Chapter 3 Guinea pigs, chinchillas and degus
Many of the pet rodents presented to the veterinarian belong to the group known as hystricomorphs. The following species are the commonest as household pets:
Consultation and handling
Although both rabbits and guinea pigs are social animals, generally the keeping of guinea pigs with rabbits is not recommended because:
1 Rabbits are often aggressive to guinea pigs and may bite and harass them. Much of this activity occurs at night and may not be noticed by the owner.
2 Guinea pigs require dietary vitamin C (see Nutritional Disorders) and may suffer hypovitaminosis if fed on commercial rabbit food only.
3 Rabbits harbour Bordetella in their respiratory tract which can be a significant respiratory pathogen in guinea pigs.
Sexing of chinchillas can be problematic as the female has a pronounced genital papilla that can be easily mistaken as a penis. The vulva lies immediately caudal to this papilla (Fig. 3.1).
Nursing care
For general concepts, see Nursing Care in Rabbits.
Fluid therapy
Fluids can be given s.c., i.p. or i.o. – indeed if there is marked dehydration, then i.p. or i.o. is preferable to s.c. Fluids can be given i.v. either by bolus or by infusion and all fluids should be warmed to 38 °C. For sites for fluid administration see Table 3.
Table 3.3 Guinea pigs, chinchillas and degus: Sites for fluid administration
| Intravenous (guinea pig) | Lateral or medial saphenous and cephalic vein |
| Intravenous (chinchilla) | Femoral, lateral saphenous and cephalic vein. Ear veins can be used for i.v. in some cases, and the use of EMLA cream greatly aids this, but is inappropriate if the chinchilla is considered hypothermic |
| Intra-peritoneal (all three species) | Hold the patient vertically downward and inject into the lower left quadrant |
| Intra-osseous (all three species) | Under GA to insert either an intraosseous catheter or a hypodermic needle into the marrow of either the femur (via the greater trochanter) or tibia (through the tibial crest). Fluids, colloids and even blood can be i.o. if necessary |
Analgesia
Anaesthesia
Beware of subclinical respiratory infections. There is no need to starve; prolonged fasting can lead to hypoglycaemia.
1 Masking down or placing in an induction chamber is often the safest way to induce anesthesia in hystricomorph rodent.
2 Guinea pigs will often hypersalivate in response to isoflurane; atropine at 0.1–0.2 mg/kg s.c. may reduce this.
3 Intubation is extremely difficult due to the narrow caudal pharynx, large tongue and small glottis. Makeshift endotracheal tubes using intravenous catheters readily block with respiratory secretions. It is often more expedient to maintain on a mask, or intubate by a tracheotomy if thought necessary.
Skin disorders
Pruritus
• Guinea pig
• Trixacaris caviae (sarcoptid mite) (Fig. 3.2). Commonly associated with immunosuppression associated with pregnancy/parturition
Alopecia
• Parasitic
• Mites:
• Trixacara caviae (sarcoptid mite) (guinea pigs). Commonly associated with immunosuppression associated with pregnancy/parturition
Other
• Barbering/fur chewing (for chinchillas – see also Endocrine Disorders). May be linked to lack of dietary fibre
Findings on clinical examination
• Areas of alopecia – may be bilateral (hormonal) or patchy (fatty acid deficiency, pantothenic acid deficiency in chinchillas)
• Swellings, often firm consistency even if abscess. Displacement of normal outline of coat may indicate swelling
• Cuts and abrasions: these may be self-inflicted in cases of severe pruritus. In guinea pigs such lesions tend to be over the shoulders and back of the neck where the guinea pig scratches with its hind claws
Investigations
6 Microscopy: examine fur pluck, acetate strips or skin scrapes to affected area and examine for ectoparasites
Treatment/specific therapy
• Treat for any ectoparasites
• Ivermectin at 200 μg/kg or as topical application (Xeno 450, Genitrix); 3 treatments given 2 weeks apart
• Pododermatitis
• Note: may also induce amyloidosis in internal organs (see Hepatic Disorders, Pancreatic Disorders, Endocrine Disorders)
• Dermatophytosis, Scopulariopsis and Cryptococcus
• Griseofulvin at 15–25 mg/kg once daily for 4 weeks. Toxic to immature and fetal guinea pigs so use on adult, non-pregnant guinea pigs only
• Lacerations/bites to the pinnae
• Debride, clean up and apply topical amorphous hydrogel dressings to encourage secondary healing, e.g. IntraSite Gel (Smith and Nephew Healthcare Ltd.)
• Fur chewing
• Can be related to poor environmental conditions, e.g. high temperatures, high humidity. In rabbits it is often related to lack of provision of long fibre such as hay
• Fur chewing chinchillas often have hyperthyroidism and hyperactive adrenal glands (see Endocrine Disorders)
• Treatment involves elimination of other possible aetiologies correction of environmental conditions
Respiratory tract disorders
See also Cardiovascular and Haematological Disorders.
Dental disorders
Findings on clinical examination
• Chinchilla and degu incisor teeth are naturally highly coloured orange or yellow; this often fades with dental disease. Such fading may indicate a hypovitaminosis A (see Nutritional Disorders)
• Mandibular swellings (unilateral or bilateral) due to bone remodelling to accommodate tooth root overgrowth
• Maxillary swellings rostral to eye; painful on palpation – maxillary root overgrowth (especially chinchillas)
Investigations
1 Otoscopic examination of oral cavity
a Normal guinea pig or chinchilla always has a significant amount of food/caecotrophic material in its mouth obscuring the dental arcades; if this is not the case then it is likely to be eating very poorly
d Otoscopic examination does not constitute a complete examination of the oral cavity as structures at the back of the pharynx can be difficult to see due to its depth and the large size of the tongue
2 Radiography
b Left and right lateral oblique views of skull to allow assessment of individual tooth roots. Any divergence of maxillary or mandibular tooth roots away from each other suggests abnormal root elongation
Management
3 Syringe feeding with commercial feed suspensions, e.g. Critical Care (Oxbow) or Recovery diet (Supreme Petfoods). May require nasogastric tube or tube feeding
5 Only use antibiotics if indicated. Many cases do not require their use, which can be counterproductive
Treatment/specific therapy
• Regular coronal reduction
• Always burr overgrown incisors in preference to clipping due to risk of fracture, pulpal haemorrhage and infection
• For cheek teeth, this will likely necessitate heavy sedation or a GA. ‘Concious’ dental work on the cheek teeth is stressful to the rodent and risks serious traumatic to the oral cavity and spine
• Often coronal reduction alone is insufficient; often by the time of presentation, dental disease has progressed to a quite advanced stage
• Surgical debridement of tooth root abscesses including removal of infected bone and affected tooth roots, followed by:
• Packing with antibiotic-impregnated methyl-methacrylate (bone cement or similar) and/or marsupialization leaving ostium for recurrent povidone-iodine/antibiotic application during second intention healing
• Antibiosis
• Usually a broad-spectrum such as enrofloxacin at 5 mg/kg s.i.d. p.o. or co-trimoxazole at 30 mg/kg b.i.d. p.o. plus
• Drilling out of tooth root apices to initiate tooth root death where extraction is not viable. Note that aggressive dental work in guinea pigs can trigger neuronal degeneration of afferent nerves in the periodontal ligament with subsequent degeneration of the mesencephalic trigeminal nucleus resulting in dysphagia, postural abnormalities and death (Azuma et al 1999, Kimoto 1993) See Neurological Disorders and Cardiovascular and Haematological Disorders
• Where possible, wean the animal on to a diet high in long fibre, i.e. grass and hay, as this encourages normal chewing and dental wear on the back teeth. Provision of a pumice stone may encourage gnawing behaviour
• Note that many chinchillas with dental disease have adrenal hyperplasia (Crossley 2001) (see Endocrine Disorders)
Gastrointestinal tract disorders
It is normal for guinea pigs, chinchillas and degus to coprophage, especially at night (Kenagy et al 1999).
