What Is the Controversy? Should Spaying and Neutering Be Delayed in Dogs for Behavioral Reasons?

Surgically altering dogs at 6–7 months of age has been the standard for a generation of veterinarians. Within the last decade, evidence has mounted medically and behaviorally to indicate that for some individuals, alteration at a young age may have deleterious effects. With that said, there is continuing evidence that spaying and neutering reduces relinquishment and various unruly and sexual behaviors. The purpose of this paper it not to persuade the reader to a specific conclusion, but to present representative studies to stimulate critical thinking and discussion.

Does Early Spaying Increase the Likelihood of Aggression and Fear in Female Dogs?

In a study by Kim, Yeon, Houpt, et al. 16 dogs between 5–10 months of age were randomly divided into spay and control groups. Their behavior was analyzed at 4 months and 5 months post op. Dogs who were spayed showed increased duration and deeper pitched territorial barking.

Duffy reported that in a survey of 1552 dog owners who were also members of pure bred dog breed clubs that owners of spayed dogs were significantly more likely to report aggression toward strangers, fear of people and sensitivity to touch. In addition, evidence was presented to support that spaying increases interdog aggression, but only in certain breeds. In another survey by the same author of 3593 dog owners who visited the author’s website to take the online survey, owners of spayed dogs were significantly more likely to complain of dog and owner directed fear and aggression; touch sensitivity and fear. Dogs who were spayed were calmer.

Does Keeping Male Dogs Intact Protect Them from Cognitive Dysfunction?

Hart found that in a group of 76 male dogs that intact male dogs were significantly less likely to suffer from age-related cognitive impairment. With dogs living well into their teens, more dogs will be at risk for cognitive impairment and leaving them intact may slow these changes at the end of life.

Does Neutering Male Dogs Make Them More Aggressive or Fearful?

In the study of 3593 dogs conducted by Duffy and mentioned above, owners of male dogs were significantly more likely to report dog and people directed aggression in neutered male dogs. Dogs who were neutered were less likely to urine mark and were calmer.

Farhoody and Zink reported significant differences in levels of aggression in intact dogs versus neutered dogs. Dogs who were neutered at less than 12 months had the highest levels of aggression with dogs neutered at 13–18 months being the closest to the intact dogs in aggression level. In addition, fear and anxiety was significantly higher in groups of dogs who were neutered when compared with intact dogs. In this study, the target of the aggression (e.g., human, dog) and the type of aggression (e.g., territorial, fear) was not identified making it difficult to draw very specific conclusions about the results.

However, in all three groups of neutered dogs, the level of aggression and fear was significantly higher than the intact dogs.

Hart and Eckstein found that urine marking, mounting and fighting with other dogs were all reduced significantly or eliminated by neutering in 50–60% of the dogs. There was no change in the behavior of dogs who had fear related aggression and territorial aggression. In a similar study by Maarschalkerweerd, Endenberg et al. 60% of dogs who were neutered showed a decrease in sexual behavior, inter-male aggression, roaming and marking. In 50% of the dogs who were neutered, owners reported that the dog was calmer.

Spain, Scarlett et al. found that dogs who were spayed and neutered prior to one year of age were more likely to exhibit noise phobias and sexual behaviors while they were less likely to exhibit separation anxiety, inappropriate elimination when frightened and to be relinquished.

In conclusion, we can’t make a blanket statement about what is right for all patients. Behavior disorders are not of singular etiologies. Clearly spaying and neutering at any age has benefits behaviorally, eliminating unwanted behaviors that increase the likelihood of relinquishment. It is essential when looking at behavioral outcome studies to consider that environmental factors and genetic factors strongly influence behavior patterns. In addition with the exception of the Yeon study mentioned above, the studies here are retrospective or survey studies relying on owner report. Most studies listed here used the same questionnaire. As with everything in veterinary medicine, all studies should be looked at critically. Many would say that there is, however, enough doubt that at a risk-benefit analysis should be done for each patient when considering when to recommend spaying or neutering.