Biomethodology of the Rabbit

General Biology

Of the many breeds of the domesticated European rabbit (Oryctolagus cuniculus), the albino New Zealand White is the most common breed utilized in biomedical research. The visibility of the peripheral vasculature in albino rabbits is advantageous to the biomedical use of this rabbit. Non-albino breeds such as the black and white Dutch belted rabbit tend to be preferred where pigmentation is required (i.e. ophthalmological research). Rabbits like rodents have two large upper incisors and two large lower incisors. Unlike rodents, however, an additional pair of incisors is located caudal to the large upper incisors (peg teeth). This additional pair of upper incisors is greatly reduced in size and is why rabbits are members of the order Lagomorpha rather than the order Rodentia.

Rabbits have several unique anatomical characteristics. As previously mentioned the long slender ears of the albino New Zealand White breed facilitate phlebotomy procedures. The long backbone predisposes rabbits to spinal fractures, if not captured and restrained properly. Rabbit teeth continue to grow throughout life. Malocclusion occasionally occurs in rabbits preventing normal tooth wear resulting in severe overgrow of the teeth inhibiting normal mastication. The neutrophil of the rabbit resembles an eosinophil due to the numerous intracytoplasmic eosinophilic granules.

Rabbits can be grouped by their microbial colonization: "Specific Pathogen Free" (SPF) rabbits are free from several common pathogenic organisms such as Pasteurella , Encephalitzoonois, and Coccidiosis. SPF rabbits are bred specifically for research use. "Conventional" rabbits tend to be colonized with the preceding organisms which can occasionally be detrimental to their health and longevity. Conventional rabbits are bred primarily for food and fur. Unlike SPF rabbits, conventional rabbits are widely available and if appropriate for the project can represent a substantial savings upon purchase. The investigator must weigh these considerations when choosing the type of rabbit for purchase. Numerous genetic mutations have been noted in the rabbit2 and several inbred rabbit strains have been produced.

Sources and Ordering

Conventional rabbits are readily available from several commercial sources. Typically, for commercially available rabbits, animals ordered by Wednesday will arrive the following week. SPF rabbits and genetically unique animals are not as readily available and may take longer to acquire. A source list of mutant and inbred rabbits is available from the Institute of Laboratory Animal Resources.3

Behavior

The rabbits are gentle animals and if care is taken become accustomed to handling if they are not upset by the experience. Inappropriate handling can result in toenail scratches to the handler from the toe nails on the powerful rear legs . Rabbits are herbivores and have the unique characteristic of reingesting soft fecal pellets directly from the anus. This process of "pseudorumination" allows the acquisition of B vitamins that have been produced by microorganisms in the cecum.

Basic Biological Data

Adult body weight: male

2-5 kg1

Adult body weight: female

2-6 kg1

Life span

5-6 up to 15 years1

Food consumption

5 g/100 g/ day1

Water consumption

5-10 ml/100 g/day6

Rectal Temperature

38.5-39.5C4

Heart rate

205-235/minute6

Respiratory rate

30-60 per minute1
           

Basic Husbandry

Most rabbits are housed in stainless steel cages with a fenestrated floor to allow feces to drop through into a pan. Absorbent material is placed in the pan to collect urine and minimize ammonia release due to the bacterial breakdown of urea. Caged rabbits are typically housed individually, however, some cages allow for pair housing. Rabbits less than 2 kg in weight are provided with 1.5 square feet of floor space. Rabbits weighing from 2-4 kg are maintained in 3 square foot cages. Water is typically provided through a lixit that provides water at all times. The lixit on cages is checked frequently to make sure it has not become plugged. Water may also be provided via a standard 1 liter water bottle attached to the wire front of the cage. Food is provided by a J-hopper attached to the front of the cage. J-hopper's prevent the rabbit from defecating in their food, which occurs with the use of food crocks (bowls).

The drop pans are changed by the caretaking staff twice per week, and the rabbit is placed into a new sanitized cage every two weeks. Water lixits and feed hoppers are checked daily by caretakers to insure the provision of food and water.

Pelleted natural ingredient diets are used to feed all rabbits and are composed primarily of cereal grains which are supplemented with additional protein, vitamins and mineral. Rabbits receive a high fiber diet which tends to minimize common gastrointestinal disorders. Due to the nature of natural ingredient diets, the exact composition can vary substantially from each vendor. Rabbits are fed a specified amount of diet daily in order to prevent obesity which tends to occur if rabbits are fed ad libitum. The water provided to animals is chlorinated tap water. Rabbits are provided with a 12 hours of light each day with the light phase starting at 6 am.

Identification

Cage cards are utilized to identify the strain of rabbit, sex, number, principal investigator, and research protocol. Cage cards should not be removed from the cage to avoid misidentification of the animals. Temporary identification of individual rabbits can be accomplished by pen marks on the fur, or dyeing the fur. Pen marks or dyes will only last 1-2 days. Permanent identification methods can be achieved by ear tattooing which will be performed by husbandry personnel upon request.

Handling

When handling rabbits it is advisable to wear latex gloves to prevent the development of allergies and to provide some safety from rabbit scratches to the handler. Rabbits seldom bite but can inflict painful scratch wounds, especially with the hind feet. They should be held in a way that directs their hind feet away from the handler's body. Grasping the loose skin over the neck and shoulder with the head directed away from the holder is the best method of initial restraint (picture ). When lifting a rabbit, the lower part of the body must be supported by the other hand to prevent serious injury to the rabbit's back (picture ; picture ). Rabbits should never be restrained or lifted by the ears. If the rabbit begins to struggle violently, it should immediately be placed on a solid surface and calmed. Struggling frequently leads to fracture of lumbar vertebrae and injury to the spinal cord that may necessitate euthanasia. If properly used, commercially available rabbit restrainers help to avoid injuries (picture ).

Rabbits may exhibit sudden violent efforts to escape during restraint. In the process, intravenous needles, gavage tubes, etc. can be dislodged causing spills or otherwise endangering themselves or personnel. Therefore, complete restraint should be accomplished before attempting such procedures and rabbits should never be left unattended in restraint devices. Training in the use of these devices can be arranged through the DVR.

Breeding

Rabbit colonies tend to be very labor intensive and are only appropriate for rabbits which are not readily available commercially (i.e. Watanabe rabbits). Investigators requiring the establishment of breeding colonies should consult with the DVR to assure proper management of the colonies. Breeding animals have different requirements (i.e. nutrition), which if not provided, will have a detrimental effect on reproductive performance.

Restraint Devices

Several types of devices are commercially available to restrain rabbits. Quality devices prevent the animal from turning around or twisting yet allow easy access to the head and ears. Care should be taken when placing a rabbit in a restraint device since struggling may result in damage to the spine. Struggling is reduced if the device snugly secures both the head, back and hindlegs (picture ).

Sexing

Rabbits can be sexed by causing eversion of the penis or vulva when slight pressure is applied to the external genitalia.7

References

1) Harkness JE, Wagner JE 1989, The Biology and Medicine of Rabbits and Rodents ; 3rd Edition, Lea and Febiger, Philadelphia

2) The Biology of the Laboratory Rabbit. Manning, P. J., Ringer D. H., Newcomer, C. E., (1994) The Biology ofthe Laboratory Rabbit . Academic Press, New York, New York.

3) Institute of Laboratory Animal Resources, National Academy of Sciences, National Research Council, 2101 Constitution Avenue, Washington DC.

4) Ruckebusch, Y., Phaneuf, L. P., and Dunlop R. (1991). Physiology of Small and Large Animals Dekker, Philadelphia, Pennsylvania.

5) The UFAW Handbook on the Care & Managment of Laboratory Animals 6th ed; editor Poole, Trevor B. Longman Scientific & Technical, Endland, 1986.

6) Manning, P. J., Ringer D. H., Newcomer, C. E., (1994) The Biology of the Laboratory Rabbit. Academic Press,New York, New York.

7) Fox RR, Crary DD A simple technique for the sexing of new born rabbits. Lab. Anim. Sci . 22:556-8, 1972