Mammals – an introduction

2 Mammals – an introduction

Small mammals are commonly kept as pets. Various species may be presented to the veterinary clinician, often with diverse husbandry requirements and disease predispositions. Presenting signs may be subtle and vague. This chapter will aim to discuss some basic biology and husbandry for these species, as well as providing the clinician with an outline on basic techniques to assess and treat the animals. The ensuing chapters will demonstrate approaches to an assortment of cases.

Taxonomy

Taxonomic classification of mammals commonly seen as pets is given in Table 2.1.

Table 2.1 Taxonomic classification of mammals commonly seen as pets

Biology

This is a brief synopsis for common pet species. Further information may be found in Table 2.2, specific case reports later in the text or in references listed in the Further reading section.

Table 2.2 Biology of selected mammals commonly kept as pets

Leporidae (rabbit)

Rabbits are highly social, and should be kept with a companion (preferably both neutered). They dig burrows in the wild. An exercise area should be provided. Wood shavings and hay or straw are commonly used as substrates. Outdoor hutches should be secure. Indoor rabbits can be litter-trained; care should be taken to ensure cables and houseplants are protected from chewing. Chewable toys can be offered, e.g. cardboard boxes. Scent is an important sense to rabbits. As a prey species, fear elicits either immobility or a flight response. Thumping of the hindlegs is an alarm call.

This species is herbivorous, adapted to a low-quality, high-fibre diet – eating grass and weeds in the wild. Captive animals should be fed similarly, usually on a diet of good quality meadow hay supplemented with leafy green vegetables and wild plants such as dandelions. Concentrate mixes should be avoided, particularly ‘muesli’-type mixes where selective feeding is possible. Water is usually provided in a sipper bottle, as the dewlap may get wet and skin infection could result if a bowl is used.

The dental formula is: incisors 2/1, canines 0/0, premolars 3/2, molars 3/3. All teeth are continuously growing (hypsodontic, with open roots). Rabbits cannot vomit. Gastrointestinal transit time is rapid in these hindgut fermenters, with bacterial fermentation in the caecum. Indigestible fibre stimulates gastrointestinal motility. The colon separates fibrous from non-fibrous particles; the former are excreted as hard faecal pellets. Soft mucus-covered caecal pellets are expelled separately and eaten (caecotrophy), allowing absorption of nutrients and bacterial fermentation products, as well as digestion of previously undigested food.

Rabbits should be vaccinated against myxomatosis and viral haemorrhagic disease.

Sciuridae (chipmunk, prairie dog)

Chipmunks

are omnivorous, eating seeds, buds, leaves and flowers in the wild. Captive animals are fed a commercial mix supplemented with fresh or dried fruit, vegetables and occasional nuts. These little rodents are escape artists, and their enclosure needs to be secure. Cage furniture should include branches, ropes and drainpipes. They can be housed singly, in pairs, or as a harem (with one male to two or three females). The testes descend in mature males during the breeding season (January–September).

Prairie dogs

are social animals. They should be provided with tunnels and deep bedding (such as wood shavings or paper) for digging. Prairie dogs are herbivores, and hindgut/caecal fermenters. They can be fed on rodent food and grass hay, with fresh greens as a treat. Obesity is common in pet prairie dogs. Water is provided in a sipper bottle. Males have an open inguinal canal (as in guinea pigs), and the testes may be retracted intra-abdominally.

Muridae (mouse, rat, hamster, gerbil)

These species also exhibit coprophagy; they cannot vomit. The dental formula for this group is: incisors 1/1, canines 0/0, premolars 0/0, molars 3/3. The incisors are hypsodontic, while the molars are brachyodontic (permanently rooted).

Mice

are omnivorous or herbivorous. Pet animals are usually fed a commercial rodent diet supplemented with a small amount of fresh food, fruit and vegetables. They are housed in either a wire cage with a solid plastic bottom, or a plastic enclosure with a mesh roof. Sawdust or wood shavings are utilized as substrate, with shredded newspaper or commercial rodent bedding in the nest box. Cardboard boxes and paper to tear, drainpipes and wheels are useful enrichment. Cage hygiene is important.

Rats

have a similar diet and housing requirement to mice. Fur yellowing is normal in aged animals.

Hamsters

have large cheek pouches for food storage. They are omnivorous and hoard food. Commercial hamster mixes are available for captive animals. They have bilateral pigmented sebaceous glands on their flanks; these are used for territorial marking and mating behaviour. Common species kept as pets include Syrian (Mesocricetus auratus), Chinese (Cricetulus griseus) and Russian (e.g. Roborovski, Phodopus roborovskii) hamsters. These animals are escape artists, and enclosures should be secure. They are usually housed in wire cages or plastic enclosures with tunnels. Paper or hay should be provided in the nest box. Exercise wheels are used at night.

Gerbils

have a large ventral scent gland on the mid-abdomen, used for territorial marking. The gland is more pronounced in young males. Urine is very concentrated in this desert adapted species. Commercial rodent mix can be supplemented with fresh fruit and vegetables, hay, and occasional treats of raisins. Gerbils are highly social and should be maintained in a group (ideally same sex), usually in a glass or plastic tank. The ‘gerbillarium’ should have a deep (15 cm) substrate of sawdust, wood shavings or peat and hay. Sand should be avoided, as rostral abrasions are common.

Caviidae (guinea pig)

Guinea pigs have sebaceous glands over the dorsum, rump and perineal areas. As with other Hystricognathi, they have large tympanic bullae. Digestion is mainly by caecal fermentation. They should be fed a diet of hay, fresh vegetables, and some commercial mix. Guinea pigs have a daily requirement for vitamin C, approximately 30 mg/kg per day (higher levels are required during pregnancy, lactation and illness). The dental formula for hystricognaths is: incisors 1/1, canines 0/0, premolars 1/1, molars 3/3. All teeth are continuously growing (hypsodont).

They are usually housed in a hutch with a large run area. They are a sociable species and usually kept in single-sex groups (castrated if male to reduce aggression), pairs or harems. At least one hide area should be provided per guinea pig. The flooring should be smooth, with a substrate of wood shavings or shredded paper.

Male guinea pigs have large seminiferous vesicles. A vaginal membrane is present in females, except during oestrus and parturition. Both sexes have a pair of inguinal nipples.

Chinchillidae (chinchilla)

Chinchillas have very dense fur, with up to 90 hairs per follicle. They are hindgut fermenters. They should be fed mainly hay with a small amount of commercial pellets; fruit and green vegetables can be given as occasional treats.

This species is usually housed in pairs, single-sex groups or a harem (one male with up to five females). Enclosures should be multilevel to permit horizontal and vertical activity. The enclosure is usually composed of wire mesh (15 × 15 mm) with wooden shelves and nest box. Dust baths should be provided for 10 minutes daily. Originating from the Andes, chinchillas are adapted to low humidity and cooler temperatures.

Octodontidae (degu)

Degus are native to Chile, and susceptible to heat stress (in environmental temperatures greater than 30°C). They are used in sleep biology and jet-lag studies, but very few medical data are published on this species. Degus are hindgut fermenters. Tail slip is common if they are incorrectly restrained.

The captive diet should be predominantly grass hay, with rodent mix and a small amount of fresh greens. Degus are sociable and kept in pairs or groups. Their enclosure is similar to that for chinchillas, although they should be provided with bedding for digging and storing food. They will use an exercise wheel, and may use a dust bath.

Erinaceidae (African pygmy hedgehog)

African pygmy hedgehogs (or four-toed hedgehogs) originate from equatorial and central Africa. They are nocturnal and solitary. Novel objects may result in ‘anting’ or ‘anointing’ behaviour, where the hedgehog hypersalivates to create a foam which it then spits onto itself. Animals may hiss or ‘puff up’ in defence. Unlike the European hedgehog (Erinaceus europaeus), they do not hibernate.

The dental formula for hedgehogs is: incisors 3/2, canines 1/1, premolars 3/2, molars 3/3. Wild hedgehogs are insectivorous and omnivorous, requiring a relatively high-protein and low-fat diet. Captive animals are fed cat food or insectivore diet, vegetables, insects and a vitamin/mineral supplement.

Their enclosure should have smooth walls, deep (10 cm) bedding and a hide box. The ambient temperature should be 24–30°C, often requiring some form of supplemental heating. The hedgehogs like to dig and use exercise wheels, and may swim or bathe in shallow water.

Petauridae (sugar glider)

Sugar gliders are nocturnal and arboreal. The gliding membrane (patagium) stretches from the fifth digit of the forepaws to the ankles, and they can glide up to 50 m. For this reason, large areas should be made available for exercise. The enclosure should be a minimum of 2 m wide × 2 m long × 1.8 m high, with branches at either end to allow gliding. Supplemental heating is usually required to prevent the animals entering a state of torpor. They are sociable and kept in groups. Scent marking allows group members to recognize each other. Males develop a scent gland on their forehead, and have anal glands and scent glands on their chest; females have scent glands within their pouch but scent mark with urine.

In the wild, the diet of the sugar glider varies seasonally – being mainly gum/sap from eucalyptus or acacia trees during the winter, and mainly insects for the rest of the year. Sugar gliders have specialized incisors for gouging bark. Several ‘recipes’ have been developed for the sugar glider diet, usually a mix of insectivore/carnivore diet and Leadbeater’s Mixture (a honey, protein, vitamin and mineral supplement mix). Sugar gliders should be fed in the evening.

As marsupials, sugar gliders have a common opening for the urinary and digestive tracts, the cloaca. Assessment of core body temperature via a cloacal probe is less reliable than rectal probes in other species.

Mustelidae (ferret)

Some ferrets are kept as working animals (particularly in the UK) and others purely as pets. They are carnivorous, and are fed on either whole carcasses (e.g. pigeon or rabbit) or a commercial ferret diet. The gastrointestinal transit time is quite rapid, being approximately 3 hours.

The heart is relatively caudal (at the level of the sixth to eighth ribs). Ferrets should be vaccinated against canine distemper virus. Dental disease is common and the teeth should be brushed if possible.

Ferrets should be housed in an enclosure measuring at least 55 × 50 × 40 cm. The substrate is usually wood shavings. Most animals like to sleep in a towel or blanket, in a hammock or a box.

Callitrichidae and Cebidae (common marmoset, squirrel monkey)

Non-human primates are rarely kept as pets, many species require a licence to be kept as such legally in the UK. Callitrichids (marmosets and tamarins) are the most common species seen. Zoonotic diseases should be considered when handling primates.

These species are omnivorous, but exact dietary requirements vary. Callitrichids eat a large proportion of fruit, but commercial kibble diets are available for most species. Besides the primate’s daily requirement for vitamin C, New World primates (particularly callitrichids) require vitamin D3 so should be exposed to ultraviolet light (UV-B) to enable calcium and phosphorus metabolism. Where invertebrates are fed, these should be gut-loaded with calcium supplement.

History

Some pertinent topics to discuss with owners during the initial consultation with an exotic pet mammal are listed in Box 2.1. Although the basic outline is very similar to that for other companion animals, it is noteworthy that greater emphasis is paid to husbandry conditions (including housing and diet). This is to gain an understanding of any factors that may predispose disease in the animal. Unfortunately husbandry-related disease is common in exotic pets.

Tags: Saunders Solutions in Veterinary Practice Small Animal Exotic

Sep 3, 2016 | Posted by admin in SMALL ANIMAL | Comments Off

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