The Tortoise Myth-Busters: Episode 7

Fruit for Arid Habitat Tortoises - 'Treat' or Tragedy?

A Centrochelys sulcata gorges on ripe water melons... what are the risks in this?

Keepers are, understandably, often baffled and confused by the contradictory advice they will undoubtedly encounter. It's everywhere, especially online in social media, One can hardly blame them for not knowing what, or who, to believe.

Our own advice in this situation is not just "believe us", but instead, take a step back and carefully think through what is being discussed critically, and carefully. At the most basic level does a piece of advice make sense, or not? Does what is being suggested fit in with what we know of the species in the wild? Are there scientifically credible arguments for it? Or against it?

As usual in this series, lets start with some examples of advice recently seen in various 'tortoise groups':

• "My Hermann's loves fruit. If he likes it then it must be good for him"

• "I only use fruit as treats. Sometimes she won't touch anything else"

• "A bit of peach can't hurt, surely"

• "Mediterranean tortoises must eat fruit in the wild too".

Taking these in turn:

• Unfortunately, it is sadly the case that what tortoises 'like' does not equate to what is appropriate or even safe for them. It is similar to a child in a candy store... they might 'like it' and would eat nothing else, but it can end up as tooth decay, obesity and diabetes. Tortoises are much more delicate, less flexible and much more highly specialised feeders than are humans, too. So damage can occur much more quickly.
  

• Tortoises can be highly 'addictive' feeders. There are two approaches. 1) Withdraw the unsuitable items totally and only offer suitable items 2) Slowly change the diet over the course of a week or two. They may refuse to change over for quite a while. This is no problem. Offer water and only suitable items. Eventually they will accept them. They absolutely will not starve themselves to death meantime.
  

• Arid habitat tortoises are adapted to live on ultra-low sugar, low digestible carbohydrate diets with incredibly high fibre content (30-40%) feeding fruits of any kind (that includes squashes, bell peppers or similar, let alone things like peaches) can be rapidly disastrous, and even fatal. Some years ago we dealt with a case where five adult leopard tortoises died within 24 hours of being 'treated' to over-ripe peaches by the owners who thought it would help to 'hydrate' them. What it actually did was send their digestive tract into hyper-fermentation mode producing huge quantities of internal gas and the change in gut pH severely damaged the intestinal walls: a combination of which killed them.
  

• No, Mediterranean tortoises do not normally encounter fruit in the wild. There are very few truly native fruiting species to be found in these habitats. It is almost exclusively low-growing herbaceous shrubs and seasonal wild flowers. They might sometimes encounter introduced agricultural species, but these are not part of the natural diet and come with exactly the same drawbacks and dangers as any other fruits. It is (again) worth thinking this through. Tortoises are not equipped to take fruits from trees. Birds are very good at that. Fallen fruits also attract rats, foxes and similar scavengers long before any tortoise would get a chance. Even if it was true that there were fruiting native plants in a habitat, they would do so for a very short period indeed, and again, tortoises are not well-equipped to take advantage of them. The suggestion that fruit is a normal part of Testudo diets is simply false. The same applies to Leopard and African Spurred tortoise diets.
  

Hydration

One common myth is that feeding water-rich fruits helps 'hydration'. Any 'help' in that regard is instantly offset by the gastric disruption caused by the sugar content which results in loose droppings and excess fluid loss by that route. The best way to ensure hydration is to provide adequate fresh drinking water, This is a) Safe b) Effective.

A typical example of a faecal pellet from a wild Mediterranean tortoise. It is densely packed with coarse fibres. Compare to the loose, runny droppings from most captive tortoises, especially those that are provided with fruits or root vegetables.

Typical Testudo habitat in the Mediterranean. No fruits here...

Let's now take a brief look at EXACTLY WHY fruits are so bad for these arid-habitat species. Remember, we are not here referring to equatorial tropical species of tortoise such as Chelonoidis denticulata (Yellowfoot tortoises) or Hinge-back tortoises (Kinixys), etc. These have very different dietary requirements and their digestive tracts are equipped to handle them. They are, for example, biased more towards omnvivory than strict herbivory to varying degrees, and will also eat things like mushrooms (something else entirely unsuited to arid habitat species). We are here discussing semi-arid terrestrial tortoises, particularly Testudo, Stigmochelys and Centrochelys species, though other species from similar habitats such as Angulate tortoises, Radiated tortoises and Indian Star tortoises are closely related, diet-wise.

In order to do this we need to dive a little bit into the digestive tract biology of tortoises. We will try to simplify this as much as possible, but it is important that people try to understand how this all 'works'.

Nutritional Disorders

Disorders may be usefully divided into two main groups consisting of:

• Diseases of excess

• Diseases of deficiency

Both are equally damaging, and are often seen in combination.

The intestinal microflora of herbivorous chelonians is geared to processing relatively large quantities of coarse fibrous cellulose matter. There is some reason to suppose that protozoans and ciliate organisms may play a role in this process together with the more unusual bacterial agents. Non-specific enteritis is common in captive collections accounting for up to 40% of total mortalities in some cases. Deficiencies of dietary fibre are certainly one factor and an adequate intake of dietary fibre may also be of importance in regulating populations of potentially pathogenic parasites, as well as in preventing impaction by sand and stones, etc. An additional factor responsible for the high incidence of gastrointestinal disease noted may be inclusion of food items of animal origin or fruits to which the slow fermentation process of the herbivorous reptile’s digestive system appears ill-suited.

We have discussed the critical importance of dietary fibre separately.

Non-structural carbohydrates include sucrose in fruits and plant sap, to starch in seeds and roots. These are found in all plant parts, but the highest concentrations occur in fruits, seeds, stems and roots. The precise content varies enormously, not only with seasons and general growth cycles, but also as a function of photosynthesis. Levels are higher late in the day than they are in early morning, for example.

In purely practical terms, one implication is that the feeding of of fruit to those species where this is not a natural dietary items (e.g., most arid habitat and savannah habitat tortoises) can have the effect of seriously accelerating gut motility, increasing gas production (tympanites), altering gut pH, and severely disturbing normal digestive processes and symbiotic microflora balance. Conversely, attempting to maintain those species adapted to readily digestible high starch and pectin intakes on grasses could result in a serious energy deficit.

Carbohydrates represent the prime energy source in herbivorous reptile diets. Excess intake can be stored either as glycogen in the liver, or as fat (reserves of these substances are critical in those species that brumate). Excess intake of readily fermentable carbohydrates and sugars in species ill-adapted for such diets can, however, result in profound disturbance to the animal's entire metabolism. In cattle and horses, ruminal acidosis is a well-known phenomenon (Nocek, 1991, Stock and Britton, 1991). Specific pathologies associated with this condition include:

• Clostridial infections

• Liver abscesses

• Malabsorption syndrome resulting from ruminal wall tissue damage

• Sudden death syndrome (think back to those Leopard tortoises)

• Diarrhoea and dehydration

It should be noted that the digestive mechanism of tortoises and herbivorous lizards is functionally almost identical to those of mammalian ruminants. The background of the condition is that starch-rich foods (cereal grains, corn, for example) are broken down into sugars (glucose) in the digestive tract. Alternatively, sugar-rich foods are metabolised directly and very rapidly (quantities of fruit, for example). In the hind-gut, symbiotic bacteria ferment the carbohydrates to form volatile fatty acids which are absorbed and are an important source of energy, representing, on average, between 30-40% of total requirements in some herbivorous reptiles studied (McBee and McBee, 1982, Troyer, 1984b). High intakes of carbohydrates such as starches and sugars can overwhelm the system, however, and ferment much more quickly than the fibre contained in dry grasses and hays.

The result is a massive increase in acids produced by bacterial action.. These acids are primarily acetic, propionic and butyric acid with lower levels of lactic acid and volatile fatty acids (McBee and McBee, 1982). Following over-consumption of starches and sugars the pH of the gut shifts to become highly acidic initiating a chain of serious consequences (typical gut pH ranges of herbivorous reptiles are in the order of 6.8-7.0). One particularly serious effect is the generation of high levels of endotoxins produced as the normal symbiotic and commensal gut bacteria begin to die in the out-of-range acidic environment created (approximately pH <5.5). The gut wall integrity can begin to degrade in these conditions, causing subsequent malabsorption of nutrients. Liver abscessing is a typical consequence of this condition as these highly toxic bacteria are absorbed into the bloodstream via the gut wall, and seed themselves in the liver. In this context it is important to take note of the fact that liver diseases are one of the most common causes of death in captive arid habitat chelonia, representing up to 72.6% of all mortalities studied (Rosskopf, Howard, Gendron, Walder, and Britt, 1981). Some of the foods most commonly associated with causing severe gastric disruption (including sudden death) in arid habitat and savannah species in captivity include peaches, strawberries, plums, pears and apples - all of which are very high in easily digestible soluble carbohydrates and fruit sugars.

We have discussed this many times previously, but tortoises are REPTILES and their digestive processes are also heavily influenced by TEMPERATURE. If they are deprived of cooler periods, and are, for example, kept unnaturally hot overnight, then this too accelerates digestion and energy extraction, resulting directly in EXCESS GROWTH with all the attendant dangers of developing Metabolic Bone Disease. The absence of cyclic (natural) feeding patterns is another major contributor to what we now call 'Overdrive Growth Syndrome'.

That is specifically caused by three things:

1. Far too-digestible, energy-rich diets.

2. Failure to provide cyclic temperatures with adequate cooler periods.

3. Forced continual activity and feeding for species that naturally might only be active and feeding for 3-4 months per entire year.
   

Species that appear particularly susceptible to such problems include:

• Leopard tortoises (Stigmochelys pardalis)

• African Spurred tortoises (Centrochelys sulcata)

• Mediterranean Testudo species

• Egyptian tortoises (Testudo kleinmanni)

• Russian tortoise (Testudo horsfieldii)

• Indian Star tortoises (Geochelone elegans)

• North American Gopherus species

• South African Homopus, Psammobates and Chersina species

• Pancake tortoises (Malacochersus tornieri)

• Radiated tortoises (Geochelone radiata)

There are other effects too, some longer term, one of which is that all of these things tend to be extremely poor in calcium, but sky high in phosphorus. That is a direct recipe for developing Nutritional Secondary Hyperparathyroidism, or osteomalacia. The low levels of calcium in the diet cause the parathyroid gland to produce too much parathyroid hormone. This hormone then causes the body to remove calcium from the bones, which eventually results in the disease. There are some actual examples of what goes on 'inside' when that occurs in this separate, in-depth article.

A typical example of a Testudo hermanni raised in an enclosed vivarium environment with a diet severely deficient in calcium, far too high in phosphorus, and that included fruits such as bell peppers and melon, combined with commercial 'tortoise foods' in pellet form. The carapace is flattened and depressed, the scutes are severely deformed, and the high rate of growth generated has resulted in weakened, fragile bones.

The condition is preventable by providing appropriate diets. High fibre, low grain content, low carbohydrate (low fruit sugar) foods are appropriate to most arid habitat and savannah species, while many humid equatorial habitat tropical species have a natural tolerance to higher intakes of sugars and carbohydrates (though with lowered tolerance to, and less ability to digest, silica-rich grasses compared to savannah species).

High fibre intakes are therefore one of the most effective practical measures to prevent acidosis in susceptible species, along with resisting the temptation feed totally unsuitable items, even as a 'treat'.

Because fruits also release - quickly - large amounts if energy, this also causes VERY RAPID GROWTH, and combined with the calcium-deficient but phosphorus-rich nature of these items, is a very common cause of tortoises growing quickly, but with the severe underlying bone-growth disorders outlined here.

It is vital, however, not to attempt to raise dietary fibre levels by including bran (very high phytic acid levels) or oats (exceptionally high phytic acid and carbohydrate levels). Bread is also particularly bad on both counts (as well as being extremely high in fat). Corn is also excludable due to high carbohydrate and phytic acid levels. Meadow and orchard hays represent the most acceptable form of supplemental fibre for most semi-arid and savannah tortoise species. Many species naturally experience a shift toward drier, hay-type foods as the moist spring advances towards the dry summer season. At such times, the availability high moisture-content spring annuals declines sharply, and instead tortoises are observed to pick at dry leaves, stems, dry flower heads and seed pods.

So what can you feed?

Try to get as close to the natural diet as possible. This might not be 100% achievable, but the closer you get, the better. Look for equivalents and again, do not feed things that are known to be dangerous and damaging or are completely dissimilar from what that species eats in the the wild. So - fruits and root vegetables are total 'no-feeds' to these species.

A wild Testudo graeca graeca grazes among scrubby, herbaceous shrubs on low-lying seasonal wild flowers. This is the natural diet - and typical habitat - of Mediterranean tortoises.

Recommended basic food plants:

(Based upon observations in Greece and Turkey)

• Dandelion (Taraxacum officianale)

• Hawkbits (Leontodon spp.)

• Sowthistles (Sonchus spp.)

• Hawkweeds (Pictis spp.)

• Hawkbeards (Crepis spp.)

• Plantains (Plantago spp.)

• Clovers (Trifolium spp.)

• Honeysuckle (Lonicera periclymenum) (preferred by T. hermanni)

• Cat's ears (Hypochoeris spp.)

• Vetches (Vicina spp.)

• Trefoils (Lotus spp.)

• Mallows (Malva spp.)

• Bindweeds (Calystegia spp.)

• Sedums (Sedum spp.)

• Ivy-leaved Toadflax (Cymbalaria muralis) Additional useful graze plants:
  

• Dandelion (Taraxacum officinale)

• Red clover (Trifolium pratence)

• White clover (Trifolium repens)

• Greater Plantain (Plantago media)

• Ribgrass or Ribwart Plantian (Plantago lancealata)

• Smooth Sow Thistle (Sonchus oleraceus)

• Prickly Sow Thistle (Sonchus asper)

• White-Dead Nettle (Lamilim album)

• Red-Dead Nettle (Lamium pupureum)

• Chickweed (Stelaria media)

• Smooth hawks-beard (Crepis capilloris)

• Hedge mustard (Sisymbrium offlcinale)

You can often find edible seed mixes of such wild flowers than you can plant in pens to allow near-natural grazing behaviour.

For large savannah species, such as Centrochelys sulcata (African spurred tortoise) or Stigmochelys pardalis (Leopard tortoise), grasses and hays are a critical dietary component. Aldabra and Galapagos tortoises also do extremely well on this type of diet. Some other species also benefit from the inclusion of both fresh and dried grasses in their diet, although certain species, such as Red-foot, Yellow-foot, Hinge-back and Mediterranean tortoises are ill-equipped to digest the high silica content of grass fodder.

For species adapted to it, however, grass is not only nutritious, but its fibre content makes a significant contribution to digestive health. For leopard and African spurred tortoises, mixed grasses should comprise approximately 60-70% of the total diet.

Availability of grass types varies greatly according to location. The following list of suitable fodder grasses is based upon availability in the USA. In Europe, these particular species are rarely available - although local equivalents can usually be found. General "meadow hay" and "orchard hay" mixes are usually suitable, for example. Avoid hays that have excessively "prickly" seed heads - these can injure mouths or eyes. The use of coarse Timothy hay is excluded on this basis. Second or third cuttings of grass hays tend to have less spiny heads than first cuttings.

• Buffalo grass

• Couch grass

• Kikuyu grass

• Dallas grass

• Blue Grama grass

• Big Bluestem grass

• Darnel Rye grass

• Wintergrass or Bluegrass

• Western Wheatgrass

• Fescue grasses

Summary:

• Fruits, even in small amounts, are highly damaging to tortoises from arid (dry) habitats. They quickly disrupt the very delicate 'fermentation-based' digestive system that these tortoises rely on, sending it into 'overdrive'. This also produces large quantities of gas to build up internally that can of itself cause serious problems, and in extreme cases, rapid death.
  

• Fruits and root vegetables behave similarly in these respects. Neither have any place in a Testudo (or similar species) diet.
  

• Fruits and vegetables are also very poor in calcium but extremely high in phosphorus. This is the exact opposite of what a tortoise needs to maintain healthy growth.

As always. Do not just believe what you are 'told' - but try to understand two key things. What that species experiences in the wild and some of the underlying BIOLOGY behind the 'way things are'. That will guide you well.

Further reading:

Alderman, G. and Cottrill, B. R. (1993) Energy and Protein Requirements of Ruminants. CAB International, Oxford.

Avery, H. W. (1989) Role of diet, protein and temperature in the nutritional energetics of the turtle, Trachemys scripta: Implications for the nutritional ecology of the Desert tortoise. Desert Tortoise Council. Proc. 1987-1991 Symposia: 160.

Baer, D. J. and Oftedal, O. T. (1995) Effects of Temperature on Nutrient Utilization in Herbivorous Reptiles. Desert Tortoise Council. Proc. 1995 Symposium:54-55.

Bjorndal, K.A. (1985) Nutritional ecology of the sea turtle. Copeia 1985:736-751.

Bjorndal, K.A. (1987) Digestive efficiency in a temperate herbivorous reptile, Gopherus polyphemus. Copieia 1987:714-720.

Bjorndal, K. A., and Bolten, A. (1993) Digestive Efficiencies in Herbivorous and Omnivorous Freshwater Turtles on Plant Diets: Do Herbivores have a Nutritional Advantage? Physiol. Zool. 66(3):384-395.

Carpenter, K. J. (1994) Protein and Energy: A study of changing ideas in nutrition. Cambridge U.P.

Cooper, J. E., and Jackson, O.F. (1981) (eds). Diseases of the Reptilia. Academic Press. London.

Dantzler, W.H, and Schmidt-Nielson, B., (1966) Excretion in the freshwater turtle (Pseudemys scripta) and the Desert tortoise (Gopherus agassizii). Am. J. Physiology. 198-210.

Donoghue, S. and Langenberg, J. (1995) Clinical Nutrition of Exotic Pets. Veterinary Clinical Nutrition 2(2):57-63.

Esque, T. C. and Peters, E. L. (1994) Ingestion of bones, stones and soil by Desert tortoises. Fish and Wildlife Research 13:105-111.

Foley, W. J., Bouskila, A., Shkolnik, A., and Chosniak, I. (1992) Microbial digestion in the herbivorous lizard, Uromastyx aegyptius (Agamidae). J. Zool. Soc. Lond. (226):387-398.

Frye, F. (1993) A Practical Guide for Feeding Captive Reptiles. Kreiger, Malabar, Florida.

Golley, F. B. (1961) Energy Values of Ecological Materials. Ecology 42:581-584

Harlow, H. J., Hillman, S. S., and Hoffman, M. (1976) The effect of temperature on digestive efficiency in the herbivorous lizard, Dipsosaurus dorsalis. J. Comp. Physiology. B111:1-6.

Harris, D. M. (1982) The Phenology, Growth and Survival of the Green Iguana Iguana iguana in Northern Columbia. in: Iguanas of the World, their Behaviour, Ecology, and Conservation. Eds. Burghardt, G. M. and Rand, A.S. Noyes Publications, NJ.

Highfield, A. C. (1988) Notes on Dietary Constituents for Herbivorous Terrestrial Chelonia and their Effect on Growth and Development. ASRA. Reprinted in: The Feeding Manual, Tortoise Trust,. London.

Highfield, A. C. (1988b) Husbandry Notes: Observations on Dehydration in Reptiles. The Rephiberary nr. 131.

Highfield, A. C. (1987) Causal Factors of Mortality in Captive Collections. Testudo 2(5):15-17.

Highfield, A. C. (1990) Keeping & Breeding Tortoises in Captivity. R&A Publications, Bristol.

Highfield, A. C. (1996) Practical Encyclopedia of Keeping and Breeding Tortoises and Freshwater Turtles, Carapace Press, London.

Highfield, A. C. (1999b) Practical Care of Mediterranean (Greek) Tortoises. Carapace Press Vidi-Herp Series, London and NJ.

Highfield, A. C. and Bayley, J. R. (1996) Observations on ecological changes threatening a population of Testudo graeca graeca in the Souss Valley, southern Morocco. Chelonian Conservation and Biology 2(1):36-42.

Highfield, A. C. (1997) High growth rates and vitamin D3 - a response. The Tortuga Gazette (33)12:8-9.

Highfield, A. C. (1999) Feeding Your Tortoise. Carapace Press Video. London.

Jackson, G. and Trotter, J.A., T.H., and M.W, (1967). Herpetologica 32:139-145.

Jackson, O. and Fasal, M. D. (1981) Radiology in tortoises and turtles as an aid to diagnosis. J. Small Anim. Pract. 22:705-716.

Jarchow, J. L. (1984) Veterinary Management of the Desert Tortoise, Gopherus agassizii, at the Arizona-Sonora Desert Museum: A rational approach to diet. Gopher Tortoise Council, Proceedings 1984 Symposium: 83-94.

Holford, P. (1997) The Optimum Nutrition Bible. Piatkus, London.

Lambert, M. R. K. (1986) On the Growth of captive-bred Mediterranean Testudo in N. Europe. In: Studies in Herpetology, 309-314. Prague: Charles University.

King, G. (1996) Reptiles and Herbivory. Chapman and Hall.

Lichtenbelt, W. D. van Marken (1992). Digestion in an Ectothermic Herbivore, the Green Iguana: Effect of Food Composition and Body Temperature. Physiological Zoology. (65):649-673.

McBee, R. H., and McBee, V. H. (1982) The Hindgut Fermentation in the Green Iguana, Iguana iguana. In: Iguanas of the World, their Behaviour, Ecology, and Conservation Eds. Burghardt, G.M. and Rand, A.S. Noyes Publications, NJ.

Meienberger, C. Wallis, I. R., and Nagy, K. A. (1993) Food intake rate and body mass influence transit time and digestibility in the desert tortoise (Xerobates agassizii). Physiol. Zool. (66):847-862.

Moyle (1949) cited in: Schmidt-Neilson, op. cit.

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MacArthur, S. MRCVS (1996) Veterinary Management of Tortoises and Turtles. Blackwell Science, Oxford.

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Rosskopf, W. J. (1982) Severe shell deformity caused by a deficient diet in a California Desert Tortoise. Veterinary Medicine, Small Animal Clinician. April 1982.

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