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At What Age Should I Spay Or Neuter My Dog or Cat ?

What Are The Advantages And Disadvantages Of Neutering My Pet ?

Revisiting The Idea Of Early-Age Neutering

Ron Hines DVM PhD.................................................................click me for a larger image



Its now 2018. Even more studies now confirm that neutering pets before one year of age (or their first heat cycle) can have very serious negative affects on their health later in life. You can read those studies here, here, here , here and here.

Old habits die hard. Do your best to spread the word









I have been surgically altering dogs and cats for many years. Over the years, my thoughts on this subject have changed. During most of my career, it was a given that all pets should be neutered. We accepted that without question. Most veterinarians still do.

But with time, I began to realize that many of the reasons given for this surgery were not based on science or the long-term welfare of individual, beloved pets. Years of observing pets in my practice led me realize that many of the problems I was treating could be traced back to the pets being surgically neutered or neutered too young.


Why Do Veterinarians Spay Female Pets And Neuter The Males ?

In rural communities, veterinarians did not frequently spay dogs and cats until the late 1940s. But in urban settings, owners found the heat cycles of their female pets and the puppies and kittens that resulted were a major inconvenience.
When Pentobarbital sodium anesthetic became available in 1930, it made veterinarians more confident about entering the abdomen of dogs and cats to perform serious surgery. Soon, at owner’s requests, it became common for them to remove the pet’s ovaries and uterus to prevent heat cycles, puppies and kittens.

But it was not until the rise of the humane movement in the 1950s that public interest focused on spaying female dogs and cats and neutering male pets as a mater of "civic duty". This began in New York City in the late 1950s at the ASPCA hospital. Their staff saw sterilization as a solution for the ever-increasing problem of more adoptable pets than potential new pet owners.

By 1964, they were offering free sterilization surgeries to financially hard-pressed owners. During this same period, humane groups throughout the United States began to incorporate polices that prohibited the adoption of un-neutered orphan animals. In 1975, the Maryland SPCA began performing spay-neuter surgery on immature kittens and puppies. This was to comply with their bylaw changes that required that all adoptable pets – regardless of age - be neutered. I was their veterinarian at the time. In 1981, I worked with Amy Freeman Lee to set up a similar program in San Antonio, Texas.

Faced with the grim task of euthanizing unwanted pets, I hope you can see how kind, well-meaning people might pursue such a policy. We were inundated with puppies and kittens, many of which were the result of accidental breeding of young adult animals on their first heat cycle. Our understandable thought was: “if every dog was neutered before it could give birth, we wouldn’t have to deal with the sadness of so many homeless strays”.

Shelters across the US began to employ full-time veterinarians to do these early spays; these veterinarians organized a Society , founded a Journal that would accept their publications (ref1, ref2) , and became a potent force in the veterinary community. By 1993, the AVMA had given its blessing to early spay/neuter.(ref)

Few veterinarians in private practice questioned these policies. In the American Veterinary Medical Association, non-practicing veterinarians have a disproportionately large influence on policy decisions. These decisions eventually influence everything from State and Federal law to widely held public conceptions and misconceptions.

Veterinarians in private practice are fragmented. We do not have the time or resources to attend the many conventions and symposia at which these policy decisions are made and many veterinarians would find these conventions dry and tedious – like a day watching CSPAN.

But there was another important factor - many veterinarians preferred neutering immature pets. There are a number of good, practical reasons for this:

The reproductive tract of juvenile pets is less vascular. That is, it is less likely to undergo excessive bleeding. In younger pets, no internal sutures are needed at all.

Juvenile pets are less obese. Abdominal fat complicates the surgery and the suturing process.

Juvenile pets heal very rapidly. Within 5 days of surgery, their spay incision is hardly noticeable.

Neutering pets young avoids the complication of owners bring their female pets in when they are in heat or already pregnant. Bitches in heat bleed excessively during surgery.

Juvenile pets are smaller, easier to handle and less exhaustive of supplies and labor. One tires after a day of hoisting 60 lb dogs onto the operating table.

At that time, veterinarians knew very little of the negative implications of juvenile neutering and thought "if we neutered pets young, so much the better for everybody".

But Did Any Of These Reasons Address The Long-term Health Of My Pet ?

Yes. Some did.

Through observation, veterinarians knew that spayed female dogs were less likely to develop breast tumors later in life.

Spayed pets were also prevented from developing uterine tube infections (pyometra) because their reproductive tract had been removed. (ref)

They also knew that neutered male dogs and cats were less likely to roam and that neutered male cats were much less likely to spray urine around the house or get into cat fights.

Are There Negative Health Effects of Spay/Neuter ?

Yes. There are many. I will get to them later.

Do The Negative Effects For My Pet Outweigh The Positive Effects Or Vice Versa ?

No one can answer that question for you. It is convenient to make blanket, all-inclusive statements on what decisions are right or wrong. But that is a foolish approach – at least when it comes to neutering your pet. What you should do is consider the facts. There is plenty of information out there and you don’t need to be a scientist or a veterinarian to understand it.

What Are The Benefits Of Spaying or Neutering My Pet ?

Less Mammary Gland Tumors

Veterinarians know that the breast lumps we see in older female dogs occur most commonly in the pets that have not been spayed, or the ones that were spayed after they had had more than two heat periods. During heat (estrus), certain hormone levels in your pet spike. (ref) The more spikes or heat cycles your dog experiences, the more likely these tumors are to occur. That said, the risks are not high. One study found that the lifetime risk of mammary gland tumors eventually causing the death of a dog was only ~ 6% (6 deaths per 10,000 dog years). (ref) In contrast the risk of a 45 year old woman developing cardiovascular disease is 55.6%. (ref)

The most common ones in dogs are mixed mammary tumors. (ref) These hard nodules and lumps tend to grow slowly as the pet ages. Although some of them have the potential to become malignant and life-threatening, the majority never do. Most are quite easy for your veterinarian to successfully remove.

Mammary gland tumors are rarer in female cats. As in dogs, spaying reduces their frequency. (ref) But unlike dog, when they do occur they are considerably more serious and need immediate veterinary attention.

No Pyometra

Pyometra is a condition where pus forms in your pet’s womb due to repeated hormonal over-stimulation of your female pet’s reproductive tract. (ref) Estimates of its incidence in older, unspayed, female dogs range from 1-15%. When it occurs, it can be treated successful by surgically removing the womb.

No Estrus Mess

Most unspayed female dogs are messy during the early part of their heat cycles (proestrus). This occurs every 5-10 months and last 6-11 days. During their estrus period, female dogs often urinate more frequently, lick their genitals, drip bloody fluids and crave attention. There presence will attract the stubborn amorous attention of un-neutered male dogs running loose in your neighborhood.

Unspayed female cats cycle more frequently. During their estrus cycle they become more demanding of attention, with frequent rubbing, purring, rolling and meowing. It is not normal for them to bleed. These periods last 4-10 days.

No Humping Dogs

Many of my clients are embarrassed when they find their male dog mounting another dog - or them. Unspayed female dogs occasionally do this as well. Neutering male dogs usually ends this behavior. Male dogs are very persistent in getting to female dogs that are in heat. If a loose female dog in heat passes your yard, it is not uncommon for your pet to dig out or escape to join it.

Less Wandering

Loose, neutered dogs tend to stay closer to home and get into less trouble around the neighborhood. The same goes for neutered cats. If you let your pets run loose and unattended, they will live longer before they are killed by cars than they would have if you had not neutered them. But why are your pets out-and-about unattended?

Less Aggression

Dogs with problem aggression tend to gain weight and become more phlegmatic, and calm when they are neutered. However, because aggression has many causes, neutering does not always end the problem.

No Urine Spray

Un-neutered male cats and female cats fighting for territory tend to spray urine. This behavior usually ceases in male cats once they have been neutered.

Testicular Cancer

The rate of development of testicular tumors in normal old dogs is thought to be about 7%. That means that of 100 un-neutered male dogs, 7 will develop these tumors. These tumors, when they occur in older pets, can usually be removed very successfully.

Dogs whose testicle(s) do not descend from their abdomens have a considerably higher rate of a particular testicular tumor later in life. (ref1, ref2)In these dogs, the solution is to neuter them once they are mature.

Testicular tumors are very rare in cats. (ref)

Prostate Disorders

Prostate cancer is quite rare in dogs and cats. But prostate enlargement is a normal sign of aging in un-neutered male dogs – as it is in men. (ref)

In male dogs, prostate enlargement is sometimes associated with problems defecating. It rarely causes the urinary problems seen in men. Neutering your male dog removes the hormones that are though to be responsible for this condition. This can be done when, and if, a problem arises in your pet. There are alternative drug therapies that are sometimes more effective than surgery. (ref)

It is not a commonly recognized problem in cats.

Tumors Surrounding Your Pet’s Anus

These tumors are called perianal adenomas and adenocarcenomas. They occasionally occur in old, un-neutered male dogs. Eighty percent of these tumors are benign. (ref) They are the third most common tumor in old male dogs and they occasionally occur in females as well. The benign form occurs less commonly in neutered male dogs. But studies indicate that the number of the more dangerous adenocarcenomas formed is not decreased by neutering (same ref). Any that are still under the control of sex hormones should respond equally well to GnRH medications. (ref)

They are not a recognized problem in cats.

Helps Solve The Pet Over-population Problem

This is definitely true. If you are an irresponsible pet owner who lets your pets run loose in the neighborhood, this is a legitimate benefit of neutering. This is also an excellent way to make a "social statement" about your concern for animals in general.

It is only better behavior on the part of American pet owners that will solve the homeless pet problem. In Sweden, for example, there are virtually no homeless dogs; yet only 7% of female dogs there are spayed - They are just more responsible pet owners than we are. (ref)

What Is The Negative Scientific Information About Spay/Neuter ?

The Pet Overpopulation-Pet Neuter Fallacy

Although it is true that neutered pets cannot breed, the pets that contribute to the pet over-population problem are not the ones owned by responsible people who have their pets spayed and neutered. It is not the fact that a pet is un-neutered that causes pet over-population any more than dogs having teeth is the cause of human dog bites. Owner education and stiff fines for people whose pets run at large are much more effective in controlling pet over-population than surgical procedures.

Your Pet Will Miss Out On The “Miracle Of Birth”

I have clients that are concerned that their dog or cat will miss out on the gratification of childbirth. Many tell me they want their pet to have “just one litter” before they have it neutered. This goes for owners of male pets as well who think their pet should sire at least one litter. The emotional needs of pets are not the same as the emotional needs of people. We think differently. There is no credible evidence that pets miss having litters or romantic liaisons. What is important to them is your love.

Distorted Bone Structure

Distortion of your pet’s body by early-age neutering contributes to a number of diseases – some of which I cover below. As your pet matures, hormones produced by its testes and ovaries determine the shape and length of its bones. When these hormones are removed too soon through neutering before puberty, the bones grow for a longer period and to different proportions. This results in your pet becoming taller with abnormally shaped bones. (ref) This change in bone conformation means that angles and forces between bones and ligaments are changed from their natural design and could be more likely to fail. (ref) Your dog's knees are particularly at risk (ref). This phenomena has not been studied extensively in dogs, but it has in immature livestock and in children. (ref1, ref2) The same sitution has been confirmed in cats neutered at an early age. (ref)

Osteosarcoma (Bone Cancer)

We see these bone tumors most frequently in large and giant breeds of dogs that are already predisposed to them through their excessive bone growth. Spay-neuter before one year of age significantly increases the development of these tumors. (ref)

The problem is very rare in cats and there is no data as to any effect spay/neuter might have.


Hypothyroidism is much more common disease in dogs than cats. Neutered dogs are at a significantly higher risk of developing this condition than those that are not. (ref) You can read more about hypothyroidism here.

Weakened Ligaments, Orthopedic Disorders And Subsequent Arthritis

It is difficult to decide when torn cruciate ligaments, hip problems and arthritis occur due to the obesity that often accompanies neutering or when it is due to a decrease in joint strength and altered structure that also accompanies neutering. (ref1, ref2, ref3) The inactivity of many neutered pets may also contribute to this. Whatever the cause, veterinarians and others have noticed that all these problems increase in frequency in neutered pets. (ref)

Hip Dysplasia

Some dogs that are neutered young are prone to develop hip dysplasia. (ref) However, there are many factors responsible for the development of hip dysplasia and spay/neuter is probably not a major one. You can read more about this problem here.


Neutered and spayed pets tend to get fatter than those that remain intact. (ref) There is no denying this. That risk is increased when they are neutered before their first heat cycle. There is also no denying that limiting your pets food intake will prevent this. But that is considerably easier said than done. (ref)

When they do become too chubby, they suffer an increased risk for all the problems that overweight humans face. In cats, that includes diabetes, inflammatory bowel disease, gall bladder and bile duct problems arthritis and hepatic lipidosis. (ref1, ref2)

Cruciate Ligament tears

Spayed and neutered dogs have a significantly higher incidence of this disease. (ref) You can read more about cruciate ligament problems here.

Urinary Tract Problems

Veterinarians have noticed that it is spayed, overweight, female dogs that suffer the most urinary tract infections. Whether this is due to their obesity that causes vulvar inflammations or the urinary incontinence of low post-spay estrogen levels is unknown. When these female pets were neutered too young , some required later surgery to repair their poorly developed vulvas . (ref)

This does not appear to be a significant problem in neutered male dogs or in neutered female cats. There has been speculation, over the years, that early neutering of male cats leads to urethral blockages (ref FUS). Most cats that develop blockages are neutered males – but then almost all our male pet cats are neutered. (ref)

Urinary Incontinence

This is primarily a problem in spayed female dogs. Many of these dogs get better when given female hormone – the ones no longer present after spay.

Urinary Tract Infections

These too are more common in spayed female dogs. But these dogs tend to be overweight which may account for their increased risk.


Neutered pets tend to get fat. And in fat cats, diabetes risk increases dramatically. (ref) The situation is not as clear in dogs. The relationship between missing sex hormones, diabetes, obesity, and bone strength is more studied in humans. (ref) There is no reason to assume it would differ significantly in our dogs and cats.


This form of cancer is most common in dogs. Statistically, it occurs considerably more frequently in pets that are neutered. (ref)

font size="5" face="Arial, Helvetica, sans-serif">Do Veterinarians Disagree On This ?


There is considerable disagreement.

What About The Diseases that Spay/Neuter Advocates Bring Up As Reasons For Me To Neuter My Pet ?

There are inherent risks in living. All lives - ours and our pets - come to an end one day. All of us die from something specific, not “old age”. Something in our bodies gives out first. It is true that spay /neuter lowers the risk of your pet suffering from certain specific problems – but there is no credible evidence that neutered pets live any longer. The scientific evidence is that your pet will simply leave this Earth due to some other cause. There are lots of legitimate reasons for neutering pets - but living longer, healthier lives is not one of them.

Spay and neuter is said to be less common in Europe. But there is no evidence that pets in Europe live shorter lives that pets in the United States or Canada. Despite this, advocates of early spay/neuter tell pet owners that their pets will live longer if they are neutered. Studies indicate the opposite is true. In a 2009 study, un-neutered female rottweilers lived an average of 30% longer than a similar number of rottweilers spayed in their first 4 years of life. (ref). This mirrors the results of a study in nurses in which lifetime decreased significantly when, as patients, they had their ovaries removed before the age of 50. (ref)

It will be easy to accumulate statistics that show that neutered pets live longer than intact pets and that will probably be done soon by spay/neuter advocates. But it will be very hard for them to credibly show that it is not just pet and owner lifestyles that accounts for this. Selectivity and cherry-picking allow statistical data to be manipulated in any way the authors of the study desire. That goes for both sides of this issue. [ The only insurance study that I know of found that neutering your dog or cat had no effect on its potential lifespan. (ref)]

If Early Neutering Is Not A Good Idea, Why Is It Being Encouraged So Much ?

The American spay/neuter coalition:

There are a group of very powerful organizations that promote spay/neuter for reasons that are admirable and for some that are not. These groups work toward the same ends. I do not think that this is some devious plan – it is just a tacit alliance of powerful groups with mutual self-interest and shared agendas. It is similar in some respects, to the vaccination coalition which a Texas veterinarian fought against so valiantly.(ref)

The American Society For the Prevention Of Cruelty To Animals (ASPCA)

This is a dedicated group of individuals devoted to animal welfare. However, on the subject of spay-neuter, they have let their hearts overrule their minds. From information on their website at the time of this writing, they had total 2008 expenditures of $74,408,200 and CEO compensation package of $490,315. (ref1, ref2) Much of their energies and treasure are devoted to encouraging early-age spay/neuter.

The American Veterinary Medical Association

The AVMA's 2007 total revenues were $28,477,612. (ref1, ref2) Through their Animal Welfare Committee they make recommendations on AVMA policy – such as AVMA guidelines and the publication of brochures that gloss over the results of research published in their own journal. (ref1, ref2)

The Humane Society Of The United States. This competitor to the ASPCA had net assets in 2007 of $204,868,764 and total governmental lobbying expenses of $4,165,695. They are an active promoter of early-age spay neuter and mention nothing about the negative aspects of this procedure on your pet’s health. (ref)

With stated 2008 revenues of $34,355,526, this organization actively promotes neutering your pet “soon after the age of 8 weeks” stating that some shelters recommend doing it even earlier as “less stressful for animals”.

Winn Foundation
This organization was founded by the Cat Fancier's Organization in 1968 to improve the health of cats. Under its current leadership, it has transformed it's mission to become a strong loby for the spay/neuter of infant cats. It does not make its IRS 990 available online to the public.

The Corporate Animal Health Care Industry

There was a time when veterinarians were in charge of setting policy within the veterinary practices that they owned. That is becoming less and less the case. Decisions are being made more and more by publicly traded companies which are operated to maximize revenues.

VCA Antech Inc.
Veterinary Corporation Of America was founded in 1986 by three MBAs from the human health care industry. Their 2nd quarter 2009 revenues were $344.876,000 and their anticipated 2009 revenues, 1.36-1.39 billion dollars. Their CEO's total compensation package in 2009 is $1,760,272 . Their website brochure, as of this writing, makes no mention of the negative aspects of spay/neuter

Banfield Pet Hospitals/PetSmart
PetSmart Corporation established and owns an equity share in Banfield. I was employed by PetSmart when they established their animal hospital program.
PetSmart, had over $5 billion in revenues in 2008. As of this writing, their spay/neuter webpage makes no mention of the negative health aspects of spay/neuter.

If I Decide To Have My Pet Neutered, What Can I Do To Minimize Risks ?

I am not against neutering pets at the right time and for the right reasons. If you have a kitten, or puppy, do not rush to have it "fixed". Confining your pet to your home as a teenager is quite sufficient.

I could not live with my 4-year old male cat, Oreo, if he had not been neutered. But wait until cats are sexually mature to have them spayed and neutered. The time cats become sexually mature and the time their adult canine teeth (fangs) reach their full length generally coincide. Decisions based on hormonal analysis of the blood of your pet might be more scientific, but I have observed through many years of practice that examination of the canine teeth is quite accurate and effective.

If you have a female cat, you must be very careful not to let it escape outside during its first heat or it will most certainly become pregnant. It can be spayed during its heat period or shortly thereafter.

If you have a male cat and let it roam before it is neutered, it will fight; develop bite infections and possibly incurable feline AIDS or Feline Leukemia. Once it is neutered, still do not let it out of doors unleashed or unaccompanied.
If you have a female dog or puppy, wait until 3-6 months after its first heat period to have it spayed. Time the surgery before its anticipated second heat period.

If you have a female dog, let it pass through one heat cycle before considering having it spayed. The hormone symphony that accompanies heat affects all of your pet's body, not just its reproductive tract. (ref) This is something that proponents of early spay/neuter do not understand.

If you have a male dog, consider if you really need to have this surgery performed. My Labrador, Max, is not neutered. He is the proud father of zero puppies and will stay that way.

Mounting family members is a normal rite of passage and a sign of approaching puberty in puppies and adolescent dogs. If normal adolescent mounting behavior embarrasses you - remember it will pass , given a little patience and some instruction. It is important for your pet's long term health that these hormones flow it its body for at least a while.

<If you decide you must neuter your male dog, do not do it until well into their second year. If your pet has medical or serious temperament problems that might benefit from an earlier neuter, you might consider it a bit earlier. But there are often non-surgical ways to tackle the problem - try them first. Some owners have their male dogs neutered only to find that the problem for which it was done did not go away. If you are uncertain, have your pet receive a reversible sex hormone blocking injection first. (ref) If it has no effect on the problem, removing its testicles will not either.

Neutering pets at an older age necessitates keeping them trim. Fat pets are harder for veterinarians to work on and blood vessels become harder to identify and tie off securely. Dogs and cats will eat to please you if you over feed them. There is a long list of health reasons not to do that.

How Long Will The Practice Of Early Age Spay/Neuter Continue ?

That will depend on the efforts of pet owners like you. I am confident that there will come a time when pediatric spay/neuter of our pets is considered to have been a major error in judgment.

Organized institutional pressure to practice pediatric spay/neuter is very pervasive in America. It's proponents are highly vocal and well financed. No level of government is free of its mantra. Official publications are carefully sanitized to assure only one side of the question is presented.

The corporate and institutional interests that promote early spay/neuter have similarities to another large American corporate interest.

Both have stakeholders at many levels in the Community. Both are well-funded and sophisticated. Both are willing to exert pressure on government and others to preserve their interests. Both fund large advertising campaigns to manipulate public opinion. Both fund research likely to be favorable to their cause. Both share substantial liability issues with incentives for push-back and the suppression of negative data.

Negative health implications on the effects of smoking first appeared in scientific publications in 1950. It was not until 1963 that per capita cigarette consumption in the US dropped and until 1965 that warning labels were first put on cigarettes. (ref1, ref2)

Negative information on the side-effects of early spay/neuter first appeared in scientific publications the early 70s and continues through today.