In our previous article on the female reproductive system of dogs and cats, we showed how a complex system of reproductive organs and hormones work together to facilitate fertilisation, gestation and birth. The male reproductive system in dogs and tomcats also consists of a variety of organs and hormones that work together to facilitate fertilisation and to ensure the perpetuation of the species. It influences many of the males’ behaviours, making a good case for neutering when owners of male dogs and cats do not intend to breed with their pets.
In this article, we’ll explore the components of the male reproductive system, the function of each one, and how disorders of the reproductive system are diagnosed and treated.
The functions of the male reproductive system
The main function of the male reproductive system of dogs and tomcats is to facilitate fertilisation of the female ova, but there are other equally important functions:
- spermatogenesis or the production of spermatozoa
- production of testosterone, which determines the secondary male characteristics in dogs and cats
- the secretion of fluids that keep sperm alive and viable, and facilitate their journey into the female reproductive tract
- delivering sperm into the female reproductive tract
Components of the male reproductive system and their functions
There are a number of organs and ducts that make up the male reproductive system in dogs and tomcats. The whole system is located in the abdomen, starting near the bladder and extending into the pelvis, with some organs being visible externally. There are some structural and functional differences between the dog and tomcat’s reproductive organs, which will be distinguished below.
The organs of the male reproductive system include:
Scrotum and testes
The scrotum is an external pouch of skin that contains the testes. It is located between the dog’s upper thighs, while on the cat, the scrotum is located just below the anus. The purpose of the scrotum is to hold the testes away from the body to keep them at the ideal temperature for sperm production (spermatogenesis), which is below 40°C.
The process of maintaining the ideal temperature is controlled by the Dartos muscle, which contracts in cold weather (to hold the testes closer to the body to keep them warm) and relaxes in warmer weather (to hold the testes away from the body to maintain a cooler temperature).
Epididymis
The epididymis is a structure at the top of each testicle, made up of convoluted seminiferous tubules in which sperm and hormone production takes place. The continuation of the epididymis becomes the excretory deferent duct, or vas deferens, which runs into the pelvic cavity.
Deferent duct
There is one deferent duct (vas deferens) per testicle. These ducts begin at the ends of the epididymides, lying next to the testes before they enter the pelvic/peritoneal cavity through a structure called the inguinal canal. The ducts enter the prostate gland, where they join the urethra.
Spermatic cord
The spermatic cords are the cords that house the deferent ducts, and also contain blood vessels and nerves from the testes. Inside each spermatic cord is a cremaster muscle, which functions with the Dartos muscle to position the scrotum to maintain the optimum temperature for sperm production.
Prostate
The prostate gland is considered to be an accessory gland in the reproductive system. In both dogs and tomcats, the prostate gland is a small structure found between the bladder and the urethra, just before the root of the penis. Its function is to secrete substances to increase ejaculate volume as well as to neutralise the pH of the urethral environment so that the sperm can survive its journey into the female reproductive tract.
Urethra
The urethra is a shared tract of both the urinary system (transporting urine for excretion) and the reproductive system (expelling ejaculate for reproduction). It runs from the bladder, through the prostate gland – where the deferent ducts join the urethra from the testes – and then the urethra runs through the length of the penis to the external urethral orifice.
Penis
The penis of the dog and tomcat share similarities, but are quite anatomically different from each other, most notably in proportionate length.
Canine penis
Where the urethra exits the prostate gland, it passes over the ischial arch (pubic bone) and is surrounded by the structure of the penis, which is made up connective tissue and blood vessels. The penis is a complex structure composed of a variety different parts:
- The root of the penis is where the spongy, vascular erectile tissue begins inside the body.
- The body of the penis is the main structure that runs from the tail-end pointing forward.
- The glans penis is the spongy tissue at the front (distal portion) of the penis – the part that projects from the body and penetrates the vagina.
When the dog is excited, the erectile tissue (also called the corpus cavernosum penis) fills with blood, making it engorged and pressurised enough to be more easily introduced into the canine vagina for copulation.
This engorgement alone is not enough to complete the canine erection. To ensure the penis is rigid enough for penetration, the os penis – a narrow, bony canal – offers greater rigidity until the erection is complete. Completion occurs when the bulbus glandis or the bulb of the glans penis (also called the ‘knot’) swells up and locks the penis inside the vagina during the ‘tie’. A copulatory tie can last up to half an hour and is meant to increase the likelihood of fertilisation and to prevent other males from attempting copulation with the bitch. During this time, the dogs cannot separate, although the male can ‘dismount’ the female and remain in a rear-to-rear position until the bulbus glandis contracts and returns to normal size.
Only canid mammals (like dogs, wolves, foxes, coyotes, jackals, African wild dogs and other dog-like species) and some seals have a bulbus glandis.
Feline penis
The penis of the tomcat is somewhat different to that of the dog. It is proportionally shorter than the dog’s penis, and while it is retracted inside the body, it runs in the opposite direction to the dog’s penis – pointing back in the direction of the tail. When the tomcat is aroused and during mating, the engorged penis extends out of the prepuce and curves towards the front of the body.
Similar to the canine, the feline urethra exits the prostate gland and is covered by highly vascular tissue, which is the corpus cavernosum penis. A short distance from the prostate gland lie the bulbourethral glands. Like the prostate gland, the bulbourethral glands are also considered to be accessory glands that provide secretions to facilitate the health and path of the sperm to ensure fertilisation.
The feline glans penis is covered in tiny barbs that point backwards. Since ovulation in the queen is induced by copulation, the purpose of the penile spines is to rake painfully against the vaginal walls when the male withdraws, triggering a reflex arc that stimulates ovulation. The tomcat mates with the queen multiple times to initiate ovulation and ensure fertilisation.Prepuce
The prepuce is the visible external organ that houses the relaxed penis. In dogs, it is the sparsely haired sheath under their belly. In cats, the prepuce is a short, densely furred sheath visible just below the scrotum. The purpose of the prepuce is to keep the glans penis lubricated and protected.
Problems in the canine and feline male reproductive system
As with any complex system in dogs and cats, the reproductive system is subject to diseases, infections, disorders and other problems. Here are some of the more common issues in the male reproductive system that veterinarians see in dogs and cats.
Brucellosis infection
Brucella canis is a bacterium that infects dogs and causes reproduction failure (infertility, infection of the male sexual organs, and miscarriage in females). It spreads quickly in close confines (such as in a shelter environment) and can be sexually transmitted, as well as through the ingestion of the bacteria. In males, brucellosis causes symptoms of infection such as inflammation of the male reproductive organs – epididymides, prostate gland, and testicles. They will display a reluctance to mate as a result.
Other symptoms of brucellosis may include:
- enlarged testicles and scrotum
- enlarged lymph nodes
- testicular atrophy
- organ death due to terminated blood supply
In South Africa brucellosis is a notifiable disease because it has the potential to cause disease in humans. Brucella canis was only diagnosed for the first time in 2005, and spread to up to 4% of dogs in informal settlements and in animal shelters. Infected dogs are required to be euthanised because it is a complicated infection to treat, and treatment involves the long-term use of antibiotics, often without success. Sometimes neutering and isolation from other dogs is an alternative to euthanasia.
Cryptorchidism
The testicles of male puppies and kittens are supposed to descend into the scrotum by the age of around eight weeks old. The condition where one or both testes remain undescended is cryptorchidism. When the testicles remain in the abdomen, they cannot be temperature regulated, so the male dog or cat is rendered infertile.
Cryptorchidism is a genetic condition, so pets with this condition should not even attempt to be bred. Very often the cure for the disorder is neutering – both to prevent the animal from passing on the genetic condition, and to prevent testicular cancer, of which there is a higher incidence in animals with cryptorchidism.
Inflammation of the reproductive organs
Testes and epididymis
This painful condition occurs in both dogs and cats as a result of testicular torsion, infection, or traumatic injury (in cats, it’s rare as a result of torsion or infection). It is difficult to treat unless the veterinarian can identify the source of inflammation, and treatment must be swift to mitigate the risk of permanent damage. Castration is considered if it’s not essential for the dog or cat to remain fertile.
Symptoms can include pain, swelling of the scrotum, scrotal skin abnormalities, and testicular reduction or softening.
Penis and prepuce
Inflammation in the prepuce is called balanoposthitis, and can be caused by allergies, bacteria, the presence of foreign objects, urinary tract stones, cancer, and physical trauma. Sometimes balanoposthitis occurs in mild form in many sor balanoposthitis may include exposing and flushing the preputial cavity with a mild antiseptic or saline solution. If the inflammation is caused by a bacterial infection, the vet will prescribe antibiotics to clear it. The cause of the inflammation must be identified and treated/corrected to prevent a recurrence.
Paraphimosis
This condition occurs in dogs and cats usually after mating, when the penis cannot be retracted back into the prepuce. Often, a small band of hair entangles the penis, preventing it from being retracted. Sometimes the preputial opening is too small or the penis has suffered a trauma. Paraphimosis is a medical emergency because it involves constricted circulation, and swelling of the penis as it accumulates fluid. Exposed, the penis becomes dry and painful.
If treatment is sought before the swelling and pain become severe, the condition is relatively simple to resolve and involves lightly cleansing the exposed penis and replacing it inside the prepuce. Where entanglement is the cause, the fur around the prepuce may need to be trimmed. When circulation is no longer constricted, the swelling will go down. If paraphimosis is left too long before treatment, it may need more complex treatment and even surgery to correct.
Phimosis
Phimosis is the condition of the opening of the prepuce being too small for a dog or cat’s penis to extrude. It’s usually only diagnosed when the animal attempts to mate, but cannot. It may be a congenital condition or the result of a bacterial infection, inflammation or trauma. The vet will need to physically examine the animal to make a diagnosis, and treatment of the condition will depend on the animal’s function. If the dog or cat is not intended for breeding, the vet may simply recommend neutering.
Priapism
A persistent erection that is not caused by sexual arousal or stimulation is called priapism. It may originate due to dysfunction in the blood vessels, a penile mass or tumour, neurological problems, or it may have an unknown (idiopathic) cause. If priapism affects blood circulation, it must be treated as a medical emergency. Left too late or if there is too much tissue damage, a penile amputation may be needed.
Disorders of the prostate
There are a number of conditions and disorders that can affect the prostate gland of the dog (although they are not common in cats), which may include:
Benign prostatic hyperplasia (enlarged prostate)
This is a very common condition in older, unneutered male dogs. Most intact males over the age of six will develop an enlarged prostate as a result of hormonal influence. In many cases there are no symptoms, but the enlargement may put pressure on the dog’s bladder and rectum, causing straining and pain during elimination. There may also be blood present in the urine or semen, and a stiff gait in the back legs. If the dog is neutered, the prostate will return to normal size within a few weeks and resolve the condition.
An enlarged prostate may also be a symptom of cancer, so these need to be ruled out, especially if there are other symptoms.
Prostatitis
Inflammation of the prostate gland is called prostatitis. It is usually the result of a bacterial infection, which can also cause an abscess. Prostatitis can become a long-term condition as a result of benign prostatic hyperplasia (BPH), and may only resolve when BPH has been treated. Acute prostatitis can cause symptoms like fever and lethargy, straining to eliminate, blood in the urine, repeated UTIs, pain, dehydration and even shock.
The veterinarian will treat the dog with antibiotics for the infection, as well as IV fluids to stabilise the dog’s condition. When the infection is cleared, the recommended treatment would be neutering.
Prostatic cysts
Sterile prostatic cysts are large cysts found in or on the prostate gland. They may be caused by obstruction in the ducts that supply prostate secretions. These cysts show similar symptoms to other causes of prostatic enlargement, and only really become apparent when they grow and put pressure on the surrounding organs. They can affect the dog’s usual eliminating functions and need to be surgically removed or drained.
Prostate cancer
As with any canine cancer, prostate cancer is serious, though comparatively rare. Neutering a dog does not mitigate the risk of canine prostate cancer. The symptoms are similar to other prostate inflammation and diseases, and if it metastasises, it can invade the surrounding organs and cause problems with elimination. It is diagnosed by examination, imagining tests and biopsy. There is unfortunately no cure.
Transmissible venereal tumour (TVT)
TVT are sexually transmitted tumours that are cancerous and grow on male and female genitalia. Dogs transmit the disease when they mate or are bred, and the tumours take on the appearance of cauliflower-like growths. The tumours cause inflammation and bleeding and, without treatment, continue to grow. Treatment is multi-modal and may consist of surgical removal, and cancer treatments like chemotherapy and radiation. Prognosis is usually good if TVT is treated early enough.
Diagnosing and treating problems in the male reproductive system
It’s important to take your male pets for a veterinary check-up at least once a year. If you see your dog or tomcat is straining to defecate or urinate, or is passing bloody urine, walking stiffly, has a fever or any of the other symptoms mentioned above, taking them to the vet immediately.
The vet will perform an abdominal palpation as well as a thorough physical examination. If, based on their examination and your reporting, they narrow down the symptoms to a possible diagnosis, the vet will take blood for a complete panel as well as X-rays or other imaging, urinalysis, and – where necessary – a biopsy, to reach a diagnosis.
How to support your pet’s healthy male reproductive system
Unless you are a registered breeder, the case for neutering almost all male dogs and tomcats remains high. Not only will it help to curb the dog- and cat overpopulation problem in South Africa, but neutering promotes excellent health for your male dog.
Neutering can prevent diseases such as:
- Testicular cancer
- Benign prostatic hypertrophy
- Prostatitis
- Hernias
- Territorial aggression
- Marking territory
Be sure to take your male pets for their annual check-up, which will allow the vet to do a health screening and catch potential problems before severe symptoms manifest.