Neutering - the pro's and con's

There is a lot of misinformation regarding neutering, especially on the internet.  I hope to set out the facts as we know them in this article.  It is important to realise we do not know anything with absolute certainty, that's not how science works; we keep learning and adapting our advice to our current knowledge.



There is an overall benefit to neutering your pets

We recommend small to medium breed bitches are spayed after their first season (at 9 -12 months) and that large breed dogs are allowed to reach maturity and spayed after their 2nd season  (at about 18 months).

Male dogs should be castrated at about 12 - 18 months once they have stopped growing.

Cats are a different story.  They breed very efficiently and The Cat Group, a collection of professional organisations working on cat welfare, recommend neutering at 4 months of age in most cases.

So why should you neuter your pet? 

The most important reason to neuter is population control, which is far more important than any health issues.  Entire bitches and queens will probably fall pregnant or be caught by a male at some point in their life.   Although we have injections to stop pregnancy they are expensive and have side effects.  A bitch in heat is likely to be harassed by dogs in the park as well as suffer from false pregnancy which can be as distressing for the owner as it is for the bitch.

Castrating males can make them more sociable and less likely to roam.

So before we start discussing health issues it is important to realise that population control and social reasons are the most important reasons to neuter.

Pro-neutering and anti-neutering campaigners often justify their positions using health issues.  If I told you that by neutering your bitch you triple her risk of developing hypothyroidism (low thyroid hormone) I'm sure you would be concerned.  If you knew that 99.4% of dogs have normal thyroid levels and that your spayed bitch had tripled her risk to a 98.2% chance of having a normal thyroid level it puts the risk into perspective.

It is important to understand how likely a disease is to occur before you consider the risk factors.

We know that if you spay your bitch before her first season there is a significant reduction in risk of mammary cancer to almost zero.  The risk of cancer increases with every oestrus cycle until 3 years of age when there is no longer a reduction in risk by spaying her.  This is used to promote spaying and is a good reason to neuter as it saves lives.  In Norway where almost all bitches are not spayed, they have an incidence of up to 3.5% for mammary cancer depending on the breed of dog (at least 96.5% of dogs are unaffected by mammary cancer).  In the UK where most bitches are spayed we have an incidence of 0.5% mammary cancer (99.5% unaffected).  So Norway has up to 3% more cases of mammary cancer than the UK (this equates to 90 000 cases of mammary cancer in the UK).

Keep in mind the relative risk of developing a problem when you look through the positive and negative affects on health that neutering may have.

The Cat

On the positive side, spaying female cats

• Population control.  Queens can have up to 3 litters a year.

• Social reasons.  Queens will call every 2 weeks from January to August attracting entire male cats the area with risk of spreading disease through fighting.

• Pregnancy and birth are risky and complications can occur

• Reduces to almost zero the risk of pyometra (infected womb)

• Removes the very small risk of ovarian cancer

On the positive side, castrating male cats

• Population control

• Less fighting, more social cats.  Entire male cats fight and spread disease especially Feline Aids and Feline Leukaemia which are fatal.  They develop or cause others to develop disease and abscesses.

• They roam over a smaller territory reducing their chance of being in a road traffic accident, one of the most common causes of death in cats.

• They spray and mark their territory less.

On the negative side in both male and female cats we have no evidence of problems to date.  The following have been areas of concern

• Implications for the cat's behaviour? Results of research into behavioural development show no problems currently.

• Implications for the cat's growth and development? Studies into growth and development show no concerns with prepuberty neutering (as early as seven weeks).

• Possible decreased urethral diameter in neutered animals predisposing to bladder blockage?  Uretheral diameter worries unfounded - studies show similar diameter to post-puberty neutering.

The Bitch

On the positive side, spaying female dogs

• Population control.  A bitch can have up to two litters a year.

• Social reasons.  A bitch has approx. two oestrus cycles a year and will attract male dogs for a few weeks.  This is distressing for the bitch and owner, as you cannot walk the dog without getting unwanted attention.

• False pregnancy is relatively common after a season.  The bitch can suffer anorexia, lactation and behaviour changes that often result in the owner seeking veterinary intervention.

• Pregnancy and birth can be risky, so think carefully before breeding.

• If done before 2.5 years of age significantly reduces the 1% - 3% chance of developing malignant mammary cancer

• Reduces to almost zero the risk of pyometra (infected womb) which would otherwise affect about 23% of bitches, of which 1% would be fatal

• Reduces the risk of perianal fistulas, a rare condition causing open wounds around the anus

• Removes the small risk of ovarian cancer which affects 0.5% of dogs

On the negative side, spaying female dogs

• Can cause urinary incontinence, in 4% - 20% of dogs, mostly large breed dogs (80% - 96% of spayed dogs are unaffected).  Many incontinent dogs can be managed effectively by hormone replacement.

• If done before maturity it triples the risk of osteosarcoma, a malignant bone cancer that affects mostly heavy large breed dogs.  5% of Rottweilers and 1% of Labradors are affected, so 95% - 99% of large breed dogs are unaffected.

• Doubles the risk of splenic haemagiosarcoma, a malignant tumour that affects about 2.5% of dogs.  So 97.5% of dogs are unaffected and doubling the risk means at least 95% of spayed dogs are unaffected.

• Triples the risk of hypothyroidism that affects 0.6% of dogs, so 99.4% of dogs are unaffected and if neutering triples the incidence then 98.2% of spayed dogs will not be affected.

• Almost doubles the risk of obesity, however obesity has many factors that influence its development just as in humans.

• Increased risk of a small vulva, dermatitis around the vulva and vaginitis if spayed before first oestrus.  The true incidence of this is unknown.

• Increased risk of urinary tract infections.  Incidence is unknown.

• Doubles the small risk of urinary tract tumours which occur in <1% of dogs, so >99% of dogs are unaffected and >98% of spayed dogs remain unaffected.

• Increased risk of orthopaedic disorders but by how much is uncertain.

Our neutering policy is designed to minimise the potential health side effects of neutering while retaining the health benefits.  By neutering larger dogs later in their development we minimise the risks.  Smaller dogs can be neutered earlier.

The Dog

On the positive side, castrating dogs

• Population control, there are far to many unwanted litters

• Social reasons.  Castrated males are often less aggressive and less likely to roam.

• Eliminates the risk of dying from testicular cancer, of which >99% of male dogs are unaffected

• Reduces the risk of perianal fistulas, a rare condition causing open wounds around the anus

• Reduced risk of non-cancerous prostate disorders, usually a problem in most old dogs.

• Reduced risk of perineal hernia, a muscle weakness around the anus

On the negative side, castrating dogs

• If done before maturity it triples the risk of osteosarcoma, a malignant bone cancer that affects mostly heavy large breed dogs.  5% of Rottweilers and 1% of Labradors are affected so 95% - 99% of large breed dogs are unaffected.

• Slightly increases the risk of splenic haemagiosarcoma, a malignant tumour that affects about 2.5% of dogs. So 97.5% of dogs are unaffected.

• Triples the small risk of hypothyroidism that affects 0.6% of dogs, so 99.4% of entire dogs and 98.2% of castrated dogs will be unaffected.

• Triples the risk of obesity, however obesity has many factors that influence its development just as in humans.

• Quadruples the small risk of prostate cancer which affects <0.6% of dogs, so >99.4% of entire males are not affected.  Castrated dogs will have >97.6% chance of being unaffected.

• Doubles the small risk of urinary tract cancer, but >99% of dogs and >98% of castrated dogs remain unaffected.

• Increased risk of orthopaedic disorders but by how much is uncertain

Our neutering policy is designed to minimise the potential health side effects of neutering while retaining the health benefits. There is no benefit to early castration so dogs should have stopped growing before we castrate them.  Larger dogs mature later than smaller dogs.