Basic Husbandry and Medicine of Pet Reptiles

Chapter 178 Basic Husbandry and Medicine of Pet Reptiles

Boas, pythons, king snakes, rat snakes, and milk snakes are the most common snakes kept as pets. Iguanas, geckoes, monitors, and bearded dragons are frequently encountered pet lizards. Amphisbaenians are small, worm-like reptiles not commonly found in the pet trade. Snakes, lizards, and amphisbaenians are all in the order Squamata. The order Chelonia has approximately 235 species and consists of turtles, tortoises, and terrapins. Of the chelonians, box turtles, red-eared sliders, and a variety of tortoises are kept most commonly as pets. The order Crocodilia has only 21 species, including alligators, crocodiles, caimans, and gharials.

comparative anatomy and physiology

Body Temperature

Most reptiles need to maintain their core body temperature well above ambient temperatures for at least part of the day and generally achieve this by absorbing radiant heat. Reptiles can minimize body temperature fluctuations by modifying behavior. Reptiles that become too cool seek elevated areas to bask, lay perpendicular to the sun’s rays, maximize their surface area by expanding their rib cage, and darken the pigment of their skin to increase heat absorption. If no sunlight is available, some reptiles burrow into warm soil or lay on objects previously warmed by the sun.


Habitat Temperature Range (°F)
Tropical 85–100
Desert 80–102
Lowland temperate 70–90
Mountain temperate 70–85


Common Species Temperature Range (°F)
Boas and pythons 75–95
Rat/milk/king/garter snakes 68–95
Desert tortoises 65–105
Painted turtles 55–95
Box turtles 65–90
Anoles 70–90
Chameleons 55–75
Green iguanas 75–105

Gastrointestinal Tract

The hyoid apparatus is very well developed in most reptiles. In snakes, it usually extends to the tenth cervical vertebra, allowing the tongue to be extremely mobile. This enables the snake to breathe directly through its glottis even while swallowing prey. In chameleons, the hyoid apparatus extends the full length of the abdomen to the cloaca. This structure allows their long, well-developed tongues the motility and strength necessary to catch flying insects.

Snakes possess an open mandibular symphysis and flexible rami that allow them to swallow large, intact prey. These features also make iatrogenic injury to the mandibles common, especially while performing an oral examination.

Snakes typically have four rows of teeth in their upper jaw. The teeth of snakes and lizards are fragile and curved caudally to aid in pulling food into the mouth. Be careful not to catch materials on teeth. If items such as swabs or gauze become caught, push caudally to disentangle the fibers before pulling out, or the teeth may break. Broken teeth cause oral pain and anorexia until a new tooth emerges.

Chelonians do not have teeth but rather a horny beak made of keratin similar to that of birds. Treatment of beak problems is similar to beak repair in birds.

The esophagus is lined liberally with mucous glands. Although the musculature surrounding the esophagus is extremely strong in snakes to move whole prey caudally, the esophagus itself is thin and tears easily.

In many species of turtles, the esophagus makes a 90 degree turn before entering the stomach. Place medications administered by stomach tube in the distal esophagus. Use small volumes to prevent regurgitation. Also, in chelonians, the pancreatic and bile ducts enter the pylorus instead of the duodenum.

When present, the gallbladder usually is found near the liver in lizards and chelonians but is located caudal to the stomach in snakes. This is an important difference to recognize when performing surgery or diagnostics in this region.

The reptilian pancreas, although sometimes structurally different than in the mammal, is functionally similar. The pancreas usually is located between the ascending and descending portion of the duodenum in chelonians and lizards. In snakes, the pancreas is located caudal to the pylorus in the region of the gallbladder and spleen. In some snakes, the pancreas and spleen are fused.

The cecum is rudimentary in carnivorous reptiles such as snakes, crocodilians, and monitors. The cecum is present in chelonians and herbivorous lizards and functions in post-gastric fermentation in these species.

The cloaca is a common collecting chamber for wastes from the colon and ureters and for the reproductive tract. The cloaca also receives urine from the bladder in species that possess a bladder. It is important to note that unlike mammals, in reptiles, the ureters empty into the cloaca and not the bladder. In males, the hemipenes or phallus everts from the caudal aspect of the cloaca. In some aquatic species, oxygen can be exchanged across the cloaca. Obstruction of the cloaca affects all of the aforementioned systems and is therefore much more detrimental than mere constipation affecting the GI system in mammals.

Respiratory System

All reptiles possess a cleft palate (choana) that is necessary for nasal breathing. In contrast to birds, which have a single central cleft, reptiles have paired paramedian clefts. These clefts allow passage of air from the nares into the oral cavity and trachea.

Most reptiles lack a diaphragm, and breathing is accomplished by expansion of the chest wall by intercostal muscles (except turtles), pectoral limb movement (except snakes), and smooth muscle contraction in the lung. Crocodilians also use movement of the liver to create negative pressure. Chelonians use movement of front limbs and visceral organs instead of excursion of the chest wall, which is impossible because of their rigid shell. A minimal amount of oxygen can be extracted from water through the skin in certain species of all reptilian orders. Some aquatic turtles can exchange dissolved oxygen across their pharynx and cloaca while submerged, although these sources only provide maintenance levels of oxygen.


Reptiles (except for crocodilians) have a three-chambered heart with two atria and one common ventricle. Deoxygenated blood from the body empties into the right atrium via the sinus venosus. The left atrium receives oxygenated blood from the lungs. In non-crocodilians, both atria open on the left side of the ventricle. Blood from the right atrium tends to stay on the right side of the ventricle and enter the pulmonary artery. Reptiles have two aortic outflow tracts, the right and the left aortas, which combine caudal to the heart into a common aorta. The left aortic arch comes from the right side of the ventricle, carrying less-oxygenated blood. The right aortic arch comes from the left side of the ventricle, which has richly oxygenated blood. The right aortic arch supplies oxygenated blood to the head region before it combines with the left aortic arch.

Renal System

Most aquatic reptiles excrete ammonia, urea, and uric acid as nitrogenous waste products. Urea and ammonia require more water for their excretion compared with uric acid excretion. Terrestrial animals excrete mostly uric acid. However, sea turtles excrete almost exclusively ammonia or urea; semi-aquatic turtles excrete 0% ammonia, 40%–50% urea, and 50%–60% uric acid; and desert tortoises excrete more than 90% uric acid.

Reptiles can only produce isosthenuric urine. The reptilian nephron contains no loop of Henle and therefore lacks the ability to concentrate urine. Water can be resorbed from the bladder or cloacal wall. If renal blood flow is diminished below a critical level (as in dehydration), urates precipitate in the nephron, causing irreversible obstruction.

Reptiles possess a renal portal system that allows blood from tissues caudal to the kidneys to be shunted directly to kidneys. A valve exists at the junction of the abdominal and femoral veins. When the valve is closed, blood is shunted through the iliac vein into the kidney. When the valve is open, blood enters the systemic circulation through the abdominal vein. Blood entering the kidney through the renal portal system is supplied to the tubules and does not enter the glomerulus. Therefore, drugs such as penicillins, which are cleared via tubular secretion, can be removed by the renal portal system, but drugs cleared by the glomerulus (e.g., gentamicin) are not affected.

Not all reptiles have a urinary bladder. The bladder is most highly developed in terrestrial chelonians and some lizards. The bladder acts as a reservoir to store urine and conserve water. Isosthenuric urine from the kidneys is diverted from the cloaca to the bladder, where water is reabsorbed. The concentrated urine then is routed back to the cloaca for excretion. In reptiles without a bladder, diluted urine is moved from the cloaca into the large colon for water absorption. Salts also may be reabsorbed.

Reproductive System

Male Reproductive System

All reproductive organs, including the phallus in most species, are paired. Chelonians and crocodilians are the exception and have a single phallus. The phallus of adult crocodilians is fibrocartilaginous and is therefore palpable in the cloaca. This is a common sex determination technique used in this order. The male copulatory organs of squamates are paired and are composed of highly vascular fibrocartilaginous and elastic connective tissue called hemipenes. Erection occurs secondary to engorgement with blood and contraction of the propulsor muscle, causing eversion of the organ. Hemipenes may be ossified in some monitors and geckoes; sex determination of these individuals can be performed radiographically. Hemipenes frequently have keratin spicules to aid in maintenance of copulation. Only one hemipene is used at a time and it may prolapse if traumatized or following prolonged use.

Seasonal variation in testicular size exists in most species. This is caused by an increase in the number of interstitial androgen-producing Leydig cells during breeding season. Spermatozoa move through the seminiferous tubules and are stored in the epididymis. During breeding, spermatozoa leave via the vas deferens, cloaca, and then hemipene or phallus. The male copulatory organs of reptiles do not contain a urethra and is not involved in the elimination of nitrogenous wastes. Therefore, amputation does not affect urination but does affect breeding ability in animals with non-paired organs.

Sex Determination in Common Pet Reptiles

Special Sense Organs

Reptilian ears have no incus, malleus, or cochlea. In snakes and some lizards, the cavity of the middle ear and the tympanic membrane are vestigial. There is no external auditory opening in snakes. In these species, the stapes articulates directly with the quadrate bone. This mechanism picks up low-frequency sound and vibrations. Some snakes can “hear” vibrations transmitted from the body wall overlying the lungs. Crocodilians have a movable ear flap that is located just behind the eye. They are able to open and close this flap to keep water out of their ears.

The eyes of most reptiles (except snakes) are similar to those of mammals with a few exceptions. Bony scleral ossicles support the globe. The iris and ciliary body are composed of striated muscle and do not respond well to mydriatics. The retina contains a darkly pigmented projection called the conus papillarus, similar to the pecten in birds.

Snake eyes are unique among the animal kingdom and are thought to be the result of redevelopment of once rudimentary eyes. The lens accommodates by moving forward and backward. The eyes are covered by a spectacle that is impervious to topical ophthalmic preparations. The retina does not have a conus papillarus but is covered by a thin mat of vessels called the membrana vasculosa.




The ideal cage liner is paper, such as newspaper. It is non-toxic, inexpensive, and disposable. Change cage papers at least once daily or after feeding or defecation for animals that are fed infrequently. Artificial turf is a good alternative to newspaper. Change the turf as soon as it is soiled. It requires 48 hours to completely clean and dry turf, so make plenty of replacement pieces available. Remove loose strings to prevent foreign bodies. Rabbit or guinea pig pellets or recycled paper bedding may be used as cage substrates for herbivorous reptiles if they are replaced at least two times per week, or more often if moist, to prevent fungal and bacterial growth. Large stone gravel and bark chips also can be used but are less desirable because they can be ingested and harbor bacteria, parasites, and moisture. Thoroughly clean and sanitize or replace substrates at least once a month (can be expensive).

Sand is recommended for desert species only. Other species contaminate sand quickly and are prone to GI sand impactions. Even products commercially marketed as “reptile-safe” such as Calcisand may be ingested and can cause intestinal impactions. Some colors may be more attractive to reptiles to ingest than other colors. Dry sand potentiates low environmental humidity, which is ideal for desert species but causes dehydration in non-desert species. If sand is used for burrowing desert species, it must be changed frequently to prevent buildup of wastes.

Temperature Regulation

Maintain the ambient cage temperature as a gradient incorporating as much of the POT range as possible. One of the easiest methods of accomplishing this is to place a heat source at one end of the enclosure. The heat source should be able to heat the closer end of the cage to the high end of POT and the far end of the cage to the low end of POT. Thermal burns are a common problem. To decrease the possibility of thermal burns if heater malfunctions occur, be certain that the surface temperature at the hottest spot is no hotter than the top range of POT and never higher than 115°F. Heating pads or heating tape designed for use with reptiles are the safest to use. It is safest not to place heating elements within a cage. Instead, place the cage on small blocks to create an airspace (¼ inch to ½ inch) between the outside of the cage floor and heat sources. The air space will even out potential hot spots.

Heat lamps also can be used successfully if care is taken to prevent thermal burns. Radiant heat actually is required by many large herbivorous lizards, such as adult green iguanas. To prevent burns, check the temperature by placing a hand directly under the heat lamp (at the site that the reptile would be basking) for 15 minutes after the lamp has been on for 2 to 3 hours. If it is uncomfortable to leave your hand in one spot, the lamp light is too intense. Also, place a thermometer on the surface to ensure that the POT has not been exceeded. Hot rocks are unreliable and only provide enough heat for small species. Any heat sources placed within the cage need to be shielded to prevent animals from coming in direct contact with them.

Annual and daily temperature fluctuations may be required by some species to maintain health and stimulate breeding.


Never use an under-gravel filter because these may cause anaerobic toxins to accumulate in the gravel. Disturbance of the gravel or an overturn of tank water allows release of these toxins and may kill tank inhabitants. An out-of-tank biologic filter works best. Flush the sand, gravel, or fibers in these systems frequently to remove gross debris. Even these systems often cannot handle both fecal and discarded food loads. Therefore, offer food for limited periods in a separate tank, then return the reptile to its usual enclosure. The feeding tank does not need a filter because the water is changed completely before and after each feeding session and/or group of animals. Disinfect the tank and allow it to dry after feeding to prevent waste buildup and transmission of disease.

Overpopulation exacerbates water quality problems. A rule of thumb is 1 gallon of water per square inch of turtle carapace.

All aquatic reptiles except sea snakes and sea turtles need adequate basking space. Most “water” turtles drown because of exhaustion if not allowed to rest out of the water. In group tanks, this is often the cause of unexplained deaths of smaller animals. These losses can be eliminated by adding several basking areas, which allows the smaller reptiles to rest even when dominant individuals are defending their territories. Basking also is needed to allow drying of the skin and shell. An increased incidence of skin disease also is seen in reptiles not allowed to bask under ultraviolet (UV) light.

Maintaining appropriate water temperature is very important. A reliable waterproof heater is essential. Electric shock from non-waterproof heaters kills not only animals in the tank but also human caretakers. In addition, malfunctions resulting in overheating or failure to heat a tank may kill aquatic animals. In small tanks, an aquarium heater with an in-water thermostat works well. Heaters with thermostats above the surface may under- or overheat the water because the thermostat measures the air temperature and not the water temperature.

Take care to ensure tank inhabitants will not burn themselves if they decide to wrap around the heater. This is accomplished most easily by screening the heater. Water temperature in larger enclosures can be maintained by keeping the room temperature at the lower end of the POT range and using infrared lights or heaters at one end to maintain a gradient. Temperature gradients over the basking areas are controlled as in terrestrial cages.



Providing a complete and balanced diet is accomplished more readily in carnivorous reptiles compared with herbivorous or omnivorous ones. Most wild carnivorous reptiles eat whole animals (usually rodents or small birds), which are easily supplied in captivity. When they are fed whole prey, few nutritional deficiencies or excesses occur in this group of reptiles. Severe nutritional disease is seen in animals mistakenly fed only animal parts (e.g., all muscle, liver, etc.).

Some carnivores eat only amphibians or small reptiles of various genera. Freezing to prevent disease transmission is extremely important in these species as well. Some amphibian eaters can be trained to eat mice by placing a mouse inside a fresh frog skin or smearing a mouse with frog slime. Be careful not to attempt to feed amphibians, which produce toxic skin secretions.

Some snakes and monitors eat mostly eggs. Ideally, these eggs should be fertilized and contain embryos at different stages of development. Reptiles fed only unfertilized hen eggs suffer many nutritional deficiencies.

Some reptiles only eat crustaceans, gastropods, worms, or other specialized diets. Special attention needs to be paid to the natural history of reptiles needing specialized diets. If the suitable prey items cannot be obtained year-round, do not keep the animal in captivity.


Adult herbivores, such as green iguanas, should receive 90% to 98% of their calories from plants. Ninety percent of the plant diet should consist of a mixture of dark leafy greens, with 10% mixed vegetables and fruits. Many adult herbivorous tortoises require high-fiber diets, such as high-quality grass hay or fresh grass. Omnivores or young herbivores should receive 70% to 95% of their calories from plants. Most herbivores and all omnivores require the addition of some protein to their diets. Good sources of protein are crushed hard-boiled egg (with shell), prepared reptile diets from reputable companies, trout chow, pinkie mice, alfalfa pellets, or tofu. Dog food or monkey chow should not be fed. These foods contain excessive amounts of vitamin D and may cause metastatic calcification of soft tissues and renal failure when fed extensively. Although some experts believe that feeding any animal protein to herbivores may cause renal disease, we have found that renal disease is related to the quantity rather than the source of protein. To avoid over feeding, be aware that the concentration of nutrients and calories in animal-based food is usually at least an order of magnitude greater than in the same volume of vegetable matter.


Lizards and Crocodilians

Restrain small lizards and crocodilians by using the thumb and forefinger to grasp the caudal mandibular area. Cradle the dorsal body in the palm of the same hand. Control the abdomen, chest, and pelvis with the remaining fingers, thus allowing for respiration (Fig. 178-2).

Grasp medium-sized lizards and crocodilians over the dorsal surface of the head and neck with one hand, and grab the base of the tail and pelvis with the other hand (Fig. 178-3). Wrap the reptile securely in a towel to prevent the back legs from scratching. If necessary, restrain the back legs by taping them to the tail. To capture mildly aggressive animals, use a towel as a blind to hide the restrainer’s hand from view. If an aggressive animal is brought in a sack, use the sack as a blind and grasp the head through the sack. Peel the sack away from the body without losing control of the head. A snare or snake hook can be used to pin the head if the animal is extremely aggressive. Care must be taken to use just enough pressure to prevent escape but not enough to cause trauma. Large lizards and crocodilians can inflict serious bites and often use their powerful tails as whips. Tape the snout of aggressive crocodilians shut with duct tape. The masseter muscles are extremely strong; the digastricus muscle, which opens the jaw, is very weak.

Stroking the ventral midline or pushing on the eyes of some lizards induces vasovagal response and a short trance-like state.

Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Basic Husbandry and Medicine of Pet Reptiles
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