Human males are not the only mammalian species with a prostate gland – in fact, almost all male mammals have prostates, though their size and shape differs significantly among species. The purpose of the prostate – an accessory sex gland – is to provide protective nutrients and fluid to help sperm movement and survival when an animal mates.
In the dog, prostatic health issues are quite common and most frequently diagnosed in entire (non-castrated) males. It’s estimated that by the time an un-neutered male dog reaches 8 years of age, he has a greater than 80% chance of developing prostate disease.
Prevention is straightforward - castrating non-breeding dogs before 1 year of age essentially stops the development of the most common prostatic disorders seen in the dog.
Three prostate disease conditions occur in entire male dogs – benign prostatic hyperplasia, prostatitis and cancer of the prostate. Clinical signs are similar in all three disorders and relate to enlargement of the gland with resulting pressure on the rectum and/or the urethra.
Benign Prostatic Hyperplasia (BPH)
BPH is the most common condition seen in dogs. It is a non-malignant increase in the size of the prostate gland related directly to the influence of the hormone testosterone. It can start as early as 5 years of age but like most prostatic disease, BPH is seen more commonly in older dogs.
Prostatitis – a bacterial infection of the prostate gland – is less common and is often seen with cystitis (infection in the bladder). Alongside painful defaecation and urination, signs can include fever, depression, vomiting and an infected discharge from the prepuce. The dog will be miserable and in obvious pain.
Fortunately for the dog, prostate cancer is much rarer than in the human male but it can be very aggressive and difficult to treat. As this cancer is not influenced by testosterone, it is the only condition of the prostate to occur in both neutered and intact male dogs.
Clinical signs are similar in all three disorders and relate to enlargement of the gland leading to pressure on the rectum and/or the urethra.
In the dog, the prostate surrounds the neck of the urethra and sits below the rectum, within the bony pelvis. As it enlarges, the diseased prostate obstructs the rectum, making defaecation painful and difficult. Image courtesy Pet Education website.
As the prostate enlarges, it pushes up into the rectum, obstructing the passage of faeces. The first symptoms are usually straining and pain on defaecation. Constipation and faecal impaction are common, causing lethargy, refusal to eat and vomiting. The enlarged prostate can also press on the urethra, causing straining during urination. When an infection is present (prostatitis), a discharge may drip from the prepuce.
Dogs with painful prostates will also often have a stiff gait and walk carefully with short steps in an effort to stop putting pressure during movement on the swollen and painful prostate.
Diagnosis and treatment
All the above symptoms in an older entire male dog point towards prostate gland problems. Digital rectal examination (and ultrasound if required) will help confirm prostatic enlargement. Urinalysis can show signs of infection or help detect cancer cells.
Castration is the treatment of choice – the prostate gland decreases significantly in size within a short time following neutering. Because the prostate starts to develop by puberty, dogs that are neutered before then have minimal levels of testosterone. This slows the normal development of the prostate and male dogs desexed as pups have very little prostatic tissue as adults. When a mature dog is neutered, the gland shrinks to less than a quarter of its previous size.
If treatment for severe constipation is required, a hormone is administered to temporarily decrease the size of the gland until the dog is well and in a better condition for surgery.
For breeding males, synthetic hormone injections can be effective, but they are temporary and prolonged use can lead to diabetes or adrenal gland problems.
Dogs with prostatitis will require antibiotics to get the infection under control. This can be a prolonged and difficult process and prostatitis can become a chronic, recurring condition. Again, the most effective long term treatment is castration.
Cancer of the prostate is very difficult to treat and requires chemotherapy and/or radiation therapy. Castration has no effect on the tumour.