CHAPTER 7 SNAKES
Snakes are listed in the class Reptilia and order Squamata. Squamata include the suborders Serpentes (snakes) and Sauria (lizards). There are over 2900 species of snakes in the world. Extant populations of snakes are generally divided into three classes: Scolecophidia, Alethinophidia, and Caenophidia.1
A variety of snake species are kept in captivity. The most common, by far, are the colubrids, boids, and pythons. The colubrids (1658+ species) are the largest and most diverse group of snakes and have a worldwide distribution, except for Antarctica. Both venomous and nonvenomous species are found within this family. Colubrids are found in aquatic, terrestrial, semiterrestrial, and arboreal habitats. The boas (Boidae) (40+ species) are a diverse group of snakes that can be found in fossorial, ground-dwelling, and arboreal niches from the Americas, Central Africa, South Asia, Madagascar, the West Indies, and the southwest Pacific Islands. Pythons (Pythonidae) (25+ species) were historically included in the family Boidae. However, pythons are restricted to the Old World (Africa, Asia, Australia). Pythons, like boas, may inhabit aquatic, terrestrial, and arboreal niches within their range.
The corn snakes (Elaphe guttata) and king snakes (Lampropeltis spp.) are by far the most common snakes kept in captivity. Most corn snakes and king snakes attain a total length of 1 to 2 m (3-6 feet). These animals are known for their relatively calm dispositions, although some king snakes can be aggressive. Corn snakes make good first pet reptiles. Corn snakes and king snakes have been selectively bred over the past decades for their color morphs. A wide variety of color morphs have been developed from the common (e.g., amelanistic) to the uncommon (e.g., lavender) (Figure 7-1). The value of the snake can increase significantly based on its color. This is most evident when evaluating the other common snakes held in captivity, pythons and boids. Designer-colored ball pythons (Python regius) can range in price from the hundreds of dollars to tens of thousands of dollars (Figure 7-2). Pythons are popular not only for their beauty but also for their gentle disposition. There are certainly exceptions to this rule. The giant pythons, such as the Burmese (Python molurus bivittatus) and reticulated pythons (Python reticulatus), become too large for most pet owners and should not be recommended as pets (Figure 7-3). Instead, these animals should be handled only by those experienced herpetoculturists that accept the responsibility and liability that comes with giant snake ownership. Many state and local governments have established regulations banning large snakes. Veterinarians should become familiar with both state and local policies to ensure that they can make the most appropriate recommendations to their clients.
Figure 7-1 Corn snakes (Elaphe guttata) are members of the family colubridae. These snakes are native to North America. Corn snakes represent the first group of captive snakes bred in large numbers to promote “designer” skin patterns. Corn snakes are docile, thereby making an ideal first pet snake.
Figure 7-2 Ball pythons (Python regius) are an African species of python (Pythonidae) that are still routinely imported into the United States. These animals are also being captive bred in large numbers. “Designer” patterns have been developed, which can cost tens of thousands of dollars.
Veterinarians may be asked to work with venomous species of snakes. I recommend leaving these snakes to those with experience. Veterinarians incur a real liability, both personal and professional, when working with these animals. Unfortunately, most situations requiring a veterinarian arise after a problem has occurred rather than before an animal has been acquired. For these reasons, I limit my venomous snake medicine to those animals being housed at zoologic and educational institutions. State and local regulations regarding venomous snakes are also becoming commonplace, and veterinarians working with these animals should become familiar with these policies.
The anatomy of the snake, for the most part, is consistent across species. Therefore, developing a general understanding of organ location in one species will be beneficial in working with others. When evaluating the anatomy of the snake, it may be best to separate the snake into three sections. The proximal one third of the snake generally contains the trachea, esophagus, parathyroid glands, thymus, thyroid, and the heart. The second third contains the lung(s), liver, continuation of the esophagus, stomach, spleen, gallbladder, pancreas, proximal small bowel, and airsac. The final third contains the caudal small intestine, gonads, adrenal glands, kidneys, cecum, colon, and cloaca. This system of thirds may be useful when attempting to identify an area of interest using diagnostic imaging or when deciding on a surgical approach. In some cases, multiple images or incisions may be required to fully ascertain certain organ systems.
Snake skin is relatively inelastic, as a result of the rigid protective scales (beta-keratin). This might be considered a problem for an animal that must swallow its prey whole, but is not as a result of a thin elastic alpha-keratin region. The alpha-keratin includes the interscalar region and is most obvious in snakes during the ingestion of prey or in obese animals as their skin stretches. Snake scales originate from the epidermis. The integument of the snake is covered with two primary scale types, both originating from the epidermis. Small scales cover the dorsum and lateral surfaces of the snake, whereas larger scales cover the ventrum. It is important to make a distinction between the two scale types when considering an exploratory coeliotomy, as an incision in the ventral scales could result in significant tension on the sutures after closure and an increased likelihood of the incision becoming contaminated. I prefer to make the initial incision between the second and third rows (from the ventrum) of dorsal scales (Figure 7-4). Differences in scale shape, size, and texture can be used to differentiate snake species. For example, the presence of keeled versus nonkeeled scales is a basic taxonomic key. The snake’s integument should feel dry and warm (if it is housed under appropriate environmental conditions), which is in direct contrast to the public’s perception that snakes are cold and slimy. Snake skin is dry because it is relatively aglandular, although some reptiles have developed regionalized glands that are useful in attracting mates or in defending themselves against predators.
Figure 7-4 When performing an exploratory coeliotomy, it is important to make the incision between dorsal row scales. In this figure, the incision was made between the second and third rows (from the ventrum) of dorsal scales.
Ecdysis (shedding) is a naturally occurring process in the snake that is regulated by the thyroid gland. Snakes should shed their entire skin, including their spectacles, in one piece, although large snakes (>3 m) may shed their skin in pieces. Once the process of ecdysis is started, it generally takes approximately 14 days to complete. During this period it is not uncommon for a snake to become anorectic, appear listless, and avoid contact. Immediately before ecdysis, some snakes have increased respiratory sounds. This is generally associated with reduced airflow through the nares, resulting from a constriction of the shed surrounding the nares. A small-gauge hypodermic needle (25-gauge) can be used to remove any obstructive material. Excessive handling during the ecdysis period is not recommended, as it is possible to damage the newly formed underlying epidermis. Approximately 14 days before the shed, the snake will have a dull (grayish) appearance. The spectacles take on a “blue” color 7 to 10 days before the shed and then clear 2 to 3 days later. The dull color is associated with the lymphatics and enzymes that fill the space between the old and new epidermal layers. Captive snakes should be provided appropriate cage furniture (e.g., rock) to rub their rostrum against to facilitate the shedding process.
Snakes do not have eyelids. To compensate, snakes produce spectacles (also called brilles). Spectacles are a modification of the epidermis and provide protection for the exposed anterior surface of the globe. Because they originate from the epidermis, the spectacles are routinely shed during ecdysis. Retention of the spectacles has been associated with the development of corneal disease and panophthalmitis.
The skeletal system of snakes is unique among the reptiles. The skull of the snake is kinetic and does not have a mandibular symphysis, which allows it to ingest prey items larger than would be possible by a reptile with a fixed skull. The vertebral column is comprised of several hundred vertebrae that show minimal regionalization. Snakes do not have a sternum. The ventral aspect of each rib is attached by muscle to the ventral scales. Pelvic remnants are present in all of the Scolecophidians, but hindlimb vestiges are absent. Most Alethinophidians have both pelvic remnants and hindlimb vestiges. The vestiges or spurs can be used during copulation.
Snakes do not have an external ear, tympanic membrane, or middle ear. The stapes (inner ear cavity) is in direct contact with the quadrate bone and transmits vibrations, enabling the snake to hear low-frequency sounds (<600Hz).
The glottis of the snake is located on the floor of the buccal cavity. Snakes do not have vocal cords but instead make their characteristic “hissing” sound by forcing air through their glottis. The trachea of the snake has incomplete tracheal rings. Because these animals have a poorly developed mucociliary apparatus, they can have difficulty removing material from the trachea and lungs. To compensate, snakes position their head and neck in a manner that best allows unabated airflow. Snakes with respiratory disease are often found with their head and neck elevated in a 45-degree angle. Primitive snakes generally have two lungs, whereas more advanced snakes possess only one lung. The right lung is the primary lung in those species with two lungs. In general, the left lung is reduced or vestigial. Gas exchange occurs in the cranial compartment of the lung, and the caudal segment (air sac) serves to store air.
The snake heart is comprised of three chambers: two atria and one ventricle. The heart is located in the proximal one third to one fourth of the body. The heart is fairly movable in snakes, which allows for compression and displacement during the ingestion of prey. The heart is routinely used as a site of venipuncture and can be visualized by placing the animal in dorsal recumbency and looking in the approximate vicinity of the body (one third to one fourth the distance to the head) for the characteristic “beating” movement.
The digestive tract of the snake is a linear system that is modified to digest dense meals. The tongue is an important chemosensory structure. The tongue is inserted into the Jacobson organ, located in the roof of the buccal cavity, to differentiate odors. Because snakes hunt by olfaction, they can be trained to readily accept prekilled prey items. Snake teeth are homodontic, with the exception of the fangs in venomous species. The teeth of snakes have developed with the sole purpose of acquiring prey. Their general shape, being curved backward, is based on their need to apprehend and hold prey in the absence of limbs. To remove a snake that has bitten someone, it is important to consider the direction of the teeth, as pulling the animal directly from the site where it is attached will tear the skin and worsen the bite wound. Instead, the animal’s head should be gently directed forward as it is being removed. Of course this is easier said than done in some cases. Snake teeth also are pleurodontic, and are therefore replaced throughout the animal’s life. Of all the reptiles, snakes by far have the most teeth, with rows on the upper and lower jaws and palatine bone. Mucus excreted from the digestive glands located in the buccal cavity and esophagus lubricate prey items to facilitate ingestion. Venom glands are modified salivary glands that produce potent enzymatic compounds to assist with prey acquisition and digestion. The esophagus is a large distensible organ in the snake. The stomach is linear and produces digestive enzymes. The stomach is located approximately half the body distance from the head. The small intestine and colon are also linear structures, losing much of the coiling frequently observed in omnivores and herbivores. The cloaca is comprised of the coprodeum, urodeum, and proctodeum. The coprodeum is located in the dorsal region of the cloaca and receives fecal material from the colon. The urodeum is located ventrally and serves as the collection site for urine from the ureters. The oviducts also open into the urodeum. The proctodeum is the collecting chamber for the urodeum and coprodeum.
The snake’s liver is a linear (single-lobed) organ. The liver generally begins just distal to the heart and ends at the cranial segment of the stomach. In most species the gallbladder is not directly associated with the liver. The pancreas, spleen, and gallbladder often form a triad and are located at the caudal segment of the stomach, whereas other species have a combined hepatopancreas.
Snake gonads are found cranial to the kidneys, and the right gonad is cranial to the left gonad. Male snakes do not have an epididymis. Male snakes possess paired copulatory organs called the hemipenes. The hemipenes are invaginated and lie in the lateral base of the tail. During copulation, a hemipenis will engorge and evaginate. All fertilization is internal. The hemipenes do not serve an excretory function.
Female snakes may be oviparous or viviparous. Snakes from the families Anomalepodae, Typhopidae, Leptotyphlopidae, Anomochilidae, Xenopeltidae, Loxocemidae, Pythonidae are oviparous; those from Uropeltidae, Cylindrophiidae, Aniliidae, and Boidae are viviparous; and snakes from the families Tropidophiidae, Acrochordidae, Viperidae, Atractaspididae, Colubridae, and Elapidae have members that are both oviparous and viviparous.
Some pythons display maternal care of their eggs. The maternal investment reduces the likelihood of predation and increases the likelihood that the eggs will hatch. The coiling also serves to regulate egg temperature.
Snakes have metanephric kidneys that are linear and lobulated. The right kidney is cranial to the left kidney. Male snakes develop sexual segments during their reproductive cycle. Snakes do not have a urinary bladder.
The shape and size of the enclosure should be selected based on the snake’s biology. For example, a fossorial species should be housed in an enclosure that is long and wide. The height of the enclosure would not be terribly important for a fossorial species. In contrast, an arboreal species should be housed in a tall enclosure to ensure that ample foliage can be placed into the enclosure. Because obesity is a common problem in large captive snakes, snakes should be provided ample area with an enclosure for physical activity. The enclosure should also be large enough to provide an appropriate environmental temperature range.
Snake enclosures can be made from a variety of materials. The most common remains the glass fish tank. These enclosures are relatively inexpensive, are easy to clean, and provide direct visualization of the pet. Plastic storage boxes are another common commercial product used to house snakes (Figure 7-5). These enclosures are also inexpensive, easy to clean, and readily available. Many of these enclosures are not clear, so direct visualization may be limited. Commercial snake enclosures have become quite popular (Figure 7-6). These enclosures are aesthetically pleasing and easy to clean. One disadvantage of commercial enclosures is that they are more expensive than traditional enclosures.
Figure 7-5 Plastic storage boxes are a common method used to store large numbers of snakes. Because of the limited size of these enclosures, developing an appropriate temperature range for the animal can be difficult. In most cases, it is easiest to set the room temperature to the desired level to accommodate the snakes.
Venomous snakes should be housed in enclosures that have restricted access to nonessential individuals. The enclosures should have two locking mechanisms, in case one locking mechanism fails. The enclosure should be designed so that the snake can be visualized from the outside of the enclosure. There should always be at least two people involved with the handling of a venomous snake. Appropriate tongs, hooks, and collection tubes should be available for handling venomous snakes. Large, easy-to-read VENOMOUS SNAKE signs should be placed on the external walls of the enclosure. An emergency phone should be placed in the vicinity of the venomous snake enclosures with contact numbers for the local zoo, paramedics, and hospital. An antivenom protocol should be on hand at the local hospital.
Snakes are ectotherms and depend on the environmental temperature to regulate their core body temperature. If these animals are not provided an appropriate temperature range, their metabolic rate slows. Snakes with slow metabolic rates often have a history of being anorectic, lethargic, and depressed. An inability to maintain an appropriate body temperature can also result in a reduced immune response. In my experience, many of the snakes with chronic infections are not provided exposure to an appropriate environmental temperature. To prevent these problems, snakes should be provided an environmental temperature range. The environmental temperature should mimic the animal’s natural climate and should be separated into different gradients. It is important to realize that reptiles have temperature options in nature. They can bask under the sun on a rock if they wish or hide in the shade away from the heat to prevent overheating. This same system should be mimicked in captivity. I recommend that clients use variable wattage incandescent light to create a temperature gradient. Bulb wattage will depend on the size of the enclosure. A list of recommended environmental temperature zones for captive snakes can be found in Table 7-1. It is important to provide snakes a cooling period at night. For most of the temperate species, room temperature is acceptable, whereas for some tropical species, additional heat may be required. Visible light (e.g., incandescent bulbs) should not be used at night to provide heat. It is important that animals are provided a period of darkness. I generally recommend a photoperiod of 12 hours per day. This can be altered during the breeding cycle (lengthened) or aestivation period (shortened). When supplemental heat is required during periods of darkness, ceramic heat emitters or under-tank heating elements can be used.
|Species||Daytime temperature range||Nighttime temperature range|
|Corn snake||76–86° F (24–30° C)||70–75° F (21–24° C)|
|California kingsnake||78–88° F (25–30° C)||70–78° F (21–25° C)|
|Ball python||80–88° F (26–31° C)||75–80° F (24–26° C)|
|Boa constrictor||80–88° F (26–31° C)||75–80° F (24–26° C)|
|Burmese python||80–88° F (26–31° C)||75–80° F (24–26° C)|
|Brazilian rainbow||78–88° F (25–31° C)||75–80° F (24–26° C)|
|Emerald tree boa||80–88° F (26–31° C)||75–80° F (24–26° C)|
|Milk snake||76–86° F (24–30° C)||70–75° F (21–24° C)|
Regardless of the heat source, snakes should not be allowed direct contact with the heating element. Animals that are allowed direct contact can develop severe thermal injuries (first to third degree). Thermal injuries should be managed aggressively. Necrotic tissue should be sharply dissected and the wound protected. I apply a hyperosmotic solution (50% dextrose) onto the wound as a microbicide. The hyperosmotic is left on the wound for 2 minutes and than rinsed away with a 0.9% saline. The fluids are always warmed (to the animal’s preferred optimum) before being applied. The application of cooled or room temperature fluids can lead to a lowering of the body temperature and a reduced healing time. The hyperosmotic is applied twice daily until sufficient granulation tissue appears. The wound must be protected against desiccation. Silver sulfadiazine can be applied to the lesion to prevent desiccation and provide an antimicrobial effect. This compound is comprised of both a microbicide (silver) and an antibiotic (sulfadiazine). Bandaging these wounds can be difficult. Frye2 has suggested using condoms, but even these can fail. I have used Tegaderm (3M, Inc., St. Paul, Minnesota) with some success. These wounds can require weeks to months to heal. Snakes with severe thermal burns should be provided fluids to replenish any losses incurred either directly as a re-sult of the injury or after the injury until the integument heals. Systemic antibiotics also should be considered in the treatment plan.
Humidity is an important environmental factor to monitor for snakes. The enclosure humidity should mimic the animal’s natural climate. In general, desert species tolerate humidity levels between 30% and 50%, subtropical species from 60% to 80%, and tropical species from 80% to 90%. Snakes maintained in environments with low humidity may be predisposed to dehydration and dysecdysis. Excessive humidity is frequently associated with the development of dermatitis. Humidity levels can be monitored using a hygrometer. Digital hygrometers are preferred because they can be moved around within an enclosure to determine areas that are appropriate and inappropriate. Humidity levels can be altered in an enclosure by adding a large water bowl, aerating water within a water receptacle (e.g., bowl or mason jar), adding an incubation chamber, misting the enclosure daily, or adding live plants. Large water bowls serve as a source of humidity for an enclosure as the water evaporates into the enclosure. The overall contribution of moisture to the humidity can vary based on the environmental temperature and size of the enclosure. Daily misting is a simple method for elevating the humidity, but it may provide only a temporary increase in the humidity. Incubation chambers are an excellent method for providing snakes an increased environmental humidity. I generally place moist sphagnum moss into a plastic shoe box (with ventilation holes) to create an incubation chamber. Because most snakes naturally burrow, the incubation chamber can also provide a shelter or hiding spot. Live plants can provide an improved aesthetic appearance within an enclosure, but larger snakes may damage them.
Historically, lighting systems for captive snakes have not been given a great deal of attention. Many snake breeders maintain their snakes in stacks of enclosures, where the animals only receive indirect room lighting. Although many of these animals thrive and reproduce successfully, it is my belief that snakes, like other reptiles, should be provided high-quality, full-spectrum light. Full-spectrum light has many benefits, from the provision of ultraviolet radiation to rich, visible light. Recent work by my laboratory has found that certain snakes increase their 25 hydroxyvitamin D blood levels with exposure to ultraviolet B radiation (Figure 7-7). It is not known whether snakes require ultraviolet B radiation to initiate the synthesis of vitamin D. Many believe that these animals obtain their vitamin D through the ingestion of prey. Regardless, ultraviolet A and visible light remain important to snakes for regulating behavior and stimulating reproduction. I recommend providing captive snakes full-spectrum lighting to mimic the beneficial effects of sunlight. Snakes should be provided a 12-hour photoperiod. The photoperiod can be altered for the breeding season (lengthened) or brumation period (shortened). Research to elucidate the specific lighting needs of snakes should be pursued.
Selecting an appropriate substrate for a snake is an important consideration, as these animals, especially terrestrial species, live directly on/in their substrate. When considering which substrate is best for a particular species, it is important to attempt to replicate its natural habitat. Animals that are fossorial should be provided a substrate that will allow them to burrow, while those that are arboreal need plant accessories more than a substrate. The following is a list of common substrates: newspaper, paper towels, gravel, bark chips, aspen, and sand. Snake breeders commonly use newspaper and paper towels because they are inexpensive and can be easily replaced. These substrates do not, however, allow a pet owner to regulate certain aspects of the vivarium, such as humidity. Another benefit of these substrates is that they allow a veterinarian or herpetoculturist to monitor fecal and urine output. This is especially important for recently acquired animals. Although there is an old belief that the ink found on newspaper is potentially toxic to animals, this belief is unfounded. Gravel used for aquaria can be used for snakes, but it must be large enough that it cannot be consumed. Snakes are notorious for ingesting substrate when swallowing their prey. Orchid bark chips can be used as a substrate for those species naturally found in forested areas. For burrowing species, the depth of the bark chips should be sufficient to allow the snakes to cover themselves. Natural leaf litter can also be used, but it should be thoroughly inspected for the presence of pest bugs before being placed into the vivarium. Aspen is one of the most common substrates used for captive snakes. When snakes defecate or urinate in aspen, the aspen absorbs and holds the waste, which allows the caretaker to scoop out the material using a cat litter scoop. Sand can also be used as a substrate for snakes; however, only “play sand” (e.g., the type used for children’s sandboxes) should be used. Quartz-based sands used in aquaria are not recommended, as they are sharp-edged particulates and can become impacted in the skin or cause lacerations.
A snake vivarium should mimic an animal’s natural habitat. Accessories or “cage furniture” can be used to create an environment that reduces the stress an animal may otherwise encounter in captivity. It is important to always attempt to minimize stress, as it can lead to elevated corticosterone levels that affect the animal’s metabolic rate and immune function. Terrestrial animals should be provided an appropriate substrate and an adequate number of hiding locations or shelters. Snakes are naturally found hiding in detritus or under rocks or fallen wood. Providing these animals a similar hiding location is highly recommended. There are a number of commercially available products that can be used to meet these needs, or a pet owner can simply find a piece of fallen wood. Again, any materials found outside should be inspected for pest bugs.
Arboreal species should be provided adequate climbing areas. Not having an opportunity to climb vertically can be just as stressful to these species as not having a hiding spot. Various materials can be used to meet these requirements. Commercially available wood branches (e.g., manzanita and driftwood) can be purchased from local pet retailers. The branches should be large enough to support the animal’s weight. Branches found locally can also be used but should be free of pest bugs and insecticides.
Plants can be used to provide additional hiding areas for arboreal snakes. Plastic plants are often used because they are easy to disinfect and can withstand being climbed on. Hardy live plants can also be used. I prefer pothos (Epipremnum aureum) because it is inexpensive and capable of taking a great deal of neglect. Another benefit associated with live plants is that they can help to regulate or maintain the vivarium humidity. Plants also may be used for terrestrial species, but they should be well planted to avoid being destroyed.
Humidity chambers are important accessories for some snakes. These devices can be used to provide a focal area of high humidity, mimicking a burrow. In addition to their importance for providing increased humidity, they also serve as hiding spots. A plastic container (e.g., plastic shoe box) with a secure lid can be used to create a humidity chamber. Several small ventilation holes should be made in the sides of box, and a single large entrance/exit hole can be made on one end of the chamber. I generally prefer to use moistened sphagnum moss to create the humidity chamber. To moisten the moss, the material should be washed with tap water and then wrung out. The moss should be remoistened as needed. A hygrometer can be used to determine the humidity within the chamber and to determine when it should be rewashed. The moss should be replaced once it is soiled.
Snakes should be provided access to water at all times. A water bowl large enough for the animal to enter should be placed in the vivarium. Snakes routinely soak when provided access to water. Soaking is thought to increase gastrointestinal motility, assist with the removal of ectoparasites (e.g., drown mites), and serve as a stimulus to drink. The water should be changed whenever it is soiled or at least once weekly.
Snakes are carnivorous. The dietary habits of snakes are quite diverse, and prey selection depends on their specific anatomic adaptions. Blind snakes, false blind snakes, shieldtail snakes, and thread snakes prey on soft-bodied invertebrates in fossorial habitats. Many of these snakes are specialists that feed almost exclusively on termites. Although these snakes generally remain in subterranean habitats, they will move into arboreal (tree trunk) habitats to pursue termites. Pipe snakes and false coral snakes primarily feed on other species of snakes, although false blind snakes will also prey on amphisbaenians. Sunbeam snakes, Mesoamerican pythons, boids, and pythons generally will prey on reptiles and mammals. However, Mesoamerican pythons will prey also on lizard and chelonian eggs, and arboreal species from these groups will frequently prey on avian species. Splitjaw boas and dwarf boas prey primarily on lizards. Wart snakes are adapted to aquatic systems and prey almost exclusively on fish. Vipers, pitvipers, colubrids, and elapids prey on a wide variety of vertebrates, including fish, reptiles, amphibians, birds, and mammals, depending on their range and prey availability.
Because the gastrointestinal tract of the snake is relatively short, it is important that these animals, in captivity, are provided high-quality diets. The diet for each snake should be selected based on the animal’s normal feeding strategy. Arboreal snakes tend to prefer avian and mammalian prey items. Terrestrial species will consume a variety of vertebrate prey (e.g., amphibians, reptiles, birds, and mammals), although some are highly selective (e.g., ophiophagous species eat primarily other snakes). Aquatic species generally accept fish and amphibians, although they can be trained to accept mammalian prey too. Diversity in the diet is essential. Avoid feeding obese prey items. Always recommend feeding euthanized prey to snakes. Live prey items can cause life-threatening injuries if left unattended with the snake. Because snakes use olfaction to hunt, they can be readily trained to accept euthanized prey. Prey items should be humanely euthanized. Carbon dioxide or cervical dislocation may be used to effectively euthanize prey. Feeding frequency should be based on the caloric needs of the snake. I recommend waiting for the animal to defecate its previous meal before offering another meal. This will help reduce the likelihood of problems should gastrointestinal stasis occur. Based on this rule, juvenile snakes can be offered food every 2 to 7 days, whereas adult animals can be offered food every 7 to 21 days.
The concept of quarantine is rather foreign to most herpetoculturists and veterinarians. Although they understand its value, it is often difficult to enforce. I recommend the following: All snakes should be quarantined for a minimum of 2 months before being introduced into a reptile collection. However, it is important to realize that even a 2-month quar antine may be insufficient time to detect certain viral, parasitic or bacterial diseases in which a snake is a latent carrier. A thorough physical examination and appropriate diagnostic screening assays should be performed before the snake is placed into quarantine and before removing the animal from quarantine. A complete blood count may be done to evaluate the animal’s white blood cell status. An inflammatory leukogram may be indicative of an infectious disease. Serologic testing for snakes is limited to paramyxovirus. This is certainly a virus that a herpetoculturist would not want to introduce to a collection.
Snakes should be examined by a veterinarian on at least an annual basis. Because these animals have evolved to mask their illness, a thorough examination by a veterinarian may be the only time a potential problem is identified. A complete blood count and plasma biochemistry analysis should be done at the same time to evaluate the physiologic status of the animal. When working with large snake collections, veterinarians may consider visiting a herpetoculturist at his or her own facility.
Veterinarians should develop disinfection and sanitation protocols for their clients to minimize the likelihood of disease transmission between animals or humans (zoonoses). Various disinfectant compounds, including sodium hypochlorite and chlorhexidine, can be used to control pathogens in a snake habitat. For these compounds to be effective, it is important to remove all organic material from the surfaces being cleaned. Organic materials can reduce the potency and efficacy of disinfectants. I have used sodium hypochlorite (1000 ppt) as a method to eliminate Salmonella spp. in reptile enclosures. The compound was allowed a minimum of 15 minutes con-tact with the enclosure surfaces. Chlorhexidine (0.5%-1.0%) also has been found to be effective against a variety of pathogens. Again, a minimum of 15 minutes of contact time is recommended.
Before restraining an animal, it is important to identify its “weapons.” In snakes, their primary weapon (defense) is their teeth. In some colubrids, boids, and pythons, their ability to constrict should also be considered a potential weapon. By effectively restraining the head and body of a snake, the veterinarian will remove the animal’s weapons. Nonvenomous snakes can be effectively restrained by grasping the head of the animal at the level of the quadrate or mandible with one hand and supporting the snake’s body with the other hand (Figure 7-8). An additional handler should be used for every 3 to 4 feet of snake to support the snake’s spine. Snakes should never be draped over the neck of an individual.
Figure 7-8 Snakes can be safely restrained by grasping the animal around the base of the mandible with the index finger and thumb. The body of the animal should be supported with the handler’s free hand.
Venomous snakes should be handled only by trained professionals. Hooks and tongs should be used to remove venomous snakes from their enclosure. Once collected from an enclosure, the snake should be directed into an appropriately sized clear plastic tube. The snake should be allowed to crawl to the midpoint of the tube and then prevented from advancing (Figure 7-9). This technique allows for safe management of the snake and allows veterinarians to grossly examine the snake and collect blood from the ventral coccygeal vein. Intravenous (IV) propofol (5 mg/kg) can be administered slowly via the ventral coccygeal vein or isoflurane directed into the tube to anesthetize the snake.
Most snakes can be safely restrained manually; however, in those cases where the snake poses a risk to the veterinarian or is too fractious for a possible procedure, chemical restraint should be considered. The dissociative agents (ketamine and tiletamine) are the preferred anesthetics for these cases. Ketamine (5-10 mg/kg intramuscular [IM]) or tiletamine (3-5 mg/kg IM) will provide sedation in most snakes. In my opinion, these doses are not appropriate for procedures that may induce pain. For more complete general anesthesia, a higher dose of these compounds may be necessary (10-20 mg/kg ketamine, 5-8 mg/kg tiletamine) or different compounds altogether (e.g., propofol or isoflurane) (see Anesthesia).
A snake physical examination should always be done in two parts: a hands-off exam and a hands-on exam. The hands-off exam should be done first because it can provide insight into the animal’s condition. Special attention should be given to mentation, respiration, and locomotion. Abnormalities observed during a hands-off examination can be used to guide the clinician during the hands-on examination and for diagnostic testing. Abnormal mentation (e.g., a snake that does not appear aware of its surroundings), dyspnea, and/or an inability to right or move are all indicators of serious internal disease. A snake that is dyspneic should be handled cautiously during the hands-on examination or placed into an oxygen cage until it compensates. Animals that have abnormal mentation or locomotion should be restrained with care, as they may be more susceptible to injury.
The hands-on physical examination should be performed in a thorough and consistent manner. I start the examination at the head and then move caudally. The spectacles should be clear with no apparent indications of a retained spectacle or subspectacular disease. A minimal ophthalmic exam should be performed to evaluate the conjunctiva, cornea, and anterior chamber. Visual examination of the posterior chamber is difficult in snakes because of their small pupils and the fact that the iris is comprised of mixed skeletal and smooth muscle. This combination, along with the presence of a spectacle, limits the value of mydriatics in snakes. The nares should be clear and free of discharge and retained shed. The gular fold under the jaw should be examined for the presence of ectoparasites.
The oral cavity should be opened using a soft, pliable speculum. The mucous membranes should be pale to pink and free of thick ropy mucus. The tongue should be identified and evaluated. Snakes should protrude their tongue when they are in a new environment, as they use olfaction to characterize their environment. The tongue sheath should be examined closely for discharge and swelling. An abnormal tongue or tongue sheath is a significant finding and could result in anorexia in a snake. The glottis is located on the floor of the buccal cavity. Snakes have voluntary control over their glottis. The glottis should be examined closely for edema or discharge. The teeth and palate should be closely inspected for fractures or inflammation. Abscesses are a common sequela to fractured teeth. Gentle expression of the surrounding soft tissue in an area with swelling may reveal a caseous discharge.
The integument should be closely inspected for ectoparasites, traumatic injuries, and inflammation (dermatitis). The spine and ribs should be palpated. The epaxial muscles should exhibit normal development. The spine will be prominent in a snake with muscle wasting. The coelomic cavity should be palpated. I generally start palpating the snake at the caudal-most aspect of the jaw and move caudally. A thumb or finger can be used to gently palpate the viscera. Any abnormal masses should be further evaluated using appropriate diagnostic tests.
It is important to assess the cardiorespiratory organs of a snake. In the past this has not always been recommended, because assessing the heart and lungs of a snake using a stethoscope can be difficult. I have found that an ultrasonic crystal Doppler can be used consistently to determine the heart rate of an animal and evaluate the snake for cardiac irregularities (Figure 7-10).
The gender of the snake should be determined as part of a routine examination. Some veterinarians charge an extra fee for determining the gender of a snake; some incorporate this into the physical examination. Knowledge of the gender of an animal is important when considering the signalment and potential differential diagnoses. Male snakes have two copulatory organs, the hemipenes. These structures are located in the base of the tail, caudal to the vent. The gender of a snake can be determined by probing for the presence or absence of these structures. Stainless steel snake probes are commercially available and highly recommended. The probe should be lubricated with a commercial lubricating jelly to facilitate passage. The probe should be inserted caudolaterally (Figure 7-11), as far as it can be directed. Once the probe cannot be inserted any further, the handler’s thumb should be used to mark the position of the probe at the level of the vent. The probe should then be removed from the vent and placed on the external surface of the tail. If the probe travels farther than five scales, than the snake is (generally) a male. If the probe does not travel farther than five scales, then the snake is a female. Male snakes generally have longer and wider tails than do females. I will always probe the second side if the first probing suggests a female. Juvenile snakes can be sexed by gently everting a hemipenis. This technique is usually reserved for hatchlings. Holding the tail of a snake up to a bright light can also reveal the presence or absence of hemipenes.