Chapter 7 Lizards
|Bearded dragons (Pogona vitticeps)||Medium-sized, characterful lizards. They do like it warm, however, and the hot spot should be up to 38°C during the day||Metabolic bone disease, Isospora and foreign body ingestion. Secondary infections often are the result of inadequate temperatures|
|Leopard gecko (Eublepharis macularius)||An ideal beginner’s lizard. Feeds well on supplemented insect prey including mealworms. Available in a wide variety of colour morphs, some of which carry very high prices||Cryptosporidiosis and foreign body ingestion|
|Crested gecko (Rhacodactylus ciliatus)||Popular because of its looks and wide natural colour variations, this gecko’s wild diet is rich in fruits and so it can be kept using commercially available foods rather than live foods||Metabolic bone disease is occasionally seen, as is a muscular-dystrophy-like disease often mistaken for MBD|
|Green iguana (Iguana iguana)||A large stunning lizard as an adult, its vegetarian diet makes it prone to calcium deficiencies||Metabolic bone disease, abscessation (secondary to prolonged low environmental temperatures and aggression-related behavioral problems|
|Veiled chameleon (Chamelo calyptatus)||Chameleons are generally not good starter lizards, but the veiled chameleon, providing it is offered water via a spray and given supplemented foods will often do well||Metabolic bone disease and dystocia|
Many lizards are ‘exercised’ outside of their vivarium by well-meaning owners. This can lead to prolonged periods of the lizard being exposed to suboptimal temperatures, producing an immunosuppression and increased susceptibility to disease. Inside the vivarium, aggression between its inhabitants can mean some individuals are deprived of suitable basking opportunities, leading to immunosuppression. Some lizards require exceptionally high daytime temperatures. Bearded dragons, for example, need a basking spot set at around 38°C during the day; however, a nighttime temperature drop is no problem.
Most diurnal lizards require exposure to ultraviolet B lighting (290–315 nm) for endogenous vitamin D3 synthesis. Dietary supplementation alone is not sufficient for many species including iguanas, bearded dragons, monitor lizards (Varanus spp) and chameleons, so ultraviolet exposure is achieved by installing a full-spectrum light with a specified UVB output, e.g. 2%, 5% or 8%.
Crickets, locusts, waxworms and mealworms are commonly fed to lizards not because they are nutritionally good, but because they are easy to farm commercially and they trigger normal feeding in insectivorous species. Insects are inherently low in calcium and so this must be balanced with commercial calcium supplements. These are applied to the insects either by dusting a calcium-rich powder on to the prey, or feeding it upon a calcium-rich food. Note that many commercial calcium supplements also contain vitamins, including vitamin D3, as well as amino acids.
Small lizards such as leopard geckos can be examined relatively easily. Larger lizards may require a more managed technique involving assistance – iguanas and monitor lizards rarely bite, however (note this does not mean that they do not bite), and in preference, will attempt to fend you off by whipping with their tail.
Restraint involves grasping the animal from behind across the shoulders and across the pelvis, the handler holding the reptile away from the body. If a large lizard, such as an iguana, is especially aggressive, then placing a damp towel over its head is often sufficient to disorientate it and allow you to gain a hold (N. Highfield pers. comm.).
Many lizards, such as Chinese water dragons and young iguanas, can be temporarily immobilized by applying digital pressure to both eyes simultaneously. This technique, plus gentle handling, will allow many feisty lizards to be weighed and examined in a controlled fashion, before gentle stimulation (such as re-righting the reptile) returns it to a normal state of awareness. This may be a manifestation of the oculo-cardiac reflex.
In those lizards with hypocalcaemia/metabolic bone disease, the bones may be so fragile that fractures of the long bones, especially the femurs, can occur if excessive force is applied. A lizard that is presented as flaccid with little or no muscle tone is likely to be hypocalcaemic. Other causes can include septicaemia or poisoning but these are much less likely. In such cases, i.v. calcium is strongly recommended as soon as possible.
When beginning an examination, examine the head first. Most lizards can be induced to open their mouths even if it is in an attempt to bite you. With iguanas, firm traction on the dewlap will often induce them to open up.
Some lizards will shed their tails naturally if stressed or poorly handled (autotomy). These include iguanids, lacertids, geckos and some skinks. In these species, the tail will regrow but is usually a different shape and or markings. Note that the crested gecko (Rhacodactylus ciliatus) is an exception – unlike the other geckos in the Rhacodactylus genus, the tails do not regrow once shed.
Many lizards are sexually dimorphic as adults and can be readily distinguished, typically by the presence of pronounced pores cranial to the cloaca (pre-analpores) or medial thigh (femoral pores), combined with the presence of hemipenile bulges caudal to the cloaca (Fig. 7.2). Male veiled chameleons have a caudal spur on each hind foot, present from birth.
Reptiles lack the Loop of Henlé and are, therefore, unable to produce hyperosmotic urine. Uric acid is excreted instead of ammonia; this is sparingly soluble and can be excreted at high concentration with minimal water loss as a sludge or paste.
|Buprenorphine||0.005–0.02 mg/kg i.m. every 24–48 h|
|Butorphanol||0.4–2.0 mg/kg s.c., i.m. b.i.d.|
|Carprofen||1.0–4.0 mg/kg s.c., p.o. every 24–72 h|
|Ketoprofen||2.0–4.0 mg/kg s.c., i.m. every 24–48 h|
|Meloxicam||0.1–0.5 mg/kg s.c. p.o. every 24–48 h|
|Morphine||0.05–5 mg/kg i.c. every 6–8 h|
|Pethidine||2–4 mg/kg i.c. every 6–8 h|
All reptiles should be at their optimum temperature. Gaseous anaesthetics can be of limited use, as induction agents due to intracardiac shunting, tolerance of hypoxia and physiological diving reflexes (depending upon the species). Chameleons respond relatively quickly while semi-aquatic species may take some time.
Most lizards shed their skin piecemeal and uncoordinated – cellular proliferation and keratinization are continuous, however geckos normally shed their skin simultaneously over the whole of the body surface. Many lizards such as leopard geckos (Eublepharis macularis) will eat their shed skin.
|Species||Total T4 nM/L||Total T3 nM/L (Free T3 pM/L)|
|Sceloporus undulatus Adult||11.1–13.1||3.1–3.2|
|Ameiva undulata Adult||8.2||–|
|Dipsosaurus dorsalis Adult||3.2–14.5||–|
|Dipsosaurus dorsalis Hibernating adult||1.3||–|
|Dipsosaurus dorsalis Adult (spring)||13.0||0.5|
|Trachydosaurus rugosus Adult||3.0||0.3|
|Podarcis sicula Adult||–||0.15 (1.7)|
After Hulbert (2000).
In crested geckos, calcium is stored in bilaterally symmetrical endolymphatic glands dorsally at the back of the pharynx. In breeding females on a good calcium intake these can appear as quite pronounced whitish to greyish swellings and should not be mistaken for pathological lesions.