What Is The Best Age To Desex A Dog?

I’m going to lead you through the evidence we have for the age to desex a dog. I’m not going to give you the ‘right’ answer, but instead the tools so you can make the best decision for your dog. With the new mandatory 6-month desexing in Adelaide, this is the evidence you may need to ask your vet for a postponement.

Beware simple answers. The real world is frustratingly not in black and white; anyone who claims otherwise is either misleading themselves or others. The job of science is to get as close to the truth as is humanly possible.

Firstly, let’s establish the reasons why we desex male and female dogs. Here’s the evidence we have in favour of neutering.

Why Desex Male Dogs

  • Lifespan is increased
  • Behaviours such as inter-dog aggression, aggression towards family members, roaming, sexual behaviour & urine marking are reduced
  • Medical conditions such as prostatic enlargement, cystine bladder stones, perineal hernia, testicular tumour & perianal tumour are reduced or eliminated.

Why Desex Female Dogs

  • Lifespan is significantly increased
  • Heat periods and unwanted pregnancy are eliminated
  • Pyometra (uterine infection) is prevented

To help dog owners I tell them:

Desex males for behaviour; Desex females for health. References can be found below.

Why NOT Desex A Dog?

Apart from infertility, proven negatives associated with desexing include:

Although they sound scary, we shouldn’t be concerned about the cancers associated with desexing. That’s because there’s a trump card: neutering gives a moderate increase in lifespan to both sexes of 9 to 12 months. In other words, although some causes of death become more common, other causes of death must become less common.

I’m much more concerned about accidentally increasing the rate of debilitating non-life-threatening diseases. That’s the information I use to decide when to desex.

When To Desex Dogs

There are four times advised by different groups:

  1. Early age desexing as advocated by rescue shelters and some breeders
  2. 6-month desexing as advocated by most vets
  3. Late age desexing, typically over 12 months of age
  4. or Not at all, which from 2018 is no longer an easy option in SA

In Australia, there is a strong push from society for all dogs to be desexed. I think an impartial reading of the pros and cons of desexing male dogs will lead most people to decide it’s also in their pet’s best interests. Female dogs, who get a comparatively greater lifespan advantage, present an even more compelling case. Although you are welcome to disagree, to me the only decision is when to do it.

Now have a look at this chart, in which I’ve summarised the results of three large studies from the University of California-Davis. Feel free to focus on the details but I’ll explain the main points later. These are the only big studies that compare outcomes at different desexing ages.

desex neuter problems
Age of Desexing vs Risk of Cruciate or Hip Problems

The Problem With The Evidence

Striking isn’t it? It’s clear that early desexing increases the risk of joint diseases in susceptible dogs. The theory is that hormones influence normal development of joints in some breeds. Once a joint is fully grown, hormones shouldn’t make much of a difference. But there’s still a small problem: body weight.

Not one of these observational studies is controlled for weight. They have simply taken data from a large clinic’s files without attempting to compare dogs of the same body condition score. The desexed groups are almost certainly heavier, and we know that weight is a significant risk factor for cranial cruciate ligament disease (CCLD) and hip dysplasia (HD). This is a quote from one study:

…the occurrence of HD and CCL in early-neutered dogs is a combined function of the effect of neutering on growth plates, as well as the increase in weight on the joints brought on by neutering. Reference 1

This doesn’t change the findings, which are statistically significant for most of the large differences. However, the question remains: if an owner can control their desexed dog’s weight, is there still a risk of joint problems? Only a future study comparing puppies of the same weight will answer that question. Until then (if ever!), it’s safest to follow these guidelines…

The Best Age To Desex A Dog

New recommendations to dog owners are:

  •  6 month desexing is still likely to be the best time for most dog breeds. This avoids a heat period in females and pre-empts most behaviour change in males.
  • Late desexing over 12 months is recommended for breeds prone to hip dysplasia and cruciate disease. It may also be helpful for anxious males and leaky females.
  • Early age desexing is important for rescue shelters to avoid overpopulation. There have been very few good studies looking at 8 week desexing but in my opinion it’s likely that any effects on joints will be magnified by taking desexing even earlier. Read here about the risks of incontinence associated with early age desexing.

For dog owners wanting to preserve female hormones through life, Ovary Sparing Spay is another alternative. Follow the link to learn more.

Many owners of male dogs who opt for late desexing find problem behaviours develop that can be quite hard to manage. To these owners, we say: go as far as you can but don’t feel guilty to give up early. Bad habits can be very hard to stop once they start, and the evidence isn’t ironclad. Any delay should help.

When Desexing Exemptions Will Apply

From July 2018, with compulsory 6-month desexing in South Australia, vets will need to register an exemption of some dogs until maturity. The period can be up to 18 months. It will apply to any breed shown to be at higher risk of hip dysplasia or cruciate disease, not just the ones featured in these studies. This is speaking to the evidence in the safest way and it’s only right. It’s then up to owners if they want to exercise this option.

Up to now, there’s not enough evidence to extend this advice to other breeds but you can rely on us to keep you informed as new facts emerge.

Further Reading

References & more studies showing health effects of desexing can be found at our page on Desexing Male Dogs. The three studies quoted here are:

  1. de la Riva, G. T., Hart, B. L., Farver, T. B., Oberbauer, A. M., Messam, L. L. M., Willits, N., & Hart, L. A. (2013). Neutering dogs: effects on joint disorders and cancers in golden retrievers. PloS one, 8(2), e55937. Full Article.
  2. Hart, B. L., Hart, L. A., Thigpen, A. P., & Willits, N. H. (2014). Long-term health effects of neutering dogs: comparison of Labrador Retrievers with Golden Retrievers. PloS one, 9(7), e102241. Full Article
  3. Hart, B. L., Hart, L. A., Thigpen, A. P., & Willits, N. H. (2016). Neutering of German Shepherd Dogs: associated joint disorders, cancers and urinary incontinence. Veterinary Medicine and Science. Full Article


By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on Facebook and Twitter. Like or follow our page or subscribe via email to read the latest.

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