The short answer to the question of desexing your pet is that companion animals not intended for breeding should be desexed. Depending on the breed of animal, we recommend this occurs between 6 and 12 months of age. This advice is based on the goals of reducing unwanted pregnancies, avoiding unwanted behaviours and discharges, plus avoiding some common and life-threatening diseases. However, for the longer version of the answer, Kallangur Veterinary Surgery believes that the decision of whether, and when, to desex your pet must be made on a case by case basis, taking into consideration the pet’s age, breed, sex, intended use, household environment and temperament. When contemplating the pros and cons of desexing your pet, you should consider your pet’s health, behaviour, future activities, and the interactions of your pet with other animals and the human population.

Effects of desexing on future health

Health advantages associated with desexing

  • An increased risk of mammary cancer, ovarian cancer and testicular cancer in intact female and male dogs and cats respectively.
    1. There is an increased risk of mammary cancer with each subsequent cycle and the benefit of spaying does not disappear until the animal reaches old age.
    2. Mammary cancer is one of the most common types of neoplasia in small animals.
    3. Mammary cancer is malignant 60% of the time in dogs and 90% of the time in cats.
    4. Mammary cancer almost never occurs in bitches desexed prior to having their first heat cycle.
  • The incidence for ovarian cancer is more common in intact females, but the occurrence and mortality risk are very low.
  • The incidence for testicular cancer is more common in intact males, but malignancy and mortality are very low.
  • There is an increased risk of pyometra in both intact female dogs and cats and this risk increases with increasing age. This condition can be life-threatening.
  • There is an increased risk of prostatitis, benign prostatic hyperplasia, prostatic cysts and squamous metaplasia of the prostate in intact male dogs.
  • There is a decreased incidence of perineal and inguinal hernia and perineal adenoma when male dogs are castrated.

Health advantages associated with NOT desexing

  1. A reduced risk of hemangiosarcoma in intact bitches and dogs.
  2. A reduced risk of osteosarcoma in intact male and female dogs.
  3. A reduced risk of transitional cell carcinoma (bladder cancer) in intact dogs and bitches.
  4. A reduced risk of prostatic adenocarcinoma in intact male dogs compared to desexed male dogs.
  5. A reduced risk of obesity in intact male and female dogs and cats, which may be due at least partly to increased metabolic rate.
  6. A reduced risk of urinary incontinence in intact bitches compared to desexed bitches. But this difference is only the case if bitches are spayed younger than 5 months of age.
  7. There may be a reduced incidence of urinary tract infection in intact bitches.
  8. There may be a reduced incidence of feline lower urinary tract disease (FLUTD) in intact male and female cats which may be partly due to decreased obesity in these animals.
  9. There may be a reduced incidence of autoimmune thyroiditis and hypothyroidism in intact male and female dogs.
  10. A reduced risk of diabetes mellitus in intact female cats and possibly a reduced risk of diabetes mellitus in intact male dogs.
  11. A reduced risk of cranial cruciate rupture in intact male and female dogs.
  12. There may be a reduced risk of hip dysplasia in male and female dogs that are not desexed before 5 months of age.
  13. There may be an increased incidence of capital physeal fractures in castrated male cats that may be partially due to increased weight gain in desexed males.

Effects of desexing on behaviour

Research has shown positive and negative effects of the sex steroid hormones on behaviour. Some of the research is clear, while other areas are still a little uncertain.

Advantages of NOT desexing on behaviour:

  1. There is a decrease in shyness and hiding behaviour in intact male and female cats.
  2. There may be less aggression towards people and other animals in intact bitches.
  3. There may be a decreased incidence of cognitive dysfunction in intact male and female dogs. This means less dementia and possibly less anxiety.

Advantages of desexing on behaviour:

  1. Inter-dog aggression may be due to competition for available territory or availability of cycling animals.
  2. Urine spraying and inter-animal aggression is increased in intact male cats.
  3. There is a decreased risk of wandering and being hit by a car in desexed animals.
  4. There may be less aggression towards humans in desexed male dogs.

Health status of your pet

  1. Careful consideration should be given to the decision to desex animals with medical conditions that may result in complications during anaesthesia or surgery (eg. heart murmurs, bleeding disorders). Consider the animals age, and whether it is genetically predisposed to specific problems. Ask for a pre-anaesthetic blood test if in doubt. Also consider non-surgical options for desexing.
  2. Providing appropriate aftercare for surgical patients may not be feasible in some home situations. Your pet will require close supervision for up to ten days following surgery.

Public health considerations

The problem of domestic pet overpopulation is well recognised. It is difficult to get Australian data, but figures from just RSPCA statistics suggest there are over 40,000 unwanted dogs and over 50,000 unwanted cats presented to the RSPCA every year. Sadly, over 18,000 of these animals are euthanased annually. In the USA there are estimates of between 10 and 20 million unwanted dogs and cats being euthanased every year (Bowen, 2008). There are similar trends noted throughout the world (RSPCA, 2018). Other undesirable consequences of pet overpopulation include the economic cost of animal control programs to society, the potential for serious injuries being inflicted on other animals or humans, the potential human-health disaster that would occur should a zoonotic disease such as rabies enter Australia, and sanitation problems in cities associated with animal faeces and urine.

For public health and animal welfare benefits alone, there is overwhelming value in the general recommendation of desexing pets not intended for breeding.


There is no doubt that desexing soon after 6 months of age is the responsible choice for most pets and for society. However, there is recognition that there are some clear health benefits of the sex steroid hormones and that this benefit varies with age, sex, and breed. While the list of conditions that benefit from non-desexing seems long, the important point to consider is how common those conditions are, and how life-threatening they are. Mammary tumours and pyometra are seen very commonly in non-desexed bitches and both are life-threatening conditions. It is in the best interest of each individual pet for its owner and veterinarian to discuss the risks and benefits of desexing.

For those thirsting for more information

Try these references:

Brodey RS, Goldschmidt MH, Roszel JR. Canine mammary gland neoplasms. J Amer Anim Hosp Assoc 1983;19:61-90.

Bronson RT. Variation in age at death of dogs of different sexes and breeds. Amer J Vet Res 1982;43:2057-2059.

British Small Animal Veterinary Association. Sequelae of bitch sterilisation: Regional survey. Vet Rec 1975;96:371-372.

Bryan JN, Keeler MR, Henry CJ, et al. A population study of neutering status as a risk factor for canine prostate cancer. Prostate 2007;67:1174-1181.

Cohen D, Reif JS, Brodey RS, Keiser H. Epidemiological analysis of the most prevalent sites and types of canine neoplasia observed in a veterinary hospital. Cancer Res 1974;34:2859-2868.

Cooley DM, Beranek BC, Schlittler DL, et al. Endogenous gonadal hormone exposure and bone sarcoma risk. Canc Epidem Biomark Prev 2002;11:1434-1440.

Cowan LA, Barsanti JA, Crowell W, Brown J. Effects of castration on chronic bacterial prostatitis in dogs. J Amer Vet Med Assoc 1991;199:346-350.

Crane SW. Occurrence and management of obesity in companion animals. J Sm Anim Prac 1991;32:275-282.

Crenshaw WE, Carter CN. Should dogs in animal shelters be neutered early? Vet Med 1995;90:756-760.

Barfield, J. P., E. Nieschlag, and T. G. Cooper. 2006. Fertility control in wildlife: humans as a model. Contraception 73:6-22.

Hopkins SG, Schubert TA, Hart BL. Castration of adult male dogs: Effects on roaming, aggression, urine marking, and mounting. J Amer Vet M

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