Chelonia – The Art of the Possible
There are thirteen families of chelonia (tortoises, terrapins and turtles) containing around 244 species. It is a very successful group of reptiles, which has radiated out to occupy a wide variety of niches throughout its range and includes the tortoises, box turtles and terrapins. Box turtles require totally different husbandry from the more usual Mediterranean species, requiring a higher humidity, higher temperatures, access to bathing facilities and a more carnivorous diet. Chelonian success is due to a combination of standard reptilian characteristics (conservation of water, cleidotic egg etc) plus a rigid body wall or shell consisting of the upper carapace and lower plastron. The shell is an antipredation structure honed by long years of evolution specifically to frustrate and confuse Homo veterinarius. This obvious physical adaptation makes clinical examination difficult especially with larger and/or recalcitrant individuals, and is also confusing as it leads many people to assume that such a uniformity of physical attributes also implies a uniformity of care and husbandry. Nothing could be further from the truth. To regard chelonia as a homogenous group is often the first mistake a practitioner will make. One should become familiar with a few of the commoner species available in the UK at present.
BASIC ANATOMY
The chelonia have a standard body plan with a few obvious differences to other reptiles. The scapula (shoulder blade) has rotated around the thorax (chest) and lies in a ventral position. The ribs are uniquely modified to form bony plates that comprise the structure of the carapace and plastron. Covering these bony plates is a keratin layer (scutes). There are four limbs, each covered in heavy scales (particularly on the fore limbs). The head is retractable and the cervical vertebrae fuse into the carapacial shell. The tail is used to differentiate the sexes. It is invariably larger in the male with the cloacal orifice located further from the tip.
The head is scale covered and the scale pattern is used as one of the means of differentiating the various species. The nares are situated rostrally. These should be clear openings and free of discharge. They open into the nasal cavity which is separated by a hard palate rostrally, but caudally the nasal cavity becomes freely opening with the buccal cavity. There is no soft palate. Chelonia do not possess teeth but have a hard ketatin horny beak. A large fleshy tongue is used to swallow ingesta. No chewing is preformed.
The eyes are situated laterally on the head and are protected by a mucous membrane covered 3rd eyelid and two eyelids. Only the lower eyelid is mobile. No lacyrimal drainage appears to be present therefore excess overflows from the lower lid. The middle ear is protected form the outside by a single tympanic scale. This is visible behind the eye.
The appendicular skeleton consists of : Front-leg: a humerus, radius, ulna, carpus and 5 digits ending in claws. Hind limb femur, tibia fibula, tarsus digits and 4 claws
Species distinction can be evident from structures on the limbs. eg the single pair of thigh tubercles of the Testudo graeca. The multiple thigh spurs of the Geochelone sulcata. The 4 claws on the fore-limb of the Testudo horsfieldi.
Notes on Surgical Approach to Coeliotomy
Sexing
In general terms the male has a thinner shell profile. The male tends to have a concave plastron. This is most marked in the Redfoot Tortoise Geochelone carbonaria.
The male possesses a longer tail, and the cloaca is further away from the tip of the tail.
Additional features present with terrapins are that often the fore leg nails are longer in males (especially red eared sliders). The male is often smaller in land tortoises.
Clinical examination as ever should start with a good history
1. Length of ownership. If captive bred - will have potentially good history back to the egg. NB encourage monthly weighing and maintaining of weight and length records. Excellent historic reference showing an individuals growth and seasonal variation
If wild caught - To be discouraged. The exploitation or wild chelonia is widespread. However there are many areas of the world where development is using up any native habitat.
Wild and captive bred individuals are often easy to distinguish. Due to our poor understanding of diet requirements and our tradition of overfeeding most captive-bred animals have a distorted carapace. Ranging from the malformed, bone diseased animal to the too rapidly grown pyramidal carapace.
Many species are now covered by CITES restrictions on importation
In addition it is preferred that hatchlings are not sold before 1 year old. This way the breeder takes responsibility for the potentially high early mortality. Shipment and change of environment is more stressful on very young animals.
Assessment of age
Definitive aging is not possible in chelonia. Theoretically each ring on the shell corresponds to a period of growth. In the wild this is associated with availability of food usually in the rainy season. However in practice multiple growth periods occur with each feeding season. For captive bred animals with constant feeding often all year round the practice of ring counting falls apart. As a rough guide start by estimating its relative size for the species e.g. is it half grown? If the carapace is smooth then a slow rate of growth has occurred. If not then rapid growth has occurred and animal will be younger than the size predicts.
Evaluate the shell pattern. If the detail of the central areola is still present the animal is still a sub adult. As the animal ages the detail is worn away by mounting behaviour and burrowing. Indeed the scutes may become so worn that they become slightly translucent. In the case of young red-eared sliders the scutes are highly patterned with yellow markings on a bright green background. Older sliders have a brown/olive pattern.
Assess growth activity. If the shell is still producing fresh growth rings - fresh growth around the scute edges will appear paler than the existing colour in most species. Such an animal is still growing and is sub or young adult.
Best therefore to categorise into Juvenile, Sub-adult, adult, elderly:-
Juvenile still under adult size for species
still active growth
carapace detail - particularly central scute - very distinct 0-12years
Sub adult growth rings bunching tighter together
size close to expected adult size
central scute visible but fading 12-30
Adult growth all but stopped
central scute detail gone
sexually active 30-60
Elderly carapace very smooth no sign of growth
eyes often have a lipid deposition in peripheral cornea 60+
This is very generalized and some species fall outside this assessment. For example the giant species may not reach adult size until 40 years +. Sexual maturity is more dependent on size than age. It has been possible to fast grow tortoises to achieve adult size and sexually maturity in as few as 6 years.
Weight
Good accurate scales are required. Best to use the metric gram scale and for youngsters use a scale accurate to at least 2g. Ensure monthly weighing especially for hatchlings.
Jackson’s ratio is a rough guide assessment useful for the Mediterranean species. Be careful when assessing other species. Jackson’s ratio allowed the formulation of graphs depicting the mean and "dangerously low" mass to length curves for the Spur-thighed tortoise Testudo graeca and Herman's tortoise Testudo hermanii. However these ratios can vary depending upon the tortoise's age, sex and stage of reproductive activity (an average egg weighs around 28g), but are still a valuable adjunct to a thorough clinical examination. By far the best assessment is from an individuals chart. There ought to be a seasonal variation for adults.
For hatchlings a SLOW steady linear growth is preferred. Even better is to include a winter season of slower growth to mimic the natural reduction is food availability.
Jackson’s ratio is often used prehibernation but beware the tortoise which has not eaten well over the summer but still falls within the normal on the graph. The animal should be hibernated with caution and checked regularly (see later).
Measuring : Always use a Straight Carapace length for measurements.
Examination.
The whole integument is examined. The shell should be assessed for areas of obvious damage or erosion. Are there areas where the underlying bone is exposed? Where these are present try to gauge whether they are active lesions or old, healed ones. Often one of the caudal marginal scutes will have a hole drilled into it by a previous owner as a means of tethering the tortoise. In these often the contra-lateral front foot has very worn down nails. Areas of haemorrhagic discolouration or softness should be noted. Is the shell of an appropriate hardness for the species? In most species the carapace and plastron should be solid and non-compressable in individuals older than one year. However in some species such as the Pancake Tortoise (Malacochersus tornieri) the shell is naturally pliable. At a further extreme Soft-Shelled Terrapins (Trionyx sp.) have just that – a soft, cartilagenous shell significantly reduced in size relative to other chelonia.
The limbs should be assessed for any lesions or swellings that may indicate abcesses.
All structures of the head should be examined. The tympanic scales should be examined for signs of swelling beneath them indicative of a tympanic abcess. The eyes should be clear – attempt an ophthalmological examination as cataracts and vitreal haze have been associated with exposure to temperatures below freezing during hibernation. The nostrils should be checked for signs of rhinitis. Open the mouth and assess for stomatitis. With smaller/more placid species using a finger as a gag is acceptable: with larger, more aggressive species use a metal or wooden gag.
Further investigation will occasionally be necessary.
Radiography. Useful for assessing skeletal integrity and bone density. Evaluation of lung fields requires a series of views including dorso-ventral, lateral and antero-posterior in order to construct an accurate 3D impression. The latter two views should be done using a horizontal beam. Shelled eggs show up readily on a DV view as do bladder stones. Visualisation of soft tissue is poor. Obesity can be diagnosed by showing compression of the lung fields, whilst conversely starvation will show a greatly expanded lung field ventrally. Gut motility problems will often be associated with gravel signs. Radiolucent foreign bodies and other GIT abnormalities can sometimes be visualised following a barium meal.
Ultrasonography via the prefemoral fossa can be used to diagnose follicular stasis.
Blood sampling with subsequent haematology and biochemistry analysis can be invaluable with certain caveats. NEVER USE EDTA.
Sedation may be required with large or fractious chelonia. Recommended regimes are :
For painful procedures including surgery, a general anaesthetic may be required. The following points should be considered:
Cardio-pulmonary structures. In chelonia the lungs occupy the dorsal section of shell and are adhered to the overlying dermal bones of carapace. The carapacal wall is rigid and there is no functional diaphragm. Respiration is achieved by movement of muscle groups esp legs and pelvicum attrahans thereby altering volume inside the shell. Closure of glottis imposes a respiratory cycle. Diving terrapins are able to constrict lungs via smooth muscle (which is well innervated). This in turn increases pulmonary circulatory pressure and so allows an intraventricular shunt to occur, reducing the blood flow through the lungs. This is because chelonia have a three chambered heart (two atria, one ventricle) The ventricle functionally separates the pulmonary and systemic blood flows at systole. .
Chelonia are very tolerant of anoxia and can tolerate high lactic acid levels. Respiratory function in reptiles is controlled by PO2 and temperature. Therefore maintaining reptiles in a high O2 environment can suppress ventilation.
Because of all these effects it is often difficult if not impossible to mask down a chelonian so it is best to give induction agent. Ketamine (10-60mg/kg IM) and alphadolone/alphaxalone (Saffan) (5.0-15mg/kg IM or 4.0-9.0mg/kg IV) but long recovery time therefore induction agent of choice is propofol at 14mg/kg but must be given iv. Maintain with isofluorane - less than 1% metabolised.
Anaesthetic protocol:-
1- Maintain @ PBT before & after anaesthetic
2 -Most reptiles cease to breathe during anaesthesia therefore adopt Intermittant Positive Pressue Ventillation. Chelonia do have CO2 receptors in respiratory tract therefore on recovery often helps to ventilate by mouth because CO2 has a moderate to major stimulatory effect in many chelonia.
3 – Intubation. The tracheal rings in chelonia are complete. Traditionally an uncuffed endotracheal tube (or equivalent) is recommended. However Cooks Ltd offer a cuffed "turtle" tube which if only slightly inflated works very well and is especially good for IPPV.
4 - Monitoring can be problematic
- Reflexes
- Jugular pulse
- Heart rate - doppler or ultrasound. Pulse oximetry is becoming more useful especially with the introduction of cloacal probes.
- oesophageal stethoscope
- ECG?
5 - Respiratory stimulants eg Dopram V
6 - Neuromuscular blockade esp gentamicin.
Feeding history:
Details of how well the animal eats are important. Some tortoises are able to sustain long periods of fasting without any weight loss. Considerable periods of anorexia have been recorded lasting up to 12 months. Assess carefully dietary intake. Tortoises can become very fastidious feeders surviving solely on single feed items either through there own choice or due to poor understanding by their owners.
Stool consistency is a good indicator of dietary adequacy. If a soft messy stool often indicates inadequate fibre or too much fruit. Beware assessment at the clinic as travelled tortoises often have loose stool. Normal stool should be formed and solid. Tortoises are good water retainers so should not lose too much fluid in the faeces. Excess fruit leads to diarrhoea flatus and colic. Insufficient fibre leads to diarrhoea flatus and colic.
Housing and Environment
25-30o C in hotspot basking area
Night-time temps should not drop below 15oC.
Chelonia are ectotherms; their metabolic heat production is generally negligable. Their thermal balance is therefore regulated by external heat sources with both behavioural and physilogical mechanisms used to achieve and maintain their Preferred Body Temperature (PBT).There is generally a close correlation between the optimum temperature for a reptile's biochemical and physiological processes, and its preferred PBT. Most are heliotherms and manipulate their body temperature by a variety of means including movement into and out of the sun, adjusting their orientation to the sun, peripheral vasoconstriction or dilation, tachycardia (when warming up) or bradycardia (when cooling - reduces the rate of heat loss. In general, captive chelonia should be provided with a range of temperatures from a relatively cool temperature to a relatively warm thereby allowing them an opportunity to thermoregulate and choose its own PBT. Failure to allow them to achieve their PBT will eventually result in severe physiological disruption including immunosuppression. Other clinically important factors relating to body temperature include:
1 - Temperature Related Metabolic Rate. MR doubles with every 10C rise therefore Q10 = 2
2 - Temperature Related pH of Body fluids.This can vary from a pH of 8.3 @ 5C to 7.4 @ 35C.There is no homeostatically set constant pH as such, but a pH target value for any given temperature.
Radiotelemetry studies with Ts hermanii with surgically implanted thermistors found their PBT was around 30oC. In the wild extremes of temperature are avoided. The tortoise will seek burrow refuge in very high temperatures. For very hot climates they will remain asleep (aestivating) throughout the hottest time of year. For colder area they will remain asleep (hibernation) throughout the coldest time of year.
Lighting. Lighting is vital for a variety of reasons.
Daylength : Most chelonia are diurnal sight feeders and so daylength is a factor that governs feeding time. A reduction in daylength is a trigger for hibernation in temperate species.
Spectrum : Ultra violet spectrum of 290-320nm (UVB) is important in the cutaneous formation of vitamin D3 . Slightly longer wavelengths (320-400nm) (UVA) seems to be important in mediating normal behaviour and as it is thought that many species can see into the UVA range, possibly how they visualise their food. Glass and many other transparent materials filter out UV light so chelonia kept in greenhouses or conservatories may well receive poor levels of UV. Carnivorous and omnivorous chelonia such as terrapins and box tortoises will obtain some of their D3 from food sources.
Intensity : In the tropics, light intensity at ground level is in the region of 1 000 000 Lux, whilst on the rainforest floor it can exceed 7 000 Lux. Contrast this with a 40W incandescent bulb which has an intensity of 50 Lux at one metre. Falling light intensity is another trigger for hibernation.
As a general rule those chelonia kept indoors must be given full spectrum lighting of an appropriate intensity for 12-14 hours per day. This is especially important in the autumn to prevent early hibernation in temperate species.
Viral Diseases
Herpesvirus. Usually diagnosed by demonstration of intracytoplasmic viral inclusions in hepatocytes. Clinical picture is of persistant rhinitis varying from a watery serous to a thick mucoid discharge, often accompanied by recurring parasitism (especially with flagellates) and a non-dietary related hypovitaminosis A. Appetite remains good but diarrhoea is often a feature. This disease is untreatable as there appears to be an accompanying immunosuppression. Eventually anaemia, jaundicing ensue leading eventually to death often as a result of a secondary stomatitis, pneumonia or renal failure. The species Testudo ibera appears to be an asymptommatic carrier, with deaths in mixed collections being mostly confined to the North African Spur-thighed tortoise Testudo g.graeca. To differentiate between the two species (originally considered subspecies of Testudo graeca) look at the first vertebral scute - in T.g.graeca it has rounded edges, whereas in T.ibera the edges are markedly squared off. I have seen herpesvirus in Leopard Tortoises (Geochelone pardalis).
Bacterial Diseases
Abcesses are very common in chelonia. Reptilian pus is rarely liquid but is more often thick, caseous material. A thick fibrous capsule usually surrounds the abcess making antibiotic penetration difficult, so surgery is often resorted to to effect a cure. Where limbs, joints or extremities such as the rostral nares are affected, then radiography should be performed to check for osteolysis in the underlying bone.
Typanic (ear) abcesses are common, and present as bulging of the tympanic membrane on one or both sides. These are often the sequelae to a bacterial stomatitis, with infection ascending the eustachian tube into the middle ear cavity. Management of all abcesses is similar, involving the combination of appropriate systemic antibiosis plus the surgical removal of caseous material and debridement followed by irrigation with topical antibiotics or povidone-iodine. Although some vets will suture the tmypanic scale closed, better results are usually obtained by leaving it open.
Stomatitis (or mouth rot) is occasionally encountered especially following hibernation. There may be ulcerative, haemorhagic lesions or whitish plaques on the tongue, fauces and hard palate. Bacterial infections usually play a significant role, although viral and fungal aetiologies have been implicated. Following swabbing for routine culture and sensitivity testing, debridement under a general anaesthetic is recommended. Systemic and topical antibiotics should be used - if fungi are implicated then try clotrimazole (Canestan) topically. Importantly one should instigate supportive measures including stomach tubing with fluids such as glucose/electrolyte mixes. Chelonia with stomatits will not eat or drink voluntarily.
Septicaemia presents as ecchymotic haemorrhages in the skin and in the shell. In severe cases fluid may accumulate beneath the keratin shields of the shell. Jaundicing may be seen. In terrapins a pneumonia may result, which can give rise to areas of consolidation in the lung parenchyma. Affected terrapins will swim with a definite list to one side or another. Treat with systemic antibiotics. Also in terrapins, Septicaemic Cutaneus Ulcerative Disease (SCUD) is as the name describes, but the causitive organism is Citrobacter freudii. Treat with appropriate antibiosis, clean shell lesions with povidone-iodine and improve environmental hygiene. Much fuss is made about asymptomatic Salmonella infections, especially in terrapins, primarily hatchling red-eared sliders (Trachemys scripa elegans). Zoonotic episodes involving Salmonellae from chelonia are relatively rare and are usually due to a breakdown in hygiene and poor husbandry, allowing an environmental build up.
Runny Nose Syndrome – no definite aetiology in UK (CF USA = Mycoplasmal) ?Is sign of sick tortoise. Often have occult abcess.
Fungal Diseases
Although most "shell rot" in terrestrial chelonia are bacterial, occasionally fungal infections are seen. These are more of a "dry rot". Treat by debridement, topical povidone-iodine and anti-mycotics. Aquatic chelonia are sometimes afflicted with Saprolegnia infections, especially the soft-shelled Trionyx sp. Again topical iodine and anti-mycotics are needed, plus keep the terrapin as dry as reasonably possible.
Parasites
Flagellate infestations can be associated with gastro-intestinal disease and inappetance in chelonia, which may be seen to void large quantities of watery diarrhoea. Light microscopy will reveal huge numbers of these motile protozoa . Considered normal inhabitants of the gut fauna, in large numbers they are pathogenic - in many cases they are secondary opportunists so the possibility of concurrent disease should be considered. Treat with metronidazole delivered by stomach tube @ 100-275mg/kg once only. Occasionally Hexamita may be a cause of nephritis. Treatment is with dimetridazole @ 40mg/kg orally daily for 5 days.
Nematodes. It seems that 30-40% of tortoises carry nematode infestations, usually Sulcascaris and Angusticaecum. Large infestations will compete for the host's nutrition, and can cause blockages. Larval stages undergo visceral migration and can cause pathology in a variety of organ systems. Life cycles are believed to be indirect though they have not been elucidated - Augusticaecum can have a direct life cycle. Regular worming with Fenbendazole @ 100mg/kg twice yearly is to be recommended - during pre- and post-hibernation checks.Some authorities recommend using oxfendazole but as fenbendazole is metabolised to oxfendazole it is probably largely academic.
Hibernation
Not all species of tortoise hibernate! Tropical tortoises such as the Leopard Tortoise (Geochelone pardalis) do not hibernate and will die if made to do so. Other species such as Horsfield’s Tortoise (Ts. Horsfieldi) do very little else – in the part of their range that includes the USSR this species is active for only three months of the year (March, April and May).
Hibernation is triggered by - reducing ambient temperatures, reducing photoperiod and reducing light intensity.
Increasing temperatures alone (no light in hibernaculum or box) reverses hibernation. Chelonia on revival from hibernation show low temperature adaptation, whereby activities and some physiological processes occur at lower temperautres than would otherwise be considered normal.
Hibernating chelonia utilise fat and liver glycogen reserves over this period, and lose 0.2-0.4g/day - expect to lose around 1% body weight per month.
Other changes are that water is lost via respiration therefore the PCV rises from 0.28-0.29 l/l to 0.34-0.38 l/l. Urea levels rise from <10mmol/l to <103mmol/l (as a result of protein catabolism) as the animal does not urinate. This produces an increase in the osmolality of the blood causing a progressive reduction in kidney function. This may cause the animal to become anuric. At these low temperatures there is a suppression of WBC function and production (also due to high urea levels), and antibody synthesis and so there is an immunosuppression.
At re-emergence there is a massive rise in blood glucose from liver glycogen stores to fuel initial foraging. Tortoises studied did not start to eat until blood glucose was at least 3.2 mmol/l, and in some it went as high as 20.0mmmol/l. As a general rule a post-hibernational tortoise
- must drink within 10 days -> reduction in blood urea levels and PCV
- must eat within 3 - 4 weeks
If there were insufficient fat reserves then protein is used as an alternative energy source. Muscle catabolism occurs with a break down of muscle protein to release AAs, but this protein catabolism results in higher urea levels and therefore worsens the condition. High uraemia will not only prevent renal function, but will also suppress appetite. If all of the fat reserves have been utilised there will be a deficiency in fat soluble vitamins.
Therefore on emergence one should:
- correct dehydration
- give vitamins
- maintain at a temperature around 30oC
- give easily assimilated diet
Post-hibernational anorexia is probably best considered as a syndrome where Mediterranean tortoises awakening from hibernation occasionally will refuse to feed. Typically this is due to inadequate preparation the previous autumn with inadequate deposition of fat in the fat body. The tortoise has utilised its entire fat reserves, thereby also exhausting its fat soluble vitamins and is forced to breakdown muscle and other tissues as a protein source to provide an alternative energy and amino acid source. Blood parameters to examine include PCV, [glucose] and [urea]. As mentioned above, blood glucose levels <3.2mmol/l are associated with inappetance, whilst blood urea levels >200mmol/l carry a very poor prognosis. Other obvious causes include stomatitis, septicaemia resulting from a bacteraemia during hibernation while the tortoise immune system is compromised, blindness secondary to cataract formation as a result of exposure to excessively low temperatures during hibernation. Treatment can be prolonged, and involves maintaining fluid balance by stomach tubing with oral rehydration preparations at around 4% bodyweight per day. An easily assimilated food such as Reanimyl (Virbac) can be given twice weekly. Any specific disease conditions, such as stomatitis, should be addressed.
Egg-Binding Any female chelonian presented with non-specific signs of ill health, restlessness or persistant straining should be assessed for dystocia, or egg-binding. There are two forms:
1 - Follicular stasis. The ovaries become overloaded with retained yolks, developing into large pendulous masses which act as space occupying lesions. Diagnosis should be attempted by rigid endoscopy introduced at the prefemoral fossa or ultrasound, again directed at the prefemoral fossa. May be associated with hypothyroidism give Soloxine 1.0mg uid for 3 months and monitor with U/S.
2 - Post-ovulatory. Eggs which are shelled to varying degrees are present within the oviduct. Radiography is diagnostic.
Treatment of post-ovulatory dystocia should be attempted by first of all priming the reproductive tract over five days with parenteral calcium @ 500mg/kg of 10% calcium solution, followed on the fifth day by oxytocin @ 1.0iu/kg. If this is unsuccessful after a couple of trials then removal via a surgical flap created in the plastron is advised, possibly accompanied by salpingectomy with or without an ovariectomy. The dystocia may prove to be secondary to a wide variety of factors including environmental (no provision for egg deposition sites), hypocalcaemia, intracoelomic tumours and so on.
Nutrition
Hypovitaminosis A is occasionally encountered especially in young red-eared sliders. Affected chelonia show a variety of ocular lesions including swollen eyelids due to squamous metaplasia of the orbital glands and their ducts. A whitish cellular mass may develop behind the lower lid. Squamous metaplasia also affects the renal tubules, causing kidney damage. Affected chelonia are often anorexic as they cannot see to locate food. Treatment is with vitamin A given i.m.@ 1 000 - 5 000 iu weekly for 4 weeks, and the addition of dietry vitamin A supplements.
Shell abnormalities can arise from dietary imbalances especially in young herbivorous chelonia. Abnormalities in the calcium:phosphorus ratio (should be around 2:1) or too high a protein intake resulting in too rapid a growth rate can lead to an obvious doming of the carapacial scutes. Maintaining young at constantly high temperatures can also predispose to carapacial abnormalities therefore some diurnal temperature variation is recommended..
Bone diseases can be common in chelonia, and any swelling, fracture or paralysis should be considered as a possible sign of a bone disorder. Diagnostic procedures should include radiography and where feasible, a blood sample to assess serum calcium and phosphorus levels. Aetiologies include: dietary calcium deficiency, dietary calcium/phosphorus imbalance, dietary vitamin D3deficiency, lack of exposure to ultra violet light, dietary protein deficiency, liver, kidney and intestinal disease. However most skeletal problems are dietary linked and are often lumped together under the title Nutritional Osteodystrophy or Metabolic Bone Disease (MBD), the clinical manifestations of which can be due to a variety of related disease syndromes.
1 - Osteoporosis. Seen with protein deficient diets, prolonged corticosteroid treatment, lack of bone use and senile changes, this disease involves the reabsorption of osteoid faster than new protein is deposited leading to brittle bones and consequent often multiple fractures. Genuine osteoporosis probably quite rare in chelonia – most osteoporitic lesions are probably associated with osteomyelitis.
2 -Osteomalacia.Seen in adults only there is insufficient mineralization of the bones causing bending and fractures as well as folding fractures to occur. There is often increased osteoid deposition at tendon insertions and bone curvatures. Affected tortoises often have a characteristic sloping back when seen from the side, the highest point being at the cranial end where the neck retracted into the shell.
3 - Rickets. Seen in young reptiles, the aetiology is very similar to osteomalacia although the radiographic appearance differs slightly, with the formation of widened radiolucent epiphyseal plates.
4 - Osteodystrophy fibrosa. Chronic mineral imbalance or osteoporosis can lead to this, where osteoid is absorbed and replaced by connective tissue. Affected bones are larger than normal and soft. The mandibles in particular can be gently compressed hence the term "rubber jaw".
5 - Nutritional Secondary Hyperparathyroidism. Prolonged hypocalcaemia will cause an excessive production of parathyroid hormone which initiates the resorption of calcium from the bone matrix to try to maintain normal serum calcium levels. This results in osteomalacia (adults) or rickets (young).
Treat initially with I.V calcium @500mg/kg of 10% calcium solution. Prevention is with regular calcium and vitamin D3 supplementation with proprietary products, and exposure to UVB.