Page 972 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Urinary system 947

VetBooks.ir or ammonium sulphate (175 mg/kg/day) may be sacral parasympathetic (pelvic nerve), somatic
(pudendal nerve), lumbar sympathetic (hypogastric
more effective but are unpalatable and difficult to
administer.
Bladders that contain sabulous uroliths should be nerve) nerves and normal myogenic function are
needed for normal micturition.
irrigated with large volumes of fluid combined with Damage to the sacral spinal cord, pelvic and/
a perineal urethrotomy as the most effective way to or pudendal nerves leads to lower motor neuron
remove the uroliths. Oral administration of 50–75 g (LMN) deficits. Diseases that cause LMN bladder
of table salt once or twice a day may increase water dysfunction include EHV-1 myelitis, cauda equina
intake and diuresis, which acts therapeutically and syndrome, sorghum toxicosis, equine protozoal
prevents recurrence of calculi. Free access to water meningitis/myeloencephalopathy (EPM), arboviral
should be provided. encephalomyelitis, lumbosacral trauma and neopla-
sia. LMN bladder dysfunction can also be caused
Prognosis iatrogenically with epidural administration of differ-
Approximately 41% of horses have recurrence of ent pharmaceuticals, or after illegal tail altering pro-
cystolithiasis after treatment. This depends greatly cedures in Quarter horses. Mares are at increased
on the thoroughness of calculus removal from the risk for the development of LMN neurogenic incon-
bladder and whether an underlying lesion is present. tinence because of the potential for trauma during
High-calcium feeds (i.e. alfalfa hay) should be breeding and parturition.
removed from the horse’s diet and up to 70 g of table Upper motor neuron (UMN) bladder dysfunc-
salt added to the daily diet to promote drinking and tion is associated with damage to the supra-sacral
diuresis. Sabulous cystic deposits are mostly associ- spinal cord or/and brainstem. Micturition is disabled
ated with bladder paralysis and the response to treat- via exaggerated urethral sphincter tone, despite the
ment is poor. presence of a full bladder. Chronic UMN lesions
may, through the sacral spinal reflexes, allow partial
BLADDER PARALYSIS/NEUROGENIC voiding of urine. This kind of incontinence is rare in
INCONTINENCE horses and is caused by diseases similar to those in
LMN bladder dysfunction.
Definition/overview Myogenic problems are rare but have been reported
Incontinence develops as intravesicular pressure in geldings. They lack a specific identifiable cause and
exceeds resting urethral pressure, which results in a are likely to be of multifactorial origin rather than a
variable degree of urine dribbling. Incontinence and single underlying pathological process.
dysfunction of bladder control in horses is most often
associated with neurological disorders in the central Clinical presentation
or peripheral nervous systems, and rarely with myo- Clinical signs include dribbling of urine and urine
genic dysfunction in the bladder wall. Determining scalding of the perineum (mares) and medial aspect
the origin of bladder dysfunction is important to of the hindlimbs (males and females). Affected
plan the therapy and to establish the prognosis. horses may frequently posture to urinate and void
little or no urine. Clinical signs of underlying neuro-
Aetiology/pathophysiology logical diseases and their specific neurological defi-
Urinary outflow is controlled by a complex activity cits may be evident. UMN disorders are frequently
of somatic and autonomic nerves that (1) generate associated with recumbency and myopathy, which
sustained tone to prevent urinary leakage during are often incompatible with life. Bladder distension
bladder filling, (2) generate transient reflex increases with UMN disease may produce signs of abdominal
in pressure to prevent opening of the lumen when pain or frequent posturing to urinate. Bladder rup-
abdominal pressure rises, and (3) undergo relaxation ture may occur with UMN disease.
preceding micturition and can generate urethral Loss of anal and tail tone, faecal retention,
opening and shortening during micturition. Normal hindlimb weakness and ataxia, hindlimb muscle