When To Spay or Neuter? It’s Complicated

There’s a lot of controversy, confusion, and even conflicting evidence about when it’s best to spay or neuter your dog. Thankfully, we’ve at least evolved enough to ask what’s best for the health and well being of the animal, rather than just what’s most convenient for the humans involved. But given all the conflicting, sometimes erroneous, information out there, let’s try to lay out some of the pros and cons as simply as possible. 

The main concerns about early neutering come down to the dog’s joint health, musculoskeletal development, and risk of cancers. Neutering too early can slow down both the closure of growth plates and the growth of bones, which can, in turn, cause hip and elbow dysplasia, knee tears and ruptures, and even patella luxation, in which the kneecap pops out (ouch). 

Most dogs finish growing at around 24 months of age. So the same logic that suggests waiting until your dog is 14 months to start long distance running (for more on this, click here) might also indicate waiting until a dog is older before performing an operation that alters its hormonal and physiological growth. 

Early neutering may also slightly increase the risk for several types of cancer including lymphoma, mast cell tumors, bone cancers, and hemangiosarcoma, in which the blood vessels rupture and cause the dog to bleed to death. On the flip side, neutering does help prevent certain other cancers such as testicular, ovarian, and breast. But spay/neuter surgery would prevent these cancers regardless of the age of the dog at the time of the surgery. 

Large dogs who are neutered before six months of age have a higher likelihood of experiencing joint and bone issues while small dogs, neutered at any age, show few musculoskeletal abnormalities. Regarding cancer, only two small breeds (Boston Terriers and Cocker Spaniels) showed an increased risk of cancer when neutered prior to six months of age. But for reasons that are still unclear, Golden Retrievers, Labradors, and Shepherds showed a higher risk for certain cancers when neutered young. 

While this may seem ominous to those of us with dogs who were neutered early, please don’t fret. Not only does more research remain to be done, but the overall consensus of studies to date is that, while joint and bone growth should be considered when determining reproductive surgery age, the increased risk of cancers is minimal for dogs of all ages, sizes, and breeds (for a deeper dive into impacts of neutering on 35 dog breeds, click here or here for the results in chart form).

But what about behavior? Does neutering harm or help it? You’ve probably heard that neutering will allay a male’s aggressive tendencies due to the reduction of testosterone in the system. But some experts argue that the reduction in testosterone reduces the dog’s sexually driven behaviors to roam, claim territory, and fight for a female, but it does not necessarily reduce overall aggression. Similarly, another research study found that early neutering actually increased fear, excitability, and aggression in dogs (the same study also found that attention span and responsiveness to cues was impaired in dogs that were neutered before six months of age). 

In my own experience as a trainer, I’ve found that neutering does seem to reduce guarding, marking, and territorial behaviors, as well as a dog’s apparent (usually misguided) belief that he is stronger than all other dogs. I’ve also noticed that other dogs are less reactive to a neutered dog who is no longer putting out those stinky sex pheromones, which obviously helps with behavior all around. 

In short, the age at which a dog should be neutered or spayed varies based on breed, sex, environmental factors, genetics, and client preference (click here for a good summary). 

Neuter young and your dog may experience a slightly greater risk of joint/bone problems or certain cancers. However, many dogs who are neutered young have no problems at all. As to behavior, good training that relies on socialization and science-based, force-free methods can help all dogs become socially skilled, regardless of their reproductive status.

Bottom line: each dog is an individual with its own unique DNA, which may predispose it to certain ailments regardless of whether or when it’s spayed or neutered. So consult with your vet on the best age for your own pup, given all the many factors in play. Then make the decision that’s best for your family, your lifestyle, and, of course, your dog.