Behavioral Effects of Spay

HAHD_naughty dog


Many guardians of spayed dogs report significant behavior changes after their dog fully recovers from the spay surgery. These are generally guardians who chose to spay their best friend based upon one or more of the following reasons:

  1. the recommendation of their vet that spay would provide the best possible long term physical and psychological health for their dog
  2. the assertion of vets and behaviorists that their dog would behave better and become more manageable once spayed
  3. state law requiring that all dogs adopted from shelters/rescues must be spayed
  4. a contract with a breeder that requires spay at a prescribed time after purchase of the dog

Alternatively, many people acquire their female dog after she has been spayed and have no way of knowing how she behaved before being spayed. In either case, guardians may find their dog exhibiting unacceptable behavior, with no way to know the genesis of this behavior.

In the San Francisco Bay Area, almost every female dog we encounter in public places (e.g., dog parks, neighborhood walks) has been spayed. Additionally, almost every female dog is described by their guardian as “shy” (i.e., fearful, skittish, retreats from new people or situations), or “does not do well with people/dogs she does not know” (i.e., fearful and aggressive towards people or other dogs that scare her). From our perspective, the body language these dogs exhibit is not that of a confident, happy dog. In fact, this type of behavior in dogs seems unnatural and antithetical to the species. For example, who would ever expect to meet a skittish or unfriendly Golden Retriever?

Another common behavior issue guardians of fearful dogs share is reaction to environmental issues (e.g., thunder, loud noises, new places). The behavior their dogs exhibit ranges from mild anxiety to a full-blown “panic attack“. Separation anxiety is another undesirable behavior often exhibited in fearful dogs. Most guardians have no idea why their dog reacts as they do, and most are looking to do what they can to help their dogs. As a last resort, some guardians find themselves relinquishing these dogs back to a shelter because the dog’s behavior is not manageable for them. The San Francisco Society for the Prevention of Cruelty to Animals (SF SPCA) is the SF Bay Area’s largest and most progressive adoption agency, and their response to the widespread behavioral problems is to offer specialized “bravery classes for shy dogs“. However, they have one very significant caveat:

These classes are not suitable for dogs who have shown fear-based aggression or reactivity towards people or dogs, including lunging, snapping or having a history or incident of having bitten previously.” 

Can the evidence of significant canine behavior problems here in the SF Bay Area be tied to our high percentage of spayed or neutered dogs? Are the SF SPCA bravery classes being filled with behavior impaired students that the SF  SPCA helped to create through their aggressive spay/neuter campaign? Our study of the stress-response system in spayed/neutered dogs leads us to believe spay/neuter adversely affects the dog’s behavior and personality. In fact, the documented changes in the stress-response system would predict an increased level of fear and anxiety, which in some dogs can result in aggression.

When we examined the peer-reviewed studies on the topic of behavior after spay (see below), we find the studies confirm behavior is adversely impacted by spay/neuter and these changes are serious and potentially of epidemic proportions. So let’s see what the experts have to say…


The study “Non-reproductive Effects of Spaying and Neutering on Behavior in Dogs57 utilizes the “Canine Behavioral Assessment and Research Questionnaire (C-BARQ)15, the only peer-reviewed, reliable, standardized method for evaluating and screening dogs for the presence and severity of behavioral problems. The overarching conclusion of the study is:

For most behaviors, spaying is associated with worse behavior, contrary to conventional wisdom.

Specifically, the study found:

  • Spayed females are more aggressive towards people
  • Spayed females are more fearful and sensitive to touch/handling
  • Spayed females beg for and steal food more often
  • Spayed females are more aggressive towards other dogs
  • Spayed females are less energetic
  • Spayed females roll in and eat feces more often
  • Spayed females lick people and objects more often
  • Spayed females self-groom and bark excessively

Another study, “Behavioral and Physical Effects of Spaying and Neutering Domestic Dogs” 16, also utilizes C-BARQ. The study concludes:

“The overall trend seen in all these behavioral data was that the earlier the dog was neutered [or spayed], the more  negative the effect on the behavior.”

Specifically, the study found:

  • Spayed females are more aggressive
  • Spayed females are more fearful
  • Spayed females are more anxious
  • Spayed females are more difficult to train
  • Spayed females are less responsive to cues

The study also determined:

“The other three behavioral categories examined (miscellaneous behavior problems, attachment and attention seeking behavior, and separation-related behavior) showed some association with neutering [or spaying], but these differed more substantially depending on the age at which the dog was neutered [or spayed].”

Likewise, a study conducted in 2014, “Evaluation of the risk and age of onset of cancer and behavioral disorders in gonadectomized Vizslas”,109 concluded the younger the age at gonadectomy (spay or neuter), the earlier the mean age at diagnosis of a behavioral disorder, or fear of storms. It is clear to us that sterilization should not entail removing hormone producing glands, and this study’s conclusions seem to concur:

“Additional studies are needed on the biological effects of removing gonadal hormones and on methods to render dogs infertile that do not involve gonadectomy.”

The study, “Behavioral Assessment of child-directed canine aggression56, evaluated dogs who had already bitten a child. The study concludes:

“Historical evidence of fearful or anxious behavior in response to loud noises and thunderstorms or separation from the owner may signal a predisposition to biting in threatening situations related to anxiety or fear…

“…Fear-related aggression was the most common primary behavioral diagnosis in the dogs….Most dogs (93%)…both male and female were neutered [or spayed].  Although our data did not include age at neutering [or spaying] or whether the surgery occurred before or after the appearance of aggressive behavior, it is apparent that neutering [or spaying] does not guarantee a reduction of aggression in dogs.” 

The study, “Behavioural effects of ovario-hysterectomy [spaying] on bitches58, determined that:

“Spaying is accompanied by the risk of certain behavioural changes. There is a risk of increase in indiscriminate appetite. More importantly, there is a risk of increase in dominance aggression towards family members.”

The study, “Effects of ovariohysterectomy [spaying] on reactivity in German Shepherd Dogs59, concluded:

“The results revealed that reactivity was increased in the ovariohysterectomy dogs in comparison to the intact group.” (Note: in this study the term reactivity refers to barking, growling, snarling, lips lifting or curling, head up, ears forward, staring, widely opened eyes, lunging and/or jumping).

The aforementioned studies document the behavioral changes observed in spayed female dogs. However, they do not provide a persuasive explanation as to why or how spay creates the changes in behavior. Highly potent stressors (i.e. spay) early in life while the dog’s stress response system is still developing, can have detrimental effects on behavior and personality that are permanent.85 Please see our “Stress Response System” page for a more complete explanation. On our “Countering the Effects of Spay” page we will explore steps you can take to minimize spay’s effect on your dog’s ability to respond to stress.