A number of interesting and important research studies have been published in the last 5 years on the subject of the risks and benefits of neutering in dogs, and these have provided important information to help guide veterinarians and owners in making decisions about neutering. I published a narrative review of the literature on neutering in 2010, before most of these papers appeared, and I have been following this area of study with interest and evaluating individual papers as they are published. Though each study has its limitations, as is always true in science, and we must be careful not to overgeneralize the results of particular studies or lurch wildly from one set of recommendations to another on the basis of limited evidence, these studies are influencing traditional dogma about neutering. I have made several significant changes in both the information I give to owners and the recommendations I make about neutering based on the emerging evidence.

Another important study has recently been published which adds to the evidence in this area.

Hart BL, Hart LA, Thigpen AP, Willits NH. Long-Term Health Effects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers. PLoS ONE 2014;9(7): e102241. doi:10.1371/journal.pone.0102241

This study was produced by the same group which published an earlier retrospective study of Golden retrievers, and it is quite similar in its methods and some of its limitations. The authors reviewed medical records from the veterinary hospital at the University of California Davis veterinary college. The study looked for Golden retrievers and Labrador retrievers from 1 to 8 years of age and evaluated the occurrence of 6 diseases relative to neutering status and age at neutering.

The findings are summarized in Table 1 for Labradors and Table 2 for Golden retrievers. For comparison, I have also extracted similar data from the earlier paper by on Golden retrievers by the same group in Table 3. This paper classified age at neutering differently (early being <12 months of age and late being >12 months of age), so the studies are not directly comparable, but it is useful to scan for any possible patterns that might help us make sense of these complex data.

First off, what does the study appear to show? Well, perhaps the most important finding is that there are significant differences in the pattern of possible effects of neutering between males and females, and also between the breeds. This latter point is extremely important. People tend to jump on the findings from a study in a single breed and want to generalize those findings to all dogs and make broad recommendations based on that single study. However, if the possible effects of neutering differ significantly between two breeds as closely related and similar as Golden retrievers and Labrador retrievers, likely these effects will be even more dissimilar in breeds less closely related. A study of Rottweilers or Viszlas, for example, may tell us little or nothing about what to expect in Beagles or Poodles. This is worth keeping in mind before we rush into making sweeping recommendations for all dogs.

The findings in this study suggest some increase in the risk of some diseases with neutering, but the patterns were not very consistent. Neutering before 6 months of age appeared to be associated with higher risk of cruciate ligament disease and elbow dysplasia in male Labradors but not with the risk of hip dysplasia. In females, however, the pattern was the opposite, with neutering at less than 6 months being associated with greater risk of hip dysplasia but not the other two orthopedic diseases. But in Golden retrievers, neutering before 6 months of age was associated with greater risk of cruciate ligament disease in both sexes, but with greater risk of hip dysplasia only in males, not females.

Comparing the current study with the previous study of Golden retrievers also adds to the confusion. In the current study, risk of lymphoma seems to be higher in dogs neutered between 6-11 months than in intact dogs, but not in dogs neutered before 6 months or after 11 months. In the previous study, however, lymphoma risk appeared higher in males neutered before 12 months but not in females neutered at this age. In another example, late neutering in the first paper seemed to increase the risk of hemangiosarcoma in female Goldens but not in males. This was contrary to the hypothesis that earlier neutering might increase the risk of this cancer. However, in the current study, no differences in hemangiosarcoma risk were found for any neutered group of males or females compared to intact dogs.

There are, as always, a number of limitations that we must bear in mind when evaluating this study. As with the previous study, dogs were those seen at a university veterinary hospital. This is a very different population than usually seen at regular general veterinary practices. The veterinary hospital at UC Davis typically sees seen sicker dogs, dogs with more affluent owners, and dogs that live in different areas than those seen by regular practices in the rest of California. So we have to be careful about assuming than any relationships seen between health and neutering in this population will hold for the very different population of primary care practice patients.

Dogs younger than 12 months were excluded from this study. While the disease looked at are less common in dogs less than 1 year of age than in older dogs, they do occur. If dogs who get these diseases under 12 months are different, in terms of neuter status, from the dogs looked at in this study, that might change the apparent relationship. For example, if dogs who are intact are more likely to get one of these diseases earlier than neutered dogs, then excluding younger dogs would make neutering seem like a risk when it might actually be protective.

Similarly, dogs over 9 years of age were excluded as well. These dogs are particularly likely to get some of the cancers looked at in the study, and again if the ones who do differ in neuter status from the ones in this study, the apparent relationships identified in the study might be very different from the real relationships between these diseases and neutering.

A number of potential benefits of neutering, such as preventing mammary tumors and uterine infections in females and possibly being associated with longer overall lifespans, were not included in this study. While these are not directly related to the questions the authors sought to investigate, it is important that we consider overall risks and benefits when deciding when or if to neuter our dogs. If neutering prevents some cancers and increases the risk of others, for example, we need to make a decision about which effect is greater or more important in a particular dog. This study only looks at a small piece of that equation, namely the risks but not the benefits.

Finally, there are many comparisons made in this study, and each one is evaluated statistically. This can create a problem known as the multiple comparisons problems, in which the usual threshold for statistical significance is not appropriate. It is common, in studies which make multiple comparisons between subgroups and don’t correct for this problem to find a smattering of statistically significant results which are really the result of chance. In this study, I am not certain if a correction for multiple comparisons was made. If not, this could explain some of the significant differences found, particularly when the overall pattern is not consistent between studies or does not fit expectations based on biology.

Bottom Line
Overall, this study does suggest that neutering under 6-12 months of age might be associated with an increased risk of some orthopedic diseases in Golden retrivers and Labrador retrievers. In Labs, neutering does not appear to increase cancer risk. In Goldens, there may be some effect on cancer risk, but it differs between males and females. And in females, it may even be the case that earlier neutering is associated with a lower cancer risk than neutering later in life. But there are a number of inconsistencies and limitations which make these findings tentative at best.

The study also appears to show a strong difference in the effects of neutering on disease risk between even very closely related breeds. So it is important to recognize that the effects seen in one breed cannot reliably predict those that might be seen in another.

No single, universal recommendation for neutering or not neutering dogs of any sex, breed, or age is justified by the scientific evidence. There is some suggestion that females may experience significant health benefits, particularly in prevention of pyometra and mammary tumors, though the evidence concerning mammary tumors is weaker than generally believed. For males, there does not seem to be a compelling, consistent health benefit to neutering, and in large breeds there may be some benefit to waiting until after 1 year of age. In any case, as I always stress, it is important to balance potential risks and benefits carefully.

And not all benefits of neutering are related to the health of the individual dog. Millions of unwanted dogs are born and euthanized in the U.S. every year, and while every client I talk to dismisses the possibility that their dog could contribute to that problem if left intact, most of these dogs are the product of breeding by owned pets. So if you choose to keep your dog intact for health reasons, it is important to accept that this creates an additional responsibility to make sure he or she does not contribute to the serious problem of overpopulation and the suffering and euthanasia of unwanted dogs.

With my own clients, I discuss the complexity and inconsistency of the evidence, the general trends that seem to be apparent, and the important of making individualized decisions based on all the relevant factors, including age, breed, sex, intended purpose, and the circumstances of the owner. For the most part, I recommend neutering of females before their first heat, though the evidence is still not ironclad and more work needs to be done to elucidate the details of potential risks and benefits in different breeds and with different neutering ages. For males, I no longer see a compelling reason to neuter unless there is clear evidence of aggression towards other dogs, however I emphasize to owners that they must be aware of the added responsibility to prevent roaming and unwanted breeding.

These recommendations are different from those I gave when I first graduated from veterinary school, and they have changed as a result of changing and improving evidence. Likely they will continue to evolve as more research is done and we have a better understanding of the issue.

Table 1

Table 2

Table 3

I write regularly about the American Holistic Veterinary Medical Association (AHVMA) and its fundraising arm the American Holistic Veterinary Medicine Foundation (AHVMF). These organizations are very much the tip of the spear for pseudoscience in veterinary medicine. Unfortunately, despite peddling ideas which are often fundamentally incompatible with well-established science and with the evidence of history that science is the best way to understand the world and improve health, these organizations are remarkably effective at pretending to have a genuine interest in scientific research of alternative therapies, raising large sums of money (AHVMA and AHVMF financial statements), and then using that money and that superficial appearance of accepting the importance of science to infiltrate academic institutions and veterinary organizations.

From time to time, the leaders of these organizations share their true feelings about science and science-based medicine, and I feel it is useful to draw attention to those so that, hopefully, the truth beneath the façade will be visible and both veterinarians and pet owners can make fully informed judgments about the intentions and agendas of these groups.

In a recent interview in Natural News, a well-known platform for promoting the most egregious anti-science quackery, the president of the AHVMF, Dr. Barbara Royal, presented an honest and quite bizarre characterization of science-based veterinary medicine.

Dr. Barbara Royal, president elect of the American Holistic Veterinary Medical Foundation, believes that mainstream American physicians and veterinarians are only educated in one way.

“MDs and DVMs learn a lot about surgery, a lot about medications, a lot about disease…but they don’t learn about the causes of health.”

Royal believes in an integrative approach to health, NOT interventionist medicine. She strives to focus on supporting pet health as a first priority instead of treating disease after it has developed. This philosophy is challenging the status quo. Today’s mainstream veterinary students are taught to treat pets with an approach emphasizing drugs and surgery.

Throwing a drug at the problem often leaves pets with side effects and an impending death. The philosophy of, “take this drug, we don’t really know how it works, good luck,” is a symptom cover-up approach that reaps more consequences in the end. Although mainstream veterinarians mean well and want to help, their philosophy – the way they were taught – is a patch work that ultimately leads to unintended consequences.

The clichés that conventional medicine treats only symptoms without any interest in the underlying causes of disease, that preventative healthcare is ignored by conventional veterinarians, and that science-based medicine ignores all interventions except surgery and pharmaceuticals are often repeated by proponents of alternative approaches despite being obviously and manifestly untrue.

Dr. Royal offers a few tidbits from the alternative perspective the AHVMF advocates, which include further clichés, such as blaming mysterious toxins, conventional diets, vaccines, and of course medicines (ah, I mean “drugs”) for illness and suggesting that without the products of science-based medicine our pets would be living natural, healthier lives. It is hard to imagine anyone making such an implication with a straight face given the overwhelming evidence that human health and longevity has improved dramatically since the advent of the scientific approach to a degree unimaginable during the thousands of years of pre-scientific approaches to health that sound very much like the “natural” approach the AHVMF advocates, complete with ancient healthcare strategies based on pseudoscience and mysticism like Traditional Chinese Medicine, Herbal Medicine, Acupuncture, and so on. (See the graphs below for a couple of illustrations of this well-documented history)**

She encourages pet owners to eliminate corn and wheat from their pet’s diets, because these are pro-inflammatory, unfamiliar ingredients to an animal’s body. She teaches about pet food processing methods that create heterocyclic amines and acrylamides, which are potent carcinogens.

She talks about concepts like the lack of moisture content in kibbles which lead to dehydration in the animal. She talks about the amount of glycotoxins in dog food that cause inflammation in pets.

Royal also warns against overdoing those things that could cause harm. She teaches not to over medicate or over-vaccinate a pet, teaching how this interferes with an animal’s natural ability to heal.

Like other leaders of these organizations, Dr. Royal pays lip service to the value of science when speaking to those who truly do recognize the importance of the scientific approach, but when speaking with fellow believers in alternative therapies, she makes no reference to scientific evidence at all but is quick to  offer the well-respected testimonial/anecdote as validation for the preceding rejection of science-based medicine and its philosophy and methods:

On the inspiring stories page of the AHVMF page, one can find many testimonials of pets cured through holistic means.

Despite being psychologically compelling, such miracle stories are not a reliable way to evaluate whether a healthcare intervention is safe and effective. But they are very effective as a marketing tool, which ultimately matters more to the AHVMA and AHVMF that inconveniences such as what is true.

The fact that Dr. Royal and others in these organizations have a deep, genuine faith in their methods is not in itself objectionable. What is disturbing, and dangerous for our patients, is that they seem able to obscure the fundamental rejection of science and science-based medicine at the core of their ideology.  The fact that an organization run by individuals who blithely mischaracterize conventional medicine, as Dr. Royal does in this article, and who reject the basic philosophy or the need for science can be welcomed as an affiliate within the American Veterinary Medical Association and as a source of funding for research and educational activities at schools of veterinary medicine is bizarre and disturbing. The growing influence of these organizations does not bode well for the future of veterinary medicine as a profession or, more importantly, for the continued progress in healthcare that benefits our patients.
**Here is a chart which reminds us that before the 20th century, and the advances in agriculture, sanitation, and medicine brought about by the accumulating scientific knowledge of the preceding two centuries, human life was short and few children could count on living to adulthood, much less a ripe old age. This pattern had remained unchanged for thousands of years despite the “ancient wisdom” of trial-and-error folk medicine now advocated by the AHVMA and AHVMF. The chart below, while more speculative that the one above, illustrates this based on all the evidence currently available.

This is the reality the AHVMA is so eager to ignore in favor of a naïve image of a Golden Age of health and well-being prior to the development of science and technology. No one can deny that the fruits of science have not always been benign or wisely used. But denying that overall human life is longer and healthier thanks to science than it ever was during the millennia we relied on more “natural” methods is irrational and dangerous.

Though I’m a little late, I’m a forgiving sort, so I won’t be mad at myself for forgetting my blogiversary. June 4 marked five years of the SkeptVet Blog! The project has grown in so many ways. In the early days, I was excited to get fifty hits in a day, and in the last year it has been routine to get 800-1000 per day. Still small potatoes by Internet standards, but gratifying nonetheless. My goal has always been to provide a useful informational resource to pet owners and veterinarians, and to provide an alternative perspective on many therapies for which the only information on the internet is biased and unjustified marketing hype. The more people who know the blog is here, the more useful it is likely to be.

I have also expanded to discuss a much wider range of topics, even leaving the domain of alternative medicine more and more often. And in writing articles every week for five years, hopefully I have become a more effective communicator. I cringe when I look at the style and tone of some of my early posts, but I choose to view that as a good sign since it must mean I have grown and changed.

Writing this blog has provided me with opportunities to talk about evidence-based medicine more widely, to veterinarians and students and the general public, through my own lectures and presentations, writing opportunities, and interviews in the media. Hopefully, these activities will add an under-represented perspective, that of science and skepticism, to conversations within these communities about the best way to protect and restore health in our animal companions. I’ve never claimed to have all the answers, but I think I have some important and useful questions.

And writing this blog has certainly stimulated discussion and feedback. I have reviewed the negative comments before because I believe they are instructive in understanding the beliefs, values, and emotions that support pseudoscience and impede the effective use of science to improve veterinary medicine and animal health. But as an anniversary present to myself and those who find this project useful, I thought I’d review some of the positive feedback I’ve received. As well as being fun, this will help maintain the energy needed to keep going, which I fully intend to do. (All comments have been anonymized).

As a side note, another way to maintain this energy is going on vacation, which I will be doing starting this weekend. So activity, including responses to comments and emails, will be pretty light here for a few weeks. Never fear, I will keep up as best I can while I’m travelling, and I will dive back in with responses to your questions and comments and new articles with renewed vigor when I get back.

Finally, I offer a heartfelt “Thank you!” to all who have taken the time to provide supportive comments, questions or suggestions for topics to discuss, and thoughtful, substantive criticism. Your feedback does a great deal to neutralize the vacuous and angry responses a blog such as this inevitably draws and to maintain my faith in the possibility of civil, rational, fact-based discourse.

Thank you very much for taking the time to respond to my email and for providing a thoughtful response. .. Thank you for all the information you provide on your website as well.

Thank you. I asked my vet about XX again after I read your post…. I want to thank you for your honest “second” opinion before I started her on both meds. Knowing the possibility of “unknown” side effects makes me want to rethink…

Thank you very much for the information. .. Again, your advice is much appreciated in a difficult time for us.

I was very pleased the day I found your blog. You have excellent epidemiologic insight, which is rare among vets…. So, I applaud you for your post on media coverage of healthcare research.

Thank you so much for your timely response and thoughtful answers. I greatly appreciate you effort.

Thank you so much for your reply and the referenced article…Thank you so much for taking the time to answer my original email. I never expected to receive a reply, let alone a quick reply. The ACVIM Consensus Statement was extremely helpful.

I am so touched that you have replied so promptly and it is really fantastic to have such a well considered and scientifically based answer. Thank you very much, I truly appreciate it.

Thank you so much for your quick and detailed reply! I will be reviewing the links today. I so appreciate the work that you do and your personal reply to inquiries. I know that you receive a lot of negative feedback but I know there are also many, including myself, that appreciate your time, research, analysis and pragmatic consideration.   As a pet owner who loves her dog, I of course am in search of anything that won’t harm but could be helpful beyond the standard of care that we will be doing. I try to do diligent research on any recommended unconventional treatments.  Not just for my own dogs but when I am assisting in the treatment of patients at our hospital…This is something I take very seriously.  Reviewing your information I hope will help me make the best, most informed decision…

I just wanted to thank you for your blog. I have training in research design and statistical methods, but not as a biologist or veterinarian. I always want to read peer-reviewed research when something is wrong with my dog, but don’t understand the medical terms. Your blog is really a godsend. Keep up the good work!

I had originally intended to reply…in a private e-mail with encouragement and praise for speaking up for the rest of us in the “silent majority.”  Its a tough role to play and I continue to be impressed with your eloquence…Keep it up.

I’m so glad to see some common sense in the world. Your blog exposes a lot of the craziness which I really appreciate, especially coming from an MD background… It’s fascinating to me how quickly people gravitate towards alternative medicine, towards theories that sound magical and assume that they are just correct without any scientific evidence to back it up. Thanks for keeping it real!

I did try do my own review from primary literature, but I do not know the journals or the field at all, so your review was exactly what I was looking for, thank for that! My local vet now has a few extra facts to consider…As for the rest of your site, I enjoyed that too, and I’m very thankful that you take strong, and informed standpoints on CAM issues.

Good luck, and keep up the good work!

I wanted to drop a quick note to thank you for taking the time to post your thoughts and observations regarding various common and/or popular veterinary treatments…The net is long on anecdotes, short on science. Finding your blog has gone a long way towards filling the gap.

Just a quick thank you for your website and blog site. I’ve followed your sites for a while, and your citations to sources and reference materials are helpful in allowing me to share your information to family, friends, and our vets. The (sometimes) desperate urge to “do something” for our ailing pets clouds the minds of owners and vets alike, it seems. And some have a very hard time getting out the cloud.

First I wanted to thank you for posting your lecture, I shared it far and wide and hope that some of my colleges and friends were able to get what I was able to get out of it…Thank you for your response, your response far exceeded my expectations and I appreciate that.

You are doing a great service to pet companions of all stripes! we just struggled with putting down our beloved dogs in the past year, and the pressure to do all sorts of extraordinary but probably not effective treatments for them made it much more stressful.

Thank you so much for taking the time to reply!  Your message has helped very, very much.  We (pet people and their pets) are fortunate to have someone as thoughtful and generous as you are.

I’m new to your website as of today, came across it while searching for evidence-based information on dog food. What a great find! I completely appreciate your world view…Thank you for providing such a great source of well-researched and thought out information.

Just a quick note to tell you of my appreciation for you site. For years I have tried to educate my clients about the problematic proof supporting many of the alternative therapies other clinicians have been promoting… keep up the good work…

I appreciate your articles and perspectives. It’s so difficult to know how to best care for one’s pets in the face of so much contradictory information out there. .. Thanks so much!

Want to thank you for all of your efforts. Greatly appreciated and just hope that the folks who should be reading your site, somehow find it.

Thank you so much for your response. It is quite disheartening that there are so few veterinarians who are willing to speak out against organisations such as the American Council of Animal Naturopathy.

Skeptvet has superpowers It takes not only a extensive knowledge of vet medicine but the ability and time to put in writing that knowledge so others can understand the issues. I have seen other vets with extensive general small animal and human medicine knowledge. I have seen other vets that were great writers. But never a vet that had both knowledge with his ability to write. I find it difficult to believe only one person is at work here in this blog. It’s amazing what one person in the field of vet medicine is capable of accomplishing if they have the knowledge, training and dedication to do it.

Thanks for keeping it real, skeptvet, it’s frustrating to read some of the rants that occur here by those with an obvious ax to grind.

Skepvet, I’ve enjoyed the dialogue between yourself and dfg. I also appreciate your blog as source of information.

Thanks for the science-based common sense!

Thank you, Thank you !!! For writing such a clear, well documented and intelligent and thorough response and work.

Thanks for taking the time to compose this article…Your review was applicable and timely.

Hiya, just wanted to say and thanks. I’m getting a kitten and was considering a barf diet, but after doing my research, and coming across your site, I’m relieved to say I won’t be feeding my pedigree any raw food.

I just found this blog, and I’m so glad I did. There is way too much woo and pseudo-science out there for people who genuinely care about companion animals to wade through when trying to make informed choices on anything from medication and nutrition to training techniques.

Caveat emptor. Skeptvet, thank you for taking the time to elaborate. I found it helpful and I hope that others will as well.

Thank you for providing this valuable perspective.

I am still looking for the product I need. But, in the meanwhile I read your blog, loved it. Made perfect sense to me. And such a perfect way to confuse the writers, with fact.

Thanks for what you do generally, and specifically for providing a clear and reasonable overview of the literature on this issue. Like you and many others, I find the lack of quality controlled research here unfortunate

I am SO happy to have found your website! Will be following faithfully form now on. Thanks!!

Excellent blog post, as always, Skeptvet. Thank you for all you do.

Thank you again for producing this blog. I’m sharing this entry as part of my ethical duty to spread knowledge about the inefficacy of homeopathy.

Thanks for yet another well presented summary of the fallacies of magical thinking,

Thank you so much for this excellent summary based on SCIENCE.

Someone needs to stand up to faith masquerading as science, and people who would try to twist evidence to support their own agenda. Someone needs to hold the high ground when such people start flinging ad hominem abuse and sarcastic crap in defence of their idealism. But it’s so hard, and most of the time it’s a thankless task. I feel for you.

Thank you so much for offering a balanced view point of this.

Thanks for the facts. I trust a well argued appeal to reason and peer-reviewed evidence over the numerous emotional online sources decrying the substance.

Thank you thank you thank you ! The Dr. Dean Edell of veterinary medicine