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Is Early Neutering Hurting Pets?

By Alice Villalobos, DVM

Early neutering has become the norm in the U.S. Some states are asking voters to pass initiatives requiring citizens to sterilize their pets no later than puberty. Overpopulation is the driver.

But what if large-scale studies found that early neutering jeopardizes the health of our pets?

What if we found enough epidemiological evidence that early neutering of pet dogs may open them to orthopedic, behavioral, immunologic and oncologic issues?

A veterinarian who treats canine athletes has raised questions about early neutering. In an opinion article, Christine Zink, DVM, Ph.D., Dipl. ACVP, weighs the advantages and disadvantages of early versus late neutering when considering the performance and health of canine athletes.

The article, “Early Spay-Neuter Considerations for the Canine Athlete: One Veterinarian’s Opinion,” appears on Dr. Zink’s website. Click here to review the thought-provoking article and to look at the references.

Zink assembled 18 references to support her article. Some show that dogs spayed or neutered early are taller than dogs spayed at an older age. Zink notes that sex hormones have a role in bone density. She concludes that the structural and physiological differences in dogs neutered early may be the reason veterinarians are seeing a higher incidence of orthopedic disease such as CCL rupture and hip dysplasia than in dogs neutered after 5 1⁄2 months of age.

30-Year Campaign
For the past 30 years, our profession has urged the public to spay and neuter dogs and cats for a host of beneficial reasons, including population control and the avoidance of breast and testicular cancer. With client education and marketing, our profession has succeeded in making early spay-neuter programs our national custom, primarily for control of the population explosion.

Shelter medicine experts developed the concept of ultra-early neutering of kittens and puppies before adoption. This practice was embraced by thousands of rescue organizations across the nation, including the Peter Zippi Fund for Animals– founded in 1977 by yours truly–which has rescued and placed more than 11,600 animals.

Our organization looked at the data and felt that early spay-neuter was the best answer to address the horrible situation in American shelters, where animals are euthanatized because they were born feral, dumped or unwanted. 

Mounting epidemiological evidence shows that we might be jeopardizing the well-being of pet dogs with the early neuter policy. The data are not persuasive for felines, but there are some issues with the size of the urethra in early neutered tom cats that may affect their health.

My special interests in practice have been cancer medicine and pet hospice. It is earth shattering to consider that some of the cancers we have been battling may have been enhanced by early neutering instead of the reverse! 

Zink points out a retrospective study published in 1999 by Ware, et al, that found a five times greater risk of cardiac hemangiosarcoma in spayed vs. intact female dogs.

Hemangiosarcoma is one of the three most common and devastatingly fatal cancers in larger dogs, especially German shepherds and golden retrievers. We see it most commonly as malignant growths in the spleen, but 25 percent of cases involve the heart and 25 percent appear in multiple locations. 

Ware’s study also found a 2.4 times greater risk of hemangiosarcoma in neutered dogs as compared to intact males.

This information has been around in journals for almost a decade, but it takes time to consider large epidemiological studies as evidence-based medicine useable in decision making.

A 2002 epidemiological study of 3,218 dogs done by Cooley and Glickman, et al, found that those neutered before age 1  had a significantly increased chance of developing osteosarcoma. Another study showed that neutered dogs were at a two-fold higher risk of developing osteosarcoma.

Lack of Proof
We need to re-examine the common belief that neutering dogs helps reduce prostate cancer. In fact, Obradovich, et al, in 1987 reported that neutering provides no benefit in protecting dogs from prostate cancer. Neutering definitely offers protection from recurrence of androgen hormone dependant perianal tumors.

Clear epidemiological evidence exists that female sex hormones cause mammary cancer. There is a slightly increased risk of mammary cancer in female dogs allowed to endure one heat cycle and the risk is increased with each additional estrus until the dog is 21⁄2 years old.

In dogs, 30 to 50 percent of mammary tumors are malignant. In cats, the rate of malignancy is 95 to 98 percent. Therefore, all mammary tumors in dogs and especially in cats should be surgically removed and biopsied as soon as they are detected. Early detection and excision can improve the prognosis.

It is well known that the incidence of urinary incontinence in early-spayed female dogs is higher than in non-spayed female dogs. This is due to the role that ovarian hormones play in the maintenance of genital tissues and urogenital contractility. 

Aron, et al, in 1996, reported that male dogs neutered early had an increased risk of developing urethral sphincter incontinence. A health survey of several thousand dogs by the Golden Retriever Club of America showed that spayed or neutered dogs had a greater risk of hypothyroidism. In 2001, Howe and Slater reported an increase of infectious diseases in dogs spayed or neutered at or before 24 weeks of age versus over 24 weeks of age. The 2005 AKC-Canine Health Foundation reported a higher incidence of vaccines reactions in neutered dogs as compared to intact dogs.

The Vaccine Question
It is evident that we need more information and more leadership from our academicians to clarify our positions on early neutering. This reminds me of the profession’s dilemma over the issue of using certain vaccines that were known to be potentially carcinogenic in 1 in every 1,000 to 10,000 cats.

If it was your cat that got feline vaccine-associated sarcoma, it is a huge and important issue. The actual rate of disease is difficult to assess and is most likely under-reported in pet animals, given the stringent requirements of informatics reporting.

Many organizations that breed service dogs, such as Guide Dogs for the Blind and the Morris Animal Foundation are keeping records that may answer these questions.  

I suspect that the abnormalities discussed above are real and underreported in the veterinary literature. The best thing we can do is to advise our concerned clients individually, looking at each animal’s role (agility, sports, jogging buddy, sled dog, service dog) within the human-animal bond. <HOME>

Alice Villalobos, DVM, offers insights into the human-animal bond, animal welfare and the relationships among pets, owners and veterinary practitioners. She is a member of the American Assn. of Human-Animal Bond Veterinarians and is on the editorial review board of the Society for Veterinary Medical Ethics.


Posted: Dec. 1, 2008

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Is Early Neutering Hurting Pets?

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Reader Comments
Had my beautiful Samoyed castrated at 6 months old,at 30 mnths old he was diagnosed with osteosarcoma of hind leg,lost him when he was 38 mnths old 11 jan 2013 ,left devastated and heartbroken.
Cindy, International
Posted: 5/17/2013 1:14:35 AM
(LINK Spayng too soon has got to have some debilitating affects on a dog's health and longevity. Innately, we as pet owners know it. Consequently, some of us have chosen to wait until our dog is of spaying age. The result is that we sometimes experience unwanted or accidental litters that add to dog overpopulation. For those who choose to wait, there is another option-a dog chastity belt ( We are selling our pet anti-breeding system (PABS) in over 30 countries. We are now seeking to spread the word in the US that you can wait with confidence. Please visit our crowd funding page and support our effort to get the word out. (LINK Spread the word to your network and help us make a generation of longer living healthier dogs.
Patrick, Dallas, TX
Posted: 2/10/2013 3:02:31 PM
I agree with this. My dog's healh deteriorated somewhat after she had to be spayed owing to development of Pyometra. It was an emergency situation, and there was no choice other than spay surgery, to save her life.
It is possible of course, that the Pyometra, and her subsequent development of kidney insufficiency (successfully treated)....mammary cancer (again successfully treated with radical surgery)...and eventual Hemangiosarcoma -all within the space of eight months -could have been age-related. That, of course, cannot be proven.
However I noticed that even at age 12-13 and even going on 14 she was remarkably fit and well, to an amazing degree, (equal fitness and condition to a four-five year old dog) -as an "entire bitch".

I am pretty sure (?) her development of mammary cancer was directly related to her being entire all of her life, yet it is strange that this only developed AFTER she was spayed (about a year later) -when a previously benign small breast tumor, which had been needle-aspirated twice, had been there for at least four years, and I opted not to have removed, suddenly grew rapidly and turned malignant.

While entire she was the fittest healthiest dog you can possibly imagine. After spaying she was still having a great life, and still pretty athletic, but was not the same -not quite. She was my dog, and I could sense subtle changes in her. Nothing profound, and nothing worrying, but she was just "different" slightly. Although she was showing no normal signs of aging, such as failing senses, arthritic joints, etc.

Tentatively, I would say from my own (layperson's) opinion, based on observance alone, that she was fitter as an entire bitch, than after she had been spayed.

However, that said, it's wise to be extremely watchful for signs of Pyometra in entire bitches. It can be difficult to spot as it is just beginning. In my dog's case there was only mild lethargy at first, and she even ate food! It was only because I was educated about Pyometra that I took her straightaway to emergency when I noticed mild contractions in her belly muscles. This would be easy to miss.
Pyometra can kill an otherwise healthy dog in hours, and it is extremely common.

(I am sorry but I had no option than to fill in the "state" box in order to submit my comment. I am based in the UK)
Sylvia, Bath UK, AL
Posted: 7/25/2012 8:21:23 AM
Had My Male Pyrenean Pup castrated at 9 months old as he was a big boy and starting to demonstrate some dominant behaviour traits. Within 10 months he had developed a lameness which was diagnosed as osteosarcoma 8 weeks later. By the time the tumor was discovered it had matastisis to his lungs. We lost our beautiful boy at just 22 months of age. It broke our hearts!
Sue, Lancashire UK, AL
Posted: 6/16/2012 4:17:50 AM
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