If it’s time to start considering the options for neutering your dog (otherwise known as castration), then please read on.


There are a number of practical, medical and behavioural benefits to castration.  This includes: an unneutered bitch in the same household; requirements of doggy day-care; urine marking; hypersexuality; unwanted litters; roaming away from home to track bitches in heat, unwanted social behaviour e.g. inter-male competitive behaviour and physical health benefits including testosterone related diseases.  Medical benefits include: eliminating the risk of testicular cancer, this is particularly important if your dog is found to have a cryptorchid (undescended) testicle.  Neutering also protects prostatic diseases commonly seen in unneutered dogs including inflammation and overgrowth of the prostate gland.
At Millennium, we assess each dog individually to find out your needs, reasons for castration, your dog's breed and maturity and any behaviour or training concerns.  We will not book your dog's operation, without a conversation with one of our vets or nurses within the last 3 months of your enquiry.  Contrary to popular belief castration doesn’t always calm your dog down and many excitable and unwanted behaviours are not influenced by male hormones!  We want you to be fully informed and make the right choice for your dog, before we take him to surgery – or not.

Behaviour changes and signs:

Discussing the reasons why you wish to have your dog castrated is important.  Some of the information and advice available, particularly on the internet, is misguided when interpreting the signs of developing sexual maturity.   Mounting behaviours for instance isn’t restricted to amorous behaviour, but can also be, e.g. anxiety, frustration, play and /or learnt behaviour.  Some unwanted behaviours are not influenced by male sex hormones and again reasons such as anxiety and/or learnt behaviours can be the cause.  Castration will not calm all dogs down, as is often the reason owners want to have their dogs castrated, especially in young dogs.   The age of castration will often come at the same time as adolescence and our advice to you will depend on the needs and behaviours your dog is showing.  This includes any changes in behaviour in unneutered mature dogs.

Anxiety is a natural mammalian response, nature’s way of keeping us safe.  Like people, some dogs may experience higher levels of anxiety than others depending on their parentage, rearing environment and life experiences.  Testosterone is thought to aid a dog’s confidence.  It follows that if dogs are castrated too early and before considering their behavioural needs, withdrawal of testosterone at this stage could make their anxiety worse.   Surgical castration is not reversible.

Age and breed considerations:

The time to do this will depend on your dog’s age.  Castration can be performed from 6 months of age but this very much depends on the individual dog and breed.  In general, small dogs are often castrated earlier, the recommended age rises developmental stages for their breed.   Larger dogs take longer to reach skeletal maturity and the hormone testosterone has a role to play in bone development. Castrating your dog involves the complete removal of his testicles and with this, the removal of your dog’s testosterone.  Therefore we usually recommend waiting longer to castrate larger breed dogs.  The following minimum age examples are a guide only:

  • Giant breeds, e.g. St Bernards and Great Danes from 15mths +
  • Large Breeds, e.g. German Shepherds and Labradors from 12 months
  • Medium Breeds, e.g. Cocker Spaniels and Staffordshire Bull Terriers, from 9 - 12 months
  • Small breeds, e.g. Miniature Schnauzers and cockerpoos from 7 - 9 months
  • Very small breeds, e.g. Chihuahuas and Yorkshire Terriers from 6 months

Temporary castration - chemical castration:

In some cases, leaving your dog entire may be the best advice.  Knowing which parts of his unwanted behaviour is influenced by his sex hormones or not, will help to make the right decision.  And this is where we can use an implant.  The size of a grain of rice, the implant is injected under the loose skin between their shoulder blades and can be given during a routine vet appointment.  Like their microchip, you may be able to feel the implant under your dog's skin when you stroke him.  The implant provides him with a temporary form of chemical castration.  Once given your dog will be infertile after 6 weeks and lasts for 6 months.  There is no difference in the age of giving the first implant or choosing surgical castration, again this comes down to age and breed as both have the same effect (be it a short term versus long term method).

Note:  Infertility is not instant with either method as you dog can remain fertile and able to breed up to 6 weeks later.

Under the influence of the implant the dog’s testicles will reduce greatly in size.  If during these 6 months your dog’s unwanted behaviour has reduced, without the development of any other behaviour concerns (or has remained unchanged), then it is a good indication that surgical castration will be the right decision for him.  Once the implant has worn off their testicles will return to normal size and they will once again become fertile.  Surgical castration can be performed before the implant wears off.
Some owners choose or are advised to use the implant as an ongoing treatment rather than opting for surgery.  In these cases your vet may recommend using a 12 month implant.
 For further information, follow these links: 

  1. Neutering male dogs: https://www.apbc.org.uk/wp-content/uploads/APBC-Neutering-Male-Dogs.pdf
  2. Implant video:  https://www.youtube.com/watch?v=G2uhQfMcnP4

The decision to castrate your dog permanently / temporarily or not at all, is specific to you and your dog.  For further advice please contact us.


  • If after discussion, we advise surgical castration and your dog is uncomfortable during his vet visits - additional support may be advised to minimise their stress while staying with us.  We can discuss this with you.
  • For surgical castration, dogs are admitted as day patients and the surgery is performed under general anaesthetic.  The natural need for calories reduces following neutering as their metabolism slows.  Weight monitoring is important from this point onwards, as is often the trigger for the start of weight gain if not.  We recommend weighing your dog 2 - 4 times a year.
  • If your dog's behaviour is of growing concern, we offer initial behaviour support advise and where required, advise referral to a registered Clinical Animal Behaviourist.  This may delay plans to neuter your dog.
  • When the implant is first given the hormonal changes that take place can in a very few cases cause any pre-existing aggressive behaviour to worsen as the implant starts to take effect in the first two weeks.  Your vet will discuss this with you in more detail as not all dogs will be suitable candidates for the implant.