7 Mar 2011
Livia Benato and Chris Shepherd discuss, in the first of a two-part article, approaches to this common affliction and detail methods for performing radiographs
RABBITS are now the third most popular pet in the UK after dogs and cats.
As a result, ever-more knowledgeable owners are presenting rabbits to general practitioners in increasing numbers.
One of the more common problems seen is urogenital disease, as a result of poor diet and management. This article describes the clinical approach to common urogenital diseases normally seen in general practice. Diagnostic tests are described and suggestions for treatment and prevention are provided.
The anatomy of the rabbit’s urinary tract demonstrates marked differences to canine and feline tracts, and is more similar to other small mammals.
Rabbits have unipapillate kidneys; only one papilla and calyx enter the ureter, while in most mammals kidneys are multipapillate. A healthy rabbit’s kidneys are surrounded by adipose tissue, making them difficult to evaluate on abdominal palpation.
Ultrasound is, therefore, the preferred diagnostic modality if kidney pathology is suspected.
Rabbit kidneys play an important role in calcium excretion, as rabbits will absorb most dietary calcium passively and then excrete approximately 50 per cent via the kidneys and two per cent in faeces.
Vitamin D has an important role in the distribution of calcium once absorbed, but it doesn’t have any role in absorption. In high-calcium diets, such as alfalfa-based feeds, it is normal for large amounts of calcium crystals, usually calcium carbonate, to be eliminated in the urine. For this reason, normal rabbit urine is often thick and cloudy in appearance.
The female genital tract (Figure 1) is bicornate with two ovaries, two oviducts, two uterine horns (but no uterine body), two cervixes and the vagina.
No uterine body is present in the female rabbit’s reproductive tract. The vagina is extremely elongated and easily visualised during routine ovariohysterectomy.
The male genital tract is comparable with other species, with bilateral testes connected via the spermatic cords to the penis.
Accessory sex glands are present. The inguinal ring in the male rabbit is, however, open and the testicles can move freely between the scrotum and the abdomen. This anatomical characteristic must be considered during surgical castration to avoid inguinal herniation.
Although cryptorchidism in male rabbits has been reported, if testicles are not palpable in the testes during physical examination, it is usually possible to gently palpate them from the abdomen into the scrotal sacs.
It can be difficult to determine the gender of rabbits, especially in young animals.
Although the anogenital distance in male rabbits is slightly longer than in females, it can be difficult to distinguish between genders, particularly when only one rabbit is available and thus you have no comparison with the other sex.
An adult entire male rabbit will also have two scrotal sacs caudally to the penis.
In cases of urogenital disease (Table 1), owners will typically first notice anorexia or lethargy associated with pain.
Haematuria may be noted in the history or observed on clinical examination, along with sludge in the urine (Figure 4), urine scalding and dysuria.
Typical clinical signs of genital tract disease (Table 1) are vulvar or preputial discharge, vaginal prolapse, enlarged mammary glands and pale mucous membranes. Cases of uterine adenocarcinoma may present as dyspnoea due to metastasis of the primary tumour to the lungs.
A presumptive diagnosis of urogenital disease can be made after a complete history, including a detailed record of husbandry and the rabbit’s diet, and a full physical examination. Confirmation should then be sought with diagnostic tests, depending on the clinical signs.
Urinalysis is one of the simplest and most useful diagnostic tools. A urine sample can be collected in several ways. The least stressful for the rabbit is to collect the urine sample directly from the kennel. An incontinence pad with the non-absorbable side uppermost can be used as bedding. However, a sample collected in this way is not suitable for bacterial culture.
Cystocentesis should be considered a last resort, owing to the risk of damage to the caecum and peritonitis. It will, however, determine if the presence of blood in the urine is likely to be from the genital tract, rather than the urinary tract.
To collect urine from the bladder by catheterisation, the rabbit should be supported in sternal recumbency or in a “sitting” position, with the back well supported by an assistant. A well-lubricated four to six French catheter should be used. Protrusion of the genital opening facilitates the insertion of the catheter into the urethra (Suckow and Douglas, 1997). In female rabbits, the urethral opening is positioned on the floor of the vagina, and catheterisation in sternal recumbency is the easiest technique.
Once collected, the urine should be tested with a dipstick multi-test and the sediment examined under a microscope. Bacteriology and culture should ideally be performed prior to beginning antibiotic treatment if an infection is suspected.
Haematology and biochemistry provide information on the rabbit’s overall condition. Blood samples can be obtained from the marginal ear vein or the jugular, cephalic or saphenous veins.
An air-dried blood smear should always be prepared to obtain a manual count and observe the morphology cells.
A full blood biochemistry and haematology is necessary to assess possible renal failure, infections of the urogenital tract, hypercalcaemia, dehydration and the severity of anaemia, if suspected (Melillo, 2007).
Serology can be used to rule out diseases such as Encephalitozoon cuniculi and Treponema cuniculi (rabbit syphilis).
Radiographic examination can yield important information, but should always be performed under sedation (such as midazolam) or general anaesthesia to reduce stress.
Typical radiographic changes in urogenital disease are bone density changes, enlarged renal outline, nephroliths, ureteroliths, sand in the bladder (Figure 7) and mineralisation in the urinary tract (Harcourt-Brown, 2007). If bladder disease is suspected, the use of both positive and negative contrast can help in reaching a definitive diagnosis.
Common clinical changes in radiographic examination of the genital tract include an enlarged uterus and enlarged ovaries as a result of cystic or neoplastic disease. Foetal skeletons may be visualised in late pregnancy. If primary uterine neoplasia is suspected, metastatic spread should be investigated with thoracic radiographs.
Ultrasonography can be easily performed with the rabbit conscious, unless very stressed.
If the rabbit is conscious, it can be difficult to restrain in lateral recumbency for extended periods and it is easier for the ultrasonographer and less distressing for the rabbit if it is held while well supported in a “sitting” position (Figure 8).
During the procedure, a small area of the abdomen should be shaved and prepared, but spirit should be avoided to prevent hypothermia.
The urogenital tract should be systematically examined for lesions, obstructions and changes in size or wall thickness along the entire length. Lesions may be further investigated by ultrasound-guided fine-needle aspiration to access cellular content.
When finished, the rabbit should be thoroughly cleaned, dried and placed in a warm, quiet place to rest.
The authors would like to thank Anna Meredith and the rest of the Exotic Animal and Wildlife Service, University of Edinburgh, for their support.
Chris Shepherd
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Livia Benato
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