In the horse, as in humans, the urinary bladder stores urine until it is full. When a certain level of fullness is perceived, the horse assumes a urinating posture to void the bladder in one constant controlled stream of urine. Horses with urinary incontinence may constantly dribble urine or may frequently posture to urinate but only produce small squirts of urine.

Urinary incontinence in adult horses is a condition that owners can find very difficult to manage. Urine scalding of the hind limbs by urine constantly dribbling out often makes these horses impossible to keep without a massive commitment to nursing care and veterinary management. Finding the exact cause of the dysfunction can be difficult and frustrating.

Understanding how the bladder works helps your veterinary surgeon to figure out what is causing the incontinence and whether anything can be done to manage or fix it. The bladder expands as it fills, facilitated by relaxation of the detrusor muscles that contract the bladder. Tone in the muscles of the urethra at the mouth of the bladder prevents urine from exiting the bladder as it fills. Contraction and relaxation of the bladder and urethra are coordinated, such that when the bladder relaxes, the tone in the urethra increases to retain urine in the bladder; when the bladder contracts, the urethral muscles relax to allow the urine to be voided. The bladder relaxes and contracts automatically; initially, as it fills, the bladder muscles relax; when it reaches a certain fullness, contraction is stimulated and the urethra relaxes. This activity is controlled by a variety of different nerves from the spinal cord. The muscles of the urethra can also be controlled intentionally to a certain degree and normal horses voluntarily assume a particular stance before urination begins.

Causes of urinary incontinence in adult horses include local damage to the urinary tract and damage to its nerve supply. Incontinence is sometimes seen in older mares that have had a number of difficult foalings, due to stretching and distortion of the urinary tract and its local nerve supply within the pelvis. These mares may exhibit dysfunction of the urethra or of the bladder muscles. Incontinence may also be seen in male or female horses with urinary stones. This may be accompanied by painful and/or blood-tinged urination which is evidence of inflammation and/or infection of the urinary tract.

Damage to the nerve supply to the urinary tract can be caused by any disease condition affecting the spinal cord. Some examples of spinal cord disease in Ireland include trauma to the sacral segments of the spinal cord, equine herpes virus infection of the spinal cord, cauda equine syndrome (polyneuritis equi), equine degenerative myelopathy, even Type 2 Wobblers syndrome (arthritis in the neck joints, commonly seen in older sport horses). Any of these conditions can result in incontinence which often does not become apparent for a long time after the initiating neurologic condition was first noticed.

VICIOUS CYCLE

Incontinence can become a vicious cycle. Normal horse urine contains a lot of tiny calcium carbonate crystals. If the bladder doesn’t fully empty because the muscles are weakened and do not fully contract, these tiny crystals begin to accumulate in the bladder. Anything that prevents the bladder emptying fully can result in a build-up of crystals. One commonly seen instance of this is where because of a painful musculo-skeletal condition, horses are unable to assume the normal posture to urinate and consequently fail to completely empty the bladder. Eventually the build-up of sabulous or sand-like crystals becomes highly irritating to the lining of the bladder, causing a severe cystitis and infection of the bladder and serious pain and discomfort to the horse. Overtime, this chronic irritation and infection can also affect the ability of the bladder muscle to contract, further worsening the incontinence.

Your veterinary surgeon can investigate urinary incontinence by performing a selection of tests including rectal examination of the urinary tract, rectal ultrasonography of the bladder, a complete neurological examination and laboratory analysis of blood and urine to evaluate concurrent disease processes. It is also possible to perform endoscopy of the interior of the bladder where the inside surface of the bladder can be seen and assessed for inflammation and infection.

The earlier the condition is identified, the more likely it will be that an underlying cause may be identified and corrected and the easier it will be to manage the incontinence so that the deterioration to inflammation, infection and chronic muscle dysfunction can be avoided.

Dr Vivienne Duggan MVB PhD Dipl. ACIM & ECEIM is President of Veterinary Ireland Equine Group and is a lecturer in Equine Medicine at the UCD School of Veterinary Medicine.

Email: hq@vetireland.ie

Telephone: 01-4577976