Emergency Management of the Blocked Ferret

By Christal Pollock, DVM, DABVP-Avian

Diagnosis of urethral obstruction in the male ferret is rarely a diagnostic challenge, but the need to place a urinary catheter in a 1-kg patient can be intimidating.

Urinary catheter placement can be challenging in the male ferret because of its small size and its J-shaped os penis. Locate the prepuce on the ventral abdomen just caudal to the umbilicus. The os penis is palpable. After gently extruding the penis, it may help to grasp the base with a gauze square. Aseptically prepare the penis, and use a 24-gauge catheter with the needle removed to find and dilate the urethral opening. The urethral opening is located on the ventral surface of the penis just proximal to the J-shaped curve.

After the urethral opening is found and dilated, pass a urinary catheter. A 3.5 Fr red rubber catheter may be used in a very large male, however most individuals require a smaller tube. A 3-Fr 11-in urinary catheter specifically designed for ferrets is available (Slippery Sam, Global Veterinary Products; New Buffalo, MI) or a 22- or 20-gague jugular catheter may be used. Pre-measure red rubber catheters and jugular catheters. Leave the jugular catheter stylet in place to facilitate passage, but manipulate the catheter carefully. Resistance most often occurs as the catheter travels around the pelvic flexure. Gently flush the urethra with sterile saline to facilitate catheter passage.

· Anesthesia is required for adequate muscle relaxation. Most individuals should be intubated and maintained on isoflurane or sevoflurane when anesthetized for extended periods. Avoid ketamine in ferrets with urethral obstruction.

· When urinary catheterization proves difficult, remove a small amount of urine once via cystocentesis to reduce pressure and allow passage of the urinary catheter. Repeated cystocentesis is not recommended because of thin bladder wall. In rare cases, percutaneous cystostomy may be performed when catheter placement fails.

· Suture butterfly tape strips near the prepuce to secure the catheter. Use tape to fasten the catheter or attached tubing to the tail base to minimize tension on the line. Bandaging the abdomen may also minimize the risk of rotation. Create a closed collection system by attaching a small intravenous bag and monitor urine production. The average 1-kg ferret produces 26-28 ml of urine over a 24-hour period (range: 8-48 ml).

· To catheterize the female ferret, place her in ventral recumbency and elevate the rear with a rolled towel. Aseptically prepare the vulva and perivulvar region, and then insert a sterile vaginal speculum or otoscope. Locate the urethral opening on the vestibule floor 1-cm cranial to the clitoral fossa. Insert a 3.5-Fr red rubber catheter, which may be fitted with a wire stylet.

The most important cause of dysuria or stranguria in the male ferret is prostatomegaly secondary to adrenal disease. Struvite urolithiasis may also cause urethral obstruction, however the incidence is relatively low now that ferret food is commercially available. (Cystitis and prostatic abscesses are uncommon but potential causes of stranguria and dysuria in the ferret). History and physical examination may provide clues to the underlying cause of urethral obstruction, but signalment is not particularly helpful. Most affected ferrets are middle aged to older, although any age may be affected.

	Adrenal disease	Struvite urolithiasis
Diet	Good diet (Animal protein-based)	Bad diet (Plant protein-based)
Exam findings	Dorsal symmetrical alopecia	—–
Laboratory results	+/- Urinary tract infection Non-regenerative anemia	Urinary tract infection Crystalluria
Radiographs	Unremarkable	Radiopacity
Ultrasonography	Prostatomegaly Adrenomegaly	—–

· Ferret adrenal disease is associated with an elevation in sex steroid hormones, and elevated androgen levels can leads to prostatomegaly. Dorsal symmetrical alopecia is also a common clinical sign.

· Ferrets require high quality, animal-based dietary protein. Therefore a low quality, plant protein-based diet promotes development of alkaline urine and struvite crystalluria.

· Ferrets normally have relaxed abdomens that are easy to palpate. Although pain will cause the abdominal muscles to tense, the over distended bladder is still palpable. There may also be evidence of urine dribbling and the prepuce may be red from excessive licking.

· Normal ferret biochemistry is similar to that in other mammals with a few exceptions. Creatinine in the ferret generally ranges from 0.1-0.3 mg/dL with values almost always less than 0.5 mg/dL. Creatinine from 0.7-1.0 mg/dL signifies azotemia.

· Obtain whole body survey radiographs using tabletop technique, high-speed film, and fine screen cassettes. Contrast radiography may be useful in identifying urethral stones. Enlarged adrenal glands are rarely visible on radiographs, and ultrasonography is needed. Note that renal cysts are a common incidental finding.

· Ferrets are relatively stoic animals, but do not ignore pain management. Provide preemptive analgesia, and monitor ferrets carefully for signs of discomfort. Signs of pain may include anorexia, lethargy, crying, stiff movements, squinting, and an inability to sleep in a natural, curled position.

References & Further Reading

Castanheira de Matos RE, Morrisey JK. Common procedures in the pet ferret. Vet Clin North Am Exot Anim Pract 2006; 9: 347-365.

Esteves MI, Marini RP, Ryden EB, et al. Estimation of glomerular filtration rate and evaluation of renal function in ferrets (Mustela putorius furo). Am J Vet Res 1994;55:166-172.

Pollock CG. Emergency medicine of the ferret. Veterinary Clinics of North America: Exotic Animal Practice. 10(2): 463-500, 2007.

Quesenberry KE, Carpenter JW, eds. Ferrets, rabbits, and rodents: clinical medicine and surgery. 2^nd ed. St. Louis: WB Saunders Co, 2003: 2-134.