Can Spaying Lead to Bad Behavior?

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By Sophia Yin, DVM, MS March 5, 2009

On an episode of “It's Me or the Dog,” a show on Animal Planet, British dog trainer Victoria Stilwell tackled the problem of a bull terrier that exhibited mounting behavior. The first solution was to send the dog for a time-out when he mounted. However, the mounting was so severe that the trainer finally recommended neutering, which solved the problem. 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 Dogs

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

The decrease was marked.

These behaviors decreased by 90% in 40% of the study dogs
And decreased by 50% in 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, with 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.

spay leads to worse behavior

Misbehaving Male Cats

For cats, the story may be even more promising. “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 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 were unexpected.

According to Katherine Houpt, VMD, PhD, DACVB, 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 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. 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.

“Of course, theoretically, the real cure would be to spay and then give progestins,” Houpt added. “This was done years ago and worked well until the dogs became diabetic and had increased appetites. Sometimes you could cure the territorial aggression, but then they became food-aggressive. It is not something we recommend now.”


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.

The original version of this article originally appeared in Veterinary Forum in November 2008.

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13 responses to “Can Spaying Lead to Bad Behavior?

  1. I just want to share the experience we have of castrating our then two-year old male dog, and spaying our then two-year old female dog: The results for the male dog is less urine marking inside, but no less aggression towards unfamiliar dogs and humans (mounting was never a problem). The results for the female dog is far more aggression towards unfamilar dogs. There were also side effects, like more fur (thicker coat) and more shedding, bigger apetite (constant battle to keep the weight down) and periodic urine leakage. So I do not think I will neuter any of my future dogs, if not for medical reasons.. In Norway it is against the law to spay or neuter dogs without medical reason, and that might well be a good thing…

  2. Thanks Therese:
    In U.S., where spays are performed regularly the urine leakage is not common but it can occur later in the dog’s life. Spayed/neutered animals may have a change in appetite but it’s usually not an issue if you measure your dog’s food. It is a problem if you keep the pet’s food out all the time. But this type of feeding is detrimental in terms of enrichment and training and in terms of being able to monitor your pet’s appetite well. Vets usually recommend feeding a measured amount of food. Behaviorists recommend the food be place in some type of toy or used for training.
    Regarding the aggression, there are some confounding factors. Dogs who are fearful (most dogs that are aggressive are aggressive due to fear) would be expected to get worse after any traumatic episode. e.g. for dogs fearful of people, the visit/surgery at the vet may be considered traumatic because it is a situation they fear. So the increase in aggression people say they see after a surgery if often due to the fact that dog had a traumatic event rather than the spay.
    In U.S. the reason to spay/ neuter is that many animals get pyometra and mammary tumors otherwise. being intact female is a huge risk factor. And in U.S. because of the size, government has less ability to prevent breeding. As a result we have a huge overpopulation problem. But if one has a female dog who is already showing signs of aggression, then may be a hysterectomy is best. (And behavior modification!).

  3. Thank you Dr. Yin! What wonderful knowledge and insight you have!! Personally, I was doubtful about the correlations between wolves and domestic dogs that have been taught throughout the years. Your articles on dominance were very informative and revealing. And your studies and views seem to make a lot more sense than those other teachings from years ago. Your website has been very enlightening for me!! I share my life with 4 dogs, and have read several different books on training throughout the years! I’m always looking to broaden my knowledge and understanding of dogs and you have helped me out immensly! Thank you…and I look forward to receiving your breaking news and other updated material.


    Anni Sautner

  4. Hi
    My Employer owned two reindeer which he uses at his christmas tree farm in NC. Unfortunately, one of the reindeer passed away, and restrictions prevent our obtaining another. What animals would be compatable to live with the reindeer? I have heard that it would most likely be goats.
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  5. I’d love to see more information on the relationship between food, caloric needs after spay/neuter, and the dogs actual hunger or interest in food. My experience with a male dog neutered at 7 years of age was that his caloric needs to maintain weight dropped dramatically, but his hunger did not decrease. He began counter surfing for food, attempting to steal food from the other dogs, and in general he appeared grumpy and….hungry. In my opinion he become somewhat more aggressive, which I attribute to chronic hunger. I know when I’m on a diet I’m grumpy and snappish too, and I hate to subject a dog to constant hunger if that is a common result of spay/neuter.
    I’m currently trying to decide for or against spaying an 8 year old bitch. She’s already a rather hungry dog and an easy keeper. I’m very concerned that cutting her calories significantly is going to make her grumpy, which would likely lead to more problems with the other female dog in my house. I’m having trouble coming up with a reason to spay at this age except for my convenience.

  6. My shihtzu bitch was a lovely sweet natured girl until she was spayed never again will i neuter another she’s turned really horrible and aggressive and i really don’t know what to do she’s 18 months old now

  7. We have a 7 year old Female Rottweiler who has become aggressive towards our 1 yr old male Goldendoodle since she was spayed a week ago. How can we effectively stop this behavior without making it worse? The male is very submissive, never challenges her and after her shows of aggression completely avoids her. Is this due to her being spayed or is there something else going on that we are missing?

  8. We have a 7 year old female Rottweiler that was recently spayed who has become aggressive towards our 1 yr old male Goldendoodle. He is very submissive, never challenges her and after her shows of aggression completely avoids her. How can we effectively stop,this behavior without making it worse? Is this due to her being spayed (surgery was a week ago) or is there something else we are missing? We need to again restore relaxation and happiness in our home and ensure the dogs are comfortable with each other and she does not see him as a threat to her status. PLEASE HELP!

  9. Dear dr. Yin, i have a 19 month female dog. She is nice to everyone except my mom. My mom feeds her and basically she stays all day night at home with my mom. But sometimes she attacks my mom suddenly. She bit my mom twice. Especially, when my mom changes clothes to go outside or she goes home from outside, she aggressively barks and tries to attack my mom. I spayed her lately, she seems more calming but yesterday when my mom changes clothes, she was aggressive again. Please help me.

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