New study offers more fodder to spay/neuter discussion

The age at which large-breed dogs are spayed or neutered has become a hot topic with regard to obesity and nontraumatic orthopedic injuries, and a new study published July 17 in the journal PLOS ONE and based on data from the Morris Animal Foundation Golden Retriever Lifetime Study provides more information for veterinarians.

Researchers analyzed health data collected on more than 3,000 golden retrievers over the course of six years. This study was conducted by asking owners and veterinarians to complete yearly online questionnaires about the health and lifestyles of their dogs. Biological samples were collected from the dogs, and each dog had a physical examination every year.

Of those 3,000 dogs, about half had been spayed or neutered. These dogs were between 50% and 100% more likely to become overweight or obese when compared to retrievers who hadn’t been spayed or neutered, regardless of the dogs’ ages at the time of the surgeries.

NEWStat reached out to corresponding author Missy Simpson, DVM, PhD, an epidemiologist with the Morris Animal Foundation, to find out more about the study’s findings.

NEWStat: How big a risk factor is the age at which a dog is spayed or neutered?

Missy Simpson: Based on this study . . . spaying or neutering was associated with approximately two times increased risk of [being overweight or obese] compared to intact dogs, regardless of the age when it occurred. However, only the dogs who were gonadectomized prior to six months of age had increased risk for orthopedic injuries, even after adjusting for body condition; this association persisted, which suggests a role for reproductive hormones.

NEWStat: Is there an optimum time for spay or neuter that minimizes the different health risks?

MS: Our paper only looked at [being overweight/obesity] and orthopedic injuries: for these outcomes, our data suggest [that] waiting until a dog has been through puberty prior to [a] spay or neuter may reduce the risk for orthopedic injuries. It is very important to note that there are many health outcomes for which we do not know the association between spay/neuter and the risk for developing these conditions, and still other conditions where the risk is much higher when a pet is left intact (mammary tumors and testicular cancer, for example). The association between reproductive hormones and health is complex, and researchers are just starting to explore these questions systematically. Ultimately, the best recommendation is that a dog owner discuss their needs and goals with their veterinarian in order to make the best decision for their pet.

NEWStat: Your study focuses on golden retrievers. How likely is it that same risks apply to other breeds?

MS: We don’t know. This association may hold for other large-breed dogs, such as Labrador retrievers, but maybe not for toy dogs or giant-breed dogs. More research is needed to characterize these associations in other breeds.

NEWStat: Do smaller dogs run the same health risks as big dogs?

MS: Not typically. Orthopedic injuries are different in small- versus large-breed dogs. For example, if a Chihuahua presents for a hind leg lameness, it is far more likely to be a luxating patella than a torn cranial cruciate ligament. One important note is that being overweight or obese is an important concern for all dogs; the risk factors may differ between small- and large-breed dogs but the problem affects 65% of pet dogs overall, according to some studies.

NEWStat: What advice would you give veterinarians dealing with clients concerned with the possible health risks of spaying or neutering their dog?

MS: I would advise them to carefully consider the potential advantages and disadvantages of the timing for [a] spay/neuter in terms of the health of the dog and to make sure they clearly understand the client’s needs prior to making a recommendation. An experienced dog owner who brings in a puppy they want to train to become a competitive field-trial dog will get a [very] different recommendation than a client who is a first-time dog owner and just wants a nice family pet.  

NEWStat: In what ways does your study build on the landmark 2013 University of California, Davis, study that also found an elevated risk of cancers and joint disorders in Golden Retrievers?

MS: Even though there are some methodologic differences between these two studies, our results regarding orthopedic injuries are comparable. We have not looked at spay/neuter in relation to cancer yet. The similarities in our findings are important because they show that this association holds up in different populations of dogs: even though we were both studying golden retrievers, their study focused on dogs who presented to a referral hospital for care, and our study expands on their findings in that our cohort receives care at many different types of veterinary hospitals. In a follow-up study by the same team, they found that spayed and neutered Labrador retrievers [and golden retrievers] had [a] similar risk for joint injuries.

NEWStat: Any last thoughts?

MS: Everyone at Morris Animal Foundation thanks the dogs, owners, and veterinarians [who participated in the Golden Retriever Lifetime Study]. Their contributions are tremendous and this study is possible because of them.

Watch for the 2019 AAHA Canine Life Stage Guidelines, which will be published in the November/December issue of JAAHA.

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