Ch 23: Rabbits

Lesson 1: Introduction

Rabbits are friendly, burrowing, herbivorous (plant eating) animals. Domestic rabbits descended from the wild rabbits of Western Europe and northwestern Africa. There are many breeds of rabbits, from giant breeds like the Flemish to small breeds like the Dutch Belted. The most commonly used rabbit in the research laboratory is the New Zealand White (NZW), one of the larger breeds of rabbits. Rabbits serve as animal models for a number of diseases, most notably atherosclerosis and ophthalmologic illnesses. They are also used for serum antibody production and drug screening and testing.

Lesson 2: Taxonomy

The scientific name of the laboratory rabbit is Oryctolagus cuniculus. Rabbits used to be considered rodents. However, they are now classified in a separate group, lagomorphs, because they possess anatomical and physiological characteristics that differentiate them from rodents.

Lesson 3: Anatomy & Physiology

Unique Anatomical Features

The rabbit has several unique anatomical features. Most noticeable are the long, vascular ears used for thermoregulation. If a rabbit becomes overheated, the vessels of its ears will dilate to allow greater blood flow. The air circulating around the ears cools the blood as it flows through the ears and back into the body. Consequently, body temperature is decreased. Another unique anatomical feature is their unusual teeth. Unlike rodents, rabbits have a second set of upper incisors just behind the first set, called peg teeth. Rabbits’ incisors continue to grow throughout life, and consequently malocclusion can develop. Like with other species, this condition can be treated by trimming the incisors.

Care and Handling Recommendations

Rabbits have very light skeletons that make up only about 8% of their body weight. Rabbits are also very muscular, especially in the hind limbs. The combination of a light skeleton and very strong muscles can result in injuries, the most common being a broken back. Thus, care is required when picking up or handling a rabbit.

Rabbit toenails grow rapidly. Wild rabbits keep their nails worn down by digging and running. In cages, rabbits have no way to wear down their nails, so they must be clipped regularly. The nails should be clipped bluntly, being careful not to cut the nail so short as to cause bleeding.

Digestion and Metabolism

Rabbit feces are round pellets, but they also produce a special kind of stool called “night feces” which is very soft and covered with thick mucus. The animal eats this stool as it is expelled, often early in the morning. Because the rabbit eats it directly from the anus, it is rare to see this material on a cage pan. The purpose of night feces is to recycle protein, water, and B vitamins. Eating stool is called coprophagy, and is common in both rabbits and rodents. However, the rabbit is the only species that produces a special stool for that purpose. Urine varies in color from clear red or yellow to a milky yellow. High amounts of minerals account for this color variation.¹

Rabbits are very sensitive to changes in their gut flora. Transportation stress, changes in diet, and other factors may induce diarrhea. Some antibiotics may destroy the gut flora, and as in guinea pigs, this loss of flora is lethal to rabbits.

Lesson 4: Sexing & Reproduction

The female rabbit is called a doe, and the male is called a buck. Newborn rabbits are called kits. The anogenital distance is not significantly different between males and females, so sexing rabbits can be challenging. To sex a rabbit, restrain the animal, place your thumb and forefinger on each side of the genital area and apply gentle pressure until the vagina or penis becomes visible. You can determine whether the animal is male or female by looking at the opening of the expressed organ (Figure 23.1). If it is rounded, it is the penis of a male; a V-shaped slit indicates that the rabbit is a female. Testes are evident in mature bucks. Sexing younger rabbits or weanlings can be difficult for the untrained.

Other physical characteristics help differentiate between male and female rabbits. Female rabbits have a narrow head and a large dewlap (a fold of loose skin that hangs from the neck) under their chins (Figure 23.2). Male rabbits lack the dewlap, and have a much larger head than the females.

Female rabbits are induced ovulators, meaning that they only ovulate after the act of mating. They do not have a distinct estrous cycle otherwise. The doe typically ovulates 10 to 12 hours after mating (Table 23.1).

Mating and Pregnancy

Male and female rabbits are hand mated. The doe is always taken to the buck’s cage. If a buck is placed in the doe’s cage, he will be attacked by the doe. Once the doe is bred, she is removed from the buck’s cage and placed back into her cage.

Feed requirements are increased during pregnancy, so does should be given extra food. A nest box must be placed into the cage several days prior to parturition to allow enough time for the doe to build a nest; if provided after parturition, the mother will not use it. The doe pulls fur from her chest and stomach and lines the nest box with it. She gives birth in the nest box. If a nest box is not provided, there is a good chance that the newborn rabbits will be trampled by the mother or die by hypothermia.

Rabbit Kits

The nest box provides a warm, safe environment for the growing kits. Rabbit kits are altricial – meaning they are born hairless, with their eyes and ears closed. The mother nurses them once or twice a day; the milk is rich in fat. Rabbit kits are weaned at 5 to 8 weeks, when they are readily eating pellets and drinking from a bottle or automatic drinking device. Once out of the nest, kits are very active. They dart around the cage, and may try to escape when the cage is opened.

Lesson 5: Behavior

General Behavior

Rabbits are active, curious animals that spend a lot of time exploring objects in their environment. They are adept at escaping from unsecured cages. Cage cards must be placed where the rabbit will not chew them. Rabbits normally sit on all four feet, with their body weight evenly distributed and the head held level with the top of the back. They move around the cage by hopping, and occasionally stand on their hind legs. At rest, especially if hot, a rabbit may stretch out on its side or stomach with its head resting on the cage floor.

Aggressive Behavior in Rabbits

Rabbits are generally calm, nonaggressive animals with a very high flight response to fear. In the laboratory, rabbits rarely bite, and can become very trustworthy animals. Occasionally you will encounter a rabbit that aggressively protects its cage. The rabbit will usually warn anyone who approaches with a series of foot stomps. If the foot stomps are ignored and the cage door is opened, the rabbit may rear up on its hind end and attack with its mouth open. In some instances, the rabbit will vocalize or fling urine. To safely remove an aggressive rabbit from the cage, toss a drape cloth or towel over the rabbit and then quickly and firmly, but gently scoop the rabbit out of the cage. Once the rabbit has been removed from its cage, it is no longer defensive and can be safely handled by routine methods. If the rabbit attacks and tears at the tossed drape before you can remove the animal from the cage, toss a second drape over the rabbit. The first drape distracts the rabbit, allowing you to cover the animal with the second drape and remove it from the cage.²

Generally, rabbits do not vocalize unless they are in severe pain or extremely stressed, when they produce a loud scream. A rabbit in great pain can also sound like a person crying.

Lesson 6: Handling & Restraint

Removing from Cage

As mentioned previously, rabbits have very sensitive backs, so handling and restraint is a major concern. It is necessary to support the hindquarters at all times. Rabbits’ ears are also easily injured. Never pick up a rabbit by its ears.

A rabbit can be removed from the cage by scruffing the nape of its neck with one hand and supporting its hind end with the other hand (Figure 23.3). A rabbit should be held this way only for short periods, such as during cage changing. If a rabbit must be carried across a room or to another room, the “tuck” or “football” method should be used. Support the rabbit’s hindquarters with one hand, and tuck its head in the crook of your arm. This method frees your other hand to open doors or cages as needed, but should not be used to restrain the rabbit for procedures that may excite the animal.

Immobilization

To manually immobilize a rabbit for technical procedures, scruff the nape of its neck with one hand and gently grasp its hind legs at the hock (the joint below the knee on the hind leg) with the other hand. You can then carefully stretch the rabbit out lengthwise so it cannot move.

There are several devices used to immobilize rabbits when manual restraint is not advisable. Plastic restrainers use a head gate, back piece, and head stabilizers. Be careful when placing an animal into or removing an animal from a restrainer. If an improperly sized restrainer is used, an injury such as a broken back may result. A restraint bag or a Snuggle restrainer (Figure 23.4) can also be used to restrain a rabbit. A rabbit can be placed in this simple canvas bag, which exposes the head and ears for manipulation. With gentle and skilled handling, rabbits can be lulled into a hypnotic-like state in which they lie calmly, are immobile, and are not responsive to mild stimuli.³

Lesson 7: Identification Methods

Rabbits can be identified in several different ways. Ear tags, tattoos, microchips, dyes, and unique characteristics such as coat color or pattern are used. The pinna of the ear can be marked with a plastic numbered tag or tattooed with numbers or letters for identification (Figure 23.5). When tattooing or placing ear tags, be careful to avoid the central ear artery. Microchips are placed subcutaneously, usually at the nape of the neck; they can be uniquely programmed for identification and may even provide other data, such as body temperature.

Lesson 8: Husbandry & Diet

Room Temperature

The optimum room temperature for most rabbits is 16 °C to 22 °C (61 °F to 72 °F). The lower temperature reduces the amount of shedding, and subsequently problems with gastrointestinal blockage by hair balls. Even with lower room temperatures, however, rabbits shed large quantities of hair. The hair accumulates on cages, walls, floors, and in the room air filters. Frequent cleaning of these filters is necessary to maintain proper air flow in rabbit rooms.^4,5

Housing

Single housed rabbits are housed in stainless steel racks with or without a plastic cage insert. There are usually 6 to 8 cages per rack.

In recent years, the Guide, with the support of AAALAC International, has recommended social housing of young rabbits as the default housing method. However, the social benefits of social housing should be weighed against the potential for aggressive behaviors in the establishment and maintenance of social hierarchy. Therefore, some rabbit racks have a divider that can be removed to make two small cages into one large cage that can accommodate two rabbits. Since there is no set standard caging for group housed rabbits, some facilities have used converted pig and dog pens since they offer the appropriate amount of space to house multiple rabbits. The size of the pen will determine how many rabbits can be housed together. The Animal Welfare Act and Regulations provides information on the minimum required floor space per animal, as reflected by the recommendations in the Guide. It has been shown that attempting to group house rabbits has a better chance of succeeding if the rabbits are paired at a younger age. Some believe that applying male urine to the heads of females increases the chances of successful pairing. Generally, females are easier to pair house, because males tend to be more aggressive.

Technicians should be aware of any signs of fighting, like vocalization, thumping, large amounts of hair loss, excessive chasing, scratches and open wounds. If the animals are fighting, they should be separated into different cages. A pair can be reintroduced or placed with new partners, but only after testing to see if they are compatible.

When stainless steel racks are used, collection pans are lined with either bedding or a pan liner and are placed under each cage to catch urine and feces. The pans under each cage should be changed at least three times a week. Litter boxes can also be used in larger pens to reduce cleaning time during daily husbandry. Litter boxes should be changed a minimum of twice a week. Some cage racks and pens are equipped with automatic flushing pans that periodically produce a flow of water to wash feces and urine into a drain. Rabbit urine contains large amounts of minerals which remain on surfaces when the urine dries (urine scale). Pans, litterboxes, floors, and other cage surfaces are usually treated with an acid solution prior to washing to remove urine scale. The racks and pens should be sanitized either weekly or every two weeks.

Water, Diet and Feeding Overview

Water can be provided by either water bottles or an automatic watering system. Rabbits should be fed a high-fiber, pelleted diet in a stainless steel J-feeder. The fiber is good for the gut flora, helping to keep the gut functioning well. Rabbits will eat continually if fed ad libitum, causing obesity. Therefore, the amount of feed offered to the rabbit should be determined according to the weight of the animal. Adult New Zealand White rabbits typically receive approximately 50 grams/kg of feed once a day.

When feeding rabbits, it is important to observe the collection pan for normal feces and urine output. Always check the feeder for leftover feed from the previous day. If a rabbit has not eaten its ration from the previous day, the first thing to be checked should be the water supply because if the animal is unable to drink, it will not eat. Report any animal that is not eating to the veterinary staff. Feeders should be dumped to remove leftover pellets and feed dust prior to adding new feed.⁶

Lesson 9: Environmental Enrichment

Edible environmental enrichment for rabbits should be offered several times a week. However, offering too much edible enrichment could cause the animal to reject the pelleted diet or have gastrointestinal problems. Carrots (including the tops), kale, broccoli, apples, bananas, and other fruits and vegetables are commonly offered to rabbits. Hay can also be provided as an edible enrichment. Treats such as chew blocks and pineapple sticks may also be provided. In addition, hard plastic balls, chains with metal pendants hanging on cage doors, and nylon chew bones are common environmental enrichment devices.

Lesson 10: Signs of Pain, Distress, or Illness

A rabbit will try to hide pain or injury; in the wild, this behavior serves as a defense mechanism to prevent predators from attacking. Technicians must be very thorough in their observations of rabbits to pick up on the subtle behavior differences that indicate the animal is in pain.

Rabbits are easily stressed. Improper handling, inadequate housing conditions, experimental procedures, and transportation are possible stressors. Signs that a rabbit is stressed or sick include anorexia (loss of appetite), lethargy, tooth grinding, vocalizations, and pale mucous membranes. Any animal exhibiting these signs should be reported to the facility veterinarian.

Lesson 11: Euthanasia

Rabbits may be euthanized with an overdose of barbiturates, with or without prior anesthesia. It is not recommended to euthanize rabbits with CO₂ because of their tendency to hold their breath. As with other laboratory animal species, death must be verified. Your institution’s SOPs may require an additional procedure to be performed for this verification. Carcass disposal should be according to the facility’s guidelines.