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So, When Exactly Should You Spay or Neuter Your Dog?

The research is confusing — here are some guidelines.

by Dr. Alycia Washington, DVM
February 28, 2023
Young Man With Retriever Puppy
Vradiy Art / Stocksy

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Adopting a new puppy comes with a bunch of decisions about everything from toys to preventative care. Some of those decisions will involve if and when to pursue surgery for a spay or neuter. Spaying and neutering are very effective at preventing unwanted litters and can also carry certain health benefits. 

For a long time, it’s been normal to sterilize your pup before they turn nine months old. But is early sterilization the best for all dogs? What about large-breed dogs? Should you consider alternative methods of sterilization? Spoiler alert: It depends. Today is World Spay Day, so there’s no better time to get into the details.

Important Definitions

First, let’s get a little academic and go over some useful definitions. Sterilization is a procedure performed to permanently prevent dogs from reproducing. Gonads are sex organs — ovaries and testes — that release the sex hormones, such as estrogen and testosterone. 

Sterilization surgery in North America typically involves complete removal of the gonads. Female dogs undergo an ovariohysterectomy, commonly known as a spay, which is the surgical removal of both ovaries and the uterus. Male dogs undergo neutering, or surgical removal of the testicles.

Benefits Of Early Sterilization

Vets have long recommended performing spays or neuters early in life for population control and health benefits. There’s no doubt that sterilizing puppies before they are adopted ensures the puppies will not be used for breeding in the future. Many shelters adhere to this method, and it has done wonders for population control and the prevention of unwanted litters. 

When spayed before the first heat cycle, a female dog’s likelihood of developing mammary cancer is less than one percent, which is much lower than the risk for intact females. Vets have also recommended early sterilization to prevent diseases of the reproductive organs, such as pyometra (uterine infection), testicular cancer, and prostate disease. These procedures are often performed to prevent certain dangerous behaviors (roaming and aggression among them), as well as annoying habits such as mounting and urine marking. 

Possible Disadvantages of Early Sterilization

Recent studies have explored the relationship between early sterilization and specific health and behavioral concerns. Though previous studies suggested that early sterilization decreased aggression, more recent studies indicate that undesirable behaviors, such as aggression and fear, have a greater decrease over time in intact dogs than in sterilized dogs. It’s important to remember that proper training and socialization are also key in preventing and correcting unwanted behavior. 

A study published in 2013 evaluated the effects of early neutering — defined as occurring before one year of age — on Golden Retrievers. The results showed a lower incidence of lymphoma, hip dysplasia, and cruciate (knee) injury in male dogs who were neutered later in life. The results for female dogs were a little less straightforward. Female Golden Retrievers who were spayed early in life had a higher incidence of cruciate injuries, but females spayed later had a higher incidence of mast cell tumor and a cancer called hemangiosarcoma. 

Even with this information, it’s hard to make blanket recommendations about the best time to perform a spay or neuter. We also can’t assume that the results of this study can be applied to all breeds. 

Another concern with early sterilization is the increased likelihood of obesity. Multiple studies have shown that sterilized dogs have slower metabolisms and are more likely to become obese, which puts them at risk for a variety of health issues. We should note that not every sterilized dog is destined to become obese. Mindful feeding and regular exercise can prevent this in any dog. And leaving a dog intact does not mean they will remain svelte as they age. 

What About Large-Breed Dogs?

When discussing spaying and neutering, any dog who weighs more than 45 pounds is considered a large dog. Back to our anatomy lesson: The sex hormones that the gonads release are not only crucial for reproduction; they are also important for bone, muscle, and ligament development. When gonads are removed early in life, sex hormones are not present to help with proper development. 

Large-breed dogs take longer to reach maturity and grow into their adult weight and size. Giant breed dogs take even longer. So, the recommendation is to wait until these dogs reach sexual maturity, typically between 12 and 18 months of age. Some dogs don’t reach full maturity until they are two years old. Large breed dogs who are sterilized before they are 12 months old have an increased risk of developing orthopedic issues, such as hip dysplasia, elbow dysplasia, and cruciate injury. 

Are There Alternatives to Consider?

Though less common, there are alternative sterilization methods. For male dogs, a vet can perform a vasectomy, which involves cutting the spermatic cord so that sperm never leaves the testes. In female dogs, an ovarian-sparing spay removes the uterus while leaving the ovaries behind. 

Both of these methods prevent unwanted pregnancies and allow for longer exposure to sex hormones. Male dogs may still display mounting and urine-marking behavior, and female dogs will still go into heat, which could lead to complications if males attempt to mate with them. 

The March 2023 issue of the Journal of the American Veterinary Medical Association published the results of a survey looking at the health outcomes of dogs who underwent vasectomies and ovarian-sparing spays versus intact dogs and those who underwent traditional sterilization. The authors reported data from over 6,000 dogs. 

The results showed that dogs who underwent vasectomy or ovary-sparing spay had similar health outcomes to sexually intact dogs, with a lower risk of certain types of cancer and joint problems than traditionally sterilized dogs. These dogs also had similar behavior outcomes, with lower odds of aggression and fear behaviors as they aged.  

The main takeaway here is that dogs who underwent sterilization using techniques that allowed for longer exposure to sex hormones experienced similar health benefits to dogs who were left intact. 

Just the Cliffs Notes

Despite the potential benefits of sex hormones, dogs who undergo sterilization of any kind have longer lifespans than dogs who are left intact, regardless of size or breed. The age at which to pursue sterilization varies. 

For dogs under 45 pounds, sterilization between six and nine months of age is a good rule of thumb. For smaller female dogs, spaying before the first heat cycle greatly reduces the risk of mammary cancer later in life. For larger dogs, waiting until they reach maturity should decrease their risk of developing orthopedic issues and certain cancers. This typically means waiting until they are at least 12 months old. 

Alternative methods, such as ovarian-sparing spay and vasectomy have the benefit of preventing unwanted litters while allowing longer exposure to sex hormones, which can help reduce some orthopedic, health, and behavior issues. These procedures may become more popular over time.

So, what if you have a large-breed female dog? Should you prioritize preventing mammary cancer or orthopedic issues? What if your large-breed male dog is displaying testosterone-driven behaviors? Do you try to nip that in the bud and neuter him or wait until he grows? The answer is: Once again, it depends. Deciding when, or how, to sterilize your dog should be considered on a case-by-case basis. A conversation with your veterinarian about your dog’s size, breed, and general health concerns can help you choose an optimal time and method.  

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Dr. Alycia Washington, DVM

Alycia Washington, DVM, is a small animal emergency veterinarian based in North Carolina. She works as a relief veterinarian and provides services to numerous emergency and specialty hospitals. Dr. Washington is also a children’s book author and freelance writer with a focus on veterinary medicine. She has a special fondness for turtles, honey bees, and penguins — none of which she treats. In her free time, Dr. Washington enjoys travel, good food, and good enough coffee.