15 Reptiles – an introduction

Reptiles are among some of the more unusual pets seen in veterinary practice (Fig. 15.1). An approach similar to that for other pets may be taken with regard to their clinical history and examination, although species-specifics must be known in order to interpret findings pertinent to husbandry conditions. The metabolic rate is in general slower with these ectothermic animals than with mammals, and hence disease processes tend to be more prolonged with reptiles. Investigative techniques and some basic husbandry requirements for selected species will be outlined in this chapter.

Figure 15.1 Basic internal anatomy for (a) chelonia, (b) lizards, (c) snakes.

Taxonomy

Taxonomic classification of reptiles with some examples of those that may be seen as pets are given in Table 15.1.

Table 15.1 Taxonomic classification of reptiles, with some examples of those that may be seen as pets or in collections

Biology

It is impossible to detail husbandry requirements for the huge range of reptile species that may be seen by the veterinary clinician in practice. The reader is referred to other texts for further information. Husbandry advice for some common species is listed below.

Unless housed outdoors with access to sufficient sunlight, most species will require supplemental UV-B light to synthesize vitamin D, which is necessary for calcium metabolism. Carnivorous species can obtain minerals from digestion of bone in their diet.

As reptiles are ectothermic (relying on environmental temperature to control their body temperature), most require supplemental heating in their captivity enclosure. A temperature range should be provided across the enclosure, to allow the animal to select an appropriate temperature. This preferred optimum temperature range (POTR) varies between species. Many heating sources can be thermostatically controlled, but the environmental temperature should still be monitored using a digital maximum–minimum thermometer (strip and dial thermometers may be inaccurate). Heaters should be protected to prevent accidental burns. In species that hibernate, care should also be taken to control and monitor the environmental temperature during this period.

Most reptiles carry potentially zoonotic pathogens, such as Salmonella spp, in their gastrointestinal tract. Although these rarely cause disease in humans, general hygiene precautions should be observed when handling reptiles or cleaning their enclosure, in particular ensuring that transmission does not occur via the faeco-oral route. Enclosures should be spot-cleaned daily, and intermittently disinfection should be carried out and the substrate changed.

Sexing of reptiles depends on the species concerned. In general, adult male tortoises have a longer tail than females; males may also have a concave plastron. Male terrapins may have longer claws on their fore-feet. Some lizards are sexually dimorphic, with males having more prominent pre-femoral pores (such as bearded dragons) or various facial adaptations (such as crests or horns in chameleons, or the dewlap in green iguanas). Few snakes are sexually dimorphic. Where obvious external characteristics do not enable gender identification, probing the hemipenes in situ caudal to the cloaca may be used to sex lizards and snakes. An alternative is coelioscopy or coeliotomy to visualize the internal gonads.

Chelonia

This group is divided into tortoises (terrestrial species), turtles (aquatic marine species) and terrapins (aquatic freshwater species). Owing to space restrictions, smaller species are most commonly kept as pets. Most chelonian species prefer to be solitary, but same-sex individuals may be housed together if accommodation is large enough with several hide areas.

Although low numbers of some endoparasites appear to assist with digestion, large numbers are usually associated with disease. Faeces should be examined for parasites annually.

Hibernation

Many species of chelonia (and some other reptiles) will hibernate in the wild for varying periods of time (Box 15.1). In captivity, it is usually advisable to keep this period to a maximum of 12 weeks, otherwise, metabolic reserves will become dangerously low during hibernation and it may be difficult for the tortoise to eat sufficiently during the warmer months in preparation for hibernation. Tortoises should be fasted for 1 month before hibernation to allow the gastrointestinal tract to empty; otherwise continued fermentation may lead to gas build-up and pressure on the lungs, resulting in dyspnoea. During this pre-hibernation time, the tortoise should be bathed to encourage drinking. Water is stored in the urinary bladder for reabsorption during hibernation.

BOX 15.1 Important note

Geochelone species such as the leopard tortoise (Geochelone pardalis) and African spurred tortoise (Geochelone sulcata) do not hibernate. They should be over-wintered, ensuring sufficient environmental temperatures are maintained despite outdoor temperatures dropping.

Traditional hibernaculums include boxes insulated with straw, but these are susceptible to environmental temperature changes. Some animals housed in gardens may dig into soil as their free-ranging counterparts do, but monitoring is nigh on impossible in this situation. Often, owners do not actually know where the tortoise has buried itself, and owners digging in gardens during spring have caused traumatic injuries to hidden pets. A safer alternative is to build an indoor insulated terrarium with thermostatically controlled heating coils underneath protective matting, covered with soil to permit digging. A reasonably constant temperature can be maintained using a refrigerator. It can be helpful to have bowls of water in the fridge to ensure the air does not become excessively dry.

Hibernation is induced below 15°C, and maintained between 2 and 9°C. Temperatures below 0°C will result in pathology such as blindness. The environmental temperature should be measured constantly, for example using a maximum–minimum digital thermometer. Tortoises should be checked daily and weighed weekly during hibernation. If a tortoise urinates during hibernation, it should be awakened and ‘over-wintered’ (i.e. kept awake and maintained in conditions similar to the warmer months). Similarly if a tortoise loses >5–10% of its body weight during hibernation (or >1% in a week), it should be awakened.

Tortoises should begin eating within a couple of days of wakening from hibernation. Bathing in shallow warm water will encourage the tortoise to drink and urinate. Often they will pass a large amount of urates at this stage. If they do not start to eat within a week, tortoises are deemed to have ‘post-hibernation anorexia’, and veterinary investigation and treatment should be instigated.

During excessively hot dry periods of summer, some tortoises (such as free-ranging desert tortoises, Gopherus agassizii) may undergo a metabolic change similar to hibernation, called aestivation.