Geochelone sulcata - African Spurred tortoise - an arid habitat species adapted to a high fiber, very low protein diet.
Compiled by A. C. Highfield
Q. My friend says that no vitamin or mineral supplements should be necessary if the diet is correct and well-balanced. Is this true?
A. Mineral supplements are recommended because the soils upon which captive animals are maintained are not identical to those experienced by free-ranging wild animals, the variety of graze is rarely as great, and because several calcium sources available to wild tortoises are rarely available in captivity.
In terms of vitamin supplements, herbivorous reptiles obtain their D3 requirement as a result of the action of UV-B radiation acting upon sterols in the skin, in a process that also depends upon adequate levels of radiant heat. Within their natural range this is not, of course, a problem; outside it, in cloudy, northern latitudes, UV-B levels are simply inadequate to promote sufficient UV-B generation and thus, supplements containing D3 are generally advised. There can be exceptions to this, for example, where very high output UV-B lamps and adequate basking facilities are provided. In general, though, use of such supplements is recommended. There is more to this than just a “correct and well-balanced” diet, environment also plays a part - a part that can be very difficult, if not impossible, to replicate adequately in captivity.
Q. Do tortoises obtain all their calcium from plants, or do they use any other sources”?
A. This is why availability of supplementary sources of calcium in particular is so very important. The typical mineral concentrations of many plants consumed by tortoises in the wild are in fact very high . Some typical examples include Plantago sp., with Ca:P ratios of above 20:1 and Opuntia sp., where Ca:P ratios can be as high as 78:1 (Jarchow, 1984). The typical diets adopted by many keepers, based upon commercial salads and fruit often contain little calcium and an excess of phosphorus (Boyer, 1996). Many tortoises certainly do seek out additional calcium sources in nature (Esque, 1994), and have been observed to consume calcium-rich desiccated snail-shell fragments, bone, and calcium-rich pebbles. Most responsible keepers therefore do choose to offer some level of supplementation to ensure that this need is adequately supplied. There is no scientific evidence whatever that sensible levels of supplementation with calcium carbonate, for example (as recommended by the Tortoise Trust) poses any health hazard whatever. Frye (1991) states “Only where combined with an excess of D3 is an over abundance of calcium a problem”.
It is worth examining exactly what wild herbivorous tortoises really do consume. Take special note of the mean protein levels, the fiber levels, and the mean Ca:P ratio of 6.4:1
Adapted from data published by Hansen, Johnson, and Van Devender, Herpetologica 32:247, 1976.
By selecting plants that are relatively high in calcium, by avoiding those containing high levels of calcium-inhibiting compounds, and by careful use of a phosphorus-free supplement an adequate calcium intake can be assured.
Q. One veterinary website I visited says that tortoises should be given fruit regularly, other sites disagree. Which is true?
A. None of them are correct. The problem here is that the term “tortoises” is being used in a far too general sense. You just can’t do that. There are many different species, from vastly differing habitats, and they each have individual needs. Some tropical species eat fruit regularly. It is part of their natural diet and causes them no harm at all - they are adapted to it. The Yellowfoot tortoise, Geochelone carbonaria, is a good example. Other species, usually from more arid environments, hardly ever consume fruit in nature, for example, Testudo graeca or Geochelone sulcata. These species are not well adapted to it, and if it is given, they can suffer very serious consequences, including severe diahrea, colic, and imbalances of the gut pH (acidity), acute cases of which can result in rapid death or major damage to the gut walls. Be very careful when reading advice which is framed in such inaccurate and general terms. Always seek species-specific advice and avoid advice which is so generalized as to be useless, or even dangerous.
Q. “The same website states that 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”
A. This is another gross generalization, and factually incorrect insofar as many individual species are concerned as numerous highly regarded field studies conclusively demonstrate (Hansen, Johnson and Van Devender, 1976, Swingland, 1984, Luckenbach, 1982). For example, even Red-Eared slider turtles are predominantly herbivorous as adults (Clark and Gibbons, 1969). There is not one credible field study that we are aware of that supports the view that in nature species such as Testudo graeca or Gopherus agassizzi consume animal protein on any kind of regular basis. They are herbivores, plain and simple. There are not “numerous publications” that demonstrate these species eat “dead mice, birds… or crickets” in the wild. There are, as far as we know, none. Stating that “tortoises eat a variety of foods” is completely meaningless as pointed out previously. Tortoises will typically eat almost anything that is placed before them in a captive situation. This does not mean that it is therefore safe or appropriate or that they would encounter the same items in nature. In simplistic terms, a child may be happy to exist on a diet of fries, burgers and candy - but this is certainly not healthy and in no way constitutes a balanced diet.
Q. “I have been told that excess fibre intake can lead to distension of the gastrointestinal tract - bloat - and that I should avoid feeding too many high fiber foods, is this true?”
A. That terrestrial herbivorous tortoises in nature consume very high fiber intakes compared to captive animals is easily confirmed by fecal-pellet analyses. Donoghue and Langenberg (in Mader, 1996) state: “Dietary fiber is a concern when feeding herbivorous reptiles. Tortoises on low fiber diets (less than about 12% DM) have loose feces. Although it is not well-documented, low-fiber diets may also predispose herbivores to bloat and/or lactate induced diahrea from too-rapid fermentation of carbohydrate”. Far from too much fiber being a concern, then, the opposite is the case according to Donoghue and Langenberg. Wet and loose feces is in fact a typical characteristic, as any competent keeper can attest, ‘supermarket salad and fruit’ based diets. Jarchow (1984) published a detailed analyses and comparison between a diet based on supermarket produce (lettuce, kale, mustard greens, chard, tomatoes, endive and green beans) and reported crude fiber contents ranging from 6.8 to 14.1%. An equivalent analysis of typical wild foods revealed a crude fiber content ranging from 9.3 to 36.9%, with an average well above 20%. Hansen and Van Devender, et.al, conducting a similar study, found wild tortoises consumed vegetation with an average DM fiber content in excess of 30%. Jarchow concludes that diets based upon ‘supermarket produce’ items fail to supply adequate levels of crude fiber to herbivorous tortoises, and also fail to supply adequate levels and ratios of calcium. This is an opinion we unreservedly endorse. The facts speak for themselves.
Q. “I have been told that warnings about protein in tortoise foods are an over-reaction, and that protein is essential to life. If this is true, why do you insist that it can cause problems?”
A. The Tortoise Trust has never stated that protein, per se, is a problem. We
have stated that the amount of protein consumed has to be regulated according
to species. Some species are strict herbivores. These animals mostly
occur in arid areas, where they face severe constraints upon their water
balance and nitrogenous waste metabolisms (high protein intakes require large
amounts of water to eliminate the waste generated). Some species are omnivores,
eating both animal prey, or carrion, and vegetation. These species typically
occur in moister habitats where water availability is better. Other species may
be largely carnivorous, such as snapper or softshell turtles. It is no
coincidence that these inhabit aquatic environments (Moyle, 1949). What you
cannot do safely is to feed a species adapted to very low protein herbivorous
diets a high protein diet instead. These
animal’s entire metabolism is simply not geared up to cope with the very high
blood urea levels that will result. Stuart MacArthur MRCVS, (1996) is very
clear on this point: “Abnormally high protein diets, and other unsuitable
unbalanced diets, regularly result in high blood urea and urate levels and in
fluid retention. This may precipitate and exacerbate renal failure”. Another
side-effect will be rapid and excess growth, this in turn places extra demands
upon the calcium metabolism, and such animals have a very much greater chance
of developing abnormal bone and shell growth, and conditions such as MBD
(Metabolic Bone Disease). The key to this is really very simple indeed: feed
diets that are specifically balanced for the particular species you are working
with. There is not, and never can be, a ‘universal tortoise diet’. The
requirements of say, a Leopard tortoise (Geochelone
pardalis) are totally different from the requirements of an American box
Q. “According to your web site, peas and beans are "far too high in protein, and have a terrible calcium to phosphorous ratio". I read one website where it said that this was wrong. I’m confused!”
A. The claims of the Tortoise Trust are neither misleading nor inaccurate. There are multiple published tables that support this statement, including current USDA figures. One very comprehensive table is that compiled by Jenniffer Swofford and which is freely available on the Internet. This demonstrates conclusively and consistently that peas and beans typically feature a negative calcium to phosphorus ratio. Frye (1991) also published very comprehensive tables. These also indicate peas and beans having very poor calcium to phosphorus ratios. One important reference is the very MAFF (UK) table by McCance and Widdowson . Let us take a close look at this table (values in mg/100g):
Item Calcium Phosphorus Ratio Result
Blackeye Beans 81 410 1:3.45 (-)
Chick Peas 160 310 1:14.55 (-)
Green/French Beans 36 38 1:1.05 (-)
Mung Beans 89 360 1:4.4 (-)
Red Kidney Beans 100 410 1:4.1 (-)
Runner Beans 33 34 1:1.03 (-)
Soya Beans 240 660 1:2.75 (-)
Mange-Tout Peas 44 62 1:1.41 (-)
Peas 21 62 1:6.19 (-)
Every single item listed in this table has a seriously negative Ca:P ratio, and as such they are all totally unsuited for routine inclusion in a tortoise’s diet. Not one item has a positive (beneficial) ratio.
The figures cited in any event are for ‘raw’ chemical compounds. They totally fail to take account of the very high phytic and oxalic acid levels also found in these vegetables that severely limit the availability of the calcium they do contain. Thus, in practice, their useable calcium to phosphorus ratio is very poor indeed, and even worse than the tables suggest (and that is bad enough).
Donoghue and Langenberg, writing in the highly respected veterinary reference text ‘Reptile Medicine and Surgery’ (Mader, 1996), state very clearly that peas are high in oxalates and that “oxalates bind calcium and trace elements, inhibiting their absorption”. They also warn against the high purine content of peas and beans suggesting that these are inappropriate for routine use with herbivorous reptiles. We concur with this view. Due to their poor availability of calcium, and their high oxalate, phytic acid and purine content therefore, we totally disagree that beans of any kind are an “excellent raw ingredient to feed to reptiles”. We recognize that some texts do recommend these, but our opinion, based upon our own extensive research and experience, and based upon every published chemical analysis we can find, suggests that they are in no way appropriate.
It is almost universally accepted by animal and human nutritionists alike that peas and beans are towards the very top of the list of all vegetable items in terms of their protein content. “Beans contain the highest protein content of all commercial seed crops” (USDA, 1980). “The best vegetable sources of protein available include green peas, lentils, chick peas, alfalfa sprouts, mung beans, and beans of all kinds; kidney, lima, aduki, navy beans, and soy beans” (Michael Klaper, MD writing in Vegan Nutrition). "Even though peas are high in both protein and starch content, containing 20-25% CP and 41-54% starch, they are usually thought of as a protein supplement” (“Erasmus Okine, Beef Nutritionist with the University of Alberta, Canada).
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