Q: In Europe, there is a tendency not to neuter dogs, but the opposite is true in the United States. I lived in Germany for four years. Dogs were welcome in many establishments and were seldom aggressive, and unwanted litters and strays seemed not to be an issue. Why is there such a difference?
A: First, let’s discuss terminology. The term “spay” refers to sterilizing female pets by surgically removing their uterus and ovaries. “Neuter” can refer to sterilizing male pets by surgically removing their testicles. But sometimes neutering can refer to surgical sterilization of both male and female pets. For simplicity, I’ll use the term neutering in this column for both male and female pets.
In the last month, I’ve treated more sexually intact dogs with problems related to neuter status than I’ve seen in years. Perhaps this relates to findings that have emerged over the last decade regarding possible health risks of neutering. Or perhaps all those puppies adopted during the pandemic (that were never neutered due to limited access to vet care or other perceived obstacles) are now old enough to develop these problems. Regardless, the pros and cons of neutering have generated more heated conversations among vets and dog owners in the last few years than in the last half-century.
On one side, early neutering is considered responsible pet ownership in many Western countries (including the United States, Australia and New Zealand). That mindset has led to mandatory neutering laws, shelter programs, campaigns and discount incentives. In the United States, more than 60 percent of owned dogs and 80 percent of owned cats are now neutered. The neutering movement began in the United States in the early 1970s, when there were high rates of pet euthanasia and free-roaming dogs due to pet overpopulation. (The movement was famously popularized by Bob Barker, who concluded episodes of “The Price Is Right” with a plea for people to get their pets spayed or neutered.) A reduction of pet euthanasia rates — from about 13.5 million animals in 1973 to about 1.5 million animals per year today — followed. However, changing attitudes toward pets, including a trend to treat them more like family members, might also have contributed to this decline. Recent studies suggest that while neutering programs still help reduce shelter intakes for cats, for dogs, they are more important in controlling free-roaming populations.
On the other side, countries including Norway and Germany have laws that prohibit neutering dogs unless it’s medically necessary, so well under 10 percent of dogs are neutered. Yet stray dogs have not been much of a problem, possibly because of a greater culture of social responsibility. These countries do, however, permit neutering of cats to reduce feral populations. Regulatory authorities in these countries consider routine neutering of dogs unethical and a form of mutilation, alongside practices like ear-cropping and tail-docking. The same authorities do not think male dogs’ embarrassing humping behaviors — or the mess that a female dog creates when in heat — sufficient justification for neutering, regardless of how annoying they might be.
Here’s a breakdown of the medical arguments for and against neutering, and the best time to do it.
The case for neutering
1. It reduces pet overpopulation.
Pet overpopulation leads to overcrowding of shelters and unnecessary euthanasia. It also threatens wildlife and contributes to public health problems like rabies, animal bites and parasite infestations. It’s been suggested that overpopulation problems could be addressed just by spaying females, but that wouldn’t address other behavioral issues common in intact males.
2. It reduces problematic behavior.
Neutering dogs can also help with aggression, roaming and other nuisance male behaviors like humping and frequent territory marking. Although there are studies that suggest that neutering might increase some types of aggression in dogs, such as fear aggression, the effect of neutering on anxious behaviors in dogs might also be confounded by owner behavioral factors.
In male cats, neutering reduces both urine spraying behavior and the pungent smell of their urine.
3. It has health benefits.
Overall, neutered pets — especially females — live longer, in part because they are less likely to roam, which puts them at lower risk for trauma (vehicle or animal fights) and infectious diseases.
Neutering might also increase lifespan because it can prevent life-threatening reproductive tract disorders later in life. In male dogs, these include serious prostate problems, like prostatic infections and testicular cancer, and other less serious diseases (especially benign prostatic hyperplasia).
In female dogs, neutering prevents pyometra (a serious bacterial infection of the uterus that often requires emergency surgery). It can also prevent mammary tumors, which affect around 1 in 4 dogs spayed after 2 years of age (half of these tumors are malignant). In contrast, only 1 in 200 female dogs spayed before their first heat (around 6 months of age) develop mammary cancer; after their first heat, 1 in 13 will develop mammary cancer. This alone could be considered justification for neutering.
When cats are spayed at any age, their risk of mammary cancer is reduced by 40 to 60 percent, and when they are spayed at less than 6 months, it’s reduced sevenfold. Cat mammary tumors are particularly serious — 85 percent are malignant and metastasize. Most veterinary organizations recommend neutering cats by 5 months of age.
The case against neutering
In addition to the cost and the risk for anesthetic complications, studies suggest that — at least for some breeds — neutering might increase the risk for obesity, orthopedic problems and certain types of nonreproductive cancers (like lymphoma, hemangiosarcoma and bone cancer). The studies include those led by Ben and Lynette Hart, veterinary behaviorists at the University of California at Davis — as well as big data studies using medical record information from veterinary corporate hospitals.
Michael Kent, a board-certified veterinary oncologist at the University of California at Davis, urges caution. “Studies that have shown these effects often rely on medical record data (which can be incomplete or inaccurate), include very low numbers of specific dog breeds and are often not adjusted for age,” he said. In a study of golden retrievers led by Kent, for example, age was the most important factor influencing development of nonreproductive cancer, not neutering. Because orthopedic problems and nonreproductive cancers are most common in geriatric dogs, and intact dogs often don’t live to advanced age, it can appear as if neutering predisposes to those problems.
Neutering can predispose female dogs, particularly large breeds, to urinary incontinence. A consensus statement from the American College of Veterinary Internal Medicine recommends delaying neutering until at least after the first heat in breeds that are at risk for urinary incontinence, although evidence for this recommendation is weak. In cats, neutering can predispose to obesity.
So, should I get my pet neutered, and when?
Bottom line — if you’re not planning to breed your pet, have it neutered. If you just adopted a puppy, talk to your vet about the right age to do this given its sex and breed. Personally, I will neuter my next cat before it’s 6 months old. For my next dog, I’ll likely have it neutered between 6 and 12 months, unless I’m worried about orthopedic issues or incontinence. But no matter what, I won’t wait for a dog’s second heat, because of the risk of mammary cancer.
Have questions about your pet’s behavior, health or other issues? Use this form to submit them to Dr. Sykes.
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