What Spaying and Neutering Actually Mean
Spaying (the surgical removal of a female animal's ovaries and usually uterus) and neutering (the removal of a male animal's testes) are collectively called desexing or sterilisation. Both procedures are performed under general anaesthesia by a licensed veterinarian and are among the most routine surgeries in companion animal medicine.
Beyond preventing unwanted litters, these procedures affect hormone production — and those hormones influence a wide range of physical and behavioural traits. That's why the decision to desex, and when to do it, carries genuine health implications worth understanding before you book the appointment.
For a broader overview of preventive care steps, see our guide on vaccinations, desexing, and microchipping.
The Health Benefits: What the Evidence Supports
Eliminates pyometra risk in females
Pyometra is a serious, often fatal uterine infection that is completely prevented by spaying. It's one of the most compelling medical reasons to desex female dogs and cats.
Removes risk of reproductive organ cancers
Spayed females cannot develop ovarian or uterine cancer. Neutered males have zero risk of testicular cancer, which is not uncommon in older intact dogs.
Reduces prostate problems in male dogs
Neutering greatly lowers the likelihood of benign prostatic hyperplasia, a condition that causes painful urinary and bowel issues in older intact males.
Lowers disease exposure through reduced roaming
Particularly for cats, neutering reduces the drive to roam and fight — cutting exposure to FIV, FeLV (feline leukaemia virus), and traumatic injuries.
Reduces unwanted hormone-driven behaviours
Urine marking, mounting, heat cycles, and male-on-male aggression all decrease significantly after desexing, improving life for pets and owners alike.
The strongest case for desexing is disease prevention. Spaying eliminates the risk of pyometra — a life-threatening uterine infection that affects a significant proportion of unspayed females by middle age. It also removes the possibility of ovarian and uterine cancers entirely.
In males, neutering eliminates testicular cancer and substantially reduces the risk of benign prostatic hyperplasia (an enlarged prostate), which can cause difficulty urinating or defecating in older intact dogs. For cats especially, neutering sharply reduces roaming and fighting behaviour, which lowers exposure to infectious diseases like FIV (feline immunodeficiency virus).
Known Trade-offs and Health Risks
Possible orthopaedic risks in large breeds
Early desexing in large and giant breed dogs has been associated with higher rates of joint problems, including cruciate ligament ruptures. Timing the procedure after skeletal maturity may reduce this risk.
Potential increased cancer risk in some breeds
A small body of research links desexing to higher rates of certain cancers in specific breeds. Evidence is still developing, and the risk varies widely by breed and procedure timing.
Weight gain is a common post-procedure concern
Hormonal changes after desexing can slow metabolism slightly, making weight management more important. Adjusting portion sizes and maintaining regular activity can counteract this effectively.
Surgery carries standard anaesthetic risks
As with any procedure under general anaesthesia, there is a small inherent risk. For healthy young animals, this risk is very low, but it's worth discussing with your vet beforehand.
Does not address non-hormonal behaviour problems
Desexing won't resolve fear-based aggression, anxiety, or learned behaviours. Owners sometimes expect a broader behavioural transformation than the procedure can realistically deliver.
The health picture isn't entirely one-sided. Research — particularly in larger dog breeds — has identified associations between early desexing and a higher incidence of certain orthopaedic conditions, including cruciate ligament tears and hip dysplasia. The working theory is that sex hormones play a role in bone and joint development, so removing them before a dog reaches skeletal maturity may affect how joints form.
Some studies also suggest elevated risk of certain cancers (such as hemangiosarcoma and osteosarcoma) in some desexed large breeds, though the evidence is still evolving and should be discussed with your vet rather than treated as a definitive rule.
Breed-Specific Guidance Is Evolving
Veterinary researchers have published breed-specific desexing recommendations — particularly for dogs like Golden Retrievers, German Shepherds, and Labrador Retrievers — based on cancer and orthopaedic data. These recommendations don't apply universally, and findings continue to be refined. Ask your vet whether breed-specific research is relevant to your dog's situation, rather than applying general findings to all pets.
Behavioural Changes: Realistic Expectations
Desexing does reduce hormonally driven behaviours. In male dogs and cats, you can reasonably expect reduced urine marking, less roaming, and a lower likelihood of aggression toward other males. Female cats will no longer go into heat — a significant quality-of-life improvement for both pet and owner.
However, desexing is not a behavioural reset. It won't fix aggression rooted in fear, poor socialisation, or learned habits. A dog that already resource-guards or snaps at strangers will need behavioural training regardless of reproductive status. Understanding which health beliefs about pets are grounded in evidence is important — check out common pet health myths for more context.
~90%
Reduction in roaming behaviour in neutered male cats
Veterinary behaviourists generally cite roaming reduction as one of the most consistent and pronounced behavioural effects of neutering in cats.
~25%
Of unspayed females develop pyometra by age 10
Studies in Scandinavian dog populations have estimated that roughly one in four intact females will develop this life-threatening uterine infection by mid-life.
Timing: Why It's Not the Same for Every Pet
Veterinary guidance on timing has shifted over the years. The traditional recommendation of desexing at around six months of age remains appropriate for most cats and smaller dog breeds. For medium to large and giant breeds, many vets now recommend waiting until 12 to 24 months — allowing the skeleton to develop more fully before removing sex hormones.
Your vet will consider species, breed, size, household situation (for example, are there intact animals in the home?), and individual health history. This is a conversation worth having early — ideally at your pet's first wellness exam. See what else gets assessed at those visits in our guide to annual wellness exams.
As pets age, the context around their earlier health decisions matters more. Our article on senior pets and changing health needs explores how care evolves over time.
This article is for general informational purposes only and is not a substitute for professional veterinary advice. Always consult a licensed veterinarian for guidance specific to your pet's health, breed, and circumstances.
