Behavioral Effects of Spay

HAHD_naughty dogThe 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.