The most prevalent types of rabbits throughout the world are cottontails and European rabbits. All domestic rabbits are assortments of the European rabbit Oryctolagus cuniculus, including breeds used for research, the most common being the Californian, Florida White, and New Zealand White. For more on cottontails see Wild Rabbits.
In the wild, the herbivorous rabbit feeds on many broad leaved plants and grasses during the spring and summer; during winter rabbits will nibble on bark, twigs and any buds they can find. Rabbits generally eat and move about from dusk until dawn, and rest during the daylight hours. Adult male rabbits generally weigh between 4.4–11 pounds, while adult females weigh a little more (between 4.4–13 pounds), an unusual trait in mammals. Rabbits have excellent eyesight, hearing and smell. The position of the eyes allows rabbits to see on both sides, thereby increasing their ability to spot danger from more angles. Known as monocular vision, most prey animals have this visual arrangement, as opposed to predator species, which have binocular vision.
Rabbits are famous for their prodigious ability to reproduce. With a gestation period of only 26-30 days, female rabbits may produce up to 6 litters in one year, and litter size averages between 4–5 kits. Kits are born blind and furless but develop quickly and will have a full coat by 10 days of age. Up to 14 weeks old, a rabbit's age may be determined by measuring the size of hind feet and ears. After this time the only accurate method of age determination is by weight of the lens of the eye. The lifespan of a domestic rabbit ranges from 7–8 years, although some rabbits can live up to 15 years.
Rabbits have many natural enemies and face various dangers that keep their populations down. The rabbit’s predators include crows, weasels, opossums, hawks and owls, foxes, and snakes. In fact, up to 40% of a horned owl’s diet may consist of rabbits. Other substantial threats include loss of habitat, farming practices, diseases, cars, roaming cats and dogs, and hunters.
Rabbits, Not Rodents
Because of their gnawing ability, rabbits and their cousin the hare were mistakenly classified as rodents for many years, but in 1912 they were placed in their own order, Lagomorpha, when scientists discovered that the two types of animals differ from rodents in several distinct anatomical ways. Lagomorphs, for instance, have a second pair of upper incisors, known as "peg teeth," that are found behind the two main visible incisors in the upper jaw. Also, lagomorphs generally do not take individual steps but move along by hopping from both front legs to both back legs. Webbing between the toes helps protect their feet as they hop. The lagomorph's elongated hind legs, particularly in the hare, enable them to move at high speeds over open areas. They also have flexible necks, which allow them to turn their heads more than rodents can, although their spines are long and fragile making lagomorphs susceptible to fractures if held improperly. Startled or violently struggling rabbits or hares are capable of inadvertently breaking their back, so they must be handled with care.
Although they share many unique characteristics, rabbits and hares differ in appearance, behavior and ecology. Rabbits are born naked, blind, and fully dependent on the mother whereas hares are fully furred at birth, can see, and can maneuver on their own.
The arrangement of the lagomorph digestive system sets it apart from most other mammals. Often referred to as "hind-gut fermenters," the rabbit's digestive tract has a cecum which serves to further process food once it has passed from the stomach to the small intestine. Particles of food not broken down in the small intestine by bile and pancreatic juices enter the cecum. Here the particles stay between 2-12 hours and are further broken down by bacterial enzymes. The contents of the cecum are then deposited into the colon, where soft pellets of excreta called cecotropes are formed. Cecotropes, also referred to as "night pellets," are excreted from the colon and are sometimes reingested directly from the anus. The rabbit bends down to receive these pellets and swallows them whole. Ingestion of these cecotropes is vital to maintaining the rabbit's sensitive digestive tract, and once reingested, their re-digestion can take from 18 to 30 hours.
Digestive problems are common with domestic rabbits, and breeders of rabbits rapidly become familiar with a vast array of alimentary ailments. Exercise and room to move around are crucial to keeping the rabbit's digestive system functioning properly, as is access to a variety of types of roughage.
Rabbits and Humans
French monasteries began domesticating wild rabbit from the 6th through 10th centuries AD, although the first truly domesticated rabbits did not occur until the Middle Ages. Commercial breeding of rabbits for use as meat began in 18th century England.
Many modern breeds have been developed since then, now including several hundred varieties with different size, color, type of hair coat, and temperaments. Besides their use in the laboratory, different types of rabbits are currently used for the meat, fur, and pet industries, depending on their traits. In the United States, northern Arkansas and southern Mississippi are centers of rabbit farming, producing nearly 35 million pounds of rabbit meat each year. Rabbits farmed for their fur and meat often spend their lives in overcrowded and inhumane conditions with little or no opportunity to express normal rabbit behaviors. Farmed rabbits are killed by a blow to the skull or, if used for fur, electrocution to avoid any damage to the pelt.
Their prolific breeding potential sometimes brings rabbits in conflict with humans. Many a gardener has been vexed by wild rabbits. Such conflicts are inevitable as the rabbit's wild habitat and food sources disappear due to land development, forcing rabbits into closer association with humans. However, the proper use of fences, repellents, and relocation can be very effective tools in keeping rabbits out of gardens. Lethal means of protecting plants from rabbits are largely unsuccessful due to the rabbit's ability to replenish populations. Overall, damage to plants due to rabbits is most likely to occur during times of drought or when rabbit populations are unusually high; such damage rarely reaches economic significance. See Solving Problems with Rabbits.
The Rabbit's Life in the Laboratory
Wild rabbits and domestic rabbits in a laboratory setting have very similar behaviors and environment preferences. These similarities should be taken into account to improve laboratory conditions for rabbits, which should be as similar as possible to what rabbits would experience in the wild.
In many cases, living conditions for laboratory rabbits are designed primarily with economic and husbandry concerns at the fore, with little, if any, thought given to the psychological well-being of rabbits. Rabbits in the laboratory are typically housed alone in plastic or steel cages with grid flooring, are fed a standard pellet diet, and have very little, if any, environmental enrichment. Laboratory rabbits often experience social isolation and lack of mental stimulation, conditions that often lead to abnormal behaviors associated with stress and anxiety, including incessant chewing and scratching on cage bars. Caged rabbits are also frequently denied the opportunity for normal levels of physical activity which may lead to intestinal problems and, given rabbits' light bone density, also result in osteoporosis and bone deformities (click here for information on cage sizes and housing conditions).
Rabbits should be housed with at least one other rabbit, although groups of 4-8 adult animals are ideal to mimic normal social organization, taking into account the dominance hierarchies formed by rabbits. Females rarely show aggression but mature males may become increasingly aggressive if housed together, and dominance may be expressed by injuring the ears or scrotal region of subordinate males. Researchers have reported that in group settings, rabbit group members will stay close to those who are ill or have recently undergone surgery, which helps relieve stress and speeds healing.
As an essentially nocturnal animal, rabbits are very light sensitive and need regular light and dark cycles in a lab setting. Sudden exposure to light can result in shock and even injury when the rabbit is startled. Bedding material such as straw or shredded paper provides opportunities for rabbits to exercise some control over their environment by foraging for food, building nests, digging, and maintaining their body temperature. Although pellets may be the lab rabbits' staple food, some variation should be provided such as hay and green plant material. Wooden objects for gnawing also enrich the cage environment. At minimum, cage space should allow for a normal range of motion and behaviors such as hopping, hiding and sitting up on the hind legs.
What Protections Apply to Rabbits in Laboratories?
Two sets of federal standards address the welfare of rabbits used in research: the Animal Welfare Act and the Public Health Service Policy on Humane Care and Use of Laboratory Animals.
How Are Rabbits Housed Under These Protections?
The Animal Welfare Act specifies that, for rabbits, the space allotted is dependent on the individual's weight. For example, a rabbit between 4.4 and 8.8 pounds must be given at least 3 square feet of floor space for its primary enclosure, and 14 inches from floor to ceiling. Rabbits between 8.8 to 11.9 pounds must be given 4 square feet of floor space, or roughly the outside dimensions of a standard microwave oven, with 14 inches in height. Females with litters are given slightly more space. Unfortunately, these cage sizes do not allow for species-typical behavior, such as hopping, and this can lead to intestinal and skeletal problems, as discussed above.
Use of Rabbits in Medical Research
Rabbits are popular animals for research and testing primarily because they are mild-tempered and easy to handle, keep, and breed. In addition, rabbit physiology is fairly similar to that of humans, so they are used as models for many human diseases. According to the USDA, in the year 2002, the United States used 243,838 rabbits in research and testing; 6,324 of who were used in research that caused unrelieved pain and/or distress.
Rabbits are used in research on the cardiovascular system, skin disorders, immune system, and polyclonal antibody production for use in vaccines, the most famous of which was the development of the rabies vaccine by Louis Pasteur. Polyclonal antibody production in rabbits involves injecting the animal with a chemical that is foreign to the rabbit (an immunogen) in order to stimulate a response from the immune system; this usually involves combining the immunogen with a substance that improves the immune response (known as an "adjuvant"). Click here for information on alternatives to using rabbits for polyclonal antibody production.
Rabbits are also used extensively in the study of bronchial asthma, stroke prevention treatments, cystic fibrosis, diabetes and cancer.
Specific breeds of rabbit are used for certain medical studies, an example of which is the Watanabe rabbit that normally develops coronary disease from abnormal fat deposits in the arteries and organs. These rabbits are used in the study of arteriosclerosis, which can cause heart attacks and strokes in humans.
Cosmetic Testing on Rabbits
Skin and eye irritancy testing is frequently conducted on rabbits. In skin irritancy tests, areas of the rabbit's skin are shaved of fur and, in some cases, the shaved skin is abraded to remove several layers of skin cells. Then a test substance is applied to the skin. Such substances include individual chemicals or product formulations, such as cosmetics or household cleaning products. For the duration of the test the rabbit is restrained or the area may be covered to prevent licking, rubbing or other disturbances to the test area. The test area is periodically examined to assess any skin damage or penetration into the bloodstream and any resulting toxic effects.
Phototoxicity and photosensitization tests are similar to the skin irritancy test although the test area is exposed to light to determine what affect this will have on irritancy levels.
Rabbits are used for eye irritancy experiments because each eye has only one tear duct and test chemicals are not easily washed away. Their tear ducts are "U" shaped, and domestic rabbits sometimes require veterinary intervention if the duct becomes blocked. Since 1944 domestic rabbits have been used in the eye irritancy test known as the Draize Test which scores eye irritation from exposure to test chemicals. During the test, conscious, immobilized rabbits have test chemicals placed directly into their eyes and are left in this state up to several days to determine the irritancy level indicated by redness, ulceration, hemorrhaging, cloudiness, or blindness in the eyes.
The Draize test has been strongly criticized by scientists because it exaggerates the effects of irritants and produces results of questionable relevance to human experience. The test has also been the target of large protests regarding its cruelty. During the 1970's and 80's public outcry regarding the Draize test encouraged cosmetic companies to begin developing alternatives to live animal testing methods and led to the creation of the Johns Hopkins University Center for Alternatives to Animal Testing (CAAT).
Non-Animal Testing Methods
Progress is being made in the development and validation of non-animal testing methods that can serve as alternatives to the Draize eye and skin irritancy tests and other rabbit-based testing procedures. In January 2005, The Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM), made up of 15 federal regulatory and research agencies, began an evaluation of the usefulness and limitations of four in-vitro ocular safety testing methods that could eventually be validated as acceptable alternatives to animal testing, at least for severely irritating chemicals.
The testing methods utilize eyes from animal cadavers that are by-products of the meat industry or fertilized chicken eggs in an early stage of development. Further information about this effort and related efforts may be found at: http://iccvam.niehs.nih.gov.
Today, the majority of Americans are against using animals to test cosmetics. As a result of public pressure, many cosmetic companies no longer conduct cosmetic testing on animals. Organizations such as the Coalition for Consumer Information on Cosmetics (CCIC) work to keep the public informed on humane choices regarding cosmetic products.
Learn more about rabbits! Suggested reading: Stories Rabbits Tell by Susan Davis and Margo Demello. Lantern Books, www.lanternbooks.com
