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Desexing age recommendation has changed a lot over the past 10 years. Our previous recommendation, that all dogs should be desexed at 6 months, has become more complicated. The general recommendation now is that dogs under 15kg should be desexed at 6 months and dogs 20kg plus may be better waiting until 9 months.

The exception to the rule is Dachshunds who are better desexed as late as 2 years old. This is to try to decrease the incidence of intervertebral disk disease that causes back problems. However if male Dachshunds start to become aggressive they should be desexed earlier.

Very Early Desexing  – 9  to 15 weeks

  • This is common in animals from shelters and from some breeders.
  • Very early desexing increases the risk of urinary incontinence (leaking bladders) especially in large breed female dogs.
  • Pittwater Animal Hospital does not recommend 12 week old desexing.

Early Desexing – 6 months old – recommended for small to medium breed dogs

  • The desexing operation in a 6 month old dog is a much simpler procedure. Animals recover much more quickly with minimal pain or swelling.
  • If your dog is desexed before 6 months, lifetime registration is significantly cheaper – a saving of around $200.
  • Larger breeds that are desexed at 6 months may have a 5% increased risk of cruciate ligament disease.
  • Desexing at 6 months appears to cause no increase in the risk of urinary incontinence (leaking bladders).
  • Female dogs are highly unlikely to come into season before 6 months. Female dogs who have had one season have an increased chance of mammary tumours.
  • Male dogs desexed before 6 months are less likely to urine mark or develop aggression to humans with age.

Later Desexing 9-18 months – considered for large breed dogs

  • The operation is more complex and may need greater aftercare to avoid swelling.
  • The cost to desex is increased due to the added complexity.
  • Later desexing of larger breed dogs may slightly decrease the incidence of cruciate ligament disease.  The incidence is approximately 5% less than dogs desexed at 6 months. This may be helpful in breeds that are prone to cruciate ligament disease such as Golden Retrievers, Labradors, Border Collies, American Staffies and Rottweilers. The chances of cruciate ligament disease is significantly increased in dogs that are over weight, which is likely to be a more significant risk factor than desexing age. 
  • Anxious dogs may become more settled if desexed later – the evidence is anecdotal.
  • Male dogs may develop more aggressive behaviour towards humans if desexing is delayed. This can become learned behaviour and remain after desexing.
  • Male dogs are more likely to develop urine marking behaviour.
  • Male dogs are more likely to develop escaping behaviour.

Undesexed animals

  • Female dogs will have regular seasons – once to twice a year. This will cause blood spotting and a swollen vulva. The vulva will always be larger after a female dog has had a season.
  • Female dogs will have significantly increased risk of potentially fatal mammary tumours and uterine infections. These problems need complex surgery to treat and can be life threatening. Surgery is often required in late middle age or elderly dogs which significantly increases the stress on your pet.
  • Male dogs will have increased urine marking.
  • Male dogs may have increased chance of developing aggression towards humans.
  • Male dogs have significantly increased risk of prostate and testicular cancer as well as cancer of the anus.

A little bit of history

In Australia we have tended to desex early. Before the dog laws of the 1970s there were a lot of loose dogs in the street. Male dogs were often run over searching the neighbourhood for a female dog. Dog laws encouraging desexing and outlawing roaming dogs significantly decreased dog bites in the community as well as car accidents involving dogs. (Vets in the 70’s were fantastic at fixing fractures – a skill that is more of a specialist vet thing now.)

In the UK it is less common to desex your dog. Vets in the UK almost weekly operate on female dogs with mammary tumours and every few weeks uterine infections. Their male dogs often have prostate problems causing constipation, straining to urinate and increased anal tumours.

What is different in desexed dogs?

There are many different studies that are challenging to interpret. In general desexed dogs live 25% longer and will grow slightly taller than dogs that are not desexed. Desexed dogs are more likely to put on weight which makes it important for their owners to control how much food they are given. Adjusting the amount of food your dog is given, so that it stays in a normal weight range, is extremely important for your dog. Your veterinarian can be your guide on what is the optimum weight for your pet.


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