Uterine disease is extremely common in unspayed (intact) female rabbits and is one of the most compelling reasons for routine spaying (ovariohysterectomy). Uterine adenocarcinoma — a malignant cancer of the uterine lining — develops in an alarming proportion of intact does: studies have shown that up to 60 to 80% of unspayed female rabbits over 4 years of age will develop uterine adenocarcinoma. Other common uterine conditions include endometrial hyperplasia, endometrial aneurysm (causing life-threatening hemorrhage), and pyometra (uterine infection). Spaying before 2 years of age virtually eliminates the risk of these conditions.
Overview
The uterus of intact female rabbits undergoes hormonal changes that predispose to progressive disease:
- Endometrial hyperplasia — Thickening of the uterine lining under the influence of estrogen and progesterone. Considered a precursor to adenocarcinoma. Very common in does over 3 years old.
- Endometrial venous aneurysm — Dilated blood vessels in the uterine wall that can rupture, causing sudden, potentially fatal hemorrhage into the uterus or abdomen.
- Uterine adenocarcinoma — Malignant cancer arising from the uterine endometrium. The most common cancer in female rabbits. Can metastasize to the lungs, liver, and other organs.
- Pyometra — Bacterial infection of the uterus with pus accumulation. Can cause sepsis.
- Hydrometra — Fluid accumulation in the uterus without infection.
The risk increases dramatically with age. By 5 years of age, the majority of unspayed does have some form of uterine pathology.
Symptoms
- Bloody vaginal discharge (hematuria) — Blood from the uterus mixes with urine, causing bloody-appearing urine. This is often the first sign noticed by owners. Note: true blood in rabbit urine is abnormal (rabbits can have red-orange urine from plant pigments, which is normal — blood must be differentiated).
- Decreased appetite and lethargy
- Abdominal distension
- Weight loss
- Mammary gland changes (cysts or masses)
- Behavioral changes (aggression, nesting behavior)
- Anemia (pale ears and gums) from chronic blood loss
- Sudden collapse or death from uterine hemorrhage
- In advanced adenocarcinoma: respiratory difficulty from lung metastasis
Diagnosis
- Physical examination — Palpation of an enlarged, irregularly shaped uterus. Mammary masses may be detected.
- Urinalysis — Distinguishes true hematuria from pigmented urine (centrifuging the sample — true blood produces a red sediment and clear supernatant; pigment produces uniformly colored urine).
- Abdominal radiographs — Evaluate uterine size, detect masses, and screen for pulmonary metastasis (thoracic radiographs).
- Abdominal ultrasound — Evaluates uterine wall thickness, fluid accumulation, and mass characteristics.
- Blood work — Complete blood count (check for anemia), biochemistry panel, and liver values.
- Thoracic radiographs — Screen for pulmonary metastasis before surgery. If metastasis is present, the prognosis changes significantly.
- Histopathology — Definitive diagnosis and staging of uterine adenocarcinoma require microscopic examination of the excised uterus.
Treatment
Ovariohysterectomy (Spay)
Surgical removal of the uterus and ovaries is the treatment of choice for all forms of uterine disease in rabbits:
- Curative for benign conditions — Endometrial hyperplasia, hydrometra, and pyometra are cured by spay.
- Potentially curative for early adenocarcinoma — If the cancer has not metastasized, ovariohysterectomy can be curative.
- Palliative for advanced adenocarcinoma — Removes the primary tumor mass and stops uterine hemorrhage, improving quality of life even when metastasis is present.
Perioperative Medications
| Medication | Purpose | Key Notes |
|---|---|---|
| Meloxicam | Pre- and post-operative pain management | Given before surgery and continued for several days post-operatively. |
| Buprenorphine | Opioid analgesic | For moderate to severe post-operative pain. |
| Enrofloxacin | Antibiotic | For pyometra or suspected uterine infection. |
| Subcutaneous fluids | Hydration support | Important for peri-operative support. |
Post-Operative Care
- Syringe feed (Critical Care) if the rabbit is not eating within 12 hours of surgery
- Monitor fecal output — GI stasis is a common post-operative complication
- Pain management for at least 3 to 5 days
- Prevent the rabbit from chewing at the incision (Elizabethan collar or body wrap if needed)
- Restrict exercise for 10 to 14 days
Prevention
Spaying (ovariohysterectomy) is the most important preventive measure. The procedure is recommended for all female pet rabbits that are not intended for breeding, ideally performed between 4 and 6 months of age (after sexual maturity but well before the age at which uterine disease typically develops).
Benefits of spaying include:
- Near-complete elimination of uterine adenocarcinoma risk
- Prevention of endometrial hyperplasia, pyometra, and uterine hemorrhage
- Reduction in hormonally driven behavioral issues (aggression, territorial spraying)
- Prevention of pseudopregnancy
- Prevention of unwanted litters
Prognosis
- Endometrial hyperplasia — Excellent prognosis with spay.
- Uterine adenocarcinoma without metastasis — Good prognosis with ovariohysterectomy. Many rabbits are cured if the cancer is confined to the uterus.
- Uterine adenocarcinoma with pulmonary metastasis — Poor prognosis. Median survival time after metastasis is detected is typically weeks to a few months. Palliative spay may still improve quality of life by resolving hemorrhage.
- Pyometra — Good prognosis with timely surgical intervention and antibiotic therapy.
- Acute uterine hemorrhage — Emergency; prognosis depends on the severity of blood loss and how quickly surgical intervention occurs.
Frequently Asked Questions
At what age should I spay my rabbit? Most rabbit-experienced veterinarians recommend spaying between 4 and 6 months of age. Some vets prefer to wait until 6 months for larger breeds. The procedure can be done at older ages, but anesthetic risk increases with age and the risk of existing uterine disease rises.
Is spaying surgery risky for rabbits? Rabbit anesthesia does carry risk (higher than in dogs and cats), but in the hands of a rabbit-experienced veterinarian, spay surgery has a good safety record. The risk of the surgery is significantly outweighed by the near-certainty of developing life-threatening uterine disease in unspayed does.
My rabbit is 6 years old and unspayed. Should I still have her spayed? Yes, but pre-surgical screening (blood work, thoracic radiographs) is important at this age. Given the extremely high probability of existing uterine pathology in a 6-year-old intact doe, the benefits of surgery likely outweigh the anesthetic risks, provided no metastatic disease is found.
Can uterine adenocarcinoma be treated with chemotherapy? Chemotherapy for rabbit uterine adenocarcinoma has not been well studied and is not a standard treatment. Ovariohysterectomy is the primary treatment. Research in this area is limited.
How do I know if the bloody urine is from the uterus or the urinary tract? Your veterinarian can differentiate by examining where the blood is in relation to urination (uterine blood may be seen separate from urine at the end of voiding), by urinalysis, and by imaging (ultrasound, radiographs) to evaluate both the uterus and urinary tract.