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.

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:

Clinical parameters of common mammal species

Common bacterial diseases

2. Urine: Collected during voluntary urination

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

Rabbit urinalysis

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.