Behavioral Effects of Neuter

HAHD_mugshot-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, neutering is associated with worse behavior, contrary to conventional wisdom.

Specifically, the study determined:

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

Another study, “Behavioral and Physical Effects of Spaying and Neutering Domestic Dogs16, also utilizes C-BARQ. The study concludes:

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

Specifically, the study found:

  • Neutered males are significantly more aggressive regardless of age of neuter
  • Neutered males are significantly more fearful regardless of age of neuter
  • Neutered males are significantly more anxious regardless of age of neuter
  • Neutered males are more difficult to train
  • Neutered males are less responsive to cues

Additionally, the study noted:

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

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 aforementioned studies document the behavioral changes observed in neutered male dogs. However, they do not provide a persuasive explanation as to why or how neuter creates the changes in behavior. Highly potent stressors (i.e. neuter) 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 Neuter” page we will explore steps you can take to minimize neuter’s effect on your dog’s endocrine system.

In our own experience, supplementation with testosterone actually improved Billy’s fears. Billy never exhibited fear aggression, but rather fear caused him to retreat from perceived danger. Testosterone supplementation allowed Billy to be more comfortable with new people, dogs and experiences, and in fact he began to enjoy new things! Testosterone also allowed Billy to experience loud noises, fireworks, thunder, etc. without panicking and in fact with little or no anxiety. Understanding how neuter affects the developing stress response system explains why hormone balancing for Billy changed his behavior so dramatically.