Introduction

As the popularity of exotic small mammals grows in the United States, the practice of treating these animals and demand for veterinarians educated in small mammal medicine and techniques will continue to increase. As a practitioner who welcomes "exotic small mammal" patients, it may be surprising to learn how many exotic small mammal species are commonly kept as pets. Common small mammals presented to the general practitioner include ferrets, rabbits, rodents such as chinchillas, guinea pigs, rats, hamsters, and degus, as well as hedgehogs, sugar gliders, and short-tailed opossums, to name a few. Although all common pets, these animals vary from lagomorphs to rodents to insectivores to marsupials. Although a good grasp on mammal medicine (i.e., dogs and cats) will provide a strong foundation when presented with a case, it is important to have an understanding of differences in anatomy, physiology, diagnostic techniques, and common disease presentations in the wide variety of exotic small mammals. This presentation will aim to point out some helpful hints in terms of husbandry recommendations, variations in anatomy, approaches to diagnostic techniques, as well as point out common disease processes that you are likely to be presented with by any given species. The purpose of this lecture is to provide veterinarians with an introduction to the management of exotic small mammal species, including husbandry, physical examination, restraint, diagnostics, and therapeutics.

History

On presentation, a thorough history should be taken that includes the signalment, care and management of the animal, and any previous medical history. Specific information regarding husbandry of many species can be crucial in determining the etiology of many disease states. Since many of these patients are prey species, they are often quite skilled at masking signs of illness. Detecting any subtle changes may help to identify problems before they become critical.

Husbandry

As with most exotic pets, husbandry assessment and recommendations are an important component of annual wellness visits. Many owners are new to the care of exotic small mammals. Often they may look to their veterinarian to make diet, substrate, and housing recommendations. It is important to stress to the client how critical proper husbandry can be to the health and longevity of the animal. This can also help build your relationship with first-time owners or clients. For example, the diet of hindgut fermenters such as rabbits, guinea pigs, and chinchillas, should consist primarily of grass hay (e.g., timothy hay, orchard grass, etc.). Pellets and fresh vegetables should only compose a small amount of the diet. An adequate diet can help prevent common disease presentations such as dental disease and gastrointestinal stasis.

Basic Physical Examination

A physical examination in a small mammal is very similar to any other mammal examination, with a few exceptions that are pointed out below. A physical examination for each species should always be performed in a systematic fashion. A small mammal physical examination may be performed without an extensive amount of specialized equipment; however, there are a few items that can be helpful to keep in the exam room. A gram scale (preferably with a range of up to at least 5 kg) is extremely important in recording and tracking the weight of patients. The ability to weigh a patient to the nearest gram is crucial to help detect fluctuations on a daily basis. An ample supply of towels should always be kept in the exam room, both to provide a non-slip surface to patients, and to aid in proper restraint. A pediatric stethoscope can aid in auscultation, particularly in smaller animals such as rats or hamsters. A good light source such as a transilluminator can be helpful. Finally, a human nasal speculum is recommended to aid in oral examination of rabbits and rodents.

Rabbit

Proper restraint is the first step in any successful rabbit physical examination. A rabbit's skeleton only makes up a small portion of the total body weight. Along with powerful back legs and significant muscle mass, it is possible for them to kick out when stressed or mishandled and fracture their back. For this reason, it is important that the hind legs be restrained at all times when handling. During examination, it is often recommended to place them in a "burrito," which involves wrapping them in a towel so only the head is exposed and the hind legs are supported. This can be especially helpful when performing an oral exam.

Since rabbits are hindgut fermenters, during examination it is important to not only auscultate the heart and lungs, but to also listen for gut sounds, or borborygmi. Often when an animal has gastrointestinal stasis, gut sounds may be significantly reduced or absent, which indicates movement of the GI tract is significantly slowed. If there is a history of anorexia or decrease in fecal production, this should be considered an emergency.

Another important component of the rabbit physical examination is the oral examination. This is important because rabbits have hypsodont, elodont teeth, meaning they are open rooted and constantly growing. First, the incisors should be examined. Rabbits have 4 incisors on the maxilla, including the "peg teeth." The peg teeth are smaller incisors that sit caudal to the main incisors and should occlude with the mandibular incisors. Next, the cheek teeth should be examined for any abnormal growth, such as hooks or points, or overgrowth. In cases of severe dental disease oral ulceration may be a sequel to overgrowth of malocclusion.

Ferret

Ferrets are often extremely amenable to handling and physical examination. However, they are extremely active animals and can often be resistant to parts of the physical assessment such as obtaining a rectal temperature. For this reason, it often helps to scruff a ferret at the level of the neck and suspend them vertically, with no limbs in contact with the table. This often calms ferrets and also will often cause them to "yawn," aiding in obtaining an oral examination.

Much of a ferret physical examination is very similar to a cat. Since they are a long "tube," abdominal palpation is rewarding, and identifying individual abdominal structures such as stomach, spleen, kidneys, abdominal lymph nodes, and bladder, is often possible. Middle-aged to older ferrets often have a large spleen, with the vast majority of splenomegaly being benign. Ferrets also have a long thoracic cavity, which is most important to note because auscultation of the heart is often more caudal than for most species.

Chinchilla

When handling chinchillas, they should never be scruffed because they are susceptible to "fur slip" and can lose fur and/or skin. Proper restraint of a chinchilla can be performed in the "burrito" style of wrapping in a towel similar to rabbits, or they can also be restrained by holding the base of the tail. Another restraint technique that can be helpful during a physical examination is the "vest" hold. In this restraint, the index finger and middle finger are placed on either side of the head, cranial to the shoulders, and rest of the hand can be wrapped around the mid-body, allowing for restraint during physical examination.

Physical examination is similar to that of rabbits or other rodents. Oral examination is an important component since they also have constantly growing teeth. However, it can often be challenging in awake chinchillas since their mouths are significantly smaller than that of a rabbit. Sometimes sedation or anesthesia can aid in a complete oral exam. The chests of chinchillas are also fairly pliable and on auscultation a heart murmur can be induced if more pressure is applied with a stethoscope. For this reason, apply light pressure to the chest when ausculting.

Guinea Pig

Guinea pigs are often straightforward to restrain and can also be placed in a "burrito" for oral examination. Guinea pig teeth are also constantly growing which can lead to similar problems such as overgrowth secondary to malocclusion. However, conformation of the teeth of a guinea pig is unique because the maxilla is slightly wider than the mandible. Due to this conformation, the mandibular cheek teeth face inward or medial, and the maxillary cheek teeth face outward or lateral, both at approximately a 30–45-degree angle. When guinea pig teeth become maloccluded, often the mandibular cheek teeth continue to grow medially, causing "tongue entrapment." This can be a primary problem due to dental disease, or can occur secondary to anorexia caused by another systemic disease process.

Hedgehog

A thorough physical examination on a hedgehog is often difficult without chemical restraint due to their spines and unique ability to roll into a ball. Well- socialized animals may allow for physical examination, but often will not be amenable to the more invasive components of a physical examination such as oral examination or rectal temperature. For that reason, gas anesthesia is often recommended for a thorough and complete assessment. It should also be considered that these animals may carry and transmit Salmonella to humans, so caution and proper hygiene should be used when handling. Hedgehog mites (Caparinia tripilis) are a common disease presentation in the small animal practice that may present with severe pruritus and spine loss that is easily diagnosed via skin scrape.

Hedgehogs are extremely prone to developing neoplasia, particularly oral squamous cell carcinoma. For this reason, a thorough oral examination should always be performed. However, contrary to rabbits and most rodents, hedgehog teeth have roots and do not constantly grow, so they should never be trimmed. They are also prone to developing tooth root abscesses. Obesity is also very common in animals fed high-fat diets. A sign of obesity is the inability to properly "ball up."

Degu

Although less commonly presented to the veterinary clinic, degus are hystricomorph rodents and somewhat similar to other hystricomorph rodents such as guinea pigs and chinchilla. Like other hystricomorph rodents, they are native to South America. In the wild, they are adapted to drought conditions, so in captivity they drink very little water. When making recommendations to owners, it should be noted that they do require dust baths similar to chinchillas and should be maintained on a diet very similar to guinea pigs or chinchillas (high fiber, low carbohydrates). When approaching the physical exam, it is important to apply proper handling technique. Unlike chinchillas, they should not ever be held or restrained by their tail as they are able to "slough" their tail. They are fairly high-stress animals that benefit from little restraint and many procedures, such as dental trimming or venipuncture, may warrant gas anesthesia.

In general, there are relatively few reports of naturally occurring diseases. The most commonly reported disease in captivity is diabetes mellitus. This typically occurs spontaneously and is caused by amyloidosis of Langerhans islets. Cataracts are common sequelae and often develop within 4 weeks of disease. Like other rodents they may develop dental disease, which can be extremely challenging to treat due to the small size of their mouths. Since they are hystricomorph rodents, both their incisors and cheek teeth are hypsodont elodont (open rooted and constantly growing). This means they may need routine trims in the case of malocclusion. Degus are also predisposed to obesity if fed an improper diet.

Sugar Glider

Sugar gliders are marsupials and differ quite a bit from other exotic small mammals in terms of husbandry recommendations, anatomy, and physiology. Besides the females having a pouch, there are also many other different variations. Their reproductive tracts are quite unique: females have bilateral vaginae and uteri and males have a pedunculated scrotum that is located cranial to the bifurcated penis. Males also have scent glands on their head and chest, which can often be mistaken for alopecia. As marsupials, their metabolic rate is much lower than that of most other mammals, which is important when determining drug dosages and nutritional requirements, and also when recording physical exam data.

Sugar gliders are omnivores. Since it is difficult to replicate their natural diet, which consists of sap and nectar among other items, there are varying recommendations as to the proper diet to feet in captivity. Due to the difficulties of replicating their natural diet, they are often deficient in calcium and may present for signs of nutritional secondary hyperparathyroidism. It is not uncommon for them to be presented for seizures, tremors and pathologic fractures associated with this disease process. Their teeth are not constantly growing and should never be trimmed. However, it is not uncommon for them to develop tooth root abscess that often requires removal of the tooth. The most common presentation to a vet clinic is usually secondary to trauma and/or self-mutilation. Sugar gliders are very social animals and can self-mutilate from boredom if housed alone. However, they are also extremely territorial and new gliders should be introduced slowly into a group to avoid attacks.

Short-Tailed Opossum

Short-tailed opossums are another marsupial that is becoming more common in the pet trade. However, since they are recently increasing in popularity, little information is available as to recommendations for medical diagnostics and treatment. Although they are marsupials, the females lack a pouch and it is thought that they are nocturnal. Unlike sugar gliders, typically they are housed alone due to their solitary nature in the wild. If attempted to house together, it is likely there will be aggression issues and subsequent trauma. Another possible problem that may present to a veterinary practice is alopecia. Ectoparasites and infectious causes of dermatitis should first be ruled out, but often the cause of hair loss is unclear. It has been hypothesized that short-tailed opossums may develop an allergy to certain types of bedding and for that reason it may warrant a change in bedding or environment if other causes of alopecia are ruled out.

Diagnostics

When collecting a blood sample from a small mammal patient, it is considered safe to collect 1% of the animal's body weight. For a 100-gram patient, this would be 1 mL of blood. In a rabbit, blood may be collected from the jugular vein, with restraint techniques similar to a cat. However, when extending the neck, special care should be taken to monitor the rabbit's breathing pattern. The soft palate is elongated; extending the neck may cause the soft palate to block the airway. Alternative sites for venipuncture include the lateral saphenous vein, marginal ear vein, or auricular artery. In a ferret, the jugular vein or cranial vena cava are often the two most common venipuncture sites. In most rodents such as chinchillas, guinea pigs, rats, etc., anesthesia is recommended due to the typical venipuncture site (cranial vena cava) as well as consideration of the stress to the animal. In rats, lateral tail veins can be easily accessed.

Fecal examinations (cytology, fecal float, and wet mount) may be useful in these animals and may be performed in a similar fashion to other domestic animals. Imaging such as radiographs, ultrasound, or computed tomography (CT scan) is often a useful tool in small mammal patients. Although associated with a higher cost to the client, CT scan can be performed awake and often can provide the best resolution for small areas difficult to image in small mammal patients, such as the head and the thorax. Depending on the patient and the imaging technique, sedation or anesthesia may be useful when performing diagnostic imaging.

Therapeutics

In general, there is much less data available on pharmacokinetics and pharmacodynamics in many exotic small mammal species. For this reason, drug dosages and usage in particular species may be extrapolated from other mammals. However, there are some important differences that should be considered when treating these exotic patients.

Antibiotics

In hindgut fermenters, (rabbits, chinchillas, guinea pigs, hamsters) oral beta-lactams, lincosamides, or macrolides should never be used. These drugs can cause a fatal bacterial overgrowth or dysbiosis (imbalance of normal intestinal flora). However, some beta-lactams can safely be administered parenterally.

Glucocorticoids

Corticosteroids should be used with extreme caution in rabbits and rodents. Even low doses can cause a significant immune suppression, which can be life- threatening. This includes oral medication and also topical treatments such as ophthalmic solutions. Alternatively, ferrets can tolerate fairly high doses of glucocorticoids with minimal side effects.

Analgesics

It is often extremely important to consider pain management in many of our small mammal patients. A painful condition may cause anorexia, which in turn, may cause a potentially life-threatening ileus or GI stasis in hindgut fermenters. With the exception of ferrets, nonsteroidal anti-inflammatories are typically tolerated well at much higher doses than are typically used for dogs or cats. For example, dosages of 0.5 mg/kg of meloxicam are used fairly routinely in rabbits, guinea pigs, and chinchillas with minimal side effects. Opioids are also routinely used in many small mammals, extrapolating from dog and cat dosages.

Oral Administration

Since it is difficult to pill small mammals, compounding medications to a liquid formulation is often required. The administration of oral (PO) medications has been made easier with the different flavoring agents that are now available. To administer PO medications to a rabbit or a rodent, the syringe can be inserted in the diastema (space between incisors and cheek teeth) for ease of administration.

Supportive Care

Supportive care, such as fluid therapy and nutritional supplementation, is often necessary when hospitalizing or treating small mammal patients. Most small mammals tolerate fluid therapy well. Many have significantly higher fluid requirements than in canine/feline medicine. Critical patients may benefit from intraosseous or intravenous fluids, while more stable patients are often administered subcutaneous fluids. It is important to administer warmed fluids when possible to maintain adequate body temperatures.

Syringe feeding is important to support a wide variety of disease processes, including systemic disease that may be causing pain or nausea, as well as dental disease, which may make eating physically difficult or impossible. As previously mentioned, periods of anorexia in hindgut fermenting animals can quickly lead to a potentially fatal dysbiosis. To prevent complications of anorexia, often these animals are syringe fed, or "force fed" a manufactured herbivore diet. One example is Critical Care, a powder that can be mixed with water to achieve a gruel-like consistency, manufactured by Oxbow. It is recommended to feed approximately 20 ml/kg per feeding and feed up to 4–6 times a day. This can be challenging and time consuming in a patient that is not eating or is minimally responsive. Often they may start refusing to swallow before the desired amount is successfully delivered. In these cases, placement of a nasogastric tube should be considered.

References

1.  Mitchell MA, Tully TN, eds. Manual of Exotic Pet Practice. St. Louis, MO; Elsevier; 2008.

2.  Quesenberry K, Carpenter JW, eds. Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. 3rd ed. St. Louis, MO: Elsevier; 2011.