What is The Best Age to Spay/Neuter Your Dog?

best age to spay/neuter

We’ve all heard that spaying or neutering your pet can have many advantages. But, if you’re just hearing this for the first time – spaying/neutering decreases the risk of certain cancers developing and prevents territorial behaviour, among other benefits. Here, we’re going to talk about when it’s the best age to spay/neuter.

But what if I told you that the age when we spay/neuter (also known as gonadectomy) has a significant role in your pet’s long term health? 

So, it’s not just a matter of whether or not your pet is spayed/neutered, but we also have to consider WHEN this procedure is done and time it appropriately.

The Morris Animal Foundation is a granting agency based in the US that distributes grants to fund BIG research projects. One of the significant studies they’ve been funding is the Golden Retriever Lifetime Study for the past nine years. 

The purpose of this study was to characterize the associations between gonadectomy (aka “fixing” your pet) and two outcomes in a large prospective study of Golden Retrievers:

1) Overweight/Obesity 

2) Orthopedic Injuries

How did the study work?

The Golden Retriever Lifetime Study is the only study that has monitored the health status of a large group of Golden Retrievers and followed them as they age. Unfortunately, this particular breed has a high incidence of cancer, with nearly 60% of Golden Retrievers eventually succumbing to the disease. 

The study began with 3,044 puppies enrolled, and they were monitored annually. Some of these dogs were couch potatoes, while others were show dogs. This is important because it makes the data more reproducible and gives us budding scientists grounds to make inferences. If they were all couch potatoes, then the findings would be riddled with bias.

So, every year the pet owners and veterinarians meet to collect patient samples (e.g. blood, urine, feces, hair, nail clippings, etc.) and fill out a series of questionnaires. These questionnaires aren’t asking basic ‘Yes’ or ‘No’ questions, but instead, ask questions like:

Does your dog swim?

If Yes — Are they swimming in the ocean, lake, or river? What is the average water temperature?

Does your dog eat vegetables?

If Yes — What kind of vegetables? Bell peppers? Well, what colour of bell peppers?

They are about halfway through the study, and the researchers have made this data accessible to other researchers interested in answering “big picture” questions. For example, some have used it to look at bloodwork changes associated with raw food diets, while others have used it to look at the timing of spay/neuter and the associated health outcomes. For the purposes of this blog post, I’m going to focus on the latter. Time to find out what is the best age to spay/neuter!

Best age to spay/neuter – What are the results?

First, they divided the dogs into 3 groups based on the age of spay/neuter: 

  • < 6 months
  •  6-12 months
  •  > 12 months

The health outcomes they focused on following spay/neuter were associated with two factors:

  1. Overweight or Obesity.
  2. Orthopedic Injury (e.g. cruciate ligament tears).

The control groups consisted of dogs who were not spayed/neutered (remained intact).

After digging through the data, they found some interesting results! 

Once all other variables were equalized (eg. amount/type of exercise, body condition score, etc.), the study found that regardless of the timing for spay or neuter, your pet will have a higher incidence of obesity (independent of sex). 

That means that no matter what, if you spay/neuter your dog, they will have a higher chance of being overweight compared to a dog that still has their reproductive organs.

Obesity vs Age - best age to spay/neuter?
Kaplan-Meier failure plot for overweight/obesity as a function of age stratified by gonadectomy status in a cohort of Golden Retrievers.
Intact = dashed black line, gonadectomy = solid grey line. (Simpson et al. 2019)

Regarding orthopedic injury, dogs that were spay/neutered under six months of age DID have a higher incidence of orthopedic injury. Fortunately, the risk of injury decreased if spay/neuter was performed after six months and further decreased after 12 months of age.

Injury vs Age - best age to spay/neuter?
Cumulative counts of orthopedic injury cases by age and gonadectomy category.
The solid black line is intact dogs, the dashed black line shows dogs gonadectomized ≤ 6 months, the solid gray line shows dogs gonadectomized 6 – 12 months, and the dashed gray line show dogs gonadectomized > 12 months of age. (Simpson et al. 2019)

So why does spaying/neutering under six months of age increase the risk of orthopedic injury?

Some evidence suggests that dogs under six months of age may not have enough exposure to hormones like testosterone or estrogen, both of which are critical for the healthy development of bones, tendons, and ligaments.

Because large dog breeds reach maturity later, performing a gonadectomy too early may interfere with the proper development of the connective tissue since they would not be receiving the correct “dose of hormones.” This gives us a better understanding of when it is really the best age to spay/neuter.

Can we apply this to other breeds?

First, I want to stress that this study was looking at purebred Golden Retrievers specifically. This doesn’t mean these findings apply to every dog, BUT it does mean that we can make some educated predictions towards other breeds.. 

For example, smaller dog breeds reach puberty more quickly than larger breeds. This means the ideal time for a spay/neuter may differ, but it’s likely a good idea to wait until at least six months of age.

Also, this study was not looking at cats either, so the best age to spay/neuter may also vary among different species. 

Conclusion – Best Age to Spay/Neuter:

If you have a new puppy and plan to have them spayed/neutered, then be mindful that this procedure may make them more likely to gain weight. BUT choosing the best age to spay/neuter comes with many more advantages compared to disadvantages. With a little guidance, you can ask your vet about the Body Condition Score (BCS) and easily monitor your pet’s weight to keep them healthy.
Regardless of the dog breed, if you can wait to spay/neuter after 12 months of age, that is probably the best age to spay/neuter! Cruciate ligament tears can be extremely painful for your pet and very costly for the owners, so if we can avoid orthopedic disease altogether, then let’s do that!

If you have any specific questions related to your pet, consult your veterinarian to make sure you consider the individual needs of your pet when advising on significant health decisions.

If you missed out last post, check it out here. I show you what the real cost of studying abroad was for me after finishing my first year.

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Article Source: Age at gonadectomy and risk of overweight/obesity and orthopedic injury in a cohort of Golden Retrievers

Simpson M, Albright S, Wolfe B, Searfoss E, Street K, et al. (2019) Age at gonadectomy and risk of overweight/obesity and orthopedic injury in a cohort of Golden Retrievers. PLOS ONE 14(7): e0209131. https://doi.org/10.1371/journal.pone.0209131

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