Whether episodes of urinary incontinence develop in a young puppy or in a much loved older pet, there is no doubt this is a very frustrating and upsetting situation for any pet owner and their family. If a diagnosis is not reached or suitable management not achieved this can result in the heart-breaking decision of euthanasia due to the understandable difficulty of dealing with urinary accidents day in, day out. In the first in a series of articles, we will look at what makes a female dog incontinent.
How is urine stored and voided normally in a dog without incontinence?
The anatomy of the urinary tract
Urine is made in the kidneys and passed down to the bladder via two tubes called the ureters. The urethra is the tube joining the bladder neck to the outside. Urine is then stored in the bladder until the pet makes a conscious decision to urinate. The bladder slowly stretches to accommodate the urine collected and the urine is prevented from leaking into the urethra by the resistance in the urethra. This resistance is provided by the smooth and skeletal muscle in the urethra, natural elasticity in the urethral wall and by engorgement of small blood vessels beneath the surface of the urethra.
By a complex sequence of nerve conduction, muscle contraction and relaxation, the bladder muscle contracts, the bladder neck and urethra containing muscle sphincters relax allowing urine to flow to the outside.
So why is my dog leaking urine?
A female dog may leak urine for one of several reasons:
Cystitis
Having a urinary tract infection in the bladder (‘cystitis’) and /or kidney infection (‘pyelonephritis’) can certainly cause signs of inappropriate urine leakage and sometimes bloody urine.
Kidney stone or bladder stone
A kidney stone itself will not cause incontinence but the stone may act as a platform for infection to take hold and it will be the urinary infection that can cause urine leakage. A bladder stone is unlikely to cause urine incontinence, but if small stones get trapped lower down the urinary tract in the urethra, this could cause urine to inappropriately dribble, and again any stones can be an underlying cause for a bladder infection. Usually, a pet with a bladder stone or urethral stone strains to urinate, however, which is not a common sign in an incontinent dog.
Urinary incontinence in a much-loved pet can be frustrating and upsetting
Drinking a lot
There are a number of medical conditions which can cause pets to drink excessively and produce very dilute urine, such as over active adrenal glands (‘Cushing’s disease’), diabetes mellitus and ‘renal dysplasia’ (this means that the inside of the kidney is structurally disorganised, leading to it not working properly). Affected animals have urinary accidents and may appear incontinent.
Faulty anatomy
If there is a defect in the ‘plumbing’ – the way in which the various parts of the urinary tract are formed in an individual – then this could lead to urine leakage.
One of the commonest causes for incontinence in juvenile females is due to one or both of the ureters (the tubes which carry urine from the kidneys to the bladder) tunneling into the wall of the bladder and actually opening up into the bladder at a position much further back in the bladder neck or urethra than they normally should. This condition is called ‘ectopic ureters’. The consequence is that some of the urine volume produced is not stored in the body of the bladder, but instead just leaks backwards to the outside. A classic example of the signs of this would be a puppy with profound urinary incontinence and a constantly urine soaked bottom. For other puppies, their ectopic ureter may not cause immediate incontinence if there is good muscle tone of the bladder neck and urethra. As these patients age or if they are neutered (causing oestrogen hormone levels to drop), the incontinence due to an ectopic ureter then starts to become apparent. On rare occasions, dogs can have an ectopic ureter and this defect goes undetected until perhaps they reach 5 years of age or more.
Another quite common anatomical abnormality is a bladder neck that is not in its normal location within the abdomen and is instead located more towards the protective box of the pelvis. This is known as an ‘intrapelvic bladder neck’. In some bitches this is associated with congenital or acquired ‘urethral sphincter mechanism incompetence’. Urethral sphincter mechanism incompetence causes urine to leak out inappropriately.
There are a number of less commonly seen anatomical defects such as small bladders and out-pouching of the urethra and bladder (‘diverticula’) which may also lead to incontinence.
Reduced ‘urethral tone’
‘Urethral tone’ is the muscular and elastic tone/residual tension of the urethra (the tube that carries urine from the bladder to the outside) that prevents urine from leaking inappropriately. An under-developed urethral tone can be something a patient is born with (congenital) or can develop (acquired) with age or with a depletion of hormones such as oestrogen. Reduced urethral tone is associated with acquired urethral sphincter mechanism incompetence. Acquired urethral sphincter mechanism incompetence is most often seen in mature, female, neutered dogs.
Does neutering make bitches incontinent?
It has not been proven that neutering before a first season causes urinary incontinence. The incidence of urinary incontinence in neutered females is reported between 5% to 20%. Neutered females are approximately 8 times more likely to develop urinary incontinence than bitches who haven’t been neutered. Dogs heavier than 15kg bodyweight are 7 times more likely to become incontinent following neutering than dogs less than 15kg.
Incontinence which occurs following neutering is usually due to acquired urethral sphincter mechanism incompetence. Connective tissue forms three quarters of the female dog’s urethra. Neutered dogs have a higher proportion of collagen and lower proportions of muscle compared to dogs which haven’t been neutered. The function of the urinary tract is also affected by hormone balance. Neutering will cause a reduction in circulating oestrogens, which in turn may reduce urethral smooth muscle tone in some dogs.
Does it make any difference in the likelihood of developing urinary incontinence whether my bitch is neutered by being spayed (ovahysterectomy) or has keyhole surgery to just remove the ovaries (ovarectomy)?
No. Both procedures remove the ovaries, which result in lower circulating levels of the hormone oestrogen.
Should I have let my female dog have a season before neutering?
It has not been proven that neutering before a first season causes urinary incontinence. There is perhaps however, some merit in allowing a first season to take its course, particularly in bitches over 15kg body weight, thus ensuring the bitch benefits from the hormonal development and maturity prior to neutering.
If I do let my bitch have her first season before neutering am I then increasing her risk of developing mammary/breast cancer?
For many years it was thought that neutering a bitch before her first season reduced her risk of developing mammary cancer in later life. However, in 2012, a review was conducted of the original studies and found no consistent proof that neutering has a protective effect against developing mammary cancer.
In Part 2 in this series, we will look at the sequence of events that hopefully gets you to a diagnosis.
The Veterinary Expert| Pet Health
The veterinary expert provides information about important conditions of dogs and cats such as arthrits, hip dysplasia, cruciate disease, diabetes, epilepsy and fits.