For a long time Veterinarians have been advising that cats and dogs should definitely be desexed and it should be done while still growing at six months of age.

Some recent research is making us reassess these simple answers to what may be quite a complex decision. The internet is quick to overreact to single research findings making this potentially confusing for pet owners trying to decide what is best for their particular situation. For this reason we have summarised some of the information and presented our recommendations here. It is always best to discuss what is the latest and best option for you and your individual pet with your Veterinarian.

Is desexing actually the best option for pets?

In our view a study in 2013 involving over 40,000 dogs answered this question as yes. It demonstrated that there was a substantial increase in lifespan associated with desexing. Desexing increased lifespan by 13.8% in female dogs and 26.3% in male dogs.

Cause of death by infection, trauma, circulation problems and degenerative problems was reduced if desexed. Cause of death by immune mediated disease and cancer was increased. An increase in cancer would be expected with longer lifespan.           

Does desexing increase the risk of cancer?

A 2013 Golden Retriever study and a 2014 Vizla study started a concern as they indicated an increased cancer risk in these breeds after desexing. This started some discusion about whether desexing should be done at all or if modified procedures such as ovary sparing spey in female dogs or vasectomies in male dogs rather than a full desexing should be considered. These studies were based on patients sent to referral centres and may not have been typical of the general dog population.

A more recent 2016 German Shepherd study indicated no increased cancer risk with desexing and did show an increased longevity. A 2018 Golden Retriever study also found no increased risk of cancer with desexing and an increased lifespan.

Cancer is clearly a complex issue and in our view there is insufficient evidence to consider  altering our recommendation on desexing at this time. A ground breaking Lifetime Golden Retriever study now underway involving 3000 dogs may answer some of these questions for this breed that is at high risk for cancer.

Desexing and breast cancer risk

Breast cancer ( mammary cancer ) is the most common cancer in female dogs, being three times more frequent than in humans. Unlike in humans it is benign 50% of the time and can be cured with early surgery 75% of the time.

It has been believed that desexing before the first heat almost prevents breast cancer and has been a main reason for recommending speying female dogs before their first heat, which is however, before their bones have finished growing.

It has been generally accepted that there is an increased risk with each heat and a recent study suggested significant increased risk by the second and third heat. A 2012 study indicated studies prior to this were of inadequate quality to base a recommendation on. Our feeling is the risk of allowing one heat is still reasonable to consider as does our New Zealand Veterinary Association.

Does desexing increase the risk of joint disease?

The recent studies are all indicating early desexing prior to growth finishing at a year of age is associated with a substantial increase in future joint disease. This includes cranial cruciate ligamant disease, elbow dysplasia and hip dysplasia varying with breed studied. 2014 Labrador and Retriever study., 2018 Retriever study, 2016 German Shepherd study

This group of diseases causes a large amount of chronic pain for pets, owner concern and expense for many of our favourite medium to large breeds.

Waiting until a year of age before desexing, when bones have finished growing, may decrease risk of joint diseases in the breeds studied by upto three fold. This is such a consistent finding it likely applies to all medium to large breed dogs.

Does desexing female dogs increase incontinence risk?

Incontinence can affect around 3% of dogs as they age. Larger breeds are at increased risk.

The standard thinking has been that if female dogs are speyed after three months of age there will be no increased risk of incontinence in later life.  A large 2019 study indicates that unfortunately speying at any age will increase the risk of future incontinence.  A 2017 study suggested delaying desexing til over a year of age was of benefit in the larger more at risk breeds only. A 2016 German Shepherd study indicated an increased risk of future incontinence in this breed if desexed before a year of age. 

Desexing before puberty may result in a small recessed vulva which can sometimes result in localised skin and bladder infections later in life.

Does desexing affect male aggression?

Though the answer to this may seem obviously in favour of neutering, the studies are mixed. A 2018 study showed no significant difference whether desexed or not. The exception being dogs that were desexed between 7-12 months of age had a higher risk of biting strangers, suggesting more fear based aggression.

Another 2018 study also highlighted potential behavioural issues with early neutering of male dogs. This is important given that behavioural problems results in the euthanasia of many young dogs. This may indicate that delaying neutering to at least a year of age may be indicated in nervous male puppies especially.

General benefits of desexing

Pet Benefits


  • Over 25% of female dogs will suffer a lfe threatening uterine infection called pyometra by the age of ten if not desexed.
  • Eliminates the risk of ovarian and testicular cancer, though strangely not prostate cancer.
  • Eliminates diseases associated with pregnancy and birth
  • In male dogs, protects against benign anal tumours, some prostate conditions and perineal hernias.
  • Reduces the risk of roaming with bite wounds and traffic accidents.
  • Less risk of feline AIDs virus in male cats

Owner benefits 

  • Less likely to incur the expense from fighting and road traffic accidents
  • Avoids female heat with attraction of male cats or dogs to the property, vaginal bleeding in dogs and vocalising in cats.
  • Avoids unwanted pregnancy
  • Males will have less urine marking in the house, humping and roaming behaviour.
  • Male cats will not develop an unpleasant odour.
  • Council registration will be cheaper for dogs
  • Admission to boarding facilities and doggy day care will be easier.

Our recommendation for cats

Female cats have a series of heats until they become pregnant, often with vocalising at night when people are trying to sleep. They will usually become pregnant when they reach puberty at 7-10 months of age, hence there are so many unwanted pregnancies and stray cats.

Male cats will become aggressive to your neighbours cats and spray urine more if not desexed. They will have a large territorial range away from home with a high risk of injury and disease.

The good news is the studies indicate that cats are not affected significantly by early desexing and so the procedure can safely be performed when young. With modern anaesthetic safety protocols they can be desexed from one kilogram in weight, however for owned cats we usually wait until 4-6 months of age for added safety.

Our recommendation for small dogs

We do recommend desexing of dogs as the balance of benefits is very much in favour for the overall welfare of the pet.

Currently for small breeds under approximately 15 kilograms we are comfortable based on current evidence to recommend desexing at the traditional six months of age.

We do see cruciate ligament and hip problems in certain small breeds, behavioural and other concerns that may be influenced by timing of desexing. In the future there may be specific recommendations for certain breeds or individuals as research is done.

Our recommendation for medium to large dogs

For medium to large breed dogs such as Labradors, Retrievers and German Shepherds, a delay in desexing until growth is complete at about a year of age is worth serious consideration and is our recommendation.

This delay is highly likely to significantly reduce the risk of some very common joint disorders that lead to arthritis. The research findings are so consistent it is likely to apply to all medium to large breed dogs of both sexes. A small reduction in future incontinence risk is possible. It may also help anxious male dogs have a more balanced behaviour.

For female dogs this will involve managing your dog through one heat period which will involve some minor bleeding and confinement to prevent pregnancy. Having a heat won't suit everyones lifestyle and there is a small increased risk of breast cancer to consider.