CHAPTER 58. Reptiles
Patricia A. Schenck
GENERAL INFORMATION
Captive-born animals are often healthier and hardier than are wild-caught reptiles, especially those that have been imported from other countries.
ANATOMY AND PHYSIOLOGY
I. Body temperature
A. Reptiles have limited ability to control their body temperature. They need to maintain their body temperature above ambient temperatures for part of the day. This is accomplished by absorbing radiant heat, burrowing into warm soil, or by laying on objects warmed by the sun
B. Reptiles must be able to cool themselves to avoid overheating
C. Chilled animals are at higher risk for disease, and may go into a state of torpor
D. The environment for a reptile should contain areas of temperature at low and high ends of the preferred optimum temperature (POT) range
E. Tropical animals do not tolerate large fluctuations in temperature; desert animals are much more tolerant
II. Skin
A. The shell in turtles incorporates the sternum, vertebrae, ribs, and pelvis. It is metabolically active
B. The speculum is the epithelial covering over the eye that should shed with the skin
C. Salt glands are on the tongue or in the nose. These glands allow conservation of water by excreting excess salt. Salt is cleared by burrowing or sneezing
III. Gastrointestinal (GI) tract
A. The developed hyoid apparatus allows for tongue motility. Do not put pressure on the ventral neck region while restraining
B. The mouth should never be forced open as the teeth are fragile, and injuries to the mandibles are common
C. The esophagus contains many mucous glands but is easily torn. Use liberal lubrication if performing stomach intubation
D. The cloaca is a common chamber for the colon, ureters, and reproductive tract. Ureters empty directly into the cloaca and not the urinary bladder. Obstruction of the cloaca can affect the GI system and the genitourinary systems
IV. Respiratory system
A. Reptiles have paired paramedian clefts in the palate which is essential for breathing
B. Most reptiles do not have a diaphragm
C. Tracheal rings are complete in chelonians and crocodilians, and non-cuffed endotracheal tubes should be used
D. In most snakes, the right lung is larger than the left
V. Cardiovascular system
A. A three-chambered heart (two atria and one ventricle) is present in most reptiles except crocodilians
B. In lizards and snakes, a large central ventral vein is present on the ventral midline. This vein should be avoided and should not be used for venipuncture
VI. Renal system
A. Aquatic reptiles excrete ammonia, urea, and uric acid. Terrestrial reptiles excrete uric acid
B. Reptiles do not have a loop of Henle and therefore can only produce isosthenuric urine. If dehydrated, urates can precipitate in the nephron causing obstruction
C. The renal portal system shunts blood from caudal tissues directly to the kidneys. Therefore, do not administer drugs that can be cleared by renal tubules in the caudal half of the body
D. A urinary bladder is not present in all reptiles
VII. Reproductive system
A. All reproductive organs, including the phallus, are paired (except in chelonians and crocodilians, which have a single phallus). The copulatory organs of reptiles do not contain the urethra
B. In females, pits in the oviduct can store sperm for up to 6 years
C. Sex determination
1. Male snakes have longer, thicker tails to accommodate the hemipenes. Commercially available probes can also be used to probe the cloaca
2. In tortoises, females have a flat plastron with a notched caudal region, which allows eggs to pass. Males have a concave plastron to balance on the female and also have long tails
3. Male water turtles do not have concave plastrons, which makes sex determination more difficult
VIII. Other systems
A. Snake eyes are unique and are covered by a spectacle that topical ophthalmic preparations cannot penetrate
B. There is no external ear opening in snakes
C. Nasolacrimal ducts connect the eye to oral cavity, and mouth infections can often result in eye infection
D. The thyroid gland is at the base of the heart
E. Reptiles have lymphoid aggregates but not discrete lymph nodes
HUSBANDRY
I. Caging
A. Terrestrial reptiles
1. Caging should be nonabrasive, escape proof, easy to clean, and of adequate size. Snakes should be able to stretch out to two thirds of their length. Lizards should have at least 6 square inches of cage per inch of body size
2. Provide cage furniture to stimulate activity, and provide places to hide
3. Use paper or artificial turf for cage lining. Avoid kitty litter, gravel, or corncobs. Only use sand for desert species
4. Keep humidity low for most species
5. Maintain a temperature gradient over the POT range
B. Aquatic reptiles
1. A filter system or frequent water changes are necessary
2. Do not use an under-gravel water filter because toxins accumulate in the gravel
3. Most need adequate basking space outside of the water
4. Maintain appropriate water temperature
C. Ultraviolet (UV) light is needed by herbivorous and insectivorous reptiles to synthesize vitamin D and should be provided for 8 to 10 hours per day
D. Provide 10 to 14 hours of light and dark daily
E. Sanitation is very important. Phenol-based cleaners such as Lysol can be toxic. Diluted bleach is safe and inexpensive. Discard porous cage items when they become soiled
F. Do not mix species in the same enclosure
G. Quarantine all new additions for at least 90 days
II. Nutrition
A. Change water every 24 hours
B. Carnivorous animals are fed whole prey, which minimizes nutritional problems. Feed freshly killed or thawed prey. Live prey can cause injury to reptiles. Freezing of prey for at least 30 days minimizes transmission of parasites
C. Insectivores are typically fed crickets, mealworms, and inchworms. The insects should be fed an excellent diet to increase their nutritional value. Do not feed fireflies because they may be toxic
D. Herbivores should get more than 90% of calories from plant material. Some protein should be added to the diet, but dog food, cat food, or monkey chow should not be fed because they contain high quantities of vitamin D. Avoid calcium supplements that contain phosphorus and vitamin D
EXAMINATION AND TECHNIQUES
I. Restraint
A. Snakes. Pick up snakes mid body. Do not pick up at the head because spinal damage can result
B. Lizards and crocodilians
1. Restrain small lizards by grasping the caudal mandibular area
2. Wrap the back legs in a towel to prevent scratching
3. Tape the snout of crocodilians with duct tape
C. Chelonians
1. Hold by the dorsal caudal portion of the shell, which minimizes the ability of the animal to turn around and bite
2. Always handle over a table because dropping can cause shell fractures
II. Physical examination: History is extremely important because improper husbandry is the cause of many diseases. Observe the animal’s behavior before handling
A. Oral examination
1. In snakes and lizards, open the mouth carefully because the teeth are fragile. The jaws of snakes are easily fractured
2. In turtles, restrain the head from the sides behind the mandibles. Avoid pressure on the ventral surface of the neck
B. Venipuncture
1. In lizards, snakes, and chelonians, use the tail vein
2. In boas and pythons, blood can be collected from the buccal veins inside the mouth
3. Collect blood from the jugular vein if possible in chelonians. The tail vein can also be used
C. Injections (Figure 58-1)
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| Figure 58-1 Common injection sites in a snake (top), lizard (center), and turtle (bottom). (From Birchard SJ, Sherding RG. Saunders Manual of Small Animal Practice, 3rd ed. St Louis, 2006, Saunders.) |
1. Always give injections cranial to the kidneys
2. Administer subcutaneous (SC) fluids over the axillary region. In turtles, the skin folds around the legs can be used
3. In snakes, give intramuscular injections in the epaxial muscles; otherwise, use the front leg muscles
4. Intraosseous injections can be given because veins are not readily accessible
5. Intracoelomic injections can be given if no other route is possible. Do not use this route of administration in gravid females
D. Radiography
1. GI transit times are longer in reptiles than in mammals
2. Short exposure times are necessary
3. Ultrasound is very useful
III. Anesthesia
A. Isoflurane is the inhalation agent of choice for reptiles
C. Hypothermia should not be used as a form of anesthesia
D. Inflatable cuffs are not recommended for endotracheal tubes
E. Meloxicam has been used for analgesia
