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To Desex or Not to Desex

Desexing (or neutering) is the surgical procedure that renders a male or female unable to reproduce. The procedure is done under a general anaesthetic.

Males à castration. Involves removing the testicles; the empty scrotal sack shrinks.  The testicles produce sperm and the male hormone testosterone.

Females à spey.  Involves removal of both ovaries and the uterus.  The ovaries produce ‘eggs’ during the heat cycle and the female hormones oestrogen and progesterone.  The uterus is removed to avoid possible infection or tumours later in life.



  • Speying early (before the first ‘season’) reduces the chances of mammary cancer development in females from approx 70% (in later life) to almost nil.
  • Prevents undesired ‘heats’ and pregnancies
  • Prevents severe uterine infection (‘Pyometra’), which is a life-threatening disease, and requires emergency surgery to spey a critically ill animal. This is a high risk and high cost procedure.
  • Males also benefit as the incidence of testicular and prostatic disease and perineal hernias is very high in non-castrated adult males.


  • Avoids development of undesirable sexual behaviour – mounting, masturbation, urine spraying
  • Greatly reduces aggression related to sexual behaviour – entire males fight when bitches on heat are within smelling range. Also cats fight less, lessening the risk of abscesses and transmission of feline aids (FIV).
  • Reduces the intensity of dominance aggression – irritable aggression often seen in females in heat and with false pregnancies
  • TERRITORIAL AGGRESSION IS NOT ALTERED BY DESEXING – your dog will still protect your property if he/she is inclined to do so. (On the other hand some dogs are just too placid to guard even if entire!).
  • A desexed pet is less likely to roam and become lost or involved in territorial conflicts with other animals and car accidents
  • Reduces or eliminates inappropriate urination and defecation – caused by hormonal, territorial and sexual factors

Temperament myths

Basic personality and intelligence are not altered by desexing – in fact, many undesirable qualities under hormonal influence may be resolved.  Animals do not become less affectionate or playful if they are desexed.

The temperament of females is unlikely to improve after having a litter – in fact the opposite can occur as their maternal instincts make them over-protective and increase aggression. The temperament of males is likely to be improved after desexing as they are less unpredictable and less likely to show dominance aggression to their owners.

Potential complications of Desexing


Desexing is an operation that most vets perform on a daily basis. Although it is a routine surgery, in females especially it is still major abdominal surgery.

Complications are rare, but can include:

  • Suture reactions at the surgical site – these are often temporary and resolve with anti-inflammatories
  • Infections at the external wound site – may be resolved with daily cleaning, or may require a short course of antibiotics
  • Bleeding – this is a RARE complication of desexing in male and female dogs. The Veterinary surgeon will check very carefully that all blood vessels are tied and secure before closing the surgical site, but occasionally (especially if the animal is excessively active in the first 72 hours) internal bleeds can occur.  This may require a second surgery, but can sometimes be managed by keeping the animal quiet and still and placing pressure bandages around the abdomen.


Urinary incontinence in female dogs.

This is the only medical down side to desexing.  Some dogs, especially larger breeds, have been found to develop incontinence later in life.  This can be associated with low exposure of the bladder sphincter muscle to oestrogen, produced by the ovaries.  The oestrogen allows the sphincter muscle to be more sensitive to the chemical produced by the body that helps to keep the sphincter shut.  Not all speyed female dogs will have this problem, and there is simple daily treatment available to help ‘tighten up’ the bladder sphincter and return the bladder to normal function.

Effect on weight

Some pets may gain weight after desexing. This is due to a combination of the pet’s metabolic rate being reduced following desexing, along with a lack of adjustment of feeding habits to accommodate this.

This is exacerbated by the fact that pets are usually desexed when they are approaching their full adult size and if their food intake is not reduced at this time, then they will start to put on weight – desexed or not.

We must adjust our pet’s food intake to meet their level of metabolism and level of activity accurately or weight gain will occur.  It’s important to keep an eye on weight and adjust feeding appropriately, and avoid feeding tidbits and treats.

Our nurses run a free weight clinic where you can check your pet’s weight and discuss any changes that may need to be made to their feeding habits.

When is the best time to desex?

For male cats, any time from 6 months is ideal.

Larger breed male dogs may benefit from delaying the surgery until they are fully grown to help with skeletal development.

For females, the best prevention against mammary cancer is achieved if they are spayed at 6 months of age, which is usually before their first season.  If a female dog has been in season already, waiting till 2-3 months after the season finishes minimizes the blood supply to the uterus and lowers the risk of surgical complications.

In cats, females may repeatedly come into season every couple of weeks, so trying to catch them between these times is ideal.