Ben Hart likes to spin my head around. He is a veterinary behaviorist from the University of California at Davis, and we get together every year at the annual meeting of the International Society for Anthrozoology. Last year in Cambridge he told me about a new research project he was conducting on the downside of routine neutering of pets. Then he swore me to secrecy.
Unwanted pets have been a problem in the United States for a long time. For example, in 1867, the streets of New York were awash with homeless dogs. The city council took action. Stray dogs were impounded and drowned en masse via a device dubbed "the canine bath tub." The "tub" was an iron crate seven feet long, four feet high, and five feet across. Forty-eight dogs at a time were jammed into the heavy cage. It was then lifted up by a crane, swung over the East River and submerged. Ten minutes later, the cage was hauled to the surface, the carcasses removed, and the cage reloaded with another batch of strays. Dog catchers could kill 750 animals in a seven-hour shift.
In the 1970s, roughly 24 million dogs and cats were killed each year in American animal shelters. By 2007, however, the number had dropped to four million. There are a couple of reasons for the dramatic decline in unwanted pet euthanasia. One is that animal protection organizations succeeded in convincing Americans that adopting a shelter dog is morally preferable to purchasing a purebred puppy. (This trend has devastated the American Kennel Club. AKC puppy registrations plummeted from one and a half million in 1992 to less than 600,000 in 2010.)
An equally important reason for the decrease in unwanted pets is the success of the spay and neuter movement. Due to the efforts of animal protection organizations, a large majority of dogs and cats in the United States are now "neutered." (This practice is more accurately referred to as "de-sexing" in some countries.) Indeed, responsible pet ownership is now equated with having your companion animal's testicles or ovaries removed, and in some communities it is illegal to allow a dog to reproduce without a special permit. Given the benefits of having fewer homeless dogs and cats, it would seem that de-sexing our pets is a no-brainer. But, it turns out that removing an animal's testicles or ovaries can increase its chances of getting cancer, joint diseases, and dementia.
The Bad News: Neutering Can Be Bad For Your Pet's Health
Ben's research team examined the records of 759 golden retrievers seen at the UC-Davis veterinary hospital between 2000 and 2009. (Here is a copy of their article.) They focused on goldens because of the breed's popularity and their propensity for cancer and bone and joint disorders.) Here is a summary of the results. (Note that "early-neutered" animals were de-sexed before they were one year old.)
Hip dysplasia -- twice as common in early-neutered males as intact males. No effect on females.
Knee ligament damage -- higher incidence in early-neutered males and females.
Lymphatic cancer -- three times more common in early neutered males than intact males. No effect in females.
Cancer of blood vessel walls -- four times more common in late-neutered than intact females. No effect in males.
Mast cell tumors -- significantly more common in late-neutered females. No effect in males.
In short, the researchers concluded that early and/or late neutering increased the risks of all five diseases in golden retrievers. Their study was restricted to one breed, but other studies have also reported deleterious consequences of de-sexing healthy dogs. For example, castrated elderly male dogs are at greater risk for dementia. And another recent study found that neutering increased aggression problems in female dogs.
As you might expect, the relative health costs and benefits of routine neutering on the health of individual animals have become a topic of controversy. (For reviews, see here and here.) For example, the American Veterinary Medical Association's brochure on spay and neuter omits any mention of the negative effects of de-sexing pets. Yet several recent reviews of the impact of neutering on dogs concluded that the negative health effects may well outweigh the positive effects. Indeed, after reviewing dozens of research articles on de-sexing pets, a research team headed by Clare Palmer of Texas A&M University wrote (here), "Our overall conclusion is that routine neutering of companion animals, and notably male dogs, is not morally justified." Ouch.
The Moral Dilemma
No one wants to go back to the days when 24 million unwanted cats and dogs got the blue needle each year. But here is the ethical quandary. While neutering reduces suffering in general, it may well put your individual pet at greater risk of a serious disease such as cancer. It's a classic conflict between what is best for the individual versus what is best for society.
Is there an alternative to routine de-sexing of pets? Perhaps. While the American ideal of near universal neuter seems to be spreading, Europeans are less inclined to de-sex their pets. This is particularly true in Scandinavia. In Sweden, fewer than 7 percent of female dogs and even fewer males are neutered. Indeed, until 1988, it was illegal for Swedes to remove the reproductive organs of their dogs and cats unless medically indicated. Stine Christiansen, a Danish anthrozoologist and veterinarian, told me that when dogs are neutered in her country, it is nearly always for medical or behavioral reasons rather population control. She says that there is no pet overpopulation problem in Denmark because people simply do not let their pets run loose. The same is true in Norway, where, with a few exceptions, it is presently illegal to de-sex healthy dogs.
I mentioned the UC Davis paper on golden retrievers to Jane Finneran, a highly regarded dog trainer. Jane was not keen on the idea that dog owners who don't let their animals run loose would do better to not neuter their pets. "Far more puppies are killed in shelters from the 'oops' than any number of golden retrievers who will die from cancer!" she told me. On the other hand, when the evolutionary psychologist Gad Saad saw the study, he commented, "I have always felt very conflicted and uneasy about 'playing God' with our companion's reproductive destiny."
I expect Jane is right. But in light of the UC-Davis study and similar findings by other researchers on the health effects of neutering companion animals, I am now troubled by my unquestioning enthusiasm for plucking the gonads from every dog and cat in America.
Post Script: Ben recently sent me this e-mail. "Hal, a possible solution is vasectomy for male dogs and tubal ligation for females. These operations are much less expensive and less traumatic for the dogs. The weird thing is we don't teach these simple operations yet in vet schools, but shelter vets could learn it in an afternoon wet lab."
(For another of Ben Hart's controversial ideas, see his musings on how animals prevent and treat diseases.)
Hal Herzog is Professor of Psychology at Western Carolina University and the author of Some We Love, Some We Hate, Some We Eat: Why It's So Hard To Think Straight About Animals.