10/16/2009 05:12 am ET Updated Nov 17, 2011

Does Spaying or Neutering Your Pet Really Improve Behavior?

As a veterinarian focused on animal behavior, I see all kinds of cases and field all kinds of questions. And unlike with regular medical problems, I know that the solution will, unfortunately, require some work and habit-changes on the part of the owners. So when I get a call or email asking, "Help! My male dog mounts every dog he meets and needs to mark every object in sight. What do I do?" I am almost overjoyed. While the owners could go through all kinds of elaborate training which would involve 100% supervision around all other dogs as well as objects the dog might urine mark, they could instead opt for the easy way out.

My first recommendation is "Get him neutered first and if the problem continues at all we can add a behavior modification plan." The solution is so simple that I actually rarely have to make this recommendation. My veterinary colleagues out in general practice can make the recommendation themselves.

But this case raises two questions: What other behavioral issues can neutering help address, and what is the rate of success?

In general, it would be expected that spaying or neutering most likely affects sexually dimorphic behaviors -- those that are more characteristic for one gender or the other. This is exactly what a 1997 study conducted by researchers at the University of California, Davis, Veterinary Medical Teaching Hospital found.

Misbehaving Males

This study evaluated how neutering adult male dogs affected such problem behaviors as urine marking in the house, mounting, roaming, fear of inanimate stimuli as well as aggression toward family members, strangers, household dogs, unfamiliar dogs and human territorial intruders.

Fifty-seven dogs that had exhibited one or more of these problems before being castrated at 2 to 7 years of age were included in the study. Follow-up revealed that castration was most effective at reducing:
• urine marking
• mounting
• roaming

The decrease was marked
• 90% decrease of these behaviors in 40% of the study dogs
• 50% decrease of the remaining 60% of the study dogs

No relationship existed between the effect of neutering and the age of the dog or duration of the problem behavior before castration.

Neutering also affected aggression toward canine and human family members but to a lesser extent and in fewer dogs 25% of the study dogs improving by more than 50%.

Surprisingly, 10% to 15% of dogs showed less aggression toward unfamiliar dogs and territorial intruders. Therefore, neutering can likely provide marked improvement for many dogs that are exhibiting marking, roaming or mounting behavior and may offer some improvement in dogs that are aggressive toward people and other dogs. Neutering seems to be less successful in reducing other types of aggression, although improvement is possible.

For Cats the Story May Be Even More Promising With cats the relationship between neutering and behavior is even stronger.

"Regarding behaviors that are more specific to male animals, castration seems to be more effective [in modifying behavior problems] in cats than in dogs," says Melissa Bain, DVM, assistant professor of clinical animal behavior at UC Davis.

A study conducted at UC Davis in the 1990s found that in 90% of male cats, castration greatly reduces or eliminates
• urine spraying
• roaming
• fighting with neighborhood males

Fifty percent of the cats showed a dramatic decrease (80% decrease) in the spraying, roaming and fighting decreased in the first week, although the remaining study cats demonstrated a more gradual decline.

For Females the Effects May be Different

The study results for male dogs and cats make the course of action clear. But for female dogs, the findings on the effects of spaying on behavior, at least of German Shepherd dogs bred for military work were unexpected.

According to Katherine Houpt, VMD, PhD, DACVB, former director of the Animal Behavior Clinic at Cornell University Hospital for Animals, spaying may actually contribute to behavioral problems. In a cooperative study with the Institute of Animal Medicine at Gyeongsang National University in Korea, Houpt and her colleagues found that ovariohysterectomy (spay) in healthy German Shepherds bred as working dogs led to increased reactivity.

In the study, 14 healthy German Shepherd bitches at the Korean Air Force Dog Training Center were studied. Half of the study dogs were spayed at 5 to 10 months of age, and the other half were intact. The dogs were littermates and were split equally into both groups to control for genetics. The dogs all lived in the same kennel environment and received similar handling. Their behavioral reactions were tested at 4 and 5 months after surgery.

Each dog was tested separately in its outdoor kennel while the rest of the dogs remained indoors. An unfamiliar human with an unknown dog walked within 1 meter of the target dog's kennel, and the kenneled German shepherd's response was recorded.

In each of four different recordings for each dog, researchers recorded
• barking or growling
• lunging
• jumping
• snapping
• head high
• ears forward
• eyes staring
• lips lifting or curling.

Dogs were scored as follows
• Score of 3 if they exhibited all 10 behaviors
• Score of 2 if they exhibited 7 of 10 behaviors
• Score of 1 if they exhibited 5 of 10 behaviors
• Score of 0 if they exhibited less than 4 of the behaviors

"Ideally we would have scored the dogs before they were spayed, too," says Houpt. "Regardless, the results were dramatic. Dogs that had been spayed were significantly more reactive, with most receiving scores of 2 and 3, whereas the unspayed littermates received reactivity scores of 1."

These scores decreased in two of the seven experimental dogs on repeat testing, but by the final testing phase, five of the seven dogs still received a score of 2 or higher.

Houpt, she emphasizes that military dogs would be expected to exhibit more aggressive behaviors and such behavior on command may be desirable. These dogs would not, however, be appropriate as pet or guide dogs or for pet therapy.

From my perspective the findings in this specific population of working dogs suggests the differences might not be as dramatic in dogs that weren't bred for high arousal and this type of dog should also be tested. Although the study was small, Houpt suggests that veterinarians should consider performing a hysterectomy rather than an ovariohysterectomy for preventive health reasons in aggressive pet female dogs.

Such decisions on whether to perform surgery or not should be made with all the facts in hand since failure to remove the ovaries can increase the incidence of mammary cancer. Female dogs spayed after their second heat have a 26% higher risk of developing mammary cancer than those spayed before their first heat.


1. Neilson JC, Eckstein RA, Hart BL. Effects of castration on problem behaviors in male dogs with reference to age and duration of behavior. JAVMA 1997;211(2):180-183.

2. Hart BL, Eckstein RA. The role of gonadal hormones in the occurrence of objectionable behaviours in dogs and cats. Appl Anim Behav Sci 1997;52:331-344.

3. Im HH, Yeon SC, Houpt KA, et al. Effects of ovariohysterectomy on reactivity in German shepherd dogs. Vet J 2006;172(1):154-159.

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