General Information and Rabbit Health

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Housing:

Housing requirements for rabbits depend on climate. Minimal housing (an "A-frame" roof without sides) can be used in moderate climates, while a climate-controlled rabbitry may be necessary in hot or cold climates. Rabbitries should be located on nearly level ground and use well-drained soil or tile-drained pits for manure. Shade should be provided over as much of the rabbitry as possible. Good ventilation at all times is imperative. Narrow buildings of modular construction offer the advantages of easy ventilation and expansion as needed.

Cages and Ancillary Equipment:

All-wire cages are preferred. The standard size is 30 × 36 in. (75 × 90 cm) with a height of 16-18 in. (40-45 cm). A "Quonset" style (rounded top) with the door in front makes all corners of the cage accessible when reaching inside. The top and sides of cages should be constructed of 1 × 2 in. (2.5 × 5 cm) 14-gauge mesh welded wire; 0.5 × 1 in. (1.25 × 2.5 cm) 16-gauge mesh welded wire should be used for the floors to provide more support for the rabbits' feet. Cage dividers can be made of the same material as the top and sides or a type of wire called "baby saver," in which the mesh size of 1 × 2 in. (2.5 × 5 cm) is progressively reduced to 0.5 × 2 in. (1.25 × 5 cm). This prevents neonates born on the wire from crawling between cages.

During its manufacture, wire may be galvanized before or after welding; the latter type is more expensive but lasts considerably longer. Wood should not be used in cage construction because it can be chewed and cannot be sanitized adequately. Cages can be suspended from the ceiling with wire or set on metal frames.

The cage should be equipped with a feed hopper and a watering system. Feed hoppers are best constructed of sheet metal with holes or a screen in the bottom for removal of "fines" (small broken feed particles). Automatic watering systems used in large rabbitries consist of a series of connecting pipes with individual watering valves for each cage. Rabbits often chew on the watering valve and eventually destroy it unless it is made of stainless steel or has a stainless centerpiece. Water bottles with sipper tubes also work well. Crocks and cans are sometimes used in small rabbitries; such containers are easily contaminated and should be washed and disinfected daily.

Nest boxes should be constructed so that they can be easily placed in the cage and later removed for cleaning and disinfecting between litters. Disinfecting the nest box twice, once after cleaning and again just before placing it in the cage, helps reduce incidence of disease. The box should be large enough to prevent crowding but small enough to keep the kits warm. A standard size nest box for medium-sized rabbits is 16 × 10 × 8 in. high (40 × 25 × 20 cm). Wooden or metal nest boxes seem to work best, but welded-wire nest boxes with disposable cardboard liners are becoming popular. Nesting material consisting of straw, hardwood shavings, or shredded sugarcane serves well in either warm or cold weather. Shredded paper, hay, leaves, and other materials have been used with less success.

Sanitation:

Sanitation is important in any livestock enterprise but is especially so in rabbit production. Poor sanitation leads to disease and deaths; therefore, cleaning and sanitizing must be constant. Nest boxes must be disinfected between uses.

Cages, feeders, and watering equipment should be sanitized periodically. An effective and inexpensive sanitizing solution is sodium hypochlorite (household chlorine bleach) added to water (1 oz/1 qt [30 mL/1 L]), but this solution can be corrosive to metal; other noncorrosive disinfectants can also be used.

An active rabbitry constantly experiences a loose hair problem. Does pull hair from their bodies to make nests, and some of this hair becomes airborne. It sticks to almost any surface, including cages, ceiling, and lights, and must be removed periodically. The most effective ways to remove hair from cages are by washing or by use of a propane torch or flame. Washing, brushing, sweeping, and vacuuming also are effective in other parts of the rabbitry.

Frequent manure removal is essential. Excess manure leads to unacceptable levels of ammonia in the air, which predisposes to respiratory disease. The manure can be composted in an efficient pit system.

Reproduction:

Rabbit breeds of medium size are sexually mature at 4-4½ mo, giant breeds at 6-9 mo, and small breeds (eg, the Polish Dwarf and Dutch) at 3½-4 mo of age. The rabbit is an induced ovulator and, contrary to popular belief, has a cycle of mating receptivity; rabbits are receptive to mating ~14 of every 16 days. The degree of mating receptivity is indicated by the color of the vaginal orifice and by the amount of moisture on the labia. The vaginal color cycle runs from a pale whitish pink to a reddish purple. A doe is most receptive when the vagina is red and moist. Does that are not receptive have a whitish pink vaginal color with little or no moisture. Many breeders test mate the doe 10-16 days after breeding, as a means of detecting pregnancy, but this is a poor practice because sometimes pregnant does will breed and nonpregnant does will not. Palpation of the doe's abdomen for "grape-sized" embryos in the uterus is a much better technique for detecting pregnancy. The best time to palpate is 12 days after breeding.

A ratio of 1 buck to 10 does is common practice, but many commercial growers find that 1 buck to 20-25 does is more economical. Bucks can be used daily without decreasing fertility; more frequent use requires periods of rest. The doe should always be taken to the buck's cage for breeding. The breeding program should continue year round. Does that have experienced long periods of rest between litters tend to become obese and difficult to breed. Does that are constantly in gestation and lactation may become underweight, and their receptivity to the buck and fertility decrease dramatically. If breeding is delayed several weeks and the doe is given full feed, weight is quickly regained.

The gestation period is ~31-33 days. Does with a small litter (usually ≤4) seem to have a longer gestation period than does that produce larger litters. If a doe has not kindled by day 32 of gestation, oxytocin (1-2 IU) should be given to induce parturition; otherwise, a dead litter is almost always delivered sometime after day 34. Occasionally, pregnant does abort or resorb the fetuses due to nutritional deficiencies or disease.

Nest boxes should be added to the cages 28 or 29 days after breeding. If boxes are added too soon, the does foul the nests with urine and feces. A day or two before kindling, the doe pulls fur from her body and builds a nest in the nest box. The young are born naked, blind, and deaf. They begin to show hair on day 2 or 3 after birth, and their eyes and ears are open by day 10. Rebreeding can occur any time after parturition. Some commercial growers use accelerated

breeding schedules and rebreed 7-21 days after parturition, while most people raising for show or home use rebreed 35-42 days after parturition.

Most medium-size female rabbits have 8-10 nipples, and many kindle 12-15 young. Such a doe is generally unable to nurse all the kits effectively, so some kits are fostered. Kits are removed from the nest box during the first 3 days and given to a doe of about the same age with a smaller litter. If the fostered kits are mixed with the doe's own kits and covered with hair of the doe, they are generally accepted. Moving the larger kits to the new litter instead of the smaller kits increases the chance of success.

Breeding Stock:

Selection of breeding stock is vital to successful reproduction. The genetic potential of the individual buck and doe contributes to the overall production of the rabbitry. Good-quality stock is best obtained from successful breeders. The type of breeding stock to select depends on the purpose of the grower: meat, wool, or show. Common meat breeds are the New Zealand White and the Californian; common wool breeds are the English, French, and German Angora. For rabbit shows, 45 breeds are recognized by the American Rabbit Breeders Association.

Nutrition:

Proper feeding is an important management practice. It is easy to overfeed or underfeed does and growing, adolescent rabbits (fryers). The amount to feed depends on the age of the fryers or on the stage of pregnancy or lactation of the does. A general rule in feeding fryers is to feed all that can be consumed in 20 hr, with the feed hopper empty 4 hr/day. Does are usually fed ad lib once they kindle. The general practice is to bring the doe from restricted to full feed slowly during the first week of lactation. Does that are bred to kindle five times during the year generally have their feed restricted between litters; those bred intensively should be on full feed continously once they begin the first lactation. Feeding rabbits has been greatly aided by nutritionally complete commercial pelleted diets. Adult pet rabbits not intended for breeding should be fed a pellet diet, restricted to ¼ - ½ cup/5 lb body wt/day to prevent obesity. At this level of restriction, ad lib hay is necessary to avoid trichobezoars and general gut stasis.

In the early morning or at night when they are unobserved, rabbits ingest part of their feces by contorting themselves so that the mouth touches the anus. They ingest only the soft matter that has been processed in the cecum. Coprophagy, or pseudorumination, is normal in rabbits and not a sign of nutritional deficiency. It serves an important nutritional function by supplying the rabbit with intestinally synthesized B vitamins and protein. Stability of the normal intestinal microflora may depend on normal coprophagy. Wire-mesh cage flooring does not prevent coprophagy.

Other Management Techniques:

Rabbits may be carried by grasping the loose skin over the shoulders with one hand and placing the other hand under the rump to support the weight. If they are not held properly and securely, fractures or luxations of lumbar vertebrae may follow struggling. Also, the toenails on the rear limbs may severely scratch unprotected arms of handlers.

Some breeders tattoo or place ear tags on their rabbits for identification purposes. For show purposes, the right ear is reserved for registration marks applied by registrars of the American Rabbit Breeders Association.

Although sex can be determined at birth, it is usually done at weaning. By depressing the external genitalia, the mucous membrane can be exposed. In males, the mucous membrane protrudes and forms a circle; in females, it extends and forms a slit. Castration has no advantage for meat-type rabbits; the growth for males and females is about the same until after market age. Angora rabbits kept for >6 mo are sometimes castrated. The technique is similar to that of castrating cats, although the testes in the scrotum are lateral and anterior to the penis, as in marsupials and not as in most other placental mammals.

Most techniques for physical examination and restraint suitable for dogs and cats may be applied to rabbits. However, general anesthesia of rabbits with barbiturates often results in significant mortality; inhalation agents, eg, halothane and isoflurane, are safer. Use of such preanesthetic agents as chlorpromazine hydrochloride (25 mg/kg), diazepam and propiopromazine (5 mg/kg), or fentanyl and droperidol (a combination product, given at 0.22 mL/kg) allays apprehension, may reduce the dosage of general anesthetic by 50%, and often prolongs anesthesia. Ketamine (35-60 mg/kg) and xylazine (5-10 mg/kg), given together, result in adequate general anesthesia.

Bacterial and Mycotic Diseases

Pasteurellosis 

Pasteurellosis is common in domestic rabbits. It is highly contagious, transmitted either by direct or indirect contact. The etiologic agent is Pasteurella multocida , a gram-negative, nonsporeforming, nonmotile coccobacillus. Rabbits develop little effective immunity after infection. In conventional colonies, 30-90% of apparently healthy rabbits may be asymptomatic carriers.  Carriers can be identified by an indirect fluorescent antibody test on nasal swabs. A technique that uses small, saline-moistened, pediatric nasopharyngeal swabs has proved superior to the standard, larger nasal swab. The swab is directed medially through the external nares past the turbinates and onto the dorsal surface of the soft palate. The swab is then retracted and can be used in the fluorescent antibody test or plated onto a culture medium. An ELISA test for detecting antibodies against P multocida may also prove beneficial in detecting carriers. Infections vary in severity and may be manifest as any of the following: rhinitis (snuffles), pneumonia, otitis media, conjunctivitis, abscesses, mastitis, genital infections, or septicemia.

Diagnosis is based on clinical signs and isolation of P multocida . Treatment is difficult and may not eradicate the organism. Antibiotics seem to provide only temporary remission, and the next stress (eg, kindling) may cause relapse. However, in pet rabbits, enrofloxacin (2.5-5 mg/kg, b.i.d. for 20-30 days) has alleviated signs in clinical cases of pasteurellosis, and synergism of fluoroquinolones and aminoglycosides or slow-release penicillin has been seen. An effective vaccine has not been developed; therefore, the best method of control in large rabbitries is strict culling. Barrier colonies of Pasteurella -free laboratory rabbits are becoming more common.

Rhinitis ( snuffles or nasal catarrh) is an acute, subacute, or chronic inflammation of the mucous membranes of the air passages and lungs, induced primarily by Pasteurella , but Pseudomonas , Staphylococcus , and Streptococcus have also been isolated. The initial sign is a thin, serous exudate from the nose and eyes that later becomes purulent. The fur on the inside of the front legs just above the paws is matted and caked with dried exudate as a result of pawing at the nose. Infected rabbits usually sneeze and cough. In general, snuffles occurs when the resistance of the rabbit is low. Rabbits that seem to recover may remain carriers. Pneumonia can ensue.

Pneumonia is not uncommon in domestic rabbits and may occur in adults or may infect the young while in the nest box. Frequently, it is a secondary and complicating factor in the enteritis complex. The cause is bacterial, with P multocida accounting for the greatest number of cases. Other bacteria involved may be Klebsiella pneumoniae , Bordetella bronchiseptica , Staphylococcus aureus , and pneumococci. Upper respiratory disease (snuffles) is often a precursor of pneumonia. Inadequate ventilation, sanitation, and nesting material are predisposing factors. The number of cases of pneumonia is directly proportional to the level of ammonia in a rabbitry. The rabbits usually succumb within 1 wk after signs appear. Affected rabbits are off feed, listless, and dyspneic and have a fever (104-105°F [40°C]). Necropsy reveals bronchopneumonia, pleuritis, pyothorax, or pericardial petechiae. Diagnosis depends on signs and lesions. Treatment consists of oxytetracycline, chlortetracycline, or slow-release penicillin. Chloramphenicol in pet rabbits has also been effective. However, treatment often fails because the pneumonia is advanced before it is detected.

"Wry neck," a term used by rabbit raisers, is caused by P multocida or Encephalitozoon cuniculi gaining entrance to the middle or inner ear by way of the eustachian tube, thus causing otitis media or interna. An accummulation of pus or fluid in the middle or inner ear causes the rabbit to twist its head, ie, "wry neck" or torticollis. However, not all rabbits with middle ear infections show torticollis. Because treatment is long-term and the prognosis is guarded, most colony rabbits with this condition are culled; in pet rabbits, prompt antibiotic therapy has been shown to reduce or eliminate signs due to infection with P multocida .

Mature bucks and young rabbits seem particularly susceptible to conjunctivitis (weepy eye) caused by P multocida or Staphylococcus aureus ; however, the incidence is low. Transmission is by direct contact or fomites. Affected rabbits rub their eyes with their front feet. Ophthalmic ointments containing sulfonamides, antibiotics, or antibiotics and a steroid are satisfactory for treatment, but recurrence is common. In deep-seated infections, injections of slow-release penicillin should be given. Flushing the lacrimal duct with an antibiotic solution is often beneficial in chronically affected show rabbits. Conjunctivitis also accompanies rabbitpox ( Rabbitpox) and myxomatosis ( Myxomatosis)

Abscesses caused by Pasteurella may be found in any part of the body in any age rabbit. However, because other bacterial species can also cause abscesses, culture and sensitivity tests may be required for successful therapy. When bucks penned together fight, their wounds frequently develop abscesses. Septicemia and death may occur within 48 hr. Necropsy may reveal bronchial congestion, tracheitis, splenomegaly, and subcutaneous hemorrhages. With colony rabbits, it is usually advisable to eliminate rather than to treat the affected rabbit; with pet rabbits, drainage of the abscess accompanied by antibiotic therapy has been successful, although recurrence of signs is common.

Genital infections are often caused by Pasteurella , but several other organisms also may be involved. They are manifest by an acute or subacute inflammation of the reproductive tract, and most frequently are found in adults, more often in does than bucks. If both horns of the uterus are affected, the does often become sterile; if only one horn is involved, a normal litter may develop in the other. The only sign of pyometra may be a thick, yellowish gray vaginal discharge. Bucks may discharge pus from the urethra, or a testicle may be enlarged. Chronic infection of the prostate and seminal vesicles is likely and because venereal transmission may ensue, it is best to cull the animal. Antibiotics may be used to combat the infection; however, the prognosis is poor. The contaminated hutch and its equipment should be thoroughly disinfected.

Listeriosis 

a sporadic septicemic disease characterized by sudden deaths or abortions (or both) is most common in does in advanced pregnancy. Poor husbandry and stress may be important in initiating the disease. Clinical signs are variable and nonspecific and include anorexia, depression, and weight loss. In contrast to the disease in cattle and sheep ( Listeriosis: Introduction , Listeriosis: Introduction), listeriosis seldom affects the CNS in rabbits. The causal agent, Listeria monocytogenes , spreads via the blood to the liver, spleen, and gravid uterus. At necropsy, the liver consistently contains multiple, pinpoint, gray-white foci. Because diagnosis is rarely made antemortem, treatment is seldom attempted. Listeria monocytogenes can infect many animals, including man. It is difficult to isolate with normal methods, and special techniques are often required.

Staphylococcus 

In domestic and wild rabbits, Staphylococcus aureus infection is manifest as a fatal septicemia of young rabbits (usually in the nest box) or as a suppurative inflammation of older rabbits involving almost any organ or tissue, often the skin or mammary glands. The organism is transmitted by direct contact or aerosol but is a skin commensal of universal distribution. Rabbits may be colonized but show little or no clinical disease unless resistance is decreased.
Abscesses develop in chronic infections. In acute septicemia, there is usually fever, depression, and anorexia terminating in death. Diagnosis depends on isolation of the bacteria. Because S aureus is resistant to many antibiotics, sensitivity testing should precede antibiotic treatment whenever possible. Thorough disinfection of the nest box both before and after use helps prevent the septicemic form in neonatal rabbits.

Mastits(Blue breasts)  

Mastitis is common in commercial rabbitries and is occasionally seen in smaller units. Poor sanitation enhances spread throughout the rabbitry. Mastitis affects lactating does and may progress to a septicemia and rapidly kill the doe. Generally, it is caused by staphylococci, but streptococci and other bacteria have been isolated. Initially, the mammary glands become hot, reddened, and swollen. Later, they may become cyanotic, hence the common name "blue bag." The doe will not eat but may crave water. Fever ≥105°F (40.5°C) is often noted. Treatment is slow-release penicillin by parenteral injection; other antibiotics, such as cephalosporins, aminoglycosides, chloramphenicol, and tetracyclines, can be helpful. If treatment is started early (the first day the doe goes off feed), the rabbit may be saved and damage limited to one to two mammary glands. If more than two glands are lost, keeping the doe may not be economical. Because penicillin often causes diarrhea in rabbits because of a resulting microbial imbalance in the GI tract, does should be treated only after the pelleted ration has been replaced with hay or some other high-fiber diet (see enterotoxemia in Intestinal Diseases). Kits should not be fostered to another doe because they will spread the infection to the foster mother. Hand-rearing of infected young may be attempted but is difficult. The incidence of mastitis can be reduced if nest boxes are sanitized both before and after use. Vaccines have not proven to be beneficial in preventing mastitis.

Treponematosis  (Vent disease, Syphilis, Spirochetosis)  

Treponematosis, a specific venereal disease of domestic rabbits, is caused by the spirochete Treponema cuniculi . It occurs in both sexes and is transmitted by coitus and from the doe to offspring. It is not transmissible to other domestic animals or man. The incubation period is 3-6 wk. Small vesicles or ulcers are formed, which ultimately become covered with a heavy scab. These lesions usually are confined to the genital region, but the lips and eyelids may be involved. Infected rabbits should not be mated. Diagnosis is based on the lesions and observation of the spirochete by darkfield microscopy. A variety of serologic tests are also available. Hutch burn is a differential diagnosis

Benzathine penicillin G, 42,000 IU/kg body wt, SC, at weekly intervals for 3 wk, is necessary to eradicate treponematosis from a herd. All rabbits must be treated even if no lesions are present. Lesions usually heal within 10-14 days, and recovered rabbits can be bred without danger of transmitting the infection. A potential side effect of penicillin treatment is diarrhea and the possibility of an enteritis outbreak due to proliferation of gram-negative bacteria in the gut. Rabbits treated with penicillin should be switched to hay and treated with antidiarrheals immediately if needed (see enterotoxemia in Intestinal Diseases).

 Intesintal diseases 

Intestinal disease is a major cause of death in young rabbits. Although most diarrheal diseases were once lumped together (as the enteritis complex) or simply called mucoid enteritis, specific diseases are being delineated.

Enterotoxemia is an explosive diarrheal disease, primarily of rabbits 4-8 wk old. It occasionally affects adults and junior stock. Signs are lethargy, rough coat, a perineal area covered with greenish brown fecal material, and death within 48 hr. Often, a rabbit looks normal in the evening and is dead the next morning. Necropsy reveals the typical lesions of enterotoxemia, ie, a fluid-distended intestine with hemorrhagic petechiae on the serosal surface. One recognized cause is Clostridium spiroforme , which produces an iota toxin. Little is known about transmission of the organism; it is assumed to be a commensal that is normally present in low numbers. The type of diet seems to be a factor in development of the disease; enterotoxemia is seen less often when high-fiber diets are fed. Because lincomycin, clindamycin, and erythromycin induce Clostridium -related (eg, C difficile ) enterotoxemia due to their selective effect on normal gram-positive bacteria, they are contraindicated in rabbits. Enterotoxemia is a consideration for most antibiotic therapy, and it has been seen after administration of penicillins and cephalosporins. The incidence rate is 40-80% after oral penicillin therapy, which should therefore be considered contraindicated in rabbits. These diarrheas are remarkably similar to those that occur naturally and that are described above as enterotoxemia. Treatment of colony rabbits is seldom attempted because of the rapidity of death. However, when population size permits, cholestyramine has been used with promising results, both as a preventive and a treatment. Reducing stress of the young rabbits (weaning, etc) and ad lib feeding of hay or straw are helpful in prevention. Adding 250 ppm of copper sulfate to the diet of young rabbits also helps prevent enterotoxemia. Changing to a new brand of feed with different ingredients may help stop an outbreak. Diagnosis depends on history, signs, lesions, and demonstration of the organism ( C spiroforme ) by Gram's stain.

Mucoid enteropathy is a diarrheal disease of rabbits of any age but seems to be more common in adults and young >8 wk old. While the etiology is still largely unknown, it is basically the result of constipation. Impaction of the cecum or terminal part of the small intestine is a common necropsy finding. This, along with a gelatinous mucus found in the colon, is almost pathognomonic. Clinical signs are gelatinous or mucus-covered feces, anorexia, lethargy, subnormal temperature, dehydration, rough coat, and often a bloated abdomen due to excess water in the stomach. The perineal area is often covered with mucus and feces. The impaction can usually be palpated through the abdominal wall. Diagnosis is based on clinical signs and necropsy findings. Rabbits may live for ≥1 wk. Treatment is not very rewarding. Rehydration with electrolytes is sometimes beneficial. Increasing the fiber in the diet by feeding loose grass hay or straw daily usually prevents the condition and helps in stopping an outbreak.

Tyzzer's disease ( Tyzzer's Disease: Introduction , Tyzzer's Disease , Tyzzer's Disease), which is caused by Bacillus piliformis , is characterized by profuse diarrhea, anorexia, dehydration, lethargy, and death within 1-3 days in rabbits 6-12 wk old. Infection occurs by ingestion and is associated with poor sanitation and stress. The lesions consist of necrotic enteritis along with focal necrosis in the liver and heart. Diagnosis is made histologically; special stains (eg, Giemsa or silver) show the characteristic intracellular bacterium. Culturing is impractical because the bacterium does not grow on artificial media. Tyzzer's disease has not been reported in man, but it does affect other species of animals. Although antibiotics used in treatment of other animals have not been effective in rabbits, oxytetracycline has been of some value in limiting an outbreak. No vaccine is available.

Salmonellosis 

Salmonellosis is not common in rabbits, but the number of reports is increasing. It may be characterized by septicemia and rapid death but more often is asymptomatic. The most common etiologic agent is Salmonella typhimurium or S enteriditis . Young rabbits and pregnant does are most susceptible, which suggests that stress has an important role in the disease. Transmission is by direct contact or by ingestion of food or water contaminated with feces. Poultry and wild rodents are often carriers of salmonellae and can transmit them to susceptible rabbits. Clinical signs are nonspecific and consist of anorexia, depression, fever, and sometimes diarrhea. Often, only a dead rabbit is found. In peracute cases, lesions of septicemia are present—vascular congestion is seen in most organs with petechiae on the surface of abdominal and thoracic organs. In acute cases, pinpoint areas of necrosis are seen in the liver, and the spleen is enlarged. Diagnosis depends on isolation and identification of the specific agent. Treatment is rarely attempted because treated rabbits might become carriers, and rabbits suspected to be infected are best eliminated. Prevention depends primarily on sanitation. Salmonellosis is seen in many animal species, including man, and good hygiene should be exercised in an outbreak in rabbits.

Colibacillosis 

Colibacillosis appears to be much more common in rabbitries in Europe than in North America. It is caused by enteropathogenic strains of Escherichia coli , of which many different serotypes have been associated with rabbit diarrhea. Normal healthy rabbits do not have E coli of any strain associated with their GI tract. However, if the pH increases to ≥7.0, E coli begins to colonize the gut; those that attach to the mucosa and efface the epithelial cells can cause diarrhea and death.

Two types of colibacillosis are seen in rabbits, depending on age. Baby rabbits 1-2 wk old develop a severe yellowish diarrhea that results in high mortality. It is not uncommon for entire litters to succumb to this disease. In weaned rabbits 4-6 wk old, a diarrheal disease very similar to that described for enterotoxemia is seen. The intestines are fluid filled with petechial hemorrhages on the serosal surface, similar to the pathology described for

both Tyzzer's disease and enterotoxemia (see above). Death occurs in 5-14 days, or rabbits are left stunted and unthrifty. Diagnosis is made by isolating E coli on blood agar and then having the isolate biotyped or serotyped. Electron micrographs of E coli attached to the mucosa are also helpful. In severe cases, treatment is not successful; in mild cases, antibiotics are of value. Severely affected rabbits should be culled, and facilities thoroughly sanitized. High-fiber diets appear to help prevent the disease in weaned rabbits.

Ringwork (Dermatophytosis)  

Ringworm in domestic rabbits is much more common in Europe than in the USA. It is generally associated with poor husbandry. The lesions usually appear first on the head and may spread to any area of the skin. Affected areas are circular, raised, reddened, and capped with white, bran-like, flaky material. The most common cause is Trichophyton mentagrophytes granulare , which also affects man, guinea pigs, mice, and rats. Because rabbits with active infections are infectious for man and other animals, they should be either isolated and treated or killed. A degree of control can be obtained by application of powdered sulfur to all nest boxes before kindling or by use of topical agents such as those containing salicylic and benzoic esters of propylene glycol, aqueous solutions of sodium caprylate, and tinctures containing tannic, benzoic, and salicylic acids. Griseofulvin at an individual dose of 12 mg/lb (25 mg/kg) body wt daily for 2 wk or in the feed at 375 mg/lb (825 mg/kg) of feed is effective but is not approved for use in rabbits; it should not be used in rabbits intended for human consumption.

Parasitic Diseases 

Coccidiosis is a common and worldwide protozoal disease of rabbits. Rabbits that recover frequently become carriers. There are two anatomic forms: hepatic, caused by Eimeria stiedae , and intestinal, caused by E magna , E irresidua , E media , E perforans , E flavescens , E intestinalis , or other Eimeria spp . Transmission of both the hepatic and intestinal forms is by ingestion of the sporulated oocysts, usually in contaminated feed or water.

Hepatic Coccidiosis:

Severity of disease depends on the number of oocysts ingested. Young rabbits are most susceptible. Affected rabbits may be anorectic and have a rough coat. Hepatic coccidiosis is most often subclinical, but growing rabbits may fail to make normal gains. Infrequently, death may follow a short course. Rabbits usually succumb within 1 mo after a severe experimental exposure. At necropsy, small, yellowish white nodules are found throughout the hepatic parenchyma. In the early stages, they may be sharply demarcated, while in the later stages, they coalesce. The early lesions have a milky content; older lesions may have a more cheese-like consistency. Microscopically, the nodules are composed of hypertrophied bile ducts. Diagnosis of this form of coccidiosis is based on the gross and microscopic changes along with demonstration of the oocysts in the bile ducts. An impression smear of a lesion in the liver examined under light microscopy often reveals oocysts. The oocysts may also be demonstrated easily by fecal flotation.

Sulfaquinoxaline administered continuously in the drinking water (0.04% for 30 days) prevents clinical signs of hepatic coccidiosis in rabbits heavily exposed to E stiedae . However, it may not prevent the lesions. Sulfaquinoxaline may also be given in the feed at 0.025% for 20 days, or for 2 days out of every 8 until marketing. Because feed-grade sulfaquinoxaline can be difficult to obtain, liquid sulfaquinoxaline is used more commonly. Withdrawal time is 10 days for rabbits used for food. Rabbits that are treated successfully are immune to subsequent infections. Treatment will not be successful unless a sanitation program is instituted simultaneously. Feed hoppers and water crocks should not become contaminated with feces. Hutches should be kept dry, and the accumulated feces removed frequently. Wire cage bottoms should be brushed daily with a wire brush to help break the life cycle of the protozoa. Some chemicals, such as 10% ammonia solution, are lethal to oocysts and may be used to disinfect cages or ancillary equipment exposed to fecal material.

Intestinal Coccidiosis:

This form of coccidiosis can occur in rabbits receiving the best of care, as well as in rabbits raised under unsanitary conditions. Typically, infections are mild and often no clinical signs are seen. In early infections, there are few lesions; later, the intestine may be thickened and pale. Good sanitation programs that can eliminate hepatic coccidiosis do not seem to eliminate intestinal coccidiosis. Intestinal coccidiosis is generally diagnosed by fecal flotation and microscopical identification of the oocysts (species). Treatment is similar to that for hepatic coccidiosis except that sulfaquinoxaline is given for 7 days, repeated after a 7-day interval.

Larval Worm infection 

Although adult tapeworm infections are rare in domestic rabbits, the discovery of larval tapeworm cysts on the serosal peritoneum is not uncommon. Rabbits are intermediate hosts for two species of canine tapeworm, Taenia serialis and T pisiformis . Although T serialis is rare in domestic rabbits, it is somewhat more common in wild ones. The larval stage of T pisiformis is a cysticercus. Most are found attached to the mesenteries. Before forming these fluid-filled cysts, the young larvae migrate through the liver, where they leave white, tortuous subcapsular tracts. Generally, there are no clinical signs, and diagnosis occurs at necropsy. Treatment is usually not attempted, but control is accomplished by restricting access of dogs (the final host of the tapeworm) to the area in which food and nesting material are stored. Dogs should not be fed infected dead rabbits because this perpetuates the cycle. Mebendazole at 1 g/kg of feed for 14 days is reported to be an effective treatment.

Baylisascaris procyonis has been reported in rabbits. Signs are similar to those induced by Encephalitozoon cuniculi . No treatment is available.

Mite infestation 

The ear mite Psoroptes cuniculi is a common parasite of rabbits worldwide. Head shaking, ear flapping, and scratching at the ears are common signs. Torticollis and spasms of the eye muscles may be seen. Affected rabbits lose flesh, fail to produce, and succumb to secondary infections, which frequently damage the inner ear and may reach the CNS. Mites irritate the lining of the ear and cause serum and thick crusts to accumulate. With the rabbit well restrained or under general anesthesia, the brown crumbly exudate should be removed with cotton soaked in dilute hydrogen peroxide. The ear should be treated with any of the miticides approved for use in dogs and cats, or even with light mineral oil alone. Those products containing a cerumenolytic agent are particularly useful in removing the heavy, crusty material. The medication should be applied within the ear and down the side of the head and neck as well. Application should be repeated every other day for 6-10 days; additional treatments may be necessary. Hutches must be carefully cleaned and disinfected. Incidence is much lower when rabbits are housed in wire cages than in solid cages. The mite is readily transmitted by direct contact. Ivermectin has been reported to be effective in treating ear mites (see below).

Infrequently, rabbits are infested with either Sarcoptes scabiei or Notoedres cati . These mites burrow into the skin and lay eggs. The rabbits scratch themselves almost continually. There is loss of hair on the chin, nose, head, base of the ears, and around the eyes. These lesions often become secondarily infected with bacteria. It is difficult to eliminate the parasites on domestic rabbits. The condition is extremely contagious and can be transmitted to man. Euthanasia should be recommended unless the rabbits are valuable breeders. Rabbits may be dipped in a lime-sulfur preparation, or rotenone may be rubbed into the lesions. While this condition does not seem to be a big problem in North America, it is much more common in developing countries.

Fur mite infestations are common, and two genera, Cheyletiella and Listrophorus , are found worldwide. A number of different species of the genus Cheyletiella are found on rabbits. The most common in America is C parasitovorax . The genus Listrophorus has but one species, L gibbus . These mites live on the surface of the skin and do not cause the intense pruritus seen with sarcoptic mange. Fur mite infestations usually are asymptomatic unless the rabbit becomes debilitated. Occasionally, small scabs and sores are seen on the neck of adult rabbits. Transmission is by direct contact. Diagnosis is accomplished by skin scraping and light microscopy. These mites do not seem to affect man. Treatment is seldom done except for pets or show rabbits. Injectable ivermectin at 400 µg/kg body wt, two or three treatments 10-14 days apart, has been effective against both fur and ear mites; however, ivermectin is not approved for use in rabbits. A solution of 0.5% malathion used twice as a dip with a 1-wk interval is also effective in control.

Nosematosis 

Encephalitozoon(Nosema) cuniculi is a widespread protozoal (microsporidian) infection of rabbits and occasionally of mice, guinea pigs, rats, and dogs. Usually, no clinical signs are seen. The mode of transmission in naturally occurring outbreaks is not definitely known, but it is believed to be spread in the nest box from shedder does to the sucklings or from doe to doe through urine contamination. It seems to be mildly contagious in a rabbitry. At necropsy, the most significant lesion is pitting of the kidneys. Microscopical lesions consist of focal granulomas and pseudocysts in the brain and kidneys. Sometimes a severe, focal, interstitial nephritis is seen. Diagnosis is made by identifying the lesions (pseudocysts) and observing the organisms when stained with special stains. Several serologic and skin tests are helpful in screening rabbits for antibodies to the organism. Treatment has not been attempted. Prevention entails good sanitation and, possibly, serologic screening of breeding stock with elimination of positive reactors. A differential diagnosis is an aberrant migration of Baylisascaris spp into the nervous system (see larval worm infection, above). One case of nosematosis has been reported in man.

Pinworms 

Passalurus ambiguus , the rabbit pinworm, usually is not clinically significant but often is upsetting to owners. It is common in many rabbitries and is distributed worldwide. Transmission is by ingestion of contaminated food or water. The adult worm lives in the cecum or anterior colon. Diagnosis is made by observing the adults at necropsy or by finding the eggs during examination of the feces. Single treatments are not very effective, because the life cycle is direct and reinfection common. Treatment of pet rabbits with piperazine citrate in the water (3 g/L) for alternating 2-wk periods is effective. Other parasiticides such as fenbendazole and oxyfenbendazole are also effective in treating pinworm infections in rabbits. Rabbit pinworms are not transmissable to man.

Viral Diseases

Papillomatosis

Two types of infectious papillomas are recognized infrequently in domestic rabbits. The oral papilloma virus, caused by the papillomavirus, is the most important clinically and of highest incidence. The lesions consist of small, grayish white, pedunculated nodules or warts on the under surface of the tongue or on the floor of the mouth. The second type, caused by the Shope papilloma virus, is characterized by horny warts on the neck, shoulders, ears, or abdomen and is primarily a natural disease of cottontail rabbits. Shope papilloma virus is transmitted by arthropod vectors. The oral papilloma virus is distinct from the Shope papilloma virus (which is also distinct from the Shope fibroma virus). Skin tumors caused by the Shope papilloma virus never occur in the mouth. Neither type of papillomatosis is treated, and the condition usually resolves spontaneously over time.

Myxomatosis 

Myxomatosis is a fatal disease of all breeds of domestic rabbits and the European wild rabbit ( Oryctolagus cuniculus ). Cottontail ( Sylvilagus ) and jackrabbits ( Lepus ) are quite resistant. All other mammals are refractory. Myxoma virus, a member of the poxvirus group, is transmitted by mosquitoes, fleas, biting flies, and direct contact. Several strains are pathogenic.  In the USA, myxomatosis is restricted largely to the coastal area of California and Oregon, where epidemics occur infrequently, but sporadic cases are common. These areas represent the geographic distribution of the California brush rabbit ( Sylvilagus bachmani ), the reservoir of the infection. Losses in rabbitries may be 25-90%. All ages are susceptible, although young rabbits up to 2 mo old appear more resistant than adults.  The first characteristic sign is conjunctivitis that rapidly becomes more marked and is accompanied by a milky ocular discharge. The rabbit is listless and anorectic, with a fever that frequently reaches 108°F (42°C). In acute outbreaks, some rabbits may die within 48 hr after signs appear. Those that survive become progressively depressed and develop a rough coat. The eyelids, nose, lips, and ears become edematous, which gives a swollen appearance to the head. In females, the vulva becomes inflamed and edematous; in males, the scrotum swells. A characteristic sign at this stage is drooping of the edematous ears. A purulent nasal discharge invariably appears, breathing becomes labored, and the rabbit goes into a coma just before death, which usually occurs within 1-2 wk after clinical signs appear. Occasionally, a rabbit survives for several weeks; in these cases, fibrotic nodules appear on the nose, ears, and forefeet. Rabbits inoculated experimentally with laboratory strains of the virus invariably develop small nodules at the point of injection after several days; similar nodules develop later on other parts of the body, particularly the ears.  Few characteristic gross lesions are found at necropsy in the acute form of the disease. The spleen is occasionally enlarged and is almost always devoid of lymphocytes when examined histologically. In rabbits that survive longer, subcutaneus edema and nodular skin tumors are seen. The seasonal incidence of the disease, clinical signs (especially the swollen genitalia), and high mortality are all of diagnostic significance. Large, eosinophilic, cytoplasmic inclusion bodies in the conjunctival epithelial cells are also helpful in diagnosis.  An attenuated vaccine prepared from a myxomatosis virus has protected rabbits infected under both field and laboratory conditions. This vaccine is not available in the USA, and because there is no effective treatment, euthanasia and burying or burning of affected rabbits is indicated.

Rotavirus 

Rotavirus has been isolated from rabbits with diarrhea in many different countries of the world. The double-stranded RNA virus has been divided into five different groups labelled A, B, C, D, and E. However, rabbit isolates are all in group A. Group A has 14 serotypes, but only serotype 3 is found in rabbits. In serologic studies of rabbit colonies in many countries, almost 100% of the adult rabbits in some rabbitries were positive for rotavirus, demonstrating its widespread nature. Rotavirus is shed in the feces of infected rabbits and, therefore, is probably transmitted by the fecal-oral route. Young rabbits 30-80 days old are most commonly infected. Rabbits exhibit a severe mucoid or watery diarrhea, anorexia, and dehydration. Mortality is 60-80%. In pure rotavirus infection, cecal contents are fluid and mensenteric lymph nodes are swollen. The diarrhea seems to be more transient, and mortality is reduced. Histologically, villous atrophy and desquamation and degeneration of the enterocytes on the tips of the villi are characteristic. Most rotavirus infections are, however, complicated with pathogenic bacteria such as Clostridium spp or E coli . The mixed infection results in a much more deadly syndrome. At necropsy, intestines of rabbits with mixed viral and bacterial infections are distended, with petechial hemorrhages in both the mucosa and submucosa. Submucosal edema is also common, along with the damaged mucosal epithelium.  There is no treatment, but the infection appears to be self-limiting if susceptible rabbits are not continually introduced into the population. Experimentally, the virus is shed for only 1 wk after inoculation. Therefore, cessation of breeding for 4-6 wk seems to allow the disease to run its course, because seropositive does do not infect their offspring.

Viral Hemorrhagic Disease (Necrotic hepatitis)  

Viral hemorrhagic disease is an acute, highly contagious infection, primarily of domestic lagomorphs. It has been reported in China, Korea, Germany and other European countries, most Asian countries, and Mexico. The causative agent has not been definitely classified, although a parvovirus antigenically related to both porcine parvovirus, mouse and rat parvoviruses, and a virus that belongs to the Caliciviridae family have all been suggested. Aerosol transmission seems to be important, but all secretions and excretions may be sources of infection. Mechanical transmission by fomites, rodents and other vermin, rabbit by-products, and man can be important. Insects do not seem to be important vectors.  The disease most often occurs in domestic rabbits. Lactating and gestating females are most susceptible, followed by other adults; young rabbits (<2 mo old) are the most resistant. Existence of carriers in surviving domestic rabbits and in the wild has yet to be determined but is suspected to occur.  The incubation period is 24-72 hr. Typically, rabbits are found dead, with no prior indication of illness in the colony. In more protracted cases, dyspnea, congestion of the eyelids, orthopnea, abdominal respiration, tachycardia, and increased uneasiness can be seen. Before death, there is violent cage activity, with rapid turns and flips, which resemble convulsions or mania. High shrills followed quickly by collapse and death are sometimes the only signs reported. In some instances, a blood-tinged nasal discharge can be seen, and blood-stained floors under the cages in which rabbits have died have also been reported. Morbidity is estimated at 30-80%, with mortality up to 90%.  Due to the rapid course, rabbits found dead are usually in good condition. Gross lesions are subtle and generally limited to congestion of the respiratory tract and liver. The respiratory tract appears to be most affected, with intense congestion of the trachea and lungs. The trachea may be filled with froth, sometimes blood-tinged. Hemorrhages in the thymus are common. Mild to marked congestion and enlargement of the liver, spleen, and kidneys can be seen. The liver may have yellow-brown surface areas. Congestion of the meninges has been reported. Distention of the distal bowel with gas has been seen, even when necropsy was performed immediately after death. The proximal areas of bowel are usually completely filled with ingesta.  Histologically, there is submassive to massive, focal, coagulative hepatic necrosis. Disseminated intravascular coagulation is commonly seen in the kidney. In the lungs, hemorrhages into clusters of alveoli can be seen. Lesions in the spleen vary from simple congestion to necrosis and hemorrhage. Multiple focal areas of necrosis of the myocardium also can be seen. In field cases, severe necrosis of the crypts of the small intestine has been documented; this same finding was more subtle in inoculated laboratory rabbits.  The peracute course of the disease, along with respiratory distress, high mortality, and rapid spread, afford a presumptive diagnosis. Tissue suspensions of liver, spleen, and lung hemagglutinate human RBC, type O. Serum from convalescent rabbits inhibit this agglutination. Fluorescent antibody tests and immunostaining techniques also have been used to identify the viral antigen; liver, spleen, and lung are the specimens of choice because they contain high concentrations of virus. These should be shipped to the laboratory using ice, or dry ice if the shipment is expected to take >48 hr.  Viral hemorrhagic disease should be differentiated from the acute forms of other diseases in rabbits such as pasteurellosis, atypical myxomatosis, enterotoxemia, poisonings, and heat exhaustion.  A vaccine that confers protection for 5-15 mo has been developed in various countries and is marketed in Spain. The vaccine should be used only where the disease is already widespread and eradication efforts are difficult to implement. Vaccines have been used to complement control efforts, but this may be a disadvantage if the vaccine masks the infection or helps induce a carrier state in the vaccinates. Absolute quarantine measures must be applied to rabbits entering the USA or other areas free of the disease from countries where it is present.

Malocclusions 

The incisors, premolars, and molars of rabbits grow throughout life. The normal length is maintained by the wearing action of opposing teeth. Malocclusion (mandibular prognathism, brachygnathism) probably is the most common inherited disease in rabbits and leads to overgrowth of incisors with resultant difficulty in eating and drinking.  Temporary correction can be effected by cutting the overgrown teeth from time to time with bone or wire cutters. Occasionally, the cheek teeth overgrow and cause severe tongue or buccal lesions. Because malocclusion is generally considered to be inherited, rabbits with this condition should not be bred. However, young rabbits can damage their incisor teeth by pulling on the cage wire, which results in misalignment and possibly malocclusion as the teeth grow. This condition is difficult to differentiate from genetic malocclusion, and these rabbits should also be culled. Genetic malocclusion generally can be detected in young rabbits 3-8 wk old.

Hair chewing and Hairballs 

Rabbits groom themselves constantly, so the stomach contents often contain hair, which is normally passed through the GI tract and excreted with the fecal pellets. The hair becomes a problem only if excess amounts are consumed or if it accumulates in the stomach and blocks the pylorus. If this happens, the rabbit becomes anorectic, loses weight, and dies within 3-4 wk. Daily combing to remove loose hair effectively prevents this condition. Feeding hay ad lib is also preventive and will decrease the incidence of trichobezoars. Mineral oil and laxatives are not effective in removing the hair mass. Surgical removal might be attempted with valuable rabbits.

Pineapple juice contains the digestive enzyme bromelain and has been used to treat early cases of trichobezoar or hairballs; an adult rabbit is given 10 mL of fresh or frozen juice through a stomach tube or intubation needle once or twice daily for 3 days. Both the fluid and the enzyme help to break up the matrix of the hairball. Canned pineapple juice is not as effective because the canning process destroys the enzyme. Roughage (hay or straw) should be fed during the treatment to help carry the hair fibers through the GI tract and out with the feces

Hair chewing in fryer rabbits damages the pelt and renders it worthless. This type of hair chewing is generally a result of low fiber in the diet and can be corrected by increasing the fiber or feeding hay along with the pellets. Adding magnesium oxide to the diet at 0.25% also may be helpful. In some cases, hair chewing is a result of boredom. Placing distractions in the cage, eg, soda pop cans or metal rings, often halts this vice.

Heat Exhaustion 

Rabbits are sensitive to heat. Hot, humid weather, along with poorly ventilated hutches or transport in poorly ventilated vehicles, may lead to death of many rabbits, particularly pregnant does. Affected rabbits stretch out and breathe rapidly. Hutches should be constructed so that they can be sprinkled in hot, humid weather. Free access to cool water should be provided. When the environment can be controlled, optimal conditions are a temperature of 50-70°F (15.5-21°C) and a relative humidity of 40-60%, with 10-20 air changes per hour. Wire cages are preferable to solid hutches. Treatment consists of immersing rabbits in cold water during the heat of the day, especially those that will kindle in the next day or two.

Hutch burn 

Hutch burn is often confused with treponematosis and can be truly differentiated only by the absence of spirochetes on darkfield microscopy and by the lack of antibodies to Treponema cuniculi . It is caused by wet and dirty hutch floors and affects the anus and external genitalia. Also, rabbits that lack adequate sphincter control of the bladder constantly dribble urine and may be affected. The membranes of the anus and genital region become inflamed and chapped. The area soon becomes secondarily infected with any of a number of pathogenic bacteria. Brownish crusts cover the area and a hemorrhagic, purulent exudate may be present. Keeping hutch floors clean and dry and applying nitrofurazone or an antibiotic ointment to the lesions hastens recovery.

Ketosis (Pregnancy Toxemia) 

Ketosis is a rare disorder that may result in death of does at or 1-2 days before kindling. The disease is more common in first-litter does. Predisposing factors include obesity and lack of exercise. The probable cause is starvation. For some reason, not well understood, there is anorexia. Other signs are dullness of eyes, sluggishness, respiratory distress, prostration, and death. The most significant lesions are fatty liver and kidneys. The body mobilizes fat and transports it to the liver to be broken down for energy, thus the fatty liver. Diagnosis depends on clinical signs and necropsy lesions. Injection of fluids that contain glucose may be helpful in correcting the disease. Breeding junior does early, before they become too fat, is also helpful. Hairballs in the stomach are often a factor in ketosis. 

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