The prostate (commonly mispronounced as "prostrate") is a gland located near the neck of the urinary bladder of male dogs.  The urethra passes through it shortly after leaving the bladder.  The purpose of the prostate is to produce some of the fluids found in normal canine semen.

Prevalence

Prostatic disease is very common in older, non-neutered male dogs.  In one study of 177 dogs, 87 were found to have a specific prostatic disorder.

Causes/Transmission

There are at least seven diseases affecting the prostate.

1. Benign prostatic hyperplasia (BPH).  This is a non-cancerous enlargement of the gland that is frequently found in older intact (non-neutered) male dogs.  It is associated with the hormone testosterone and is the most common disease of the prostate.  The prostate gland is non-painful with BPH. 
2. Squamous metaplasia.  This is a non-cancerous enlargement of the gland caused by abnormal amounts of estrogen.  An estrogen-producing tumor called a Sertoli cell tumor is usually responsible.  As with BPH, the prostate is non-painful.
3. Cystic hyperplasia.  This condition is usually secondary to benign prostatic hyperplasia or squamous metaplasia.  It is caused by obstruction of the ducts that carry prostatic secretions to the urethra.  Multiple, fluid-filled cavities develop within the gland.
4. Paraprostatic cysts.  These are fluid-filled cysts that develop adjacent to the prostate when abnormal tissue remains from embryonic development before the puppy was born.  The cysts begin to develop shortly after birth but may not cause problems or be detected until the dog is several years old.
5. Bacterial infection.  Bacteria may enter and infect the prostate by going up the urethra or by coming down the urethra from an infection in the urinary bladder.  This inflammatory condition is usually associated with a pre-existing abnormality of the prostate, such as benign prostatic hyperplasia.  The prostate may be painful with bacterial infection.
6. Prostatic abscess.  This is a progressive form of a bacterial infection.  If the ducts that drain the prostate become obstructed, the bacteria are trapped in the prostate and form a walled-off site of infection known as an abscess.  The prostate is usually found to be very painful during rectal examination.
7. Prostatic cancer.  This form is much less common than all of the others.  It may be associated with hormones from the testicles, adrenal glands, or pituitary glands or it may occur independent of hormonal influences. 

Clinical Signs

Enlargement of the gland is common with most prostatic diseases.  Since the urethra passes through it, enlargement of the prostate compresses the urethra and urination becomes more difficult.  Complete urethral obstruction only rarely occurs, but an affected dog will spend quite a bit of time urinating and often produces a stream of urine with a small diameter.  The colon, located just above the prostate, is sometimes compressed by an enlarged prostate.  This makes defecation difficult.

In addition, some dogs with prostatic disease will have blood in the urine.  Bacterial infection of the prostate is sometimes, but not always, involved with production of the bloody urine.

Dogs with prostatic abscesses may be extremely ill.  Fever, dehydration, and toxic shock can develop, eventually leading to death of the dog.

Diagnosis

The first step in diagnosis is to determine if the prostate is enlarged and whether it is painful.  This is done by feeling its size either through the abdominal wall or through the rectal wall.  It may be confirmed by radiographs (x-rays) or an ultrasound examination.  During the physical exam, the testicles are palpated to look for potential tumor masses.

Because there are so many diseases of the prostate, it is necessary to perform several tests to tell them apart.  These tests include cultures of the dog's urine, a microscopic examination of the cells in the urine, and a microscopic examination of the cells in prostatic fluid or in the prostate itself.  Samples of prostatic fluid are recovered by passing a urethral catheter to the level of the prostate and massaging the prostate to "milk" fluid out of it.  Samples of prostatic cells are obtained by aspiration or biopsy via a needle that is either passed through the body wall or passed through the rectal wall.  If the prostate is greatly enlarged, it can be aspirated or biopsied through the body wall; otherwise, an approach through the rectal wall is necessary.  An aspiration sample is taken through a very small bore needle and only recovers a few cells.  Sometimes this is adequate for analysis; other times it is not.  A needle biopsy sample is obtained through a large bore needle that is passed into the prostate by some form of electronic guidance.  This may be with a type of x-rays or with ultrasound.  A biopsy sample recovers a piece of tissue that permits a pathologist to make a more accurate diagnosis.

Treatment

1. Diseases involving primary or secondary bacterial infections are treated with aggressive antibiotic therapy.  Because it is difficult to get many antibiotics into the prostate, treatment for several weeks will probably be necessary.  Since most of the infections are secondary to another disease, treating the infection is only part of the overall treatment.
2. Diseases associated with excessive hormone levels include benign prostatic hyperplasia, cystic metaplasia, and cystic hyperplasia.  Since testosterone and estrogen are both formed in the testicles, castration is generally very effective for all of these.  The prostate will generally be normal or smaller than normal in size within one month after castration. 
3. Paraprostatic cysts and prostatic abscesses require major abdominal surgery to drain and remove the fluid and/or pus.
4. Prostatic cancer does not respond well to any currently used form of treatment.  If it is associated with an excess of a hormone, castration may be beneficial; however, most are not and metastasize rather easily to other parts of the body.  The prognosis for these is usually poor.

Prognosis

Prognosis is dependent upon identification and successful treatment of the underlying cause. A more favorable prognosis is given for non-cancerous disorders.

Prevention

Many disorders of the prostate can be avoided with neutering of the male dog.  Unfortunately, some owners wait until the dog is older and develops prostatic disease before they will consider neutering.  Later in life, the dog is more likely to have additional medical problems, which can impact upon anesthetic risks.