VET 217: Introduction to Laboratory, Zoo, and Wildlife Medicine

GUINEA PIGS

GUINEA PIGS

INTRODUCTION

Guinea Pigs (Cavia porcellus) also known as cavies, are rodent-like animals native to the high mountain areas of South America.  In their native country they are raised for human consumption.  They are gentle animals that rarely bite or scratch.  They make good pets.

There are three varieties currently available:  American or English (smooth, short coat), Abyssinian (whorls in coat) and Peruvian (long, silky hair).  They come in all different colors and patterns.

Guinea pigs are used in research although not as extensively as rats and mice.  Guinea pigs are perhaps most famous for helping to develop the diphtheria vaccine.   Both inbred and outbred strains are used.  The two most common inbred strains are Strain 13 and Strain 2.  The most common outbred strain is the Dunkin-Hartley (American Albino).

RESOURCES

For additional information regarding guinea pigs, please visit these web sites:

American Cavy Breeders Association

American Rabbit Breeders Association

ANATOMY

Guinea pigs have open-rooted incisors, pre-molars and molars that grow continuously throughout the animal’s life.  They have a dental formula of 2(I 1/1, C 0/0, P 1/1, M3/3).  The teeth may have a yellow, orange color to them which is normal.  Normal chewing action will wear down the teeth, but if any malocclusion exists, then clipping the teeth will become necessary.  Access to the back molars can be challenging.

Guinea pigs have short tails and stocky bodies.  Their legs are short and therefore they can not climb or jump well.

Guinea pigs only have two nipples and mammary glands but are still able to raise a litter of more than two pups.  They nurse standing up.

Guinea pigs have open inguinal rings and the ability to retract their testicles into the abdominal cavity.  Care must be taken by the surgeon to close the rings after castration to prevent the possibility of evisceration.

An interesting anatomical fact about the guinea pig is that they have a large ceacum and bacterial digestion is an important part of their normal gut function.  This digestion can be seriously disrupted by the use of antibiotics, leading to a fatal enterotoxaemia.

The symphisis of the female guinea pig is fibrocartilagenous and must spread apart in order for the precocious young to be successfully delivered.  If the female guinea pig is not bred before 6 month of age, the symphisis may fuse, predisposing the female to dystocia.

PHYSIOLOGY

BEHAVIOR

Guinea pigs are sensitive to change and are easily stressed.  They should be provided with hide boxes.  They can be group housed although they may fight if overcrowded or in a breeding situation.   They have a large repertoire of vocalizations including whistling, chirps and grunts.  They are diurnal.

Normal posture is alert, bright eyed with all four limbs on the ground.  They should not have a hunched posture.  Guinea pigs will freeze when startled or may do the opposite and stamped.  This is normal for a guinea pig.

SEXING & BREEDING

In guinea pigs, the anogenital distance is fairly similar.  With adult guinea pigs, the testes can be readily seen or the penis can be manually extruded with gentle pressure.  In the female the external genitalia have a Y-shape while in the male they are I-shaped.  Male guinea pigs are called boars and female guinea pigs are called sows.

The females are continuously polyestrous and are spontaneous ovulators.  The estrus cycle is approximately 16 days in duration.

Two mating systems are used.  The polygamous (harem) system pairs one male with four to ten females.  The monogamous system pairs one male with one female.  There are advantages and disadvantages to both systems.  The system utilized will depend on the facility and the availability of space and other resources.

The pups are precocious.  That means they are born fully furred and walking.  They will begin nibbling on solid food shortly after birth. Weaning takes place around 14-21 days of age.

HANDLING & RESTRAINT

Guinea pigs respond well to gentle handling.  Use the minimal restraint needed to get the job done.  Use a two-handed method of restraint.  Place one hand around the chest and one hand under the rump.  Always watch the guinea pig’s breathing as guinea pigs are easily stressed.  There are also restraint devices on the market that can contain a guinea pig while minimizing stress.  Wrapping the guinea pig in a towel may also help.  In many private practices, small mammals are routinely anesthetized utilizing inhalant anesthesia in order to facilitate restraint.

Blood collection in the guinea pig is usually done by nicking the ear vein using a 22-25 gauge needle.  The metatarsal and the saphenous veins can also be used (25-23 gauge).  The guinea pig can also be bled using the retro-orbital sinus (anesthesia required) or cardiac puncture (terminal procedure requiring anesthesia).  These techniques are not recommended for pets.  The jugular vein can also be used.  Restraint is similar as for hitting a jugular on a cat.  Watch the guinea pig’s stress level!  Maximum blood volume drawn should be 10% of BW but in a sick animal 5% is probably a safer margin.  This is approximately .5ml/100gBW.

Injections are given utilizing a 23-25gauge needle (.3 ml) IM in the large muscles of the hind limbs, subcutaneously in the scruff (5-10 ml), intraperitoneal in the caudal quadrant of the abdomen (5 ml).   Intravenous injections are difficult to perform.   The intraosseous route may be a better choice.

HUSBANDRY

Each guinea pig should have at least 12’x12’x12’ of cage space.  A female guinea pig with a litter will require two to four times more space than this.  The cage should provide them with an exercise, nest and feeding area.  Group housing is suggested.

Many types of bedding are used.  The most common bedding is pine shavings.  There is a great deal of controversy surrounding the use of cedar shavings and they are probably best avoided.  Guinea pigs do not make nests but appreciate hide boxes.

The cage should be cleaned at least 2x a week or more often if any odor is noted. Guinea pigs can be messy and will spill food and waterers.  Ideal temperature is between 55-70 degrees F with humidity in the range of 40-70%.  A light:dark cycle of 12:12 hours is recommended.  Guinea pigs are very susceptible to heat stress once the temperature rises above 80 degrees F.

Guinea pigs should not be housed or exposed to animals that carry Bordetella such as rabbits, cats and dogs.  Bordatella causes severe, often fatal pneumonia in guinea pigs.

DIET/NUTRITION

Guinea pigs should be fed commercially prepared guinea pig chow with a protein content of at least 20%.  The diet should contain at least 16% crude fiber.  They should not be fed seed mixes.  Water should always be offered free choice.

Guinea pigs are unique in that like people and monkeys, they have dietary requirement for Vitamin C.  Guinea pig chow should have a milling date on the label and the diet should not be fed more than 90 days past the milling date.  Refrigerating the feed may help to slow the breakdown of Vitamin C.  Vitamin C rich foods can be fed as a supplement.  ¼ orange, kale and cabbage are rich in Vitamin C.  Some texts recommend adding Vitamin C to the water.  Vitamin C breaks down rapidly to a fresh mix must be offered daily.  In addition, the vitamin supplement may cause a change in the taste of the water and the guinea pig may refuse to drink.  If Vitamin C is supplemented it should be added at the rate of 1 gram Vitamin C/ 1L of H2O.

Guinea pigs can not eat standard rodent chow or rabbit pellets because they are too hard and do not contain added Vitamin C.  Guinea pig pellets are smaller, softer and Vitamin C supplemented.  Make sure to buy food from a reputable dealer and check for the milling date. 

COMMON DISEASE

Ectoparasites

Endoparasites

Malocclusion (both incisors and molars)

Respiratory diseases (Bordatella)

Starvation/dehydration

Dystocia

Abcesses

Enterotoxaemia (secondary to antibiotics)

Trauma

Pododermatitis

Scurvy (Vitamin C deficiency)

ZOONOSES

Rare.

Some people are seriously allergic to rodents.  Anaphylactic reactions are possible but the incidence of allergies to rodents does not seem to be an higher than for other allergic substances such as mites, bees, peanuts, etc.