ACVC 2001 - Clinical Approach to the Chinchilla

Clinical Approach to the Chinchilla

Heidi L. Hoefer, DVM, Dip. ABVP
West Hills Animal Hospital
Huntington, New York

The chinchilla (Chinchilla lanigera) is a small rodent originating from the Andes mountains of South America. Chinchillas are generally nocturnal and prefer a quiet environment during the day. Their lifespan is much longer than most rodent species averaging 10 years with 18-20 years possible in some individuals. The male averages 400-500 grams in body weight and the female is slightly larger at 500-600 grams.

The female has a vaginal closure membrane that is only open during estrus and parturition. They are seasonally polyestrous from November to May with an estrous cycle of about 40 days. Gestation period is long at 111 days. The female has a cone-shaped clitoris that at quick glance may resemble a penis. The male has open inguinal rings and the testes are located inguinally without a true scrotal sac. Puberty for both sexes usually occurs at 10-12 months of age in the fall.

Housing & Diet

Chinchillas are fastidious groomers and require dust as part of their daily bathing. The dust is a fine mixture of Fuller's earth and silver sand (1:9) and is placed in a container large enough for the chinchilla to roll around in. These baths need to be kept clean and free of feces and should be removed when not in use. Overuse of the dust bath can lead to an irritative conjunctivitis in some chins.

The chinchillas native habitat provides low humidity and sharp variations between daytime and evening temperatures. High temperatures and high humidity must be avoided year-round. Chinchillas are comfortable at cooler temperatures (>32^oF) and can suffer heat stroke if the environmental temperature climbs above 80^oF, especially when coupled with high humidity.

Free-ranging chinchillas survived on a diet of grasses, cactus fruit, leaves, and the bark of small shrubs and bushes. Captive chins need a diet high in fiber to prevent enteric problems. The basic chinchilla diet consists of a good quality grass hay (timothy) and a small amount of chinchilla pellets. Because the diet must be high in fiber, the sole feeding of pellets must be avoided. Limit pellets to 1-2 tablespoons per day. Small amounts of greens, and fruit can be offered as treats. Any change in diet should be done gradually and fecal output should be monitored periodically.

Restraint

Chinchillas are usually easy to handle and rarely bite. However, they can be shy and nervous and reluctant to stay still for prolonged periods. The best approach is to gently hold the animal around the thorax. Alternatively, the tail can be held at the base as long as the body is supported. Do not grasp the skin roughly; it may result in a dropped patch of fur in a frightened animal ("fur-slip").

Chemical restraint can be used if prolonged sedation is needed. Injectable ketamine/valium combinations work well either intramuscularly or intravenously. A small IV bolus (0.05 cc total dose of combined drugs) of ketamine-diazepam combination (at 1/4-1/2 of the IM dose) can be administered for quick procedures like oral examinations, radiographs, and tooth clipping. The preferred method of chemical restraint is isoflurane. It has a rapid induction and recovery time and high margin of safety. Gas delivery is through an induction chamber or a face mask. Chinchillas are very difficult to intubate; respirations and anesthetic depth must be carefully monitored during prolonged procedures.

Antibiotic Administration

Chinchillas rely on a complex balance of microorganisms in the digestive tract to ferment non-digestible fiber. Any disruption in this system can change pH, interfere with motility, and promote bacterial overgrowth. Gram-negative bacteria and clostridial overgrowths can lead to diarrhea, enterotoxemia, and death. Avoid any antibiotic that has a selective gram-positive spectrum. This includes the beta-lactams (penicillins and cephalosporins), clindamycin, lincomycin, and erythromycins.

Common Problems

The most important conditions of chinchillas includes gastrointestinal tract disease, respiratory problems (pneumonias and cardiac disease), heat stroke, and orthopedic injuries. Neoplasias are rare. A more detailed review can be found in the sited references. Much of what we know is based on personal experiences and anecdotal information from veterinarians and breeders. So, keep an open mind and perform thorough workups whenever possible.

Gastrointestinal Diseases

The chinchilla originates from an area of the Andes mountains where vegetation is tough and fibrous and low in energy content. As a result, a large amount of food is eaten and alot of chewing takes place. This results in the normal wear of the cheek teeth which are open rooted and grow continously to compensate for this wear. The dental formula is 1/1 incisors; 0/0 canines; 1/1 premolars; 3/3 molars. The incisors are yellow and grow 2-3 inches (5.5-6.5 cm) per year. The oral cavity is small and narrow and largely filled by the tongue.

Dental Disease

Dental Disease is common in chinchillas. Clinical signs include weight loss, inappetance or anorexia, and drooling or "slobbers". Some chinchillas present with increased lacrimation on the affected side. Diagnosis is based on clinical signs and a thorough oral examination. An otoscope with a light source can be used to check the cheek teeth. Human nasal speculums are available with a light source that attaches to the otoscope handle for easier observation of the cheek teeth (Welch-Allyn bivalve nasal speculum #26030). Sedation may be needed to fully examine the cheek teeth. Skull radiographs are important to examine the occlusal surfaces as well as the roots.

Tooth root elongation and crown extension is a common problem seen in some chinchillas on a low roughage diet. Pellets, grains, and most vegetation do not provide adequate chewing to wear down the cheek teeth properly and crown and root extension occurs. The roots form palpable "bumps" on the mandible and are readily seen on radiographs. Oral examination may show a somewhat normal occlusal surface and lack of points or ulcerations, although points can occur.

Treatment involves trimming of the sharp edges or overgrown teeth. The cheek teeth need to be done under sedation. A small bone rongeur (Lempert) or drill (dental or Dremel) can be used to file points. Tall crowns need to be burred down to the gum line and may be repeated every 6-8 weeks. Antibiotics are indicated for root abscesses and carries a very guarded prognosis for full return to function. Owners should be aware of the likelihood of recurrence , the need for regular dental care, and the long term poor prognosis. This condition is irreversible and may result in chronic weight loss and painful mastications. These individuals are usually on syringe feedings indefinitely, which exacerabates the lack of wear on the crowns. Euthanasia is often recommended for these chronically painful individuals.

Lower gastrointestinal disease

Lower gastrointestinal disease is a common problem seen in chinchillas. Chinchillas are hind-gut fermenters with a relatively long gastrointestinal tract. The stomach and cecum are large and the colon is highly sacculated. High fiber, low energy diets are the driving force behind this herbivores' digestive physiology. Disruption in the system results in anorexia, colic, diarrhea, hair and fecal impaction, intussusception, mucoid enteritis, ileus, bloat, and rectal prolapse. Hepatic lipidosis is a common sequelae to prolonged anorexia.

Predisposing factors include abrupt diet change, inappropriate antibiotic use, overcrowding and stress, and diets too low in fiber, and too high in fat and protein. Changes in enteric pH or normal gut flora results in bacterial overgrowth and can lead to enterotoxemia. Clostridium, E. coli, Proteus, and Pseudomonas are common isolates. Clostridial enterotoxemia (C. perfringens) causes severe diarrhea, shock, and acute death.

Diagnosis is based on clinical signs and history. Anorexia and decreased fecal output are early warning signs. Whole body radiographs are taken to assess both body cavities. Varying amounts of gas and ingesta may be seen normally in hindgut fermentors. It can be difficult to determine simple gas production from an obstructive ileus; repeat radiographs in 24 hours and administer oral barium by syringe if neccessary to aid in visualization and motility determination.

Treatment for the acute abdomen includes supportive care (fluids, temperature regulation), antiinflammatories (Banamine^�) or analgesics (buprenorphine), antibiotics, and surgery if obstructed. Human pediatric anti-gas preparations (e.g., Phazyme^�) may be helpful to decrease gas production. Keep in mind that a sick chinchilla is a poor surgical candidate and medical management may be indicated prior to abdominal surgery. Blood testing is recommended in anorexic individuals (CBC and plasma chemistry).

Other reported causes of gastroenteritis in chinchillas include Salmonella, Listeria monocytogenes, and Yersinia pseudotuberulosis. Intestinal parasitism is uncommon but nematodes, coccidia, Giardia, and Cryptosporidium can sometimes be seen in chinchillas. Low numbers of Giardia are thought to be normal in chins but an overgrowth can lead to diarrhea. Always check a direct fecal and perform a fecal flotation on any animal with diarrhea. Be careful with metronidazole administration; there are anecdotal reports of toxicity to Flagyl^� in some chinchillas, although this author has not seen it.