A range of conditions can cause enlargement of the prostate gland occurring almost exclusively in undesexed male dogs, increasing in frequency with age. The clinical signs for all these disorders are similar with a blood stained discharge from the penis and occasional difficulty passing urine or feces. The enlarged gland may be palpated through the rectum however most of the swelling occurs ventrally (downward) so the true size of the prostate can be difficult to assess without X-rays.

Prostatic hyperplasia is non-inflamatory enlargement which occurs as a result of an altered testosterone-estrogen ratio within the body in the presence of testes. This is usually a nonpainful enlargement and responds rapidly to castration. Where castration is not feasible low doses of estrogen , or antiandrogenic drugs such as delmadinone can provide a temporary reduction in the size of the prostate.

Bacterial prostatitis may produce systemic signs of fever and depression in addition to a painful swollen prostate and bloody discharge. Infection may be blood borne or ascending via the urethra. Concurrent urinary tract infections are common. Treatment requires antibiotics however castration or antiandrogen therapy has been found to accelerate the rate of recovery and reduce the incidence of recurrence. In some cases bacterial prostatitis can develop into a prostatic abscess. These are usually only partially responsive to antibiotics requiring surgical drainage to resolve.

Adenocarcinoma is the most common tumor of the prostate. The incidence of neoplasia (tumors) as a cause of prostatic disease is quite low at around 5 %. This tumor however can occur in both desexed and entire males and is the most likely prostatic condition in desexed males. prostatic adenocarcinomas regularly spread to the surrounding bone of the pelvis or spine and to the lungs so X-rays of these areas are important of r determining the prognosis. Radiation therapy has been used to help control prostatic cancer however cure is an unlikely outcome.