All about vitamins, minerals and Tortoises

Posted by : sanne

There is a great deal of misunderstanding concerning the role of vitamins and minerals. Many people believe that the more you get of both the better - this is categorically not true, indeed, some vitamins and minerals can be positively dangerous if taken in excess. What is actually required is a balanced intake of essential vitamins and trace-elements - not massive doses of individual vitamins in isolation which serve only to upset the balance and may cause relative deficiencies elsewhere.
It is also important to dispense with the myths, common among tortoise keepers, that vitamin deficiencies are the cause of a great deal of frequently encountered diseases or that a vitamin injection is necessary to assist with hibernation. Both claims are totally incorrect. In fact, genuine cases of primary vitamin deficiency (that it a deficiency caused by a lack of the vitamin in the diet rather than as a consequence of inability to metabolise the vitamin due to some other health problem) are quite rare. In the last 7 or 8 years we have encountered maybe 5 or 6 cases of primary vitamin deficiency in tortoises. In all of the cases we have seen, the base-line diet of the animals concerned was by any standards grossly inadequate and limited in range. There is virtually no chance of vitamin deficiencies occurring in tortoises which are fed on a well balanced, varied diet.

There are two common ways in which additional vitamins may be given:

Oral vitamin supplements

These are useful as a guarantee that all necessary vitamins are being supplied - but again, they are not essential if the base-line diet is of high quality and is sufficiently varied. Animals on natural browse do not need vitamin supplements, although calcium supplements may still be necessary.

Vitamin injections

These should only be used to deliver specific vitamins in cases where a specific vitamin deficiency is known to exist. We are totally opposed to the routine use of vitamin injections - in most cases, they serve no useful purpose and indeed are a frequent cause of introduced infection via the injection site. Very few deficiencies are so acute that the much more effective and safer oral delivery route is not a satisfactory mode of treatment. Acute vitamin-A deficiencies may be dealt with by injection, but few other cases require this treatment. The use of a routine "vitamin booster" before or after hibernation is a complete waste of time.


Many people are unclear as to the difference between vitamins and minerals, and especially about how the two interact (many minerals, calcium for example, depend upon the presence of certain vitamins such as vitamin-D before they can be absorbed).

Vitamins are organic substances which help regulate bodily functions. Acting as co-enzymes, vitamins aid the action of enzymes during the metabolism of dietary nutrients. There are about a dozen major vitamins, a deficiency of any one of which will result in a serious deficiency disease. Vitamins are only required in relatively small quantities, but have a major effect upon the body's reproductive, digestive, nervous and muscular systems. Vitamins also affect tissue growth and anti-body production.

Some important vitamins are:


Important to the condition of the skin and mucous membranes, eye (especially retinal) condition, biochemical and reproductive functions. Plants contain carotene which is converted to true vitamin-A in the body.


The B-complex vitamins are water soluble and excesses are excreted in the urine. Vitamin B1, thiamine, is a regulator in the carbohydrate metabolism; Vitamin B2, riboflavin, is a co-enzyme in energy release and interacts with vitamin B6 and vitamin B12; Vitamin B3, niacin, is also crucial to the energy metabolism and is often obtained by converting the amino-acid tryptophan - this process requires the presence of thiamine, riboflavin and pyridoxine; Vitamin B6, pyridoxine, is involved in energy conversion from glycogen and in the synthesis of haemoglobin and antibodies; Vitamin B12 interacts with folic acid to govern the production of red blood cells. A deficiency causes pernicious anaemia and neurological symptoms. This vitamin is only produced within the gastro-intestinal tract when various micro-organisms act upon trace level cobalt. Deficiencies can occur following malabsorbtion syndrome or as a consequence of severe parasite infestations. The B-complex is just that. A matrix of interacting and inter-dependant compounds.


Sometimes called 'the sunshine vitamin', vitamin-D is a fat soluble vitamin which is essential to the absorption and utilisation of calcium and phosphorous, as such, it plays a major role in bone formation. It can be obtained either naturally, by the action of ultra-violet light on sterols in the skin, or orally by supplementation - virtually all specialist calcium/mineral supplements intended for reptile use contain vitamin D in sufficient quantity.


Vitamin-C has many functions, but as it is present in almost all fruits and green vegetables, deficiencies are extremely unlikely in tortoises.


Many plants contain vitamin-E which is an antioxidant and works in conjunction with vitamins A and C.


A fat-soluble coagulation vitamin. This vitamin is synthesised in the gut by bacterial action and is also found in plant foods. It is especially abundant in green, leafy plants.


Minerals are quite different from vitamins and are both chemical regulators and construction materials - Calcium forms a major part of a tortoise's body, more than any other mineral. Calcium deficiency is also extremely common as a growing tortoise requires substantial quantities of this mineral in order to build its skeleton.
The building of healthy bone tissue is the result of many vitamins and minerals acting in cooperation with each other.
It is essential to note that calcium is poorly absorbed by the body whereas phosphorus is readily absorbed - if a diet is heavy in phosphorus in relation to calcium, the excess phosphorus will prevent the uptake of calcium to the bone. It is very easy to feed a diet too concentrated in phosphorus because it is available in nearly every foodstuff whereas calcium is relatively rare. We must knowingly choose calcium bearing foods when designing diets for captive animals.
Calcium and phosphorus together account for three-fourths of the mineral elements in the body, and five other elements account for most of the rest. It is important to note that their actions are interrelated; no one mineral can function without affecting the others.
The major function of calcium is to act in cooperation with phosphorus to build and maintain bones. Calcium is essential for healthy blood and also helps to regulate heartbeat. In addition, calcium assists in the process of blood clotting and helps prevent the accumulation of too much acid or too much alkali in the blood. It also plays a part in muscle growth, muscle contraction and nerve transmission. Calcium aids in the body's utilization of iron, helps activate several enzymes (catalysts important in metabolism), and helps regulate the passage of nutrients in and out of cell walls.
Calcium absorption is very inefficient. Two factors effect absorption directly; the availability of calcium in the diet and the current body need. Unabsorbed calcium is excreted.
Certain substances interfere with the absorption of calcium. When excessive amounts of fat combine with calcium, an insoluble compound is formed which cannot be absorbed. Other substances that can disrupt this process include oxalates and phytic acid.


Phosphorus is the second most abundant mineral in the body. It functions along with calcium. A balance of calcium and phosphorus is needed for these minerals to be effectively used by the body.

Phosphorus plays an important part in almost every chemical reaction within the body. It is important in the utilization of carbohydrates, fats and protein for growth, maintenance, and repair of cells and for the production of energy. It aids in the transference of heredity traits from parents to offspring. It is also necessary for proper skeletal growth, kidney function and transference of nerve impulses.
If phosphorus content is high, additional calcium must be taken to maintain proper balance. Phosphorus is available in a wide variety of foods and further supplementation is not necessary.

Miscellaneous trace elements

Calcium, chlorine, phosphorus, potassium, magnesium, sodium, and sulfur are present in relatively high amounts in the body tissues. Other minerals are present in the most minute quantities but are essential for proper body functioning. Iron, copper, and fluorine are present in sufficient quantities from deep green leafy plants. Iodine is needed to maintain a positive calcium balance, so a multi-mineral mixture containing iodine should be provided in addition to supplementation of raw calcium.


Try to ensure that all diets are as varied as possible - in this way, a wide cross-section of trace elements will be made available.
Do not dose with 'pure' vitamins unless under veterinary direction - some pure vitamins (such as vitamins A & D are highly toxic if taken in excess). These should only be used as part of a treatment program to correct a properly diagnosed specific deficiency.

Provide vitamins orally rather than by injection for preference.

The regular use of a safe, properly formulated multi-vitamin and mineral preparation will ensure that dietary deficiencies do not occur.

Aim for a high calcium - low phosphorous

balance in tortoise diets

Tortoises and Turtles are popular pets - but what should they be fed ?

Provet has recently conducted a review of the literature on feeding Tortoises and Turtles, and if ever there was a justification for banning the keeping of these creatures in captivity it would be because of the lack of sound scientific information about their nutritional requirements. For most domesticated species there is an independent authority (the National Research Council in the USA) which reviews the world wide literature and makes recommendations about the nutritional requirements for the species. There are also Authorities that set down standards for the conducting of feeding trials (eg AAFCO - the Association of Animal Feed Control Officials). There is no such independent authority for reptile nutrition..

As a result, the nutritional requirements of reptiles for almost all groups of nutrients is unknown. Published recommendations about what to feed tortoises and turtles are currently based upon observations of the eating habits of wild tortoises and turtles. However, despite these observations, many captive specimens still develop nutrition-related diseases ...which indicates that the basic ration that they are being fed is inadequate in some way. As the old saying goes : "the proof of the pudding is in the eating" and if an author has to advise a mineral or vitamin supplement to prevent nutritional disease, the basic ration is fundamentally inadequate .

AÂ similar situation occurred in captive Chimpanzees because for many years early observers believed that they were vegetarians. It was only when 24 hour surveillance in the wild was performed over a long period of time that they were observed eating animal material, and it was confirmed that they were actually omnivores. This explained why Chimpanzees kept in zoos would readily bite off and eat the fingers of children who poked them through perimeter wire fences !

There are serious problems with the anecdotal observational method of dietary recommendation. Nutritional deficiencies, toxicities or imbalances which result in gross anatomical deformities such as poor growth rate, shell deformities or skeletal fractures are easily recognised by clinicians, but other possible results of nutritional inadequacy, such as impaired immune responses and increased susceptibility to infections, may not be so obviously recognised as having a basis in poor nutrition. So, apparently healthy-looking individuals may in fact be suffering from a serious nutritional disorder ...but the presence of the problem is not realised.

ACCORDING TO NUMER0US PUBLICATIONS. Tortoises and Turtles eat a variety of foods - mainly vegetarian, but in the wild they sometimes eat meat such as dead mice or birds and they also eat various invertebrates such as crickets and worms. Terrapins are mainly carnivores eating fish and crustaceans.

Tortoises (Testudo spp) are claimed to eat a wide variety of plants including vegetables, fruits, grasses and flowers : alfalfa leaves, apples, banana, beans (runner and french), bean sprouts, bindweed, blackberries, broccoli, Brussel sprouts, buttercup, cabbage, carrot, cauliflower, chickweed, clover, courgettes, cucumber, dandelion, grass, hawkweed, lettuce, melon, nectarines, parsnips, peaches, pears, peas, plums, raspberries, strawberries, tomatoes, watercress. Some authors also say that they can also be given hard boiled eggs or a spoon of canned pet food once a week.

Other tortoises such as box turtles (Terrapene spp) are omnivores when adult, but mainly carnivorous as youngsters and eat a variety of food sources including : crickets, earthworms, insects, fish, mealworms, snails, slugs, woodlice as well as plant materials.

Terrapins eat fish and crustaceans including : herring, insect larvae, mackerel, pilchards, prawns, shrimps, snails (aquatic), sprats, tadpoles, water beetles, whitebait and some water plants eg watercress, pond weed and algae.

HOWEVER - there is serious disagreement between some "experts" on the subject of tortoise and turtle nutrition - for example some strongly advise that herbivorous Tortoises should not be fed certain foods , for example dog or cat foods, beans, fruit or "supermarket" products, whereas others do not Advice given is often opinion, not supported by scientific facts and sometimes it is simply scare-mongering....but which are truths and which are myths ?


Water is an extremely important, essential nutrient - even for desert dwelling species. The majority of a tortoises water requirement may be provided in the food that they eat, but a supply of fresh clean water should also be available at all times, and for tortoises it can be provided in shallow bowls which they can also lie in. Fruit contains a high water content, and so observed water intake is likely to be less in reptiles getting fruit in their ration.

Dehydration is common in ill reptiles, and patients developing stone formation in the urinary tract, hyperuricaemia or gout in which uric acid crystals form in joints or soft tissues, should have their hydration status checked. High purine content foods (such as liver) should also be avoided in such cases.


All organisms need to eat food containing energy-providing nutrients which can be in the form of proteins, carbohydrates or fats. Minerals, vitamins and water are all essential to life as well, but they are not sources of energy. For carnivorous reptiles (including aquatic turtles)Â the main sources of energy in the diet are fats (30-60% of requirement) and proteins (25-60% of requirement), for herbivorous reptiles (most tortoises) the main sources are carbohydrate (55-75% of requirement) and protein (15-35% of requirement). Omnivorous reptiles (including Box turtles and forest tortoises) obtain most of their energy from carbohydrate (20-75% of requirement) and either protein (15-40% of requirement) or fats (5-40% of requirement). Fermentation of fibre in the intestinal tract of herbivores can also produce fatty acids which provide an additional energy source.

Unlike mammals, birds and other warm-blooded species reptiles do not require energy to maintain body temperature, so their energy requirements are considerably less than for other species.

In general, energy requirements increase as the activity level increases, and also during growth and reproduction , in particular during egg production and laying. During hibernation energy reserves in the body need to be sufficient so that the tortoise or turtle can survive until it can seek out food again once it re-awakens. Fortunately, during hibernation the metabolic rate becomes extremely slow, so very little stored energy is used up.

The energy intake of reptiles should be reassessed if the animal is either underweight or overweight, and food intake should be adjusted accordingly. Obesity due to overfeeding is a common problem in captive reptiles.

The precise energy requirements for tortoises and turtles has not been established.


The dietary protein requirement of most reptiles is not known. Carnivorous species may consume a ration containing anything from 30-60% protein, whereas Green iguanas seem to require about 28% protein.

Individuals fed large quantities of fruit may fail to eat sufficient protein because fruits are highly palatable and contain a high water content, and clinical protein deficiency has been reported to occur under such conditions.

High protein intake increases the excretion of nitrogenous waste products including uric acid in urine, however, providing the reptile is adequately hydrated, this should not cause a problem.

The precise nutritional requirement for proteins and essential amino acids in tortoises and turtles has not been established.


Fats are an important source of energy - especially for carnivorous species of reptile, and they also provide essential fatty acids which are important as :

- Constituents of cell walls, and for
- Normal skin function

In addition, fats carry with them fat-soluble vitamins such as vitamin A, D and E.

Excessive fat intake (especially polyunsaturated fatty acid sources such as cod liver oil, and fatty fishes) can be harmful, and may exceed the antioxidant capabilities of naturally occurring vitamin E and cause a serious disease called steatitis (see below)

The precise nutritional requirement for fats for tortoises and turtles has not been established.


Carbohydrates are an important source of energy for tortoises and turtles. They are present in foods as simple sugars, and also as complex carbohydrates which are part of the group of food ingredients called "dietary fibre".


In Botany the term "fibre" is used to describe the fibrous content of a plant, which generally increases as the plant ages. The term "dietary fibre" is used in human and animal nutrition to describe a group of substances of plant origin which are inert to mammalian digestive includes complex carbohydrates, the soluble and insoluble fibres and lignin.. These substances are not available as nutrients and pass through the gastrointestinal tract undigested and they are not absorbed into the body. In the large intestine, however, bacteria can act on the fibre and metabolise products (fatty acids) which can be utilised by the body.

Such terminology is inappropriately used in reptilian nutrition because their mechanisms of digesting and absorbing food is different, especially in herbivorous species, which can utilise fibre. The natural diet of tortoises and turtles is relatively high in fibre content Although a useful nutrient for tortoises and turtles, excess fibre intake can lead to distension of the gastrointestinal tract - bloat.

The precise nutritional requirement for carbohydrates and fibre in tortoises and turtles has not been established.


It is believed that reptiles have a nutritional need for the main minerals that are required by mammals, but few scientific studies have been performed to establish their precise requirements. In some cases there is evidence of disease occurring as a result of deficiency or toxicity and the clinical signs may be prevented by modifying the diet. Mineral concentrations are relatively low in plants, and some observers suggest that reptiles (including tortoises) obtain their mineral requirement by eating soil or small stones in their environment.

Insufficient amounts of calcium, or excessive amounts of phosphorus in the diet lead to a condition called nutritional secondary hyperparathyroidism. This causes excess production of parathyroid hormone which results in bone being demineralised and weakened.... one of a group of a metabolic bone diseases. These bones may bend or fracture. In addition the shell, plastron and carapace may become deformed giving the tortoise a spherical or pyramid appearance. Other signs include lameness and difficulty moving around.

Calcium:phosphorus ratio

For different species of tortoise and turtle the precise nutritional requirements for calcium and phosphorus are not known, nor is the optimum calcium:phosphorus ratio. However, in common with mammalian species, reptiles fed a ration containing insufficient calcium, or with a grossly inverse calcium to phosphorus ratio (ie containing a lot more phosphorus than calcium) can develop the metabolic bone disease called nutritional secondary hyperparathyroidism. This disorder results in poor bone mineralisation and the development of spontaneous fractures. It is usually advised that the Ca:P ratio of the total ration is between 1:1 and 2:1.

When assessing the mineral content of a ration it must be remembered that is is the total intake over a period of time that is important, not the content of a single ingredient. So, a small amount of an ingredient with an inverse calcium:phosphorus ratio may have little or no impact on the overall mineral balance of the whole ration. A policy of banning all ingredients that have an inverse ratio is not valid, especially if the foodstuff contains other beneficial nutrients. However, it would be prudent to avoid feeding a ration consisting of a large amount of ingredients with an inverse calcium:phosphorus ratio.

According to one web site peas and beans are "far too high in protein, have a terrible calcium to phosphorous ratio" Well this information is simply inaccurate and misleading as the following chart illustrates (Reference: The Composition of Foods, McCance and Widdowson Published by The Royal Society of Chemistry and MAFF):


Raw Ingredient

Protein (g/100g)

Calcium (mg/100g)

Phosphorus (mg/100g)

Ca : P ratio

Blackeye Beans




1 : 3.45

Chick peasÂ




1 : 14.55

Green beans/French Beans




1 : 1.05

Mung Beans




1 : 4.04

Red Kidney Beans




1 : 4.1

Runner Beans




1 : 1.03

Soya Beans




1 : 2.75

Mange-tout Peas




1 : 1.41





1 : 6.19

Based upon this information, and assuming :

  1. that the optimum Ca:P ratio of a total ration for tortoises should be between 1:1 and 2:1
  2. Tortoises should be fed a "low" protein ration

as quoted in the literature :

  • From a calcium:phosphorus ratio point of view Mange-tout peas, Green Beans, French Beans and Runner Beans are excellent raw ingredients to feed to reptiles because they only have a small inverse ratio, and small quantities of the others as part of a balanced ration would probably have little effect on the overall mineral balance of the ration. Only chick peas should probably be avoided because they do have a very high ratio.
  • For protein content Green Beans , French Beans, Runner Beans , Mange-tout peas and Peas are certainly "safe" and small amounts of the others as part of a balanced ration would probably have little effect, although Soya Beans do have a very high protein content and are probably best avoided.

Beneficial nutritional content in these beans / peas includes the following (per 100g):

  • Green beans/french beans - energy 24kcal, Potassium 230mg, Iron 1.2mg, Carotene (a precursor of vitamin A) estimated 330 micrograms, Vitamin E 0.2mg, Folate estimated 80 micrograms, Vitamin C 12 mg.
  • Runner beans - energy 22kcal, Potassium 220mg, Iron 1.2 mg, Carotene 145 micrograms, Vitamin E 0.23 mg, Folate 60 micrograms, Vitamin C 10mg
  • Mange-Tout peas - energy 32kcal, Potassium 200mg, Carotene 695 micrograms, Vitamin E 0.39 mg, Thiamin 0.22mg, Vitamin B6 0.18 mg, Pantothenate 0.72mg, Biotin 5.3 micrograms, Vitamin C 54 mg.

Incidentally, Red Kidney Beans are included in this list for completeness. In humans raw Red Kidney Beans contain a toxin which can be fatal if they are not cooked sufficiently. Wild herbivores can often eat plants that are toxic to other mammals, and owners should appraise themselves of known potentially toxic plants for their species.

It is worth comparing the content of these beans with the content of other plants which have been recommended for the feeding of tortoises by various authors worldwide. Please note: not all authors agree on which of these ingredients is appropriate for feeding to specific species. This is NOT a list of foods recommended by Provet. :


Raw Ingredient

Protein (g/100g)

Calcium (mg/100g)

Phosphorus (mg/100g)

Ca : P ratio





1 : 0.03

Alfalfa hay early bloom




1 : 0.17

Alfalfa hay full bloom




1 : 0.18

Bermuda Grass hay




1 : 0.51

Clover - red hay




1 : 0.17

Clover - white




1: 0.09

Orchard Grass




1 : 0.41

Ryegrass - fresh




1 : 0.63

Timothy - midbloom fresh




1 : 0.79





1 : 1.75





1 : 4.67





1 : 0.75





1 : 1.55

Brussels Sprouts




1 : 2.96





1: 2.27





1 : 0.6





1 : 3.05





1 : 1.8





1 : 2.72





1 : 0.35





1 : 1





1 : 0.65





1 : 3.14





1 : 1.80





1 : 3.14





1 : 1.18





1 : 1.77





1 : 1.24





1 : 1.5





1 : 3.43





1 : 0.3

Despite warnings from some authors, vegetables are not particularly high in protein content, and there are few on this list that would represent a significant problem from their Ca:P ratio if they are fed only occasionally as only a small part of the total ration.

HOWEVER there may be other reasons why some of these ingredients should not be fed ...for example the well publicised risk of hypothyroidism when feeding excessive amounts of brassica plants (eg cabbage, Brussels sprouts, broccoli and spinach). This condition is most often seen in terrestrial chelonia - especially Giant Land Tortoises, whose natural diet is particularly high in iodine content . Dietary supplementation (as sodium iodide) may be needed to prevent the hypothyroidism in these cases.


Iodine deficiency is reported to be common in tortoises, which results in inadequate amounts of thyroid hormone being produced ( a condition called hypothyroidism. This condition is seen most often in Giant Land Tortoises which have a high requirement for iodine , and also in reptiles fed high quantities of brassica plants (a group of plants which includes cabbage, cauliflower, kale. rape, swede, turnip, Brussels sprouts, and broccoli).


Reptiles are extremely good at regulating their body sodium. Sodium is present in most feedstuffs, and as a result sodium supplementation is only required when marine reptiles are being kept in a fresh water environment.

The use of mineral supplements

Most references advise the use of mineral supplements in addition to feeding a mixed ration of ingredients. HOWEVER the indiscriminate use of mineral supplements is a highly dangerous practice for several reasons :

  1. If the base ration already contains sufficient mineral content excessive supplementation may result in toxic levels or mineral imbalances
  2. Metabolic bone disease can result from excessive mineral intake as well as deficiency
  3. High amounts of calcium in the form of mineral supplements may not be digested and used by the animal, and this calcium can pass through the digestive tract and interfere with the availability of other minerals (eg copper, iron, zinc) in the ration by :
    1. Competing for receptor sites in the gastrointestinal tract
    2. Binding with other minerals making them unavailable to the animal

If mineral supplements have to be given to avoid deficiency disease because the base ration is inadequate, they should be used sparingly and with caution.


The precise nutritional requirements for vitamins in tortoises and turtles has not be determined.

In a natural environment sufficient vitamins would be available in the self-selected foods , with the exceptions of Vitamin D which can be synthesised in the skin when exposed to ultraviolet rays in sunshine, vitamin C which can be synthesised in the kidneys and also several vitamins which can be synthesised by microflora in the gut..

Vitamin A (a fat-soluble vitamin)

Vitamin A deficiency (called Hypovitaminosis A) is extremely common in young aquatic and semi-aquatic turtles and it is usually recognised by opacity of the corneal surface of the eye due to poor epithelial development. The eyelids become inflamed and swollen and the animal may have difficulty breathing with wheezing. Other signs of vitamin A deficiency include :

  • Abnormal development with distortion and overgrowth of the horny parts of the mouth
  • Thickening of the horny layers of the skin
  • Impaired immune function leading to increased susceptibility to infections
  • Swelling of the limbs due to fluid accumulation (oedema) because of liver failure

Correction of diet is important to rectify vitamin A deficiency, dietary supplements can be given and in severe cases vitamin A can be given by injection. However, excessive supplementation can lead to toxicity (called Hypervitaminosis A) which causes a dry skin that sloughs off leaving red raw patches, abnormal bone development and liver enlargement.

Vitamin D (a fat-soluble vitamin)

Vitamin D precursors can be present in food, or can be synthesised in the skin when it is exposed to ultraviolet sunlight. So maintaining levels of this vitamin should not be a problem for most wild tortoises which tend to live in arid, dry, environments with long sunshine hours. However, it is different when these animals are shipped and kept in colder climates, or if they are kept indoors out of direct sunlight*. For non-carnivores on a deficient ration, and not exposed to sufficient sunlight, vitamin D supplementation may be necessary. HOWEVER there is some evidence that reptiles may be inefficient at absorbing vitamin D from the gastrointestinal tract. In addition, excess supplementation must be avoided as this can lead to problems of excess calcification.

*There is evidence that artificial ultraviolet light sources may be ineffective at maintaining skin synthesis of vitamin D.

Vitamin D deficiency (true rickets) results in :

  • Poor bone mineralisation with soft bendy bones or brittle bones that fracture easily
  • Muscle tremors

Vitamin D excess (which is common following oversupplementation) results in calcification of soft tissues.

Vitamin E (a fat-soluble vitamin)

A relative lack of vitamin E occurs if too much fish or fish oil containing polyunsaturated fatty acids is given to reptiles, and this results in oxidation of the excess fatty acids which go rancid and cause a serious disease - inflammation of body fats - called steatitis. Signs of this disorder include :

  • Inappetance
  • Sloughing of the skin
  • Incoordination
  • Adhesion formation between abdominal organs
  • Liver necrosis
  • Ulcers on the tongue
  • Death

Excess oily fish or fish oil supplements should be avoided, and vitamin E supplementation at a dose rate of 15-25 IU vitamin E/day has been recommended to reduce the likelihood of steatitis developing in reptiles fed on a high fish ration.

Vitamin E deficiency (with/without selenium deficiency) may also result in cardiac or skeletal muscle weakness leading to myopathy and cardiomyopathy.

Vitamin K ( a fat-soluble vitamin)

Vitamin K is normally produced by bacteria in the intestinal tract. If prolonged antibiotics are given this can upset the normal bacteria resulting in adequate vitamin K production. Deficiency results in spontaneous bleeding. It has mainly been reported to occur in crocodilian reptiles

Biotin (a water-soluble vitamin)

Biotin deficiency may occur in reptiles (especially lizards and Gila Monsters)Â fed raw egg white which contains a substance called avidin. It has not been reported to occur in tortoises or turtles. Signs include :

  • Inappetance
  • Lethargy
  • Muscle weakness
  • Muscle tremors

Riboflavin (a water soluble vitamin)

Deficiency of riboflavin (vitamin B2) has been reported to cause hindleg paralysis in lizards.

Thiamin (a water-soluble vitamin)

Some fish (including smelt, cod, green snapper, and gray mullet) contain thiaminase , an enzyme that destroys the vitamin B1 thiamin. Signs of thiamin deficiency in reptiles include :

  • Weight loss
  • Muscle tremors and twitches
  • Muscle atrophy
  • Paralysis

Bacteria in the gastrointestinal tract can synthesise thiamin, but they may be affected by oral antibiotic use

Vitamin C

Vitamin C can usually be synthesised in sufficient quantities in the kidney, and also by microflora in the gastrointestinal tract, of reptiles, so they may not have a dietary requirement for this vitamin. However, Vitamin C deficiency is suspected to be important in the occurrence of stomatitis in reptiles and also other problems such as poor wound healing, so supplementation is sometimes recommended.

Nutritional Deficiencies

Common nutritional deficiencies reported to occur in reptiles include :





Deficiency when fed muscle or invertebrates

Oversupplementation can cause toxic side-effects and also affect the availability of other nutrients

Deficiency - inadequate rationÂ

Oversupplementation can cause toxic side-effects and also affect the availability of other nutrients


Deficiency in animals fed too much calcium

Deficiency in animals fed too much calcium


Deficiency in animals fed too much calcium

Toxicity if over-supplemented

Deficiency in animals fed too much calcium

Toxicity if over-supplemented


Toxicity if over-supplemented

Toxicity if over-supplemented


Deficiency in animals fed too much fruit


Toxicity if over-supplemented

Toxicity if over-supplemented

Vitamin A

Deficiency when fed mainly muscle meat or iceberg lettuce

Toxicity if over-supplemented

Toxicity if over-supplemented

Vitamin B - Thiamin

Deficiency due to feeding fish containing thiaminase

Vitamin D

Deficiency - if diet deficient and/or insufficient exposure to ultraviolet light

Deficiency - if diet deficient and/or insufficient exposure to ultraviolet light

Vitamin E

Relative deficiency from feeding a ration containing too many polyunsaturated fatty acids


Deficiency in reptiles fed too much calcium

Supermarket products

Some authors do not recommend buying fresh products from supermarkets :

  • "Avoid reliance upon "supermarket" greens and fruits which typically contain inadequate fibre levels, excessive pesticide residues, and are too rich in Sugar.

These concerns are really unfounded :

  1. The fibre content of a plant depends upon the species of plant, the environment under which it is grown and the stage at which it is harvested. Basically the later in the growth period the higher the fibre content. Provet could find no evidence that produce bought in Supermarkets contains significantly less fibre than home-grown or wild produce kept under the same conditions and harvested at the same stage. Of course desert dwelling reptiles may get limited exposure to young luscious plants except following heavy rains, so the bulk of their ration may consist of ageing, highly fibrous plants....but these are not commercially available for the herpetologist to buy.
  2. The widespread use of pesticides in agriculture and horticulture means that even wild plants or garden plants may be contaminated. However, there are now strict controls in place to ensure low residues and the standards of "Organic" produce ..and one of the main sources of these are Supermarkets.
  3. The amount of sugar in a fruit depends upon the stage of growth, and the content increases as the fruit gets ripe. In the wild tortoises have access mainly to fallen fruit, which is fruit that has reached its maximum ripeness and contains the highest sugar content, so the levels present in consumer products should not present a problem.

Feeding Dog or Cat Foods to Tortoises

Many standard references recommend feeding small amounts of cat or dog food to tortoises and turtles (including The Biology , Husbandry and Healthcare of Reptiles by Lowell Ackerman, the BSAVA Manual of Exotic Pets and the web site of the Tortoise Trust in the UK). However, there may be serious dangers in doing this...even for carnivorous species.

Complete cat and dog foods have been specifically formulated to meet the nutritional requirements of these two species - which are very different to each other. These products have undergone feeding trials and safety tests before they are sold for use in these species, and, in Provet's opinion they should NEVER be fed to tortoises or turtles unless properly controlled feeding trials have been performed and safety has been confirmed. There are several reasons for this recommendation, including :

  1. Individual nutrient levels may be far too high or too low and result in a deficiency or toxicity. For example, cat foods are fortified with the beta-amino acid taurine. How do reptiles handle this amino acid, and what are the consequences of high dietary intake ? Nobody knows.
  2. The balance of nutrients may be grossly incorrect from a reptilian point of view.
  3. Pet foods contain a variety of ingredients - binding agents (eg guar gum), preservatives (eg antioxidants), colouring agents, acidifiers (especially cat foods) which may or may not be safe for reptiles to consume. In particular acidifiers such as the use of "digest" on dry cat foods may significantly alter the acidity of the contents of the gastrointestinal tract, and so alter the local environment for normal bacterial flora as well as creating a metabolic acidosis.

Tortoises fed exclusively dog or cat food develop anatomical shell and skeletal abnormalities and do not survive...which should not surprise us. HOWEVER claims* that deaths in tortoises fed dog or cat foods are due to the "high" protein content in these rations could not be substantiated from the published literature. In addition, Provet was unable to find evidence to support the claim that "Mediterranean tortoises fed on cat or dog food, or other high protein food items such as peas or beans , frequently die from renal failure or from impacted bladder stones of solidified urates" . Tortoises do die from renal failure, and they do develop stones in their urinary tract...but feeding dog or cat foods is not necessarily the reason why these disorders occur.

In the absence of controlled feeding trials and safety studies there are many factors in cat and dog foods which could cause death in reptiles.

Feedback Request* (If you are aware of a scientific report that does confirm these statements please let us know at

General Recommendations on feedingÂ

Tortoises and turtles should be fed a wide range of fresh foods daily and a supply of fresh, clean water should be available at all times.

In general a very mixed ration should be fed, and too much of one ingredient should be avoided, particularly ingredients with extreme analyses. Potentially dangerous feeding practices should be avoided - for example, too much cabbage, Brussels sprouts or buttercup flowers can all be poisonous to tortoises, and excess oily fish fed to terrapins can contaminate the environment food not eaten after 20 minutes should be removed from the tank/pond.

By A.C. Highfield