6–181.3) | 68.3 (47.7–82.5) | 6.3 (0.2–13.1) |
Mouse, baby | 20.7 | 68.7 | 20.1 | 9.9 | 1.5 | 1.8 | 22.4 | 247.6 | 103.6 | 4.8 | |
Mouse, 25–35 g | 40.4 | 56.1 | 27.1 | 9.7 | 3.5 | 1.8 | 14.7 | 204.7 | 0.4 | 7.8 | |
Guinea pig, adult | Cavia porcellus | 33.6 | 46.0 | 39 | 11.1 | 2 | 3.1 | NA | NA | NA | NA |
Guinea pig, baby | 29.1 | 51.2 | 34.7 | 14.1 | NA | NA | NA | NA | NA | NA | |
Guinea pig, 10 wk | 31.3 | 51.4 | 46.1 | 9.2 | 3 | NA | NA | NA | NA | NA | |
Rabbit, adult | Oryctolagus cuniculus domesticus | 31.8 | 59.9 | 22.5 | 14.2 | 2.3 | 2.3 | NA | NA | NA | NA |
Birds | |||||||||||
Day-old chick | Gallus domesticus | 25.7 (25.0–27.7) | 64.4 (60.0–72.4) | 24.1 (22.4–28.1) | 7.1 (6.4–7.4) | 1.3 (0.8–1.7) | 0.9 (0.5–1.2) | 2.6 | 52.3 | NA | NA |
Chicken, whole | 33.5 | 43.1 | 35.2 | 12 | 2.7 | 2.1 | 3.6 | 122.2 | 11.6 | NA | |
Chicken leg | 40.3 | 49.9 | 36.7 | 6.4 | 1.7 | 2.7 | NA | NA | NA | NA | |
Chicken liver | 26.3 | 81 | 10.5 | 5 | 0 | 1.2 | 18.7 | 358.8 | 125.6 | ||
Quail | Coturnix japonica | 34 | 63.7 | 28.7 | 10.3 | 3.7 | NA | NA | NA | NA | NA |
Insects | |||||||||||
Cricket, adult | Acheta domestica | 32 | 62.6 | 20.4 | 5.2 | 0.3 | 1 | 20.2 | 153 | 154 | 26.3 |
Cricket, juvenile | 33 | 45 | 10 | 9.1 | 0.7 | 0.8 | 9.6 | 197 | 159 | 53 | |
Grasshopper | Locusta migratoria | 31 | 67.5 | 14 | 6 | 0.1 | 0.7 | NA | NA | NA | NA |
Bee, drone + worker | 30 | 18.6 | 3.2 | 5.2 | NA | NA | NA | NA | NA | NA | |
Cockroach | 38.7 | 20.9 | 11 | 1.3 | 0.1 | 0.2 | NA | NA | NA | NA | |
Fish fly | 26.5 | 16.9 | 5.2 | 1.5 | 0.1 | 0.3 | NA | NA | NA | NA | |
House fly, maggot | Musca domestica | NA | 50.4 | 18.9 | NA | 0.5 | 1.6 | NA | NA | NA | NA |
Fruit fly | Drosophila melanogaster | 30.9 | 68 | 19 | 7.2 | 0.2 | 1.3 | NA | NA | NA | NA |
Insect larvae | |||||||||||
Mealworm | 32.8 | 52.8 | 36.1 | 3.8 | 0.3 | 0.8 | NA | NA | NA | NA | |
Buffalo worm | 50 | 24 | 11 | 9 | NA | NA | NA | NA | NA | NA | |
Bloodworm | 9.9 | 5.2 | 1 | 1.1 | 0.04 | 0.09 | NA | NA | NA | NA | |
Black soldier fly larvae | NA | 42.9 | 2.6 | NA | 7.6 | 0.9 | NA | NA | NA | NA | |
House fly maggot meal | NA | 50.4 | 18.9 | NA | 0.5 | 1.6 | NA | NA | NA | NA | |
Silkworm pupae meal | NA | 60.7 | 25.7 | NA | 0.4 | 0.6 | NA | NA | NA | NA | |
Morio or superworm | 38.2 | 68.1 | 14.3 | 6.2 | 0.1 | 0.7 | NA | NA | NA | NA | |
Abbreviations: Ca, calcium; Cu, Copper; DM, dry matter; Fe, Iron; Mn, manganese; NA, no available data; P, phosphorus; Zn, zinc. | |||||||||||
For More Information
Also see pet owner content regarding diet for reptiles.
References
Maslanka MT, Frye FL, Henry BA, Augustine L. Nutritional considerations. In: Warwick C, Arena PC, Burghardt GM, eds. Health and welfare of captive reptiles. Springer; 2023:447-485.
Vosburgh KM, Brady PS, Ullrey DE. Ascorbic acid requirements of garter snakes: Plains (Thamnophis radix) and Eastern (T sirtalis sirtalis). J Zoo Anim Med, 1982;13(1), 38-42. doi:10.2307/20094561
Parkinson LA, Mans C. Investigation of the effects of cricket ingestion on plasma uric acid concentration in inland bearded dragons (Pogona vitticeps). J Am Vet Med Assoc. 2020;257(9):933-936. doi:10.2460/javma.257.9.933
Bernard JB, Oftedal OT, Ullrey DE. Idiosyncrasies of vitamin D metabolism in the green iguana (Iguana iguana). Proceedings of the 1996 Comparative Nutrition Society Symposium; 1996:11-14.
Bernard JB, Oftedal OT, Barboza P. Response of vitamin D-deficient green iguanas (Iguana iguana) to artificial ultraviolet light. Proceedings of the American Association of Zoo Veterinarians Conference; 1991:147-150.
Oonincx DGAB, van Keulen P, Finke MD, Baines FM, Vermeulen M, Bosch G. Evidence of vitamin D synthesis in insects exposed to UVb light. Sci Rep. 2018;8(1):10807. doi:10.1038/s41598-018-29232-w
Lindgren J. UV-lamps for terrariums: Their spectral characteristics and efficiency in promoting vitamin D3 synthesis by UVB irradiation. Bull Chicago Herp Soc. 2005;40:1-9.
