Enlarged prostate in dogs – symptoms and treatment

Overview

The prostate is part of the male reproductive system and lies around the bladder neck. The urethra passes through it immediately after leaving the bladder.

Prostatic fluid makes up about 90% of the liquid volume of semen. BPH is short for benign prostatic hyperplasia, in which the gland enlarges without malignant growth.

BPH is the most common prostate disease in uncastrated males. Visible or microscopic changes consistent with BPH have been described in about 80% of uncastrated males over five years old.

The corresponding proportion in those over nine years is about 95%. These tissue changes do not mean that all these dogs have noticeable symptoms.

The gland's volume may be about 2–6.5 times that of a healthy dog of the same size.

Causes

Hormones and tissue growth

In BPH, both the number and size of prostate cells increase. Testosterone released by the testicles is converted to dihydrotestosterone, or DHT, within prostate cells.

An enzyme called 5-alpha-reductase enables this conversion. DHT stimulates gradual, fairly even outward growth of prostate tissue.

Ageing changes the balance between oestrogen and testosterone, which may increase the prostate's sensitivity to hormones. Oestradiol and other growth factors also contribute to enlargement.

Initially, the change mainly involves an increase in glandular tissue; later, small fluid-filled sacs called cysts may form. Increased blood supply within the prostate can cause bloody discharge even when the dog is not urinating.

The development of BPH involves multiple factors, and the reason it occurs in each male cannot always be explained. Oxidative stress is an imbalance between the formation of reactive oxygen compounds and their removal.

Genetic material damaged by oxidative stress may promote changes in prostate cells and enlargement of the gland.

Why does passing stools become difficult?

The prostate lies below the rectum, so substantial enlargement can press on the bowel. This can obstruct the passage of stools and increase straining during defaecation.

Risk factors

The main practical risk group is ageing males whose testicles continue producing hormones. However, glandular enlargement may begin as early as about 2.5 years of age.

Cystic changes usually begin to appear after four years. Older studies also found BPH in 25% of dogs aged 1–3 years and 88% aged 5–10 years.

Estimates of breed predisposition are conflicting: a possible predisposition in large breeds has been suggested, but so has an absence of breed predisposition. Proximity to females in season can trigger or worsen symptoms in a male already affected by BPH.

A stud dog may be affected even when outwardly well.

Typical symptoms

A dog may initially have no symptoms at all.

• Blood-stained discharge drips from the penile sheath without urination.

• Blood is visible in the urine continuously or intermittently.

• Blood is found in the semen, known as haematospermia.

• Your dog strains to pass stools or is constipated.

• Urination takes longer or the urine stream becomes thin.

• Urine dribbles involuntarily.

• Sexual interest or fertility decreases.

Urination difficulties are fairly uncommon in dogs with uncomplicated BPH.

Blood in the urine also occurs with other conditions, so visible blood does not automatically identify a prostate problem.

Painful prostate disease may make a dog reluctant to walk or move in other ways.

Chronic prostatitis may also cause weight loss and deterioration in coat condition.

Complications and consequences

Infection and abscesses

An enlarged gland is more susceptible to bacterial infection of the prostate, called prostatitis. Infection often ascends from the urinary tract into the prostate.

Chronic infection can recur and progress to acute prostatitis or an abscess. An abscess is a localised pocket of bacterial infection within the gland.

Complete urethral obstruction is uncommon in prostate disease, but possible.

Effects on fertility

BPH can reduce semen quality without making the dog completely infertile. Reduced sperm motility and more structural abnormalities have been found in affected dogs.

Sperm DNA damage has also been observed. Hormonal changes, oxidative stress and changes in prostatic fluid composition may contribute to fertility effects.

Concurrent chronic bacterial infection may further reduce semen quality. However, blood in semen does not automatically prevent a dog from fathering puppies.

Semen from dogs with BPH has been found to be poorer in quality than semen from healthy dogs of the same age.

Diagnosis at the vet

Palpation, ultrasound and laboratory tests

Assessment begins with the symptom history and a clinical examination. The prostate can be felt with a finger through the rectum.

In typical BPH, the gland is often symmetrically enlarged and not painful to palpate. Ultrasound through the abdominal wall helps assess prostate size and tissue structure.

Ultrasound may reveal thin-walled fluid-filled sacs within the gland. Paraprostatic cysts lie outside the glandular tissue and are often larger than internal cysts.

An X-ray may show enlargement of the gland. Urine culture investigates whether a bacterial infection is present.

A blood cell examination looks for changes suggesting systemic inflammation or infection. Blood biochemistry helps detect abnormalities in other organ functions.

The CPSE blood test measures a marker related to a protein secreted by the prostate and can be used to screen for BPH. CPSE is not specific to cancer or BPH, so it does not reliably distinguish all prostate diseases.

When assessing gland size by ultrasound, measurements may be compared with the aorta's internal diameter, reducing the influence of body condition on interpretation.

Samples and ruling out other conditions

Cell examination of prostatic fluid or semen may show bleeding and mild inflammation. Confirmation comes from a tissue sample or cell examination of a fine-needle sample from prostate tissue or an internal cyst.

A fine-needle sample may be inconclusive, making a tissue biopsy necessary. Other possible causes of prostate enlargement include bacterial infection and a tumour.

Ultrasound does not always distinguish chronic inflammation from a prostate tumour. Chronic prostatitis may be found incidentally while investigating reduced fertility.

An oestrogen-secreting Sertoli cell tumour can also cause a benign change in prostate cells.

Treatment

Monitoring or reducing hormonal effects?

BPH found on ultrasound without symptoms does not always need treatment. Whether the male's fertility is to be preserved affects the choice.

Castration, removal of the testicles, is a common first-choice treatment when the dog is not needed for breeding. Testosterone falls rapidly during the first week afterwards.

Prostate volume may decrease by up to 50% within about 2–3 weeks of surgery. A reduction may be felt through the rectum after just 1–2 weeks.

Bloody dripping usually stops within four weeks of castration. However, reduction of the gland can continue for several months.

Medication options and fertility

The vet prescribes medication based on investigations; it may reduce the effects of male hormones on the prostate. Osaterone acetate is an antiandrogen that reduces DHT's effects on glandular tissue.

With osaterone treatment, symptoms have resolved in about 50% of dogs within 14 days. The response may last about five months, but symptoms return earlier in some dogs.

A male may remain fertile and able to mate during osaterone treatment. However, temporary changes in semen volume and sperm motility can occur.

Finasteride reduces conversion of testosterone to DHT by inhibiting 5-alpha-reductase. Finasteride treatment may preserve fertility.

However, BPH may return after medication stops. Licensing and availability of finasteride for dogs differ between countries; your vet will choose a suitable option.

A hormone implant reduces testosterone production and makes the dog temporarily infertile. Prostate shrinkage associated with the implant may take about 4–12 weeks.

A brief increase in hormonal activity may occur at the start of GnRH agonist treatment; its significance is considered before choosing treatment. More research is needed before firm conclusions can be drawn about antioxidant supplements as supportive care for BPH.

Concurrent problems and postoperative care

When bacterial infection is present, both BPH and the infection are treated. The antimicrobial is chosen according to culture, susceptibility testing and the medicine's ability to enter prostate tissue.

An abscess may need surgical drainage as well as medication. Keep the castration wound clean and dry.

A protective collar prevents licking and protects the surgical site. Restrict running, jumping and rough play after surgery according to the discharge instructions.

Contact the treating practice about worsening pain, an open wound or pus-like discharge.

Prevention

Removing testicular hormone production or reducing DHT's effects can prevent benign enlargement from developing. Decisions about castration also weigh other health benefits and disadvantages for the dog.

Preventing BPH does not mean that all prostate diseases or prostate cancer are prevented. A castrated dog can still develop prostatitis, although it is more common in uncastrated males.

Persistent untreated bacterial infection can recur, so underlying BPH is also considered.

Vasectomy, division of the sperm ducts, preserves testicular hormone production and therefore differs from castration that removes it.

Important for dog owners

Record changes in bloody discharge, urination and passing stools, and when they began. Note whether discharge occurs during urination or also at rest. Tell the practice about previous urinary tract infections, medication, castration or hormonal treatments. Also mention whether you intend to use the dog for breeding.

In a stud dog, BPH may appear only as reduced fertility or blood in semen.

Ask for a plan to check the response to treatment: how symptom resolution and changes in prostate size will be monitored, and what to do if the problem returns. Keep the ultrasound report and compare later findings with earlier results.

Some certification schemes record the reason for castration and testicular status before surgery in an approved veterinary certificate when needed.

Trial and competition participation depends on the activity's rules; some require previously normal testicles and an approved certificate.

Some dog-show rules require disqualification after castration regardless of the reason, even with a certificate.

Frequently asked questions

Is prostate enlargement the same as prostate cancer?

No. BPH is benign, age-related gland enlargement. However, the prostate can also enlarge because of infection or a tumour. Diagnosis therefore relies on examination and, when needed, a cell or tissue sample. Ultrasound also helps assess cysts within the gland.

Can a dog have BPH without difficulty urinating?

Yes. Many dogs have no symptoms, and urination problems are fairly uncommon in typical BPH. The first visible sign may be bloody dripping from the penile sheath. In a stud dog, the only finding may be blood in semen or reduced fertility.

How quickly does the prostate shrink after castration?

Prostate volume may decrease by up to 50% in about 2–3 weeks. Bloody dripping usually stops within four weeks. More complete shrinkage can take several months, so symptoms and examination findings are assessed as recovery progresses.

Can a stud dog be treated without castration?

Yes. If investigations are consistent with BPH, fertility-preserving medication can be used. Osaterone acetate and finasteride are such options. A hormone implant that suppresses testosterone instead interrupts sperm production and fertility for its duration of action. BPH may return when medication stops.

Does BPH always need antibiotics?

No. Antibiotics treat bacterial infection and are not automatically needed for every case of benign enlargement. Infection is investigated by bacterial culture of urine or semen. If both conditions are found, BPH is treated too, because treating the infection alone may be inadequate.