Are There Behavior Changes When Dogs Are Spayed or Neutered?


According to two large sample investigations, there appear to be some surprising and undesirable behavior changes in dogs who are spayed or neutered.

If you believe many of the websites maintained by a number of humane societies and veterinary groups, spaying and neutering of dogs seems to be a solution for many behavioral problems. Some of these websites will even talk about “The Responsibility of Spaying and Neutering Dogs.” A sample of the statements which I found on these sites include:

  • “Spaying and neutering makes pets better, more affectionate companions.”
  • “Your dog should be spayed or neutered because sex hormones lead to unnecessary stress and aggression among dogs.”
  • “Unsterilized animals often exhibit more behavior and temperament problems than do those who have been spayed or neutered.”
  • “Many aggression problems may be avoided by early neutering.”
  • “Female dogs, like males, have an increased risk of aggression if left intact.”
  • “Male dogs display hormonally influenced aggression toward each other. Neutering eliminates much of this behavior.”

My interest in the question of possible behavior changes associated with spaying and neutering was rekindled when I had a pair of European visitors who were quite amazed at the number of dogs in North America who were spayed or neutered. According to them the idea that dog should be neutered in order to control certain behavior tendencies seems to be a uniquely North American notion. Apparently Europeans don’t buy into this idea. A Swedish study found that 99 percent of the dogs in their sample were not neutered. A Hungarian study showed 57 percent intact dogs, and a British survey found 46 percent intact dogs. In fact it is against the law to neuter dogs in Norway unless there is a specific medical reason.

The vast majority of the research done on spaying and neutering has focused on medical issues, such as the reduction of the incidence of certain cancers and hormonally related diseases and canine population control. However, since my interests focus on behavior these gave me little insight. Ultimately my search of the scientific literature uncovered two studies that appeared to be soundly designed, which used similar methodology, collected data from a large number of dogs, and directly addressed the issue of behavior changes as a result of spaying and neutering. To be honest I found that their results to be surprising and somewhat shocking.


The first of these studies was reported by Deborah Duffy and James Serpell, both at the School of Veterinary Medicine at the University of Pennsylvania. It was published in The Proceedings of the Third International Symposium on Nonsurgical Contraceptive Methods for Pet Population Control*. The second was a master’s thesis at Hunter College in New York which was submitted by Parvene Farhoody**. Both of these studies used the Canine Behavioral Assessment and Research Questionnaire (usually abbreviated as the C-BARQ) which was developed by Serpell and hisassociates. It is a long questionnaire, involving 101 items, and it has been shown to be a valid and reliable way of testing various aspects of canine aggression, fear and anxiety, attachment, excitability, energy level and other factors. It is based upon owners directly reporting the occurrence or non-occurrence of specific behaviors in their dogs in a structured way.

The number of dogs tested in these two studies is quite large. The Duffy and Serpell study tested two different samples, one of 1,552 dogs and the other of 3,593 dogs. The Farhoody study tested 10,839 dogs, thus the combined studies provide data on 15,984 dogs in total, making this an amazingly powerful data set.

There are too many measures for me to report in detail, however the main results were the same across all three samples of dogs. Given that one of the accepted behavioral reasons for spaying and neutering is to reduce aggression, the distressing results of these studies is that spayed and neutered dogs actually show considerably more aggression. Depending upon the specific form of aggression (owner directed, stranger directed etc.) the size of these effects is quite large, varying from a low of around a 20 percent increase to more than double the level of aggression in the neutered dogs as measured by the C-BARQ scoring scale. A further surprise was that these effects were similar for both males and females.

A different worrisome finding is that there was a roughly 31 percent increase in fearfulness for both sexes. This is accompanied by a 33 percent increase in touch sensitivity. The spayed and neutered dogs also showed a roughly 8 percent increase in excitability. About the only positive effect on behavior that seems to result from spaying and neutering is the roughly 68 percent decrease in urine marking.

I must admit that I was astonished and greatly bothered by the direction of these results. Farhoody summarizes her findings saying “Our data showed that the behavior of neutered dogs was significantly different from that of intact dogs in ways that contradict the prevailing view. Among the findings, neutered dogs were more aggressive, fearful, excitable, and less trainable than intact dogs.”

Considering the fact that one of the reasons recommended for spaying and neutering dogs is to correct a range of canine behavior problems, Duffy and Serpell’s conclusions expose this to be a myth when they say “For most behaviors, spaying/neutering was associated with worse behavior, contrary to conventional wisdom.”

Perhaps on this count the Europeans have it right…

引用:Psychology Today











これらの研究のうちの最初の研究は、ペンシルベニア大学の獣医学部のDeborah DuffyとJames Serpellによって報告されました。それは、ペット集団管理のための非外科的避妊法に関する第3回国際シンポジウム議事録*に掲載されました。 2番目は、ニューヨークのハンターカレッジでの修士論文で、Parvene Farhoody **によって提出されました。これらの研究の両方とも、セルパル(Serpell)および彼の関連者によって開発された犬の行動評価および調査アンケート(通常はC-BARQと略される)を使用した。それは101項目を含む長いアンケートであり、イヌの攻撃、恐怖や不安、愛着、興奮性、エネルギーレベルなどのさまざまな側面をテストする有効かつ信頼できる方法であることが示されています。それは構造化された方法で犬の特定の行動の発生または非発生を直接報告する所有者に基づいています。

これら2つの研究で試験した犬の数はかなり多い。 DuffyとSerpellの研究では、1,552匹の犬のうちの1匹と3,593匹の犬のうちの他の2つの異なる試料を試験した。ファーリディー(Farhoody)の研究では10,839匹の犬が検査されたため、合計15,984匹の犬に関するデータが得られ、驚くほど強力なデータセットとなった。

私が詳細に報告する手段は多すぎますが、主な結果は犬の3つのサンプルすべてで同じでした。 spayingとneuteringの受け入れられた行動上の理由の1つが侵略を減らすことであるとすれば、これらの研究の悲惨な結果は、去勢された去勢された犬が実際よりかなり侵略を示すということです。具体的な攻撃形態(所有者指向、見知らぬ指向など)に応じて、これらの効果の大きさはかなり大きく、約20%の低い値から、中和された犬の侵略のレベルの2倍以上まで様々であるC-BARQスコアリングスケール。さらに驚いたことに、これらの効果は男性と女性の両方で同様でした。



私は驚いて、これらの結果の方向性に大きく悩まされたことを認めなければなりません。 Farhoodyは、「私たちのデータは、去勢された犬の行動が、蔓延していない犬の行動と大きく相違していることを示している」との結果をまとめたもので、中和された犬はより積極的で恐ろしく興奮し、 犬。 “

DuffyとSerpellの結論は、「犬の去勢と去勢のために推奨される理由の1つが、イヌの行動の問題の範囲を修正することであるという事実を考慮して、DuffyとSerpellの結論は、「ほとんどの行動では、 従来の知恵に反して、