Thursday, July 24, 2008

The Spay or Neuter decision

There has been much disinformation spread by proponents of spay and neuter as a method of population control, with claimed health benefits. Many vets also recommend the procedure, claiming health benefits without explaining (or necessarily understanding) the negative risk factors. Many adoption agreements require that a pup be altered by the age of six months.

This is a decision that should be left to the owner, and a good vet will understand and explain both the positive and negative aspects of spaying or neutering your dog, rather than proactively recommending it as standard procedure.

The following was forwarded to me by Dr. Charles Hjerpe DVM, Emeritus Professor of Veterinary Medicine at the University of California, Davis, School of Veterinary Medicine. It does not address the demonstrated behavioral issues that have been seen in neutered or spayed dogs, which should also be considered.


At some point, most of us with an interest in dogs will have to consider whether or not to spay/neuter our pet. Tradition holds that the benefits of doing so at an early age outweigh the risks. Often, tradition holds sway in the decision-making process even after countervailing evidence has accumulated.

Ms. Sanborn has reviewed the veterinary medical literature in an exhaustive and scholarly treatise, attempting to unravel the complexities of the subject. More than 50 peer-reviewed papers were examined to assess the health impacts of spay / neuter in female and male dogs, respectively. One cannot ignore the findings of increased risk from osteosarcoma, hemangiosarcoma, hypothyroidism, and other less frequently occurring diseases associated with neutering male dogs. It would be irresponsible of the veterinary profession and the pet owning community to fail to weigh the relative costs and benefits of neutering on the animal’s health and well-being. The decision for females may be more complex, further emphasizing the need for individualized veterinary medical decisions, not standard operating procedures for all patients.

No sweeping generalizations are implied in this review. Rather, the author asks us to consider all the health and disease information available as individual animals are evaluated. Then, the best decisions should be made accounting for gender, age, breed, and even the specific conditions under which the long-term care, housing and training of the animal will occur.

This important review will help veterinary medical care providers as well as pet owners make informed decisions. Who could ask for more?

Larry S. Katz, PhD
Associate Professor and Chair
Animal Sciences
Rutgers University
New Brunswick, NJ 08901


Dog owners in America are frequently advised to spay/neuter their dogs for health reasons. A number of health benefits are cited, yet evidence is usually not cited to support the alleged health benefits.

When discussing the health impacts of spay/neuter, health risks are often not mentioned. At times, some risks are mentioned, but the most severe risks usually are not.

This article is an attempt to summarize the long-term health risks and benefits associated with spay/neuter in dogs that can be found in the veterinary medical literature. This article will not discuss the impact of spay/neuter on population control, or the impact of spay/neuter on behavior.

Nearly all of the health risks and benefits summarized in this article are findings from retrospective epidemiological research studies of dogs, which examine potential associations by looking backwards in time. A few are from prospective research studies, which examine potential associations by looking forward in time.


An objective reading of the veterinary medical literature reveals a complex situation with respect to the long- term health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter correlates with both positive AND adverse health effects in dogs. It also suggests how much we really do not yet understand about this subject.

On balance, it appears that no compelling case can be made for neutering most male dogs, especially immature male dogs, in order to prevent future health problems. The number of health problems associated with neutering may exceed the associated health benefits in most cases.

On the positive side, neutering male dogs

• Eliminates the small risk (probably <1%)
• Reduces the risk of non-cancerous prostate disorders 
• Reduces the risk of perianal fistulas 
• May possibly reduce the risk of diabetes (data inconclusive) 

On the negative side, neutering male dogs 

• If done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common cancer in medium/large and larger breeds with a poor prognosis. 
• Increases the risk of cardiac hemangiosarcoma by a factor of 1.6 
• Triples the risk of hypothyroidism 
• Increases the risk of progressive geriatric cognitive impairment 
• Triples the risk of obesity, a common health problem in dogs with many associated health problems 
• Quadruples the small risk (<0.6%)
• Doubles the small risk (<1%)
• Increases the risk of orthopedic disorders 
• Increases the risk of adverse reactions to vaccinations 

For female dogs, the situation is more complex. The number of health benefits associated with spaying may exceed the associated health problems in some (not all) cases. On balance, whether spaying improves the odds of overall good health or degrades them probably depends on the age of the female dog and the relative risk of various diseases in the different breeds. 

On the positive side, spaying female dogs
• If done before 2.5 years of age, greatly reduces the risk of mammary tumors, the most common malignant tumors in female dogs 
• Nearly eliminates the risk of pyometra, which otherwise would affect about 23% of intact female dogs; pyometra kills about 1% of intact female dogs 
• Reduces the risk of perianal fistulas 
• Removes the very small risk (≤0.5%) from uterine, cervical, and ovarian tumors 

On the negative side, spaying female dogs 

• If done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common cancer in larger breeds with a poor prognosis 
• Increases the risk of splenic hemangiosarcoma by a factor of 2.2 and cardiac hemangiosarcoma by a factor of>5; this is a common cancer and major cause of death in some breeds
• Triples the risk of hypothyroidism
• Increases the risk of obesity by a factor of 1.6-2, a common health problem in dogs with many associated health problems
• Causes urinary “spay incontinence” in 4-20% of female dogs
• Increases the risk of persistent or recurring urinary tract infections by a factor of 3-4
• Increases the risk of recessed vulva, vaginal dermatitis, and vaginitis, especially for female dogs spayed before puberty
• Doubles the small risk (<1%)>
• Increases the risk of adverse reactions to vaccinations 

One thing is clear – much of the spay/neuter information that is available to the public is unbalanced and contains claims that are exaggerated or unsupported by evidence. Rather than helping to educate pet owners, much of it has contributed to common misunderstandings about the health risks and benefits associated of spay/neuter in dogs.

The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically mature, or perhaps in the case of many male dogs, foregoing it altogether unless medically necessary.

The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Breed, age, and gender are variables that must be taken into consideration in conjunction with non-medical factors for each individual dog. Across-the-board recommendations for all pet dogs do not appear to be supportable from findings in the veterinary medical literature.


Andrew Campbell said...

Mike: thanks for posting this. The AVMA has done some impressive compilation of records and has reached similar conclusions. A very recent report compiled by Dr. Margaret Root Kustritz, DVM, and published in the Journal of the American Veterinary Medicine Association in December 2007, suggested, for example, that spayed female dogs run higher risks of hip dysplasia and urinary tract infections amongst other conditions -- and that the age of spaying may play an important role in mitigating a dog's subsequent likelihood of developing one of these conditions. As she concludes: "Pets should be considered individually, with the understanding that for these pets, population control is a less important concern than is health of each animal." (JAVMA, Vol 231, No. 11, December 1, 2007, p. 1671).


KathyB. said...

What a surprisingly interesting article. It caused me to say "Amen" and "Hip hip hooray", someone is actually putting into writing some questions and concerns I have had over the years about my dogs and the popular, but rarely accurate myths about dogs and canine reproductive organs.

We had a registered and healthy male Yellow Lab. After he was 2 years old we received a notice from our vet stating they had noticed we had not taken our dog in to have him neutered. The notice also went on to state all the health concerns for non-neutered dogs and then said that male dogs ran the same risks as human males regarding testicular problems, etc. Later on in the year the vet's office called me and inquired about my male dog. ( This really bugs me too, that the vet would hound me about my choices regarding my dog!)I replied that since my dog was susceptible to all the same things as human males then I assumed all the male vets had been properly castrated ! They did not call back.

Mike Spies said...


Thanks for posting this. I am similarly annoyed at the 'standard operating procedure' attitudes of vets in this regard. Of all my dogs, only one has been neutered - at the age of 11 from medical necessity.

Wayne Pacelle and the HSUS have worked hard to see that or animals are mutilated so that they cannot be bred. We need more critical thinking and less 'dogma'.

PBurns said...

I am pro-choice, and vocally anti mandatory spay-neuter, but I am not convinced that what has been presented here is very meaningful, as there is no base line.

The base line I am looking for is the health consequences of pregnancy and an intact set of testicles. That number is not zero, but I do not see it mentioned or even given a nod to.

An unspayed dog or intact male has certain things that can predictably happen to it a certain percentage of the time. Male dogs are routinely put down for aggression, for marking inside, and they also routinely escape yards looking for action, and are hit by cars. That's the base line for doing nothing in male dogs and it is a very real health consequence of having testicles (along with early mortality due to prostate problems).

The base line for female dogs is death from complications related to pregnancy.

Add to the base line for both non-altered male and female dogs is the cost of "accidental" matings which are quite predictable. Some of the resulting puppies will end up being killed in shelters, very few will be placed with real care, and the financial costs (caesarians are not free) should probably be factored in as well, as some unplanned breedings almost guarantee veterinary expenses.

Was any of this obvious stuff factored in? Not as far as I can see.

As for issues such as osteosarcoma, hemangiosarcoma, and hypothyroidism, nothing will reduce these problems faster than dumping the Kennel Club's closed registry system, banning incestuous matings, allowing outcrossings, and breeding for smaller dogs (size appears to be a big deal in some cancers, pardon the pun).

Alter your dog or not as you see fit. It's still a free country. But if you are really concerned about cancer, etc. the big decision is BREED selection, not spay-neuter.


Mike Spies said...

PBurns brings up some legitimate points... a lack of 'baseline'. However, this is not a study in the formal sense but a review of literature - about 50 papers in Veterinary Medicine that bear on the subject of spay/neuter - by a professional.

The article has adequate attribution that a reader who has sufficient interest may contact the people listed in the post, or contact me to ask for more information.

PBurns further posits the idea that "such as osteosarcoma, hemangiosarcoma, and hypothyroidism, nothing will reduce these problems faster than dumping the Kennel Club's closed registry system, banning incestuous matings, allowing outcrossings, and breeding for smaller dogs" -- This without citing any baseline or sources of his own to support the idea that these diseases are linked to genetic problems associated with 'closed registries' or 'incestuous matings'

SO take PBurns comments as opinion unsupported by fact.

Comments on this board are unmoderated and will continue to be that way. But I will reply to call BS whenever I feel it appropriate.

Anonymous said...
This comment has been removed by a blog administrator.