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Determining the Best Age at Which to Spay or Neuter a Dog


When Should You Get Your Dog Spayed or Neutered?


This article is courtesy of AKC Canine Health Foundation.


By Margaret Root-Kustritz, DVM, PhD

University of Minnesota


In many parts of the world, due to cultural or economic prohibitions, bitches and dogs are not spayed or castrated unless they have reproductive tract disease. However, in the United States, virtually all bitches and dogs are rendered sterile by surgery at some point in their life. This better allows for reproduction control in animals no longer capable of or not considered desirable for breeding, and eliminates behaviors and physical changes related to presence of reproductive hormones that dog owners find objectionable. The surgeries most commonly performed are ovariohysterectomy (removal of the uterus and both ovaries), commonly called spaying, and castration (removal of both testes and the associated epididymes). Castration is commonly also called neutering, although that term most correctly can be used for surgery of either gender. Collectively, these surgeries can be referred to as gonadectomy, removal of the gonads or reproductive organs.


Removal of the ovaries eliminates secretion of the hormones estrogen and progesterone. Removal of the testes eliminates secretion of the hormone testosterone. Elimination of these hormones obviously leads to decreases in behaviors and physical changes associated with their secretion, such as heat behavior, swelling of the vulva, and estrous bleeding in bitches, and mounting and roaming in dogs. However, reproductive hormones have effects on other tissues in the body and removal of those hormones may inadvertently impact those systems negatively. Other, less obvious, hormone changes also occur after gonadectomy, including persistent elevation in hormones that control the secretion of estrogen, progesterone, and testosterone. Whether these other hormone changes affect other systems positively or negatively often is unclear.


This paper is a review of what has been demonstrated in the veterinary literature regarding effect of gonadectomy on the animal as a whole. This discussion does not address the societal problem of pet overpopulation. The author feels that animals with no owner or guardian should be spayed or castrated before adoption into a new home as one of many initiatives necessary to decrease the number of dogs euthanized in the United States annually. This discussion instead refers to dogs with responsible owners or guardians who maintain dogs as household pets, do not allow the animals to roam free, and provide the animals with regular veterinary care.


Evidence in this context is defined as credible information from peer-reviewed research. Studies involving more dogs are more valuable than reports of single cases. Multiple studies documenting a given phenomenon are more valuable than single papers. Incidence in this context is reported as a percent; this is the number of affected animals out of a random sample of 100. In veterinary medicine, any condition with an incidence greater than 1% is considered common. Readers are encouraged to carefully read all manuscripts of interest and to ask their veterinarian for clarification if needed. This paper is condensed from a more detailed, extensively referenced manuscript that may be available through your veterinarian (Root Kustritz MV. Determining the optimal age for gonadectomy of dogs and cats. Journal of the American Veterinary Medical Association 2007;231(11):1665-1675).


Why do we perform spay or castration at 6 months of age?


Most veterinarians in the United States recommend bitches and dogs be spayed or castrated between 6 and 9 months of age. This is not based in science; no one has performed a large-scale study in which bitches and dogs underwent gonadectomy at various ages and were tracked throughout life to determine what abnormalities developed relative to age at gonadectomy. It is thought that the current age recommendation arose after the World War II, when increasing affluence of American families first permitted them to treat animals as household pets and were, therefore, more interested in controlling manifestations of reproductive hormone secretion and very interested in making sure the animal survived surgery. Anesthetic and surgical techniques available at that time necessitated the animal be at least 6 months of age.


With current anesthetic agents, anesthetic monitoring equipment, and surgical techniques, it has been demonstrated in multiple studies that bitches and dogs can safely undergo gonadectomy when as young as 6 to 8 weeks of age. Surgical complication rate does not vary between groups undergoing surgery when very young compared to those undergoing surgery at the more traditional age, with overall postoperative complication rate reported as 6.1%. The vast majority of these post surgical complications are transient and do not require veterinary care.


Effects of gonadectomy on behavior


Behaviors that are most likely to be affected by gonadectomy are those that are sexually dimorphic (seen primarily in one gender). Examples of sexually dimorphic behaviors include flagging in bitches, and mounting and urine marking in dogs. Incidence of sexually dimorphic behaviors decreases after gonadectomy in bitches and dogs, with the decrease in incidence not correlated with length of time the animal has shown the behavior prior to gonadectomy.


Those behaviors that are not sexually dimorphic, including most forms of aggression, are not decreased in incidence by gonadectomy. One behavioral consequence of spaying that has been documented in several studies is an increase in reactivity towards humans with unfamiliar dogs and increased aggression toward family members. This may be hormonally related; there may also be a breed predisposition.


There is no evidence documenting a decline in trainability of working female or male dogs after spay or castration. One study documented an increase in development of senile behaviors after gonadectomy in male dogs. However, that study had very few dogs in the intact male group and other studies, looking directly at changes in brain tissue, are not supportive of that finding.


Comments  9

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  • Disputing a statement
    10/27/2013 03:04pm

    I simply HAVE to dispute a statement made in this article. Where in the world did you find data to support saying "However, in the United States, virtually all bitches and dogs are rendered sterile by surgery at some point in their life."??? That's preposterous!

  • 02/26/2014 01:05am

    Excellent observation. Here is the South, MOST dogs and cats are NOT EVER surgically altered; there are too many antiquated cultural beliefs and mistrust of real science and medicine as well as the fact a large or majority of pets live outdoors and the owners are not recognizing many or the behaviors, and some have a close identification with their pet's sexuality and their own. Regardless of the reason, I have no earthly idea where the author came up with the idea that most or virtually all pets in the USA are sterilized at some point. Were that the case, we would not be killing over 4 million adoptable pets each year for lack of available homes, and dog bites, HBC cases, dog on dog trauma, cat bites abscesses, FIV, and countless other daily avoidable negative interactions would be drastically reduced. And how many small and medium dogs can wait till 6 months of age to spay and STILL "beat" the first heat cycle?? Large breeds, maybe so, but most smaller ones will start a first estrus cycle at 5-6 months, and many veterinarians (and owners) hesitate to spay a female while she is in active estrus, anyway. This makes me wonder about the veracity of the rest of the article.

  • 02/27/2014 02:57pm

    Pat, when I received notice of your comment, it reminded me of this post. Since it was reprinted from another source, I figured the author likely never saw our comments and felt I just HAD to follow up. I tracked the doctor down at the U of MN and emailed her. She replied:
    "Thank you for bringing this to my attention. Research has been done since this was written showing variation in spay and castration rates across the country. It is less than I stated and more than was stated by those responding.
    Dr. Peggy Root"
    How's THAT for clearing things up statistically? hahaha

  • 12/23/2015 09:30pm

    Many dogs in the US are neutered due to misinformation from vets. The information on this site is untrue, old and scientifically ridiculous.

    All of he awful things that happen to humans if neutered happen to all mammals including dogs.

    There are many scientific articles which show how bad the effects of spay/neuter on dogs.

    As a breeder of 35 years and a Phd I recommend to my puppy buyers that they NOT spay or neuter their dogs but instead use low tech birth control:
    fences and leashes to kept their pets from conceiving unwanted littes.

    Dog population in the US is at 0%. .All the dogs in the shelters are those given up or let loose by people who acquired them without first considering how they were going to take of them. and they didn't get those dogs from careful and concerned breeders like me who are fanatic about where their puppies go and the conditions in the homes they go to. I never ship puppies.
    I do lengthy interviews with my owners and I have a condition on my contract that states if the family cannot keep the dog, it comes back to me. So if the unthinkable happens no one has to worry about who will take the dog.

    I started Poodle rescue in my area and it is now a flourishing organization.
    Most purebred breeds have rescue operations.

    All the shelters in the Northeast have to import dogs from the south or out of the country in order to have any for adoption.I haven't seen dogs running loose in my area for years. Most people here take care of their pets or are forced to give them up. While all is not perfect education seems to have made a big impact on the pet owning public.

    It is pet shops and puppy mills and the new scam rescue operations that are to blame for dogs that go to inappropriate owners. We, in poodle rescue.see these dogs all the time.Scam rescue operations which go south and pick up dogs from overloaded shelters and sell them up here out of trucks have grown in a multi million dollar business.

    As a well known dog breeder/trainer I get calls frequently from people who have paid $400 or more to get a sick dog or one who had developed behavioral problems due to poor training and/or socialization. These very expensive "free" dogs cause lots of problems to people who have been made to feel they need to "rescue" a dog rather than get one from a reputable breeder. These dogs, too wind up in our local shelters.

  • Where is evidence?
    10/01/2014 05:18pm

    Where is the evidence that spaying a dog reduces her risk of cancer? Everyone throws numbers around but no one provides a reference study. It's almost like an urban legend that gets perpetuated. I found this metastudy that looked at all other related studies and it says that when you remove the studies that had a bias, there is little if any correlation:


  • 12/24/2015 05:01am

    The National Golden Retriever Club did a huge study on cancer in their breed which the second largest in the US. Goldens get hemangiosarcoma at a rate much higher than any other breed so they did a survey which included
    thousands of dogs. It was published in a recognized scientific journal and was peer reviewed.

    I showed that spayed bitches get cancer at 5 times the rate of unspayed bitches and dogs get cancer at 2 1/2 times the rate. That is huge. There are also many small studies which demonstrate the same effect.

    Dogs also get hip dysplasia, blow out their ACLs and have other bone disorders when neutered. Lack of circulating hormones isa prime cause of
    bones degradation. Just think about what happens to us when we go thru menopause.
    Vet schools are centuries behind when it comes to birth control in animals.
    We know the answers because we use them on people. Micro surgery to tie tubes is routine in people because it is safer, less painful etc. and doesn't upset the natural balance of hormones in the body.
    Europe doesn't not spay dogs. And breeders like me don't either.

    Spaying takes away one third of your dog's life. Why do my dogs live to be
    on average 18 years old. I have had some live to 20. And my dogs almost never get sick. Even dogs who have very active lives in agility and hunting almost never get injured.

    There are literally hundreds of studies on this topic. I would recommend Dr Christine Zinc's article,"EARLY SPAY-NEUTER CONSIDERATIONS for theCANINE ATHLETE" to start. By the way she is the head of Pathology at John's Hopkins Hospital for 30 years and far more knowledgeable than most vets as she is a PhD as well as a DVM.

    AS PhD myself I did a lot of research on neutering dogs and the only conclusion I can come up with is that vets make statements that there is no proof for and that there is scientific proof for the opposite. After taking some of the classes that vets have to take to renew their licenses,
    I know that many do procedures just to make money. After reading many papers on on shots, I took a class given by Dr. Jean Dodds and Dr. Ron Schultz( the acknowledged authority on canine/feline immunity) They stated it is unnecessary to give repeated shots for canine viruses. Puppy shots don't need to be given again after 20 weeks. After the lecture many of the vets said that since shots were a substantial percentage of their profit, they would continue to give them. When was the last time your doctor advised you to have a polio or other childhood shot? Never. Because they last for life if it is a virus.
    Spaying and neutering dogs is not the best thing for your beloved pet. You wouldn't do it to your child. so why do it to your dog. There are new and better ways to keep your dogs (or cats) from irresponsible reproduction, some that you already do just to keep them safe.

  • Completely misleading!!
    04/11/2016 04:15am

    How in the world can you folks at this site state such rampant lies? It has been proven over and over again that desexing before growth plates close naturally is extremely detrimental to a dogs health and life span.

    Results of a study shared by the Golden Retriever Club of America and the Canine Health Foundation:
    1. A spay/neuter before puberity have a 2-5 times greater risk for hemangio sarcoma.
    2. Osteosarcoma is significantly more common is spayed/neutered dogs
    3. Mammory cancer is increases in females left intact. But, since most all mammory cancers are benign, I'll take my chances with mammory cancer to ward off hemangio or osteosarcoma any day of the week.
    4. Uninary incontinence is greatly increased with early spay
    5. Hypothyroidism in spay/neutered dogs increases 80% males and 60% in females
    6. Decreased lifespan in spayed and neutered dogs
    7. Over growth in male and females that have been desexed early.

  • Risks of castration
    10/03/2016 11:51pm

    The statement that castration can increase health risks for dogs is very misleading. The health risks are still very, very, small. Pet dogs should always by neutered or spayed to prevent backyard litters. Pet owners are, for the most part, not prepared for unplanned litters and the total responsibility that comes with them. Not to mention finding homes for up to 12 puppies.
    Male dogs that are not castrated will wander, fight, and be a danger to the community as they try to stake out a territory. As a dog trainer I advise all my clients to spay or neuter all dogs over 6 months old. The way this article is written could give owners an excuse to not spay or neuter as they may believe that it is dangerous for their dogs health.

  • 11/25/2016 05:27am

    I have had dogs for many years, and always get them spayed or neutered, Both my King Charles were long lived Bertie died of Heart Problems at 18 plus years and Indi a female died of Heart problems at 16 years, ( Heart decease is extremely common with King Charles Cavaliers) Sophie my small female Shitzu Maltese lived until 18 and a half, and died of old age.
    They were all healthy fit dogs.
    I now have 2 more King Charles Spaniels male and Female both have been Spade and neutered, and a 17 month Small Shitzu Maltese whom will be spade soon.
    I strongly believe my dogs were healthy and long lived because of it.
    I am English and have always had long lived Healthy Happy Dogs.

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