Urine carries waste products out of the body. The amount of urine produced is the amount needed to excrete dissolved waste products and to balance blood volume, pH, and electrolyte concentrations in the body. It is the job of the kidneys to process the dissolved waste components in the blood, excreting the waste products and reabsorbing most of the water.
The pattern of urination includes the following factors:
The normal pattern of urination is different for male and female dogs. Male dogs urinate small amounts frequently in a short period of time because of the need to scent-mark their home range. Female dogs are more likely to empty their bladders in a single urination, but they, too, sometimes engage in scent-marking.
All dogs should urinate without any evidence of pain or straining.
On average, most adult dogs can go 8 hours between urinating, although they will urinate more frequently if given the opportunity. To determine increase frequency of urination, close supervision of the dog is required. It is important to not only note the frequency of urination, but also the daily amount of urine produced. An increase in the daily amount of urine produced will require more frequent emptying of the bladder and will usually be accompanied by increased water intake.
An increase in the frequency of urination without an increase in the daily amount of urine produced may be caused by sensations of pain or irritation in the bladder, urethra, or genital tract. It may not be obvious that the dog is experiencing pain or discomfort, only that small amounts of urine are produced very frequently.
Painful or difficult urination is characterized by a dog straining to urinate, taking an unusually long time to complete urination, or a small or intermittent stream of urine. This change could be caused by irritation of the bladder, urethra, or genital tract; obstruction of the bladder or urethra; infection; urinary stones; cancer of the bladder or urethra; or neurological or muscular diseases.
Urine is normally yellow in color. Urine may be discolored by the presence of blood or excess pigment from the breakdown of red blood cells. Causes of bleeding include stones, infection, cancer, trauma, parasites, ingestion of rat poison, or immune-mediated diseases attacking blood platelets.
Urinary incontinence is the loss of voluntary control over urination. It occurs much more commonly in females that in males and is not a behavioral problem since the dog is unaware that it is passing urine. Although the exact cause has not been determined, it is usually a treatable condition.