The original range of the laboratory rabbit in the wild was apparently Southwestern Europe and Northwestern Africa. Through introduction these rabbits now inhabit many other regions including Great Britain, the Ukraine, New Zealand, Australia, South America, and several portions of the United States. In most of these regions they have become widespread and abundant enough to become pests. They dig burrows in hedge rows and open fields and eat vegetation. The general coloration of the wild type is upper parts with a fine mixture of black and light brown hair, the ears the same color except for black edged tip, and the nape is buff colored and the collar is dark, the tail is light below and brownish black above, the under parts and inner surface of the legs are buff white. These animals have long hind legs, long ears, and large eyes, their feet are will furred beneath and they have large, straight claws. Unlike most of the other rabbits and hares, they dig burrows in which they live. They are also gregarious and make their burrows near those of others of their kind so that these warrens sometimes occupy more than three acres of land. One warren reportedly contained about 150 rabbits and occupied more than 2000 square meters in an open field, the feeding grounds occupied a surrounding area of 8000 square meters. Grasses and other herbaceous plants are preferred food, the bark of twigs and woody plants are also eaten when herbs are not available. This habit makes them particularly harmful in areas where the only trees and shrubs available are in shelter belts, farm plantings and fruit crops where in wintertime the rabbits may destroy the trees and shrubs by girdling the trees. Rabbits are essentially nocturnal, coming out of their burrows in the evening, retiring in the early morning. They sometimes bask in early morning sun at the burrow entrance. Wild rabbits have been extensively used for food and members of this genus are of great economic importance. Many special strains have been developed resulting in rabbits which are utilized for a great variety of purposes such as genetic and nutritional studies, laboratory experimental animals, meat and wool. In some areas where they have been introduced for the production of meat, rabbits have become pests, especially in areas where there are no predators. In Australia and some Pacific islands they have been increasing so profusely due to the absence of natural predators that they have quickly depleted the scant vegetation. In recent years a virus disease, myxomatosis, has been effectively used to control wild populations of rabbits in some countries, but after outbreaks, a resistance often develops. In the laboratory rabbit strains that have been developed, the weight ranges in size from the small Dutch rabbit to the large Flemish giant which may exceed 25 pounds in weight.
Two unique physiological aspects in the rabbit are the lack of estrus cycle and the habit of coprophagy. The rabbit is an induced ovulator and will ovulate spontaneously when the buck copulates with her. The rabbit will also exhibit false pregnancy in that attempts to breed by the buck without intermission can lead to simulated pregnancy without actual conception.
The rabbit also practices coprophagy or the ingestion of fecal matter. This practice involves ingestion of special soft fecal pellets which are excreted in the early morning hours. This is a significant practice in that the bacterial synthesis of certain B vitamins in the cecum are excreted at this time and if rabbits are prevented from this practice they will die from vitamin B deficiency within a rather short period of time.
Due to its relatively large size in comparison with other small laboratory animals, care must be taken when handling laboratory rabbits. These animals can become extremely mean and inflict severe bites or scratches from their powerful hind legs if not properly handled and restrained. Laboratory rabbits should never be handled by the ears, but carefully and gently restrained by grasping a large fold of loose skin over the shoulders with one hand and either supporting or grasping the rear feet with the other hand (see figure 1). Failing to support or hold onto the rear feet may result in the animal kicking and thrashing trying to escape which can cause severe spinal injury or a broken back. The easiest method of transporting laboratory rabbits from one place to another is to hold the animal against your side with its head in the crock of your arm under your armpit (see figure 2). In this way the rabbit remains quiet and can be easily carried from one area to another.Injection and bleeding sites in a rabbit are fairly easy as they mostly involve the utilization of the ear vessels. The marginal ear vein of the rabbit can be utilized for both injection or bleeding. Care must be taken when serial sampling or injections are going to be performed to start at the furthest aspect of the ear and work towards the body to insure availability of multiple sites. The medial artery can be utilized for bleeding with the same cautions mentioned for the marginal vein. Intraperitoneal injections can be easily performed in the lower quadrants of the abdomen and subcutaneous injections in the folds of skin over the back, shoulders and neck. Cardio puncture can be useful in obtaining large quantities of blood by an experienced operator. (Not recommended for recoverable animals.)
Sexing of the rabbit is not as difficult as the rodent, but in a young female, sometimes it is not too easy (see figures 3 and 4).
Housing and Husbandry
Rabbits are generally housed in suspended cages over bedding that can be either pelleted or paper. In many commercial colonies rabbit cages are hung over open floors or pits and the feces removed by mechanical methods. Which ever method is used, the following criteria may be used to evaluate the caging system: a) the cage should be designed with the animals' physical comfort as the primary consideration. Physical comfort as applied specifically to caging, includes factors such as keeping the animal dry and clean, maintaining the animal in a state of relative thermo neutrality, providing sufficient space to insure freedom of movement and allow for normal postural adjustment to avoid unnecessary physical restraint, providing convenient access to clean feed and water, and if the animals are housed in groups, maintain them in groups without overcrowding, separated by sex, b) functional, operation of the cage should be compatible with the maintenance of the animal in good health as measured by such factors as maintenance of normal body weight, and prevention of diseases, and c) the cage should be designed to facilitate effective sanitary maintenance and servicing. As rabbits tend to excrete large amounts of urine and feces, the caging system should be designed for easy cleaning which should be accomplished two or three times a week.
As mentioned before the majority of rabbits are maintained in some design of a suspended cage either with or without a pan and are housed singly in the majority of cases. The suspended cage should be constructed of a stainless steel with or without solid sides. When utilized with a waste pan, the pan should be suspended under the cage so the animals do not come in contact with the bedding or the waste in the pan. All cage designs should permit the rabbit to engage in coprophagy to obtain the necessary B vitamins from the night feces.
Rabbits are generally caged singly, however very young rabbits, when they are first weaned may be kept two to a cage. It is not recommended to keep adult rabbits caged other than individually as they have a tendency to be aggressive toward one another. Only rabbits of the same sex should be housed together in a room, with the rooms separated as far apart as possible. The females should be cared for first.
Feed and Water Devices
Feed and water devices utilized with rabbits vary greatly from facility to facility although standardize procedures have come more into vogue in the last few years. Previous use of water bowls and leafy vegetables such as lettuce and potatoes to supply the animal's needs have come into disfavor because on one hand water bowls become contaminated easily and on the other the rabbit does not get sufficient waste from the leafy vegetables and potatoes. Standard watering devices now include either automatic watering systems or water bottles, fitted with sipper tubes generally of the ball type. These sipper tubes have a ball mounted in the end of the tube and the animal licks this ball to obtain water and thereby reduces the loss of water due to the rabbit playing with the sipper tube. Feeding devices also vary, however, the suspended feeder hanging on the outside of the cage with an access port for the rabbit to obtain the feed is now fairly standard. Although many different designs of this type of feeder are seen, they are all basically designed to provide the same access to the feed. Rabbits tend to contaminate their feed and therefore the feeder and feed should be dumped on a daily basis and the feeder cleaned at least two or three times a week. Feed should be clean, free of contaminates, be palatable and nutritionally adequate. Rabbits should be fed in amounts sufficient to insure normal growth in immature animals and the maintenance of normal body weight in adults. Rabbits tend to become overweight easily and therefore should not be fed ad libitum but the feed limited to maintain their weight when they become mature.
Identification of rabbits is primarily limited to ear tattoos. The rabbit has generally very large ears and it is easy to apply a tattoo in large enough letters that it can be easily read and maintained throughout the rabbit's life. Other methods sometimes used are, utilization of various dyes to stain the fur and neck collars. These techniques leave much to be desired and the tattoo is the easiest to utilize in the identification of rabbits.
Husbandry covers a large area of rabbit care which includes such things as sanitation, hygiene, waste disposal, feed and watering, cage cleaning and a host of other areas. Husbandry with rabbits does not vary appreciatively from the other species but there are some individualities that must be considered.
As noted before, rabbits should have daily access to feed, but it should be limited to maintain only normal growth and maintenance of body weight so as to prevent the obesity common in ad libitum fed rabbits. The feed should be clean, free of contaminants, palatable and nutritionally adequate. As mentioned before, rabbits tend to contaminate their feed easily and therefore the feed should be dumped daily, and the feeder washed at least twice weekly to cut down on the contamination.
Rabbits should have daily access to water according to their particular requirements. As stated before the water bottle with sipper tube devices are the most satisfactory, along with automatic watering for utilization in rabbit cages. Water devices such as drinking tubes, water bottles, and automatic water systems should be examined routinely to assure their proper working and function. With automatic watering systems, it is sometimes necessary to train rabbits who have been using water bottles in the proper use of these watering devices by allowing them to drip slightly the first day or two in order for the animal to become acquainted with the location and function of the valves. Water bottles and sipper tubes should be washed and sanitized on a routine basis and should not be refilled but replaced with a clean bottle when they become empty. Utilization of the ball type sipper tube will cut down on the number of times that these water bottles need to be replaced because the rabbit is unable to regurgitate saliva into the water bottles itself.
Sanitation practices cover a large number of facets in animal facilities and are probably among the most important areas of responsibility in the husbandry of a colony. Animal facilities should be kept clean, and a regular schedule of sanitary maintenance is necessary including the provisions for the elimination of radioactive, toxic and infectious waste. Rabbit rooms, corridors, storage spaces and other areas in a rabbit facility should be cleaned as often as necessary and it is recommended that it be done daily, using the proper detergents and disinfectants to keep them free of dirt, debris and harmful contamination. Care must be taken in the selection and use of these materials, as residues may be toxic to the animals. The continuing objective should be to keep these areas neat and uncluttered. Monitoring may also be required for radiological, toxicological or infectious contamination. Rabbit cages are generally maintained in a laboratory animal facility with some type of litter or bedding and this should be changed two to three times a week or as often as necessary to keep the animal's cage dry and minimize odors which may be offensive or physiological stressful. Rabbits also shed a large quantity of hair which can easily clog filters and exhaust ducts, so care must be taken to insure proper air flow in all animal rooms by closely monitoring the clogging of these air ducts. Keeping the temperature in the room set to the low sixties will reduce the amount of hair loss. Animal cages, rack and accessory equipment such as feeders and water bottles should be washed and sanitized as often as necessary to keep them physically clean and free from contamination. Rabbit cages, should be washed at least on a weekly basis and more often is desirable. It is recommended that the bedding in the pan be changed at least three times a week and the pan washed each time. In addition, cages should always be sanitized before a new animal is placed in them. It is a good practice to have extra cages available at all times to allow for a systematic cage washing schedule. Sanitizing may also be accomplished and assisted with appropriate disinfectants. Where radioactive, infectious or toxic material are used a system of equipment monitoring should be instituted.
Equipment in rabbit rooms should be kept to a minimum and cabinets with doors or drawers should not be used in these rooms, as they are hard to maintain and can be harborers of vermin. Waste containers and implements should be maintained in a sanitary condition and it is a good practice to line waste cans with disposable plastic bags and to wash each waste can each time it is used, using the same methods that were suggested for the rabbit cages. The waste should not be left in the animal room after you are finished with the room each day.
Sanitary Waste Disposal
All waste should be collected and removed in a safe, sanitary manner. If waste cans are used, they should be made of metal or plastic, be leak proof and equipped with tight fitting lids. It is advisable to use leak proof disposable liners in waste cans for disposal of animal tissues, carcasses, and radioactive or toxic waste. Highly infectious waste should be rendered noninfectious by autoclaving or other effective means before removing them from the animal facility. Waste materials should be removed regularly and frequently. If storage of waste prior to removal is necessary, the storage area should be physically separated from the animal facility and be insect and vermin proof. Cold storage to prevent decomposition of biological waste may be required prior to disposal.
Vermin control requires that cockroaches, flies, and other insects, escaped or wild rodents and similar pests which constitute a menace in an animal facility, be effectively controlled and eliminated. This can best be done by the design of the facility and also by effective vermin control programs. Monitoring of these spaces can be accomplished by the use of insect traps or "Roach Hotels". Effective control can be obtained in older buildings even where heavy infestation has occurred. This can be accomplished by sealing or eliminating all breeding sites, by using limited numbers of pesticides and trapping procedures in conjunction with a strict program of sanitary maintenance. Pesticide applications must be carried out under professional supervision to avoid toxic affects to the animals and possible interference with experimental procedures. A harmful buildup of these materials or the disposal of undesirable quantities into public waste systems should be avoided.
Another aspect in the husbandry of rabbits is the concern for the quality and health of the animal. These concerns are derived for both humane and scientific considerations. All new animals entering the animal facility will be quarantined. Quarantine is a separation of newly received animals from animals already in the facility until the health status of the newly received animals has been evaluated. This evaluation should be made in accordance with acceptable veterinary medical practices. For rabbits obtained from a reliable sources, where the flora is known, the quarantine may be limited. Controlled quality at the source, and the knowledge of the environmental history of the animals are effective as a part of the quarantine protocol within the institution. The quarantine period is also used to condition animals and during this period some or all of which the following may be performed: a) determination as to whether the animals are appropriate for the intended use and comply with the contract specifications b) physical examination of the animals including accomplishment of an appropriate clinical and laboratory diagnostic tests and treatments, diagnosis and control of disease transmission between animals and man, destabilization of the nutritional state of the animals. All incoming rabbits that have been shipped over long distances and long periods of time should be acclimated to the facility before they are included in a research study. In some cases, isolation or complete separation of the animals either known or suspected of being diseased or carriers of disease from the animals that are in good health, is a mandatory requirement. When non-experimentally induced infectious diseases are recognized, the animals involved should be completely separated from all other animals. This may be accomplished by placing the rabbits in isolation units or separate rooms.
One of the most important aspects in the husbandry of rabbits is the physical plant. Physical condition and design of the animal facility to a great extent determine the efficiency and economy of the operation and greatly influence the standards of animal care and animal health. A well designed and properly maintained facility is an essential element in good rabbit care. Environmental factors influencing the animals while in the animal room that are most important in rabbit rooms are ventilation, temperature and humidity. Effective ventilation is necessary to regulate room temperature, promote comfort and reduce stress in the animals. The ability to minimize odors depends upon the number of animals housed in an individual room and the sanitation practices, as well as the proper design of the ventilation system. Ideally, the ventilation system should permit individual adjustments within plus or minus 2 degrees for any room temperature within a range of 16-21 C (60.8-69.8 F) although most commonly rabbit rooms are maintained at about 18 C (64.4 F). Relative humidity should be maintained throughout the year with a range of 40-60%. These conditions are acceptable for rabbits and should be maintained as closely as possible. Variations in temperature, or humidity are more harmful then slightly sub optimal levels and can lead to disease problems. Large fluctuations in temperatures can lead to stress, which can enhance many diseases and adversely effect experimental data.Air conditioning is highly recommended since it promotes environmental stability and animal facilities should be supplied with the best possible air handling capabilities. Each room or group of rooms serving rabbit facilities should have individual controls for the regulation of temperature and humidity. The system should provide 10-15 changes to 100% fresh air per hour without a draft, with air entering at or near the ceiling and exhausting near the floor. There should be no recirculation of room air unless it has been filtered to remove microbial and chemical contaminants, a requirement which will most likely result in as much energy used as 100% fresh air, with appropriate energy conservation systems. The electrical system should provide ample lighting and should be uniformly diffused throughout the area. A time control lighting system is recommended to provide a regular diurnal light cycle and this time control must be adjustable to provide flexibility in day-night cycle utilization.
Euthanasia techniques in the laboratory rabbit are similar to those utilized for rodents; however, methods such as cervical dislocation which may be satisfactory of the small rat or the mouse, are unsatisfactory for use in the rabbit. Euthanasia in the rabbit can be accomplished by the utilization of the various gas agents, by utilization of injection of barbiturate anesthetics or euthanasia solutions, and by exsanguination after anesthesia. If exsanguination is the method of choice for the research protocol, the rabbit should be anesthetized before this procedure is initiated. (During exsanguination, an unanesthetized rabbit may become excited and emit a series of distress cries which can be both unnerving for the operator and if within earshot of the other rabbits in the facility is extremely distressful to them. If anesthesia is not permitted by the research protocol, care must be taken to isolate the rabbit to be exsanguinated from the other rabbits in the colony to prevent this distress.)
The rabbit has been used in a wide variety of research studies in genetics, nutrition, toxicology, physiology, immunology, and reproduction. Classically the rabbit has been utilized in human medicine to determine pregnancy in women by injecting the serum from the patient into the rabbit and thereby inducing ovulation in the doe. The pharmaceutical industry uses the rabbit widely to test toxic effects of cosmetics and pharmaceutical in their evaluation for new drugs (greatly on the decline now) and the rabbit is the standard animal for pyogen testing of all solutions for human medical use. The rabbit is also widely used by the research community for the production of antibodies and antiserums. Due to its large size, it can be of great benefit in the production of fairly large amounts of these materials. Due to the large amount of time required to produce antibodies, the ability to continually collect these materials from the rabbit necessitates long term holding facilities for these animals and therefore turnover rates are slow and investigator studies may be restrained to some extent by the amount of rabbit holding spaces available in a given facility.
Strains and Sources
At the present time there are only a few different strains of rabbits available, the most common of which would be the New Zealand white, followed by the Dutch, the Flemish Giant and other minor strains of the domestic rabbit. The large size of the rabbit, the high cost of equipment and labor have been responsible for the limited number of sources available for laboratory research rabbits. Only large commercial breeder of rabbits, mainly for meat and fur, atone time supplied research rabbits, but because of the problems encountered in shipping and disease problems for long term holding of rabbits, that supplier is no longer in the laboratory rabbit business. The investigator should obtain the information on suppliers of rabbits in his area, and it is recommended that once an individual supplier is selected and the study is initiated, the researcher should resist changing suppliers until the individual study is completed. Although several suppliers may offer the same rabbit strain, the variability between one supplier and another can be very great and therefore, it cannot be over emphasized that extreme care and caution must be taken in the selection of sources and strain of rabbits to be used for specific research protocol. The disease profile of the colony should be carefully investigated especially if the animals are going to be held for long term or stressful studies. The laboratory rabbit is covered in the rules and regulations under the various public laws covering laboratory animals, administered by the U.S. Department of Agriculture, and therefore specific permits and licenses are required to produce these animals and they are subject to U.S.D.A. inspection of the facilities during transportation.
Signs of Disease
Signs of disease in the rabbit can be broken down into several groups:
Skin and Hair - Excessive hair loss may be one of the first signs of a skin abnormality. The ears should be checked for hair loss, increased redness, excessive buildup of debris, etc. Occasionally, rabbits will have sore hocks. Abscesses occasionally occur after injections. Most of the time, the first indication is a white-pinkish-reddish wet spot. This is a ruptured abscess and needs treatment.
Gastrointestinal - Diarrhea is not uncommon to the rabbit. It can indicate infection or just a diet problem. Drooling may occur due to malocclusion of the teeth. Not eating and/or drooling indicates that the mouth should be checked carefully. Constipation may occur due hairballs.
Respiration - Nasal discharge with crust build-up on the nose is a common problem in rabbits generally due to Pasteurella organism. Along with nasal discharge, occasionally the eye will show signs of infection by becoming redden and have a discharge.
Neuromuscular - Head held to the side/turned generally mean not a neck problem, but an ear problem. Sitting strangely, legs either under or straight out may indicate that the rabbit has broken its back. Gently wake the animal upland see if it can move around in the cage using its normally hopping motion.
Treatment - Any questionable signs should be reported to the Principal Investigator and the veterinarian immediately.
A Few of the Extraordinary Characteristics of the Rabbit