For Veterinary Practice News With a raft of publicity, a recent and widely read retrospective study that identified increased risk of certain joint disorders and cancers in neutered golden retrievers has sparked discussion within the veterinary community.
Reaction illustrates how entrenched neutering is within the U.S. veterinary profession.
Many were quick to point out the study’s limitations, including that it was retrospective; that it was conducted at a tertiary site; that the authors did not include any veterinary oncologists; that the sample size was limited; and that the intact animals may have been intact because they were likely breeding stock and therefore screened for health.
"Retrospective studies seldom look at line breeding and other statistically significant impacts of the ‘n’ being studied,” said Thomas Catanzaro, DVM, MHA, LFACHE, 2012 Bustad award winner and a practice management consultant in Australia. "This study does not qualify the breeding lines of the animals being reported, and therefore is not as significant as it is made to seem.”
The paper’s lead author, Ben Hart, DVM, Ph.D., Dipl. ACVB, a distinguished professor emeritus at the University of California, Davis, said the study is significant and should prompt immediate changes in veterinary practice.
"The results on the golden retriever are certainly clear enough to warrant immediate application with regard to neutering before 1 year of age,” he said.
"With males, compared with dogs left intact for the first year, early neutering increased hip dysplasia from 5 percent to 10 percent, cranial cruciate ligament tear/rupture from 0 percent to 5 percent and lymphoma from 3 percent to 10 percent. The likelihood of a neutered male acquiring one of these three devastating diseases is 25 percent compared to 8 percent if he is left intact.
"This is the practical message. Until we get more information, it does not seem like it is going too far to extrapolate this perspective to other large breeds.
"With females, the increased risk of hemangiosarcoma and mast cell tumor with spaying later than the first year presents a more difficult message. Late neutering brings on a 13 percent likelihood of acquiring at least one of these cancers compared to a 2 percent likelihood for females left intact. The risk of mammary cancer in goldens left intact appears to be low.”
If nothing else, some, including Dr. Hart, said veterinarians should be discussing the risks and benefits more thoroughly.
"What I think veterinarians should understand is that the time has come to talk over options with owners of puppies about when and if to neuter or spay, and let them make decisions that can impact the long-term health of their canine family companions,” Hart said.
"For shelter veterinarians, this is a tough issue because the spay/neuter policy is set by shelter administrators. The need to release only neutered or spayed dogs could be replaced by using vasectomy and tubal ligation for the dogs, with some refinements. These other procedures will be less expensive and less traumatic to the dogs. Dog adopters can then decide when and if they will neuter later.”
Other veterinarians are waiting for more evidence.
"Evidence-based medicine is not based on retrospective studies of unconfirmed populations, nor does it hinge on a single published study,” said Dr. Catanzaro. "I do not expect to see a rush by vets to change. Concurrently, there are breeders and new pet owners who will quote this research paper as if it was gospel rather than a retrospective observation not yet proven in real time replicated studies.”
By late March, the article "Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers,” had been viewed at least 24,243 times and downloaded more than 1,000 times from its publisher, the online peer-reviewed journal PLOS-ONE. It was also touted by UC Davis in a press release, shared via Facebook and Twitter more than 1,800 times and generated lay media coverage.
"That this is a charged issue is an indication that we should confront the issue and make proactive changes for the sake of our clients,” Hart said. "If the momentum comes from the dog clubs and devoted dog caregivers and the profession still resists in the face of evidence like ours, the profession may suffer a bit in what is now a highly regarded reputation.”
Evidence of Ill Effects
The study adds to a growing body of literature detailing negative health consequences of neutering, and its results also mesh with claims data from pet insurer Trupanion of Seattle.
"Our data is consistent with the results of their study, with more golden retrievers claiming for these conditions if they are spayed/neutered versus intact,” said Howard Rubin, chief operating officer of Trupanion. "In addition, trends by gender are similar between our data and the information presented in the study.”
Trupanion, which employs five full-time actuaries, looked deeper.
"Experience across breeds and species are very different, especially because these conditions are largely bone and joint-related, which varies dramatically by body type,” Rubin said. "But it’s also common for people to extrapolate to other scenarios—in this case, other breeds.
"Although not scientific, we have done additional research and data analysis and have determined that, in our data pool, the relationships determined in the study are generally consistent across all dog breeds.”
Neuter status does not factor into Trupanion’s premiums.
Tracking Neuter Status
Another insurer, Veterinary Pet Insurance of Brea, Calif., does not track the relationship between neutering status and disease incidence—yet.
VPI probably will change its claim handling process—it handled about 1.2 million claims last year—to include neutering status as the study raised awareness of the relationship at VPI’s headquarters, said Carol McConnell, DVM, MBA, VPI’s vice president of underwriting and chief veterinary officer.
Similarly, NorthStar VETS, an emergency and specialty animal hospital in Robbinsville, N.J., hadn’t tracked neuter status.
"We do not formally track the incidence of disease in neutered as compared to intact dogs,” said Kimberly Hammer, VMD, Dipl. ACVIM (SAIM).
"It is a dataset [we] could pull from our database but haven’t before. I find the study very interesting and look forward to similar studies in the future.
"I don’t find the results that surprising in the sense that we know that sex hormones have a powerful influence on the body as seen with human conditions such as osteoporosis and breast cancer. It is just a matter of time before we tease [out] more interesting data to help us determine the relative risks and benefits of neutering pets.”
Still, the issues of pet overpopulation and behavior loom larger.
"The bigger problem is still pet overpopulation, and combining that with the inability for a majority of pet owners to properly manage the behaviors of an intact dog, the best option is still neutering. I think shelter vets would agree,” said Brett Cordes, DVM, executive vice president and chief veterinary officer of Pet Genius LLC in Tucson, Ariz. Pet Genius provides pet health information and discounts to organizations seeking to add pet-related benefits to their membership perks.
"[The study] did not discuss the most important aspects of neutering, in my opinion, which is obesity and hormonal imbalance—namely Cushing’s disease.”
Hart and his UC Davis colleagues expect to have comparable information for Labrador retrievers and German shepherd dogs soon. The group also plans to look at Rottweilers, boxers and Chihuahuas.
This study builds on previous studies and may make it increasingly likely that veterinarians and pet owners will be spending more time discussing spaying and castration.
"Practicing veterinarians need to address each individual case separately and ask why is spaying/neutering being performed? Is it necessary? What are the alternatives?” said Manoel Tamassia, DVM, MS, Ph.D. Dipl. ACT, speaking in his capacity as NorthStar’s theriogenologist and not as New Jersey’s state veterinarian. "Shelter veterinarians don’t have much option as that is part of their job duties. Shelter management should re-evaluate across-the-board spay and neuter.”
VPI’s Dr. McConnell would be looking for the balance between allowing for growth plate development versus behavior issues, especially in larger breed dogs.
"If I was still in practice and was with a client with an intact dog, I’d have a longer conversation about the appropriate timing for spay/neuter,” she said. She would still recommend neutering because the behavior benefits for both sexes far outweigh the risks.
"Some behavior issues that represent a threat to people can be mitigated by neutering,” Dr. Cordes said. "Neutered dogs jump fewer fences and fewer get run over by cars while chasing bitches.”
Indeed, the timing of neutering may be the bigger issue for many, who believe the benefits of population control and behavior issues still outweigh possible health risks.
"Neutering can likely provide marked improvement for many dogs that are exhibiting marking, roaming or mounting behavior and may offer some improvement in dogs that are aggressive toward people and other dogs,” said Sophia Yin, DVM, MS, an applied animal behaviorist.
"For female dogs, the behavior benefits are not as clear. The most obvious benefit of neutering of males and females is population control.”
Compliance with local and state laws is another consideration.
"While only a handful of cities have passed mandatory spay/neuter laws for pet owners, state statutes that require the sterilization of pound or shelter animals prior to release are relatively common,” said Catanzaro. "In addition, many city ordinances and state statutes require higher licensing fees for intact animals and mandatory sterilization for dangerous or vicious dogs.”
Funded partly by the AKC Canine Health Foundation, the study could influence future debate about mandatory spay/neuter legislation.
Many breeders see such regulations, which often limit the number of intact animals a person can own, as attacks on their businesses.
"Millions of animals are euthanized every year due to overpopulation, so birth control is a priority here,” Dr. Yin said. "This overpopulation is generated in large part by accidental matings. For individual pet owners, vets still need to keep population control in mind. Most owners don’t realize how easy an accidental [mating can happen]. And owners may not be as vigilant in the U.S. about supervising intact pets as they may be in some highly regulated countries in Europe.”
The paper discussed the relative rarity of neutering animals in Europe, especially Northern Europe.
"In general countries in Europe are small compared to the U.S. such that it’s easier for the governments to impose laws and regulations on the population,” Yin said. "The citizens may be more willing to comply (e.g,. leash laws and supervising their intact pets more carefully).”
Still, overpopulation issues are being seen in Europe, especially in Southern and Eastern Europe, which there are growing populations of stray and free-roaming animals, Yin said.
The behavior benefits of neutering may contribute to far more U.S. households owning dogs than European households by making dog ownership more convenient. The American Veterinary Medical Association estimates that 36.5 percent of U.S. households own 70 million dogs (and the American Pet Products Association estimates that 46.7 percent of U.S. households own 83 million dogs). By comparison, the European pet food industry trade group FEDIAF estimates that 26 percent of all European countries own 73 million dogs.
"The benefits of neutering still outweigh the risks and always will until pet owners in the USA can focus more attention to pet training,” Cordes said.
Synopsis of ACT Position
In 2008, the American College of Theriogenology and the Society for Theriogenology issued a joint position statement on mandatory neutering.
"[We] believe that companion animals not intended for breeding should be spayed or neutered; however, both organizations believe that the decision to spay or neuter a pet must be made on a case by case basis, taking into consideration the pet’s age, breed, sex, intended use, household environment and temperament. The use of generalized rules concerning gonadectomy (removal of the ovaries or testes) is not in the best interest of the health or well-being of the pets or their owners.”
The position statement also states:
"While there are health benefits to spaying and neutering, these must be weighed against the health benefits of the sex steroids. In general, the advantages of spaying or neutering a pet include effective population control, decreased aggression, decreased wandering, decreased risk of being hit by a car, and decreased risk of mammary, testicular and ovarian cancer.
"On the other hand, the disadvantages of spaying or neutering may include increased risk of obesity, diabetes, osteosarcoma, hemangiosarcoma, prostatic adenocarcinoma, transitional cell carcinoma, urinary tract infections, urinary incontinence, autoimmune thyroiditis, hypothyroidism and hip dysplasia.
"Therefore, the decision to spay or neuter a dog or cat should be made solely by the pet’s owner with the direct input of their veterinarian and will be dependent on each particular animal’s situation.”
The organizations have posted a basis for the statement, with references, on the www.therio.org website.