Health and Behavior Considerations of Spay/Neuter Surgery

Early Spay/Neuter Considerations

Your primary source of guidance and consideration on desexing (spaying or neutering) your dog should be your dog’s veterinarian. This is a complex issue that requires more study. We make the best decisions we can based on current evidence. Our goal is to provide useful information to support you and your vet in coming to the best decision for your dog and your family. If you think your dog may have a behavior issue that would be positively or negatively influenced by desexing, I encourage you to discuss this with your vet.

Desexing involves removing some of your dog’s sex organs, which affects hormone levels that impact health and behavior. In males, the primary hormone affected is testosterone. In females, the primary hormones affected are estrogen and progesterone. Here are some of the pros and cons of early spay/neuter.

Health Benefits of Early Spay/Neuter

• The surgery is easier for the vet and faster and easier to recover from for the puppy. Simply put, there is less tissue involved when a puppy is small, especially for male puppies, and this can make the surgery less complicated and potentially painful.
• For shelter dogs or other homeless/unowned dogs, desexing at a young age guarantees the dog will not produce unwanted puppies.
• In situations where owners may be unlikely or unable to spay/neuter later on (where finances are unreliable or when regular/ongoing vet care is unreliable), vets may prefer to schedule the surgery early on just to make sure it happens.

Health Risks of Early Spay/Neuter

• Cancer. Evidence of higher rates of several types cancers among dogs that were desexed at a young age is mounting. These cancers include hemangiosarcoma, lymphoma, osteosarcoma (bone cancer), and mast cell tumors. Cancer is a serious health issue for all dogs. In certain breeds, these cancers are even more likely.
• Musculoskeletal issues, including abnormal bone growth and development. Canine cruciate ligament ruptures are more likely in dogs desexed at a young age, and hip dysplasia may be more likely or more severe in dogs neutered early. Dr. Karen Becker writes, “Studies … concluded dogs spayed or neutered under one year of age grew significantly taller than non-sterilized dogs or those dogs spayed or neutered after puberty. The earlier the spay or neuter procedure, the taller the dog. … [I]t appears that the removal of estrogen-producing organs in immature dogs – both females and males – can cause growth plates to remain open. These animals continue to grow and wind up with abnormal growth patterns and bone structure. This results in irregular body proportions, possible cartilage issues, and joint conformation issues.”
• Hypothyroidism or other endocrine issues. A dog’s hormones affect each other. When some of the hormones are removed at an early age, this may affect the other hormones on an ongoing basis. Some vets believe that endocrine diseases such as hypothyroidism and atypical Cushing’s syndrome may be more likely in dogs that are desexed early.
• Additional health risks are explained in the links provided at the end of this handout, including some breed-specific risks (e.g., Golden retrievers, Labrador retrievers, etc.)

Articles and Links on Health Considerations of Spay/Neuter

• Study on long-term health effects of neutering Golden and Labrador retrievers 
• Dr. Karen Becker on why she’s had a “change of heart” on spaying/neutering
• JAVMA (Journal of American Veterinary Medical Association) on pros and cons of spay/neuter

Behavioral Effects of Early Spay/Neuter

There is even less reliable evidence on the behavioral effects of desexing dogs. You may notice that some of the assertions in the links for behavioral considerations below contradict each other. Some long-standing assertions about the behavioral benefits of desexing are now up in the air. Still, here is my best effort at presenting what we believe, currently, about the behavioral effects of spay/neuter:

• A recent study has found that excitability, aggression, and anxiety were higher among spayed/neutered dogs of both sexes
• In males, sex-specific behaviors (marking, roaming, mounting) are likely to be reduced by neutering
• In both sexes, food drive, overeating, and obesity are more likely after desexing
• In the past, it was believed that neutering males made some types of aggression less likely. More recent studies indicate that aggression in neutered males is more likely, regardless of when they are neutered
• In females, studies indicate that spaying makes aggression more likely. Spaying before the age of 12 months markedly increases likelihood of aggression.
• In male dogs, fear- and anxiety-related behavior problems (such as canine compulsive disorder) are higher in neutered dogs than intact dogs. I have not found data on female dogs and anxiety/fear. Since aggression in both male and female dogs typically has a large fear component, this is also an important consideration with regard to aggression.

What Does This All Mean for My Dog?

Every situation is unique. It is important to discuss your concerns with your veterinarian. With my clients, I am happy to discuss the pros and cons of their particular dog.

Generally speaking (there are many variables), I recommend spay/neuter in these cases:

• Male dogs with sex-linked behavior problems (mounting/humping, roaming, or marking)
• Female dogs whose heat cycles are causing a significant management or training challenge to the owners
• Male dogs with conflict-control aggression (“dominance aggression”). This is rare. The overwhelming majority of aggressive dogs have fear-based aggression.
• Male dogs that are highly distracted, have low interest in food, and training around distraction using food is a high priority for the owner (such as a future service dog)

Generally speaking (there are many variables), I discourage spay/neuter in these cases:

• A male dog with a tendency toward anxiety, fear, skittishness, or compulsivity
• Any dog under 18 months of age – especially large-breed dogs, dogs prone to certain cancers affected by early desexing, or dogs prone to musculoskeletal issues. I encourage waiting to neuter until the growth plates close.
• Dogs under 24 months of age if they are giant or large-breed dogs, have an intended sports career or intended as mobility service dogs. I encourage waiting to neuter until the growth plates close.

Articles and Links on Behavior Considerations of Spay/Neuter

• 2010 study (PDF) by Farhoody and Zink on Behavioral and Physical Effects of Spaying and Neutering Domestic Dogs
• Behavioral Effects of Spaying and Neutering in Domestic Dogs
• The Effects of Spaying and Neutering on Canine Behavior
• Chirag Patel on Neutering: What’s behavior got to do with it?
• Dr. Sophia Yin: Can spaying make dog behavior worse?

Owner-friendly overviews of pros and cons of spay/neuter

• Spaying Your Female Dog
• Neutering Your Male Dog