Some reptiles make it easy to provide optimum nutrition. Snakes, for example, swallow whole prey that contains all of the nutrients they need to survive and thrive. Provided, of course, that the prey was also fed properly and doesn’t suffer from parasites or deficiencies. Making sure that prey is as healthy as possible by providing the necessary nutrition is called gutloading the prey. The predator then has all of its nutritional requirements taken care of. This is easier with vertebrate prey, as the bones supply the essential calcium. The prey also provides preformed, fat-soluble vitamins, such as A and D, which are often no easy for a reptile to convert from other sources.
When providing food for an insectivore or herbivore, you need to work a little smarter to provide enough calcium and other nutrients. Varied prey and properly balanced supplements help attain all of the nutritional requirements of each species. There is no one-size fits all routine, but research and discussions with other keepers can help you provide the best diet for your scaly friends.
In Douglas Mader’s Reptile Medicine and Surgery, the Nutrition section by Susan Donoghue & Julie Langenberg (151) reports generalized reptile nutrition statistics as follows:
Carnivores should consume 25-60% protein, 30-60% fat and <10% carbohydrate Omnivores should consume 15-40% protein, 5-40% fat and 20-75% carbohydrate
Herbivores should consume 15-35% protein, <10% fat, and 55-75% carbohydrate While this is a very handy guideline, it doesn't outline everything you need to know about feeding your reptile. Here are the bare basics: Carnivores eat whole prey that need little, if any, supplementation. Avoid relying on neonatal prey (pinkies or day-old chicks) as they have relatively little protein and calcium. Omnivores, including insectivore specialists, need a balance between meat, insects and vegetation. This group has a very wide range for meat vs veg ratios. Herbivores need a solid foundation of plant-based foods. Some species are more strict, such as arrid species of tortoise or Uromastyx requiring high-viber, low-fruit diets. A few tolerate a small amount (once monthly) addition of insects or other animal-based foods along with a larger amount of fruit. Within each group, variety is important and will help if you have a large collection of reptile species to feed! Avoid relying on one staple feeder (insect or vertebrate) and be sure to provide a rotation of plant foods for omnivores and herbivores.
As reptile species vary greatly even within the main three groups, you should rely on reputable feeding guides for your pet. Find these by using our Reptile Resources and cross-check everything in multiple forums, as advice may change as we learn more about our pets. We have detailed what you need to know about providing the specialized frugivore/insectivore diet for Crested Geckos and the herbivore diet for Uromastyx. Each section offers tips for commercial, pre-made formulas as well as homemade diets – along with the cautions and concerns of doing so.
These are nutrients you need in smaller amounts than carbohydrates, fats and proteins, but are vital to basic functioning and good health. They fall into broad categories of minerals and vitamins. Providing an adequate diet in captivity can be difficult due to the general uncertainty of nutritional requirements of exotic animals. While domestic animals, like livestock and typical companion animals, have been studied for decades, we know relatively little about reptiles, who are a range of herbivores, omnivores, insectivores, frugivores and carnivores. Typically, whole foods will not provide too many vitamins, but many do not provide enough or are not by themselves a balanced meal. The average grocery store cannot provide all of the needs of reptiles, who may need specialty items such as live insects, frozen or pre-killed vertebrate prey and a wide variety of plant foods. While some commercial diets exist, most are not adequate and may even be harmful. Processed foods in general are bad news for these diversified specialists.Therefore, supplements are a necessity no matter what type of reptile you are feeding. Feeding a purely “natural” diet is a nice theory, but ultimately unobtainable in practice for most keepers.
Dietary minerals, like calcium, are necessary not only for building strong bones, but also for blood synthesis and regulation, balancing pH, cellular functions, energy processing, enzyme production, and a wide variety of biological functions.
There are various trace minerals that are considered important to include in minute amounts, as the total requirements for all the different minerals is not known, even for humans. Both plants and feeders have highly variable contents of both macrominerals and microminerals. The calcium to phosphorus ratios are extremely important to the overall health of reptiles. Most insects used as feeders are highly skewed towards phosphorus, with very little calcium by comparison. Other invertebrates, such as annelids (earthworms and other ringed worms) and isopods (crustaceans) contain higher ratios of Calcium to Phosphorus. The ideal ratio of calcium to phosphorus is 2:1, although anywhere between 1.5:1 – 3:1 can be used in a balanced diet.
Other Calcium Ratios
Calcium, phosphorus, and magnesium are some of the best-understood minerals that allow for
calcium bioavailability. Let us first understand that calcium carbonate (and the major forms of calcium: calcium citrate, calcium lactate, calcium gluconate or calcium malate) are all water-soluble (as opposed to fat-soluble; they can simply be eliminated from the system).
It has been noted that many nutrients are involved processing calcium, so piling on calcium if an animal shows signs of deficiency may not solve your problem. The presence and relative abundance of vitamin D3, magnesium, and phosphorus all have a direct impact on the bioavailability of calcium. Conversely, too much calcium can interrupt the absorption of trace elements.
It is important to understand the different forms or precursors of some vitamins, such as beta carotene, which are much more tolerated than the already formed retinol. Both are sources of Vitamin A. Similarly, reptiles exposed to unfiltered sunlight or high-quality UV bulbs can make their own Vitamin D. Indoor reptiles should be fed Vitamin D3 for it to be available in the body to help with calcium uptake, among other important functions. To make things even more complicated, species react differently to both the precursors and previously formed vitamins, so there is not always an all-in-one solution. Some species or individuals may need more or less.
Most commonly, reptiles kept indoors and fed unsupplemented diets suffer from a lack of calcium, Vitamin D3, and Vitamin A. Dusting powders are commonly used to supplement calcium, but often lack vitamin D3 and other minerals. Be sure to stock both plain calcium, a multi-mineral supplement with calcium plus D3, and a balanced all in one supplement that includes minerals, vitamins and trace elements. A good idea is to keep on hand a calcium plus magnesium formula that can help with calcium crashes – which often result during egg laying or in rescued animals that have chronic calcium deficiencies.
The typical diet for reptile insectivores is a monotonous routine of crickets or mealworms, often fed cheap vegetable matter intended to promote basic survival and reproduction. Usually this feeder diet are cheap grains (cereals and bran) and potatoes, very lacking in Vitamin A. Nutritional observations of commercially reared and wild insects show that in nature, bugs dine on a variety of foods and are much higher in Vitamin A. Providing feeders with fresh produce, like carrots, sweet potatoes, and a variety of greens and fruits, rich in caratenoids such as pre-vitamin A, is a step towards proper supplementation. Combine this with the proper dusting supplements described above.
Ill health can also affect the absorption of calcium, as many vital processes involve organs like the liver and kidneys. Impairment in these organs can disrupt the metabolism of vitamin D3 and reduce the bioavailability of calcium and other nutrients.
Deficiencies of thiamine, a B-vitamin, affect aquatic turtles due to a diet high in fish, which can contain thiaminase, resulting in tremors, loss of motor control (ataxia), blindness, and slow heart rate (bradycardia). This often correlates with a vitamin E or selenium deficiency, which results in anorexia and swollen nodules beneath the skin, and with muscles loss & weakness, compromised immune system, and vision loss.
Iodine deficiency affects thyroid process and related hormones which are controlled by thyroid, pituitary, brain and other signals from elsewhere in the body. These hormones affect oxidation in cells, resulting in problems with growth, nervous system and metabolism other nutrients. A goiter results from low iodine levels where the thyroid gland becomes enlarged to compensate. Goitrogens from plant foods are a common phytotoxin that interfere with the process. Be aware that iodine can be overdosed and so should not be over-supplemented, as with other nutrients.
Other micronutrient deficiencies are seen with both carnivores, who may need taurine, and herbivores which can be tricky to feed for new keepers. Remember that excessive calcium results in zinc, copper, and iodine deficiencies. While many argue that extra calcium is harmless, that is not completely true as it out competes other nutrients and interferes with the absorption of others in different ways. A once in a while boost won’t hurt but providing more than is needed on a regular basis will cause a nutrient imbalance.
Supplements do pose a risk of over-supplementation and this should not be taken lightly.
There are risks for both under- and over-supplementation. Nutrition should be approached with research and care must be taken that a complete diet is offered, whether it’s a home brew feeding plan or a quality commercial diet.
Another risk is unbalanced supplements. The ratio of specific vitamins in particular is important to be aware of, and can help you evaluate supplements as well as commercial feed. You may remember the difference between fat-soluble vitamins and water-soluble vitamins from your school health class.
“Nutrients with the most narrow ranges of safe intakes (established in other species) include calcium, selenium, vitamin A and vitamin D3. Maximal calcium tolerances depend on many variables and, in practice, are presumed to be only three to five times corresponding minimums (e.g., three to five times 0.6% DM). Higher intakes of calcium may lead to conditioned deficiencies of trace minerals and, if combined with a high-fat diet, formation of calcium soaps in the digestive tract.”
– Reptile Medicine and Surgery, Douglas Mader, 2005 edition
Fat-soluble vitamins (A, D, E & K) are stored in fat cells and don’t need to be eaten as often, while water-soluble will pass through the body quickly if not used for various biological functions. The fat-soluble vitamins can accumulate at toxic levels if fed in large or unbalanced amounts. The generally recognized ratio of Vitamin A (as retinol), Vitamin D & Vitamin E is 10:1:0.1. Outside of this ratio, too much Vitamin A can interrupt Vitamin D and calcium absorption, causing an overdose. The level of D3 as a supplement should range from 500-2000 IU D3 per kg. Maximum tolerances suggested for many reptile species are 2.5% calcium, 1.6% phosphorus/DM, and 5000 IU/kg vitamin D3.
Clinical Veterinary Advisor, Birds and Exotic Pets
Too much Vitamin D can cause calcification of internal organs and tissues, liver damage, bladder stones, and bloat in amphibians. Along with over-feeding vitamin D, a deficiency of vitamin A can occur, as many keepers provide calcium/D3 supplements without the use of a multivitamin. Many guides recommend feeding calcium and other minerals at one feeding, and vitamins at another to avoid both oversupplementation and to reduce degradation when the two are combined. Some great commercial products use advanced suspension techniques to combine both minerals and vitamins in a single product that can be used regularly.
The other fat-soluble vitamin, K, is being studied more in-depth for its effects on other nutrients.
Lead can be a toxic contaminant in many calcium supplements, especially those from oyster shells and bonemeal. Look for synthesized, pharmaceutacle-grade calcium rather than those more suited for gardening, like bonemeal and shells. Egg shell powder is acceptable for human use but may contain growth-inducing hormones which may prove problematic for the more closely related reptiles.
If a diet is severely lacking or unbalanced, a set of related symptoms may point to a specific disorder or syndrome caused by improper feeding.
Metabolic Bone Disease
MBD is a spectrum of disorders related to calcium deficiency or malabsorption, most of which are diet related. The bioavailability of calcium is determined not only by the amount of calcium in the diet, but also the interaction of other vitamins & minerals as mentioned above. When the right balance is not present in the diet, calcium is pulled from the bones and is not available for crucial bodily functions necessary for life.
The outward signs of MBD include soft jaws, disfigured bones, swollen joints, trembling and general ill-health. Calcium is needed for more than just bones, although skeletal symptoms are prominent. Internal problems include lack of muscle control, loss of liver, kidney and nerve function, and blood clotting. Severe cases of MBD do result in death, often the result of heart failure as the organ can no longer function without this element. The healthy level of calcium in the bloodstream is roughly 1%. Blood tests may be used to diagnose MBD and rule out other issues.
It is easy to overfeed our reptiles, because as humans we eat multiple times a day and have a comparatively high metabolism. However, in the wild most reptiles do not eat as often, some going weeks to months between meals. Most will eat at every opportunity, because missing a meal could mean a long time before eating again. So they display hunting/foraging behavior and “look hungry”. Putting an entire week’s worth of food in front of them multiple times a day can quickly result in an overweight reptile! Following proper feeding guidelines is critical to avoid obesity.