Basic Approach to the Small Mammal Patient
World Small Animal Veterinary Association World Congress Proceedings, 2004
Sharon Redrobe, BSc (Hons), BVetMed, CertLAS, CertZooMed, MRCVS
Head of Veterinary Services, Bristol Zoo Gardens
Bristol, UK

Rodents

General Anatomy

Dental formula 1/1 0/0 0/0 3/3. The incisors are chisel shaped, constantly growing and a pigmented yellow colour. When gnawing the lower jaw moves forward so that the incisors oppose each other but the molars do not. The cheeks are drawn in across the diastema (the gap between the incisors and molars). This enables the rodents to gnaw without wearing the molars or swallowing debris. Rodents exhibit coprophagy--the act of eating faeces--to recover vitamins B and K.

Sexing Rodents

Rat, mouse, gerbil, hamster, chipmunk

A papilla is seen in both sexes. In the male it is the tip of the penis, in the female it is the urethral papilla. The distance between the anus and the papilla (ano-genital difference) is greater in the male. The nipples are more obvious in the female. The male hamster has obvious testes which can be seen from above.

Guinea pig, chinchilla

The female has a membrane between the urethral orifice and the anus. The penis of the male can be extruded by gentle pressure and the testes can be gently palpated either side of the anus. The retracted penis forms a Y shape in the prepuce. Beware; both sexes of guinea pig have an obvious pair of teats in the inguinal area.

Handling and Restraint, Risks to Handler and Animal

Non-aggressive animals can be gentle cupped in the hand and restrained by the base of the tail. Take care with the gerbil that may slough the skin from the tail if handled roughly. The rat, mouse, gerbil, hamster may be gently scruffed for injection or examination by holding a flap of skin at the back of the neck. Hamsters have a lot of loose skin and so can turn around in it and still bite if you have not grasped enough scruff!! Rats can beheld around the chest with the handlers thumb beneath the animal's chin to prevent biting and the hindquarters supported. Take care not to squeeze, as it is easy to suffocate the wriggling rat by accident. Handle guinea pigs using one hand around the shoulders and one hand supporting the rump. The liver can be ruptured if the guinea pig is handled roughly around the middle. Chinchillas can generally be scooped up in the hands. The base of the tail may be held for restraint. When the chinchilla is stress large amounts of hair may be lost (= fur slip) and bald patches may result. Although the hair will regrow, the owner should always be warned about fur slip before handling the animal.

Rabbits

Basic Anatomy

Rabbits are not rodents but lagomorphs. The rabbit dental formula is 1/1 0/0 3/2 3/3. They characteristically have long ears, short fluffy tail, hopping gait and powerful hind legs. Rabbits perform caecotrophy--they eat the soft, mucous covered caecal pellets straight from the anus. They also produce dry pellets that are not eaten. Urethra opens into vagina, so rabbits do not have a separate external urethral papilla like rodents.

Sexing and Methods of Breeding

Males have round penile sheath from which penis can be extruded. The large bald scrotal sacs are obvious in the mature male. The female has slit-like opening. Begin breeding of the doe between 4 and 6 months old. One buck can service 25 does. Doe taken to bucks cage and left for ten minutes. Taken to another buck if not mated. Artificial insemination is used commercially and is very successful.

Handling and Restraint, Risks to Handler and Animal

Rabbits rarely bite but have sharp claws that can inflict painful scratches on the handler. Mishandling can lead to a fractured spine of the rabbit. The rabbit has powerful hind legs and will attempt to kick out or escape if frightened. Pick up the rabbit firmly around the shoulders or by the scruff. Support the hindquarters. Tuck the rabbit's head under your arm when carrying. Once the head is covered, the animal is calmer and if it does struggle it will tend to push deeper under your arm. Place the rabbit back into the cage rear end first to prevent kicking out at the handler. For restraint, hold the animal with the rear end against your body and hands around the shoulders. To restrain for intravenous injection into the ear veins, wrap the whole body in a towel, leaving only the head exposed.

COLLECTION OF SAMPLES

1. Blood: Maximum volume removed should not exceed 10% of circulating blood volume.

Species

Av. Adult
body
weight
(g)

Av. adult
blood
volume
(ml)

Maximum
sample
volume
(ml)

Route

Mouse

25-40

2.5

0.25

Lateral tail vein

Gerbil/hamster

85-150

9

0.5

Cardiac puncture

Rat

300-500

30

3

Lateral tail vein

Guinea pig

700-1200

60

6

Ear vein

Rabbit

2000-6000

250

25

Marginal ear vein,
jugular, cephalic vein

Ferret

750-1000

50

5

Jugular or cephalic vein

2. Urine: Collected during voluntary urination

Most rats and mice urinate when restrained. Urethral catheterisation and cystocentesis are easiest in the rabbit, guinea pig and chinchilla.

Administration of Substances

For each species, site of injection and maximum volume is given in the table below:

Species

Sub-
cutaneous

Intra-
muscular

Intra-
peritoneal

Intravenous

Mouse

Scruff,
2-3ml

Quadriceps,
0.05ml

2-3ml

Lateral tail vein,
0.2ml

Hamster/gerbil

Scruff,
3-4ml

Quadriceps,
0.1ml

3-4ml

Not practicable

Rat

Scruff, flank,
5-10ml

Quadriceps,
0.3ml

10-15ml

Lateral tail vein,
0.5ml

Guinea pig

Scruff, flank,
5-10ml

Quadriceps,
0.3ml

10-15ml

Ear vein,
saphenous vein,
0.5ml

Rabbit

Scruff, flank,
30-50ml

Quadriceps,
lumbar muscles,
0.5-1ml

50-100ml

Marginal ear
vein, 1-5ml

Clinical parameters of common mammal species

Mammal

Weight
range (g)

Rectal
temperature
(°C)

Approximate
pulse rate/
minute

Approximate
respiratory
rate/minute

Chipmunk

100-250

38

200

100

Chinchilla

400-600

35.4-38

100

45-65

Guinea pig

500-1100

38

230-380

70-100

Hamster

85-120

37-38

280-500

35-120

Gerbil

45-130

39

260-600

90

Mouse

20-60

37.4

300-700

150-200

Gerbil

50-90

39

260-600

70-120

Rat

250-400

38

300-500

80-100

Common bacterial diseases

Bacteria

Clinical signs

Bordetella bronchiseptica

Conjunctivitis, pneumonia

Campylobacter

Diarrhoea, wet tail, rectal prolapse

Chlamydia

Perinatal mortality

Clostridium piliformis

Diarrhoea, weight loss

Corynebacterium spp

Arthritis, conjunctivitis, abscess, dermatitis

Fusobacterium necrophorum

Dermatitis, dental/jaw abscess

Klebsiella

Pneumonia, nasal discharge

Leptospira icterohaemorrhagica

Vascular signs

Listeria

Perinatal mortality

Mycoplasma spp

Arthritis (M. arthritides), conjunctivitis, dyspnoea,
pneumonia, nasal discharge, infertility (M. pulmonis)

Pasteurella

Pneumonia (P. pneumotropica rodent, P. multocida rabbit),
abscess, perinatal mortality, dermatitis

Pseudomonas aeruginosa

Diarrhoea, dermatitis

Salmonella typhimurium,
S. enteritidis

Anorexia, septicaemia, diarrhoea, perinatal mortality

Staphylococcus

Abscess, dermatitis (Staph aureus)

Streptobacillus moniliformis

Limb/tail inflammation, necrosis

Streptococcus zooepidemicus

Pericarditis, abscesses of lymph nodes--mesenteric, cervical

Streptococcus

Septicaemia, pneumonia, abscess

2. Urine: Collected during voluntary urination

Most rats and mice urinate when restrained. Urethral catheterisation and cystocentesis are possible in the rabbit.

Rabbit urinalysis

Parameter

Value

Urine volume/24h

20-350 ml/kg average 130mg/kg

SG

1.003-1.036

Average pH

8

Colour

Pale to dark yellow, orange, rust, mildly opaque
with 'sand' calcium carbonate

protein

Negative to trace

Ketones

Negative

Glucose

Negative to trace

Casts

None

WBC

Rare

RBC

Rare

Epithelial cells, bacteria

None to rare

Crystals

Common, triple phosphate, calcium monohydrate.
Anhydrous calcium carbonate

Other techniques

Fluid therapy can be administered by jelly cubes for rats), by syringe or dropper if intravenous catheter and drip sets in rabbits the substance is palatable, or by gavage using and ferrets. Oral administration can be a polyethylene catheter or commercial gavage achieved via the drinking water, by mixing needle. Rabbits tolerate nasogastric tubes with small amounts of food (e.g., injected into well. Placement is as for the cat.

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Sharon Redrobe, BSc (Hons), BVetMed, CertLAS, CertZooMed, MRCVS
Head of Veterinary Services, Bristol Zoo Gardens
Bristol, UK


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