Reproductive and urinary diseases of pet rabbits (Proceedings)

Medical problems in rabbits commonly involve the reproductive and genitourinary systems. This review is designed to help practitioners successfully diagnose and treat frequently seen pathologic conditions affecting these systems.

The rabbit female reproductive tract differs from that of other companion animals in that it is a fat storage area and a double cervix is present. Ovariohysterectomy (OHE) in rabbits is commonly performed. The most common reasons are to prevent uterine adenocarcinoma and to prevent breeding. Female rabbits can become territorially aggressive and OHE typically prevents this from occurring. The disadvantage of OHE is the risk from anesthesia and surgical complications. The reproductive system of the male rabbit is similar to that of the cat. Castration in rabbits is a frequent procedure, and generally will reduce behavioral problems such as aggression and urine spraying. Most rabbits are neutered at 4-5 months of age, although others recommend even earlier castration because some rabbits may become sexually mature before 4 months of age.

The urinary system of the rabbit is a common area of disease. Anatomically, the rabbit urinary system follows common mammalian patterns except the kidneys are unipapillate. Male rabbits do not have an os penis.

Reproductive diseases

Mastitis

Septic mastitis can occur in lactating does, especially those predisposed to infection by trauma to the mammary gland and poor sanitation. Affected animals are febrile, inappetent, and depressed. The skin around the swollen gland may be cyanotic. Causative organisms commonly isolated in septic mastitis include Staphylococcus and Streptococcus species. Death of neonates may occur, or death of the doe may result from septicemia. Diagnosis of septic mastitis is based on clinical signs, history of lactation or pseudocyesis, and isolation of bacteria on culture of mammary tissue or exudate. Treatment may include surgical drainage, mastectomy, hot packs, and antibiotic therapy (based on culture and sensitivity).

In contrast to septic mastitis, cystic mastitis may occur in nonbreeding females (usually older than 3 years of age), and may be associated with increased estrogen, uterine hyperplasia, or uterine adenocarcinoma. The animal will not have any systemic signs, but will have swollen, firm, cyanotic glands, with a clear-to-dark serosanguineous discharge from the treat. The condition resolves with an ovariohysterectomy.

Rabbit syphilis

Rabbit syphilis (treponematosis) is caused by Treponema paraluis-cuniculi, a spiral-shaped bacterium. Transmission occurs venerally or by direct contact of young rabbits with an infected doe. Males and females are both affected. Externally, the common signs are papules, ulcers, vesicles, and crusting on the external genitalia or, occasionally, on the nose, eyelids, lips, and perineal area. Infected does may also abort and develop metritis and retained placentas. A diagnosis is based on history, clinical signs, and on identifying the spirochetes in darkfield microscopic examination of scrapings or smears of the skin lesions. The organisms can also be demonstrated histologically with silver stains of skin biopsy sections. Serological tests are also available to determine the presence of antibodies against T. cuniculi. A fluorescent antibody test against treponemal antigen is also used, and an ELISA test is available from some laboratories to screen for antibodies against Treponema.

Treatment of rabbit syphilis consists of benzathine G (42,000-84,000 IU/kg IM q7d for 3 treatments) or parenteral penicillin (40,000-60,000 IU/kg IM q12h x 5 days). Response is rapid; lesions dramatically regress, usually after one injection.

Uterine adenocarcinoma

Decreased litter size in does 3 years of age or older may indicate developing uterine adenocarcinoma, the most common neoplasia of female rabbits. The incidence in intact does of certain breeds, such as Dutch, tan, and Havana, is as high as 50-80%; other breeds, such as rex, Belgium, and Polish, have a very low incidence of disease. Adenocarcinomas rarely occur in does younger than 3 years of age. Clinical signs are similar to those of benign uterine hyperplasia, so it is difficult to distinguish the two conditions. Endometrial changes that may precede neoplastic changes include endometriosis, endometritis, and papillary, cystic, or adenomatous hyperplasia.

In rabbits, uterine adenocarcinoma is a slow-growing tumor with a 5-24 month clinical course. Metastasis occurs late in the clinical course of the disease, with local metastasis (to the peritoneum, lymph nodes, and liver) before hematogenous spread. Clinical signs are usually inapparent during the hyperplastic stages, although decreased reproductive performance, hematuria or a bloody discharge from the vaginal area, cystic mastitis, or an increase in aggressiveness may be noted in some does.

Diagnosis of a uterine adenocarcinoma is generally based on a combination of: clinical signs (if present); complete blood count and serum biochemical analysis; an enlarged, thickened uterus or multiple rounded caudal abdominal masses on physical examination; an enlarged uterus on abdominal radiography; and abdominal ultrasonography. Ovariohysterectomy is the recommended treatment, and is successful if done before metastasis has occurred. Many rabbits are anemic, which may compromise the prognosis for surgery. The prognosis is poor if metastasis has occurred.

Preventative treatment for endometrial hyperplasia and uterine adenocarcinoma is ovariohysterectomy before a doe is 2 years of age. Spaying rabbits between the ages of 6-9 months is preferred because they have less abdominal fat than older rabbits. Alternatively, discuss early clinical signs of the disease with the client and recommend semiannual health examinations for intact female rabbits 3 years of age and older. Be aware that anesthesia may be a bit more risky in rabbits than in dogs or cats, and owners should be appropriately advised.

Endometrial hyperplasia and uterine polyps

Endometrial changes may occur along a continuum; from polyp formation, to cystic hyperplasia, to adenomatous hyperplasia, to adenocarcinoma. Uterine hyperplasia is associated with aging, as are cystic and hyperplastic changes in endometrial glands. However, some reports have found no association between cystic hyperplasia and uterine adenocarcinoma in rabbits because adenocarcinomas are associated with senile atrophy of the endometrium. Clinical signs of endometrial hyperplasia can mimic those associated with uterine adenocarcinoma, including: intermittent hematuria, anemia, and a decrease in activity. A firm, irregular uterus sometimes can be detected by palpation. Cystic mammary glands and cystic ovaries can occur concurrently with this condition. Ultrasonography is the preferred diagnostic tool to image soft tissue changes in the uterus although other imaging modalities can also provide the diagnosis of uterine changes. Ovariohysterectomy is the recommended treatment, and a thorough exploration of the abdomen is warranted.

Endometrial venous aneurysms

Multiple endometrial venous aneurysms can cause hematuria because of episodic bleeding in the lumen of the uterus. Cylindrical blood clots molded within the uterine horns are typically passed with the urine and are highly suggestive of this condition. Affected does are at high risk for fatal exsanguination from uterine hemorrhage, and ovariohysterectomy should be performed as soon as the animal is stabilized. Endometrial venous aneurysms occur in young does of larger breeds. In rabbits with this condition, the uterine horns have multiple, blood-filled endometrial varices (veins) that periodically rupture into the uterine lumen, causing the clinical hematuria. The etiology of this condition is not known.

Hydrometra

Hydrometra is the accumulation of watery fluid in the uterus. Clinical signs include an enlarged, fluid-filled uterus, increased respiratory rate, anorexia, and weight loss. Transabdominal uterocentesis yields clear fluid with a low specific gravity, a low cell count, and a moderate amount of protein. Diagnosis can be supported by radiography and ultrasonography. Ovariohysterectomy and supportive care are indicated if hydrometra is diagnosed in a pet rabbit.

Pregnancy toxemia

Although pregnancy toxemia occurs somewhat commonly in some small exotic mammals, it is seldom recognized in rabbits. On rare occasions, though, it may be seen in pregnant, pseudopregnant, and postpartum rabbits. Obese rabbits are especially at risk. During pregnancy, it is most common during the last week of gestation. An important contributing factor is an inadequate nutritional supply to the uteroplacental unit. Signs of this disease include depression, abortion, acetone odor to breath, coma, ketonuria, and death. Since treatment is usually unrewarding, proper nutrition is the best prevention.

Urinary diseases

Renal disease is not uncommon in older rabbits. Etiologies include chronic renal infections, toxins, neoplasia, or degeneration. Rabbits with renal disease exhibit polyuria/polydipsia, anorexia, diarrhea, and wasting. Physical examination may reveal abnormally shaped kidneys. Generally, the BUN, creatinine, and white blood cell count are elevated, and the packed cell count is decreased. Urinalysis reveals a poor concentrating ability. Radiographically, misshapen kidneys are observed. Ultrasound is a useful tool to determine the architecture of the kidneys, to determine if neoplasia is present, and to aid in the prognosis. Treatment of renal disease depends on the cause. Supportive care includes fluids, antibiotics, and nutritional support. The prognosis is dependent on the cause.

Thick, white urine in rabbits is not uncommon and indicates the presence of large quantities of mineral precipitates. Unlike other mammals, calcium absorption and blood calcium concentration are directly related to dietary calcium in rabbits. Excessive calcium intake will result in excretion of large amounts of calcium in the urine. Calcium is excreted in the bile in other mammals.

Possibly the most common urogenital complaint veterinarians receive from clients is that of "bloody urine". Rabbit urine is extremely turbid and can vary in color from yellow-orange to red-brown. The color is caused by porphyrin pigment or a food related metabolite. Pathology can be ruled out by use of a urine dipstick to determine if blood is present.

Dysuria and hematuria may occur and are generally associated with cystitis, cystic calculi, or uterine adenocarcinoma. Cystic calculi (usually composed of calcium carbonate and may be associated with high dietary calcium intake) occur in both male and female rabbits. Also large amounts of calcium sediment (hypercalciuria) may be visible in the bladder in rabbits excreting large amounts of calcium. Frank blood, independent of or at the end of urination, may indicate the presence of a uterine adenocarcinoma. Diagnostics would include urine dipstick, urinalysis, CBC, chemistries, culture, radiography, and ultrasonography. It is important to measure blood calcium concentrations (often as high as 19 mg/dl) in rabbits excreting large amounts of urinary calcium. Depending on the etiology, treatment may include antibiotics (trimethoprim sulfa, chloramphenicol, etc.), manual expression of the bladder (catheterization?), fluid therapy, surgery, and modifying the diet. Potassium citrate may be beneficial in binding calcium in the urine and preventing precipitation; however, its efficacy in treating rabbits is anecdotal. Cystic calculi may be removed surgically.

To help prevent calcium sediment or calculi in the bladder of rabbits, it is important to feed them an appropriate diet (i.e., a diet that does not contain an excess amount of calcium). A low to moderate amount of pelleted feed (which is generally high in calcium because it is alfalfa-based) and high quality grass hay (i.e., timothy, prairie hay) ad libitum is the preferred diet.

Urinary incontinence

Urinary incontinence can be caused by lumbosacral vertebral fractures and dislocations or by central nervous system lesions from E. cuniculi infection. Rabbits with urinary calculi or hypercalciuria often exhibit urinary incontinence and urine scalding. Clinical signs include a urine-soiled perineum and ulcerations of the vaginal mucosa and intertrigonal pouches, as well as sticky, strong-smelling urine. A positive titer to E. cuniculi and additional central nervous system signs may suggest a protozoal infection. Urolithiasis or hypercalciuria can be identified radiographically. Vertebral fractures can be ruled out on thorough neurologic examination and radiography.

Additional differentials for urinary incontinence include ectopic ureter, urinary tract infection, neoplasia, and pyoderma. Initial supportive care includes daily cleaning of the perineum and topical treatment for dermatitis with a drying agent such as Domeboro astringent solution (Bayer, HealthCare, Morristown, NJ) in addition to treatment of the primary problem. NSAIDs can be used if there is no evidence of renal insufficiency and will decrease inflammation and provide analgesia. Older, obese, and/or arthritic rabbits may choose not to urinate in their litter box and appear suddenly "incontinent" to their owner. Using a litter box with easier access (low entry point) and keeping the box clean may be beneficial in these cases.

References

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