This information is provided by Provet for educational purposes only.
You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.
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 .
A 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 numerous 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.
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) 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 :
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 enzymes...it 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.
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):
Based upon this information, and assuming :
Beneficial nutritional content in these beans / peas includes the following (per 100g):
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. :
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 :
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 :
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 :
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 :
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) fed raw egg white which contains a substance called avidin. It has not been reported to occur in tortoises or turtles. Signs include :
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 :
Bacteria in the gastrointestinal tract can synthesise thiamin, but they may be affected by oral antibiotic use
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.
Common nutritional deficiencies reported to occur in reptiles include :
Some authors do not recommend buying fresh products from supermarkets :
These concerns are really unfounded :
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 :
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 firstname.lastname@example.org)
General Recommendations on feeding
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 ....so food not eaten after 20 minutes should be removed from the tank/pond.
Updated October 2013