MARTIN P. C. LAWTON B.Vet.Med; Cert.V Ophthal; G.I. Biol. MRCVS.
(Presented at the Symposium at The University of Bristol, 1989)
Marcus, in 1981 , wrote that one of the major contributing causes of death in captive wild animals is a failure to provide an adequate diet. In the wild, they would eat a wide variety of foods, and even if they become addicted to, for example, types of beans, they would not be able to eat them the whole year round to the exclusion of any other foods. It is only in captivity where man is able to store, deep freeze, and irradiate food that we are able to offer them certain food the whole year round. This may lead to owners over indulging their pets, by feeding them their favourite food throughout the year , and not a balanced diet.
In the wild most foods would be available for 6-8 weeks, after which the animal would have to seek another source or type, thus their diet would be more varied than we offer in captivity. In captivity the terrain, environment and climate is also different so we are not necessarily able to offer them the types of food that they would eat in the wild, but it is important that we try as far as possible to mimic the more natural feeding habits, and more importantly, we should offer as wide a variety of food as possible, to maintain a balanced diet.
Inappropriate feeding is a common problem, particularly noted in the American box tortoise (Terrapene carolina) which is still, unfortunately being sold by many pet shops as an ordinary European tortoise, and thus when bought, is often fed an unsuitable diet, though considered suitable for a Mediterranean tortoise. These American box tortoises, especially juveniles, are mainly carnivorous, adults being carnivorous or omnivorous, while Mediterranean tortoises are mainly herbivorous.
Problems associated with inappropriate foods can also be seen when too narrow a choice of diet is fed. Steatitis (hardening of the body's fat), may be seen in red eared terrapins that are fed purely on white bait. These oily fish result in abnormal fat, and swelling associated with these changes throughout the body. These changes are often irreversible and may well result in severe problems.
Tortoises that are stomach tubed consistently with milk products, or fed on high protein diets, may develop problems due to build up of gas in the intestines, and a resulting colic.
Problems may also be seen in Terrapins that are fed entirely on unsuitable foods, such as bacon. Deposits in the cornea, due to the excess cholesterol in the blood levels may be seen.
All reptiles are poikilotherms (ectotherms) and are reliant on the external temperature to maintain their own body temperatures. All reptiles have a Preferred Body Temperature (PBT).
This PBT is the range within which a reptile functions most efficiently when it is active. There are species variations, together with season fluctu- ations. The PBT may also fluctuate disurnally, during the day, and at night.
The importance of keeping reptiles at their PBT is that they are less likely to succumb to disease, and their metabolism is able to work at its best.
If a reptile is kept below its PBT it may not produce enough enzymes to help digest its food, or even if it should produce enough enzymes, they may not work adequately, and therefore the food will not be broken down into its constituents and absorbed properly. Thus even a Tortoise on a well balance diet, if not kept at its PBT , may develop nutritional problems.
From a veterinary point of view, the most common creature to suffer due to being kept at a sub optimum temperature is the red eared terrapin, which is often sold in an unsuitable container and seldom are the new owners advised to keep them in a heated tank, and with a basking area, such as a lamp, under which they can stretch out and bask. This results in veterinary surgeons seeing red eared terrapins that are suffering with malnutrition, even if fed a correct diet.
Foods may be deficient in minerals or vitamins. (See Table 1 ).
Calcium, phosphorus and vitamin D3 should be considered together , as they interact and rely on a balance of each being adequate. Vitamin D3 is essential to allow the intestines to absorb calcium from the diet and utilise it. Even if adequate amounts of calcium are in the food, if the animal is deficient in vitamin D3 then it will not be able to utilise the calcium in the diet and absorb it through the intestines. Large amounts of phosphorus in relation to the calcium will reduce the availability of calcium and can result in deficiencies.
The effects of calcium, phosphorus and vitamin D3 imbalances lead to a group of conditions known as nutritional Secondary Osteodystrophy, which include conditions such as Osteoporosis, Osteomalacia, True Rickets, Osteodystrophia Fibrosa, and nutritional Secondary Hyperparathyroidism. For the ease of convenience, nutritional Secondary Osteodystrophy will be considered as though a single disease.
Nutritional Secondary Osteodystrophy results from incorrect diet, and is associated with a calcium deficiency, or even a calcium/phosphorus imbalance, or a vitamin D3 deficiency, or a protein deficiency. Nutritional Secondary Osteodystrophy may also arise if there is an ultra violet (UV) light deficiency because ultra violet light from the sun, is absorbed by the skin and is important in the manufacture of normal amounts of Vitamin D3. This is one of the few vitamins that the animal body can manufacture. Diseases, such as those that affect the kidney, liver and intestinal tract, may also result in nutritional Secondary Osteodystrophy.
Nutritional Secondary Osteodystrophy is most commonly see in the red eared terrapin, which is fed a dried terrapin food, which is low in calcium, or pieces of meat which have a calcium/phosphorus imbalance, with very little calcium but lots of phosphorus. These result in great abnormalities of the bony skeleton, with deformation of the plastron and carapace. This may result in swimming and balance problems.
Classical hypovitaminosis D3 (deficiency of) is diagnosed by the presence of a saddle shaped carapace, due to the effects of traction of the internal muscles, which pull the softened shell, as it develops, to form the saddle shape. In terrestrial chelonia, nutritional Secondary Osteodystrophy is most commonly seen in hatchlings bred in this country. Newly hatched chelonia have a normal smooth shell. If they are not getting sufficient calcium, as they get older their shells will become soft: this can be detected by a squeeze test, carefully pressing on the carapace and plastron. If not corrected at this early stage, then the tortoise will develop a deformed shell. The classic nutritional Secondary Osteodystrophy in the young tortoise is seen, as a soft and deformed shell, an inability to walk and thus lift itself , (sometimes with deformation of the limbs), there is also a tendency for the claws to be over long and abnormalities of the beak.
It is also noted that in these baby hatchlings, the slower they grow , the less likely they are to develop serious problems. If a baby tortoise is being fed on a marginally deficient diet, and it is growing rapidly, then a small deficiency will produce a marked effect, while as a baby tortoise fed less regularly,even if on the same diet, may not show the same problems. The quicker the rate of growth the more demands on the diet therefore the more important it is well balanced.
In adults, such as terrapins, which are later in life fed a calcium deficient diet, there may be collapsing of the scutes (shields).
In adult chelonia, calcium deficiencies may be associated with egg binding due to low calcium blood levels. The production of eggs further depletes the available source of calcium. The uterus may not then have sufficient calcium in order to contract and expell the eggs, leading to egg binding.
The ideal calcium/phosphorus ratio, for adults, should be 1 part of calcium to 1 part phosphorus, while in young and breeding animals, it should 1.5 parts of calcium to 1 part of phosphorus. T able 1 shows a comparison, of calcium:phosphorus ratios for some common foods which are used in the diets of chelonia. This chart has been drawn up from a large number of references.
A wider variety of foods will bring about a more suitable balance of the calcium:phosphorus ratio. However the majority of the fruit and vegetables that tortoises, in particular, tend to like in captivity, are very imbalanced in their calcium:phosphorus ratio. To this extent the use of vitamin and mineral supplements, such as Vionate (Ciba-Geigy) or Aquaboost (Vetark) are advised in order to try and correct the Vitamin D3 and Calcium:Phosphorus ratio to required for a healthy chelonia Thyroxine.
Hypothyroidism, (a lack of iodine), which results in the thyroids becoming enlarged and forming a goiter, and thus reducing the amount of Thyroxine in the body, is seen it animals are ted on goitrogenic food, these include cabbage, kale, Brussels sprouts and broccoli. It does not mean that these foods must be totally avoided. Hypothyroidism will only occur if these foods are the main constituent of the diet.
Vitamin A deficiency is the most common vitamin deficiency seen in chelonia, this is especially noted in terrapins and American Box Tortoises. The classic signs of hypovitaminosis A are swelling of the eyes, often with a plug of dead tissue, causing a foreign body reaction in the eye, and oedema ( swelling ) which is noted in the axilla and inguinal regions, usually due to kidney damage, and is seen as skin bulging out.
Lack of vitamin A affects cells throughout the body, particularly the squamous cells. This has major effects on the reproductive tract, kidneys, respiratory tracts (and may predispose them towards respiratory infection, including Runny Nose Syndrome). It also damages the lacrimal glands, which makes the eye problems worse. Affected animals stop eating, as they cannot see the food, nor smell it as well as they should. It is possible that a very low Vitamin A level in the parents, and hence the yolk, may result in hypovitaminosis A in newly hatched terrapins. Anophthalmos (lack of eyes), seen in newly hatched Red Eared Terrapins, may be the result, as already confirmed in pigs.
B Vitamins Deficiency
Vitamin Bl deficiency (thiamin) may be associated with neurological problems in reptiles, although this is mainly diagnosed on their response to treatment with this vitamin.
Vitamin B12 is used as an appetite stimulant in anorexic reptiles, where there is no medical reason for this anorexia. Again it is not possible to say by what mechanism this works not if there is a true deficiency.
The American literature tends to suggest that reptiles may also suffer with deficiency of vitamin C. Certainly, there is evidence to suggest that additional vitamin C helps reptiles in times of stress, or if there are underlying infections, such as respiratory infections, or stomatitis ( mouth rot). Vitamin E, together with selenium, may result in deficiencies and muscular dystrophy (weakness of the muscles) in young chelonia.
Obesity occurs when the diet contains too much calorific intake. By examining Dr Oliphant Jackson's graph (the Jackson Ratio) it is possible to assess, not only whether or not a tortoise is a good weight for its length and fit for hibernation, but at other times in the year whether or not there are problems with obesity. Any tortoise that is the same distance above the mean weight length as the danger line is below it, is in risk of becoming obese.
It is important that reptiles do not become obese, especially chelonia, as they have a bony shell, which will not allow them to develop a pot belly, thus, excess fat has to be stored elsewhere in the body. Fatty infiltration of the liver is a major problem in chelonia, and may result in jaundice. If the liver has large amounts of fat, which causes vacuoles throughout the liver , there will then be less tissue available for its normal functions, of breaking down waste products and toxins and the animal may become ill due to liver failure or dysfunction.
Excess fat in the body may also cause problems due to pushing the lungs up towards the top of the carapace and flattening them. This reduces the available functioning lung space, which in itself may not cause any problems, unless the tortoise develops a mild upper respiratory tract infection, which may appear more severe or result in acute pneumonia.
Because of problems associated with obesity in tortoises, especially if they are over indulged and fed on particularly high protein foods, like dog food, cat food, runner beans or peas as a sole source of food, then they may develop obesity.
In order to avoid problems in chelonia in captivity, it is advisable to feed on a controlled, well balanced diet with vitamin and mineral supplements, to mimic that which they would eat in the wild.
Testudo Volume Three Number One 1989