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Latest health and behavior news and advice from the veterinarians at Tufts University.

Features January 2013 Issue

Male Neutering: Maybe You Shouldn’t

This decision used to be automatic. But you and your vet should take the time to weigh the risks and the surprising benefits.

The directive seems simple enough. Spay and neuter your pet dog by the age of 6 months or so, and not only will you be reducing the risk for various medical conditions, you will also be playing an important role in canine population control.

Neutering your male dog will make him less aggressive, but could render him more prone to some serious illnesses.

For female dogs, the evidence for that line of thinking is clear and irrefutable. Dogs spayed before their first estrus, or heat, have only a 0.5 percent risk for developing cancer of the mammary glands, the most common type of malignant tumors in females. After just one estrus, the risk rises to 8 percent, and after two estruses, 26 percent — more than 50 times the risk for a dog spayed before she matures sexually. It is believed that spaying’s effect on the hormones estrogen and progesterone are involved in reducing the chance for cancer to develop.

For male dogs, on the other hand, the health benefits of neutering, particularly during the first year of life, are not so clear. In fact, some research suggests a dog who has undergone castration may be at increased risk for various ills.

Do Europe and other parts of the world, where castration is often frowned upon or strongly discouraged, know something that we don’t?

“For the owner of a male dog, the decision of whether to neuter is not straightforward,” says Tufts veterinarian and Your Dog editor-in-chief John Berg, DVM, “but the issue is worth exploring.”

The pluses and minuses of castration

For dogs who aren’t owned, that is, stray dogs housed in shelters, veterinarians agree overwhelmingly that the benefits of neutering outweigh all other concerns. As many as a million perfectly healthy male dogs undergo euthanasia every year. The population control conferred by castration is unmatched by any potential benefits to the health of these homeless animals. Furthermore, studies show that dogs are more readily adopted from shelters if they’re already neutered.

It’s in consideration of pet dogs already living in people’s homes that the question of whether to neuter becomes somewhat murkier.

On one hand, neutering is beneficial for a male dog because it is apt to render him less aggressive than he would be otherwise. It is well established that intact male dogs are significantly more likely to bite than neutered males, and they are also more prone to dog-on-dog aggression — both of which make them harder to keep as pets.

Neutering is also good for a male dog’s physical health because it prevents perineal hernia, a fairly common condition in which abdominal organs herniate, or protrude, through the pelvic canal. Perineal hernias are usually not life-threatening but do require surgery.

Neutering also prevents benign prostatic hyperplasia, commonly referred to as BPH, as well as some rarer prostatic conditions such as infections. All diseases can cause a male dog to have difficulty urinating or defecating.

BPH is not a a life-and-death concern because castrating a male dog at the time the problem develops will cure him. But some other prostatic diseases cannot be addressed with castration alone, and may even require prostatic surgery. Neutering ahead of time eliminates the risk, worry, and potential expense.

On the other hand, some research suggests that neutering a young dog increases his chance of developing prostate cancer later on in life by as much as two- to four-fold. But because prostate cancer is very rare in dogs, even a slightly higher rate in intact dogs is not a significant concern, Dr. Berg says.

Research also suggests that neutering increases a male dog’s risk for developing bladder cancer in the range of two- to four-fold. But like prostate cancer, bladder cancer is uncommon in dogs, accounting for, at most, 1 percent of all of their malignant tumors.

More concerning is that some data suggest neutering increases the risk for hemangiosarcoma, a cancer of the spleen. It also raises the risk for osteosarcoma, which is cancer of the bones. Both are among the most common types of canine cancer (for female as well as male dogs, but with female dogs, the drastically reduced risk for mammary cancer upon spaying trumps all other health concerns). And both are almost uniformly eventually fatal (although appropriate treatment can extend life significantly).

Castrated male dogs may have almost two and a half times the risk for developing hemangiosarcoma as their intact brethren, according to preliminary research data. And neutering early in life can increase the risk for osteosarcoma up to two-fold.

How does one make heads or tails of all this? It’s important to consider your own particular dog, including his breed, when discussing the option of neutering with your veterinarian. For instance, while the incidence of bladder cancer is quite low in dogs in general, Scottish terriers are predisposed to it, so it may be wise to avoid neutering in that particular breed.

Likewise, hemangiosarcoma tends to occur most commonly in large-breed dogs, especially German Shepherds, Golden Retrievers, and Labrador Retrievers. Osteosarcoma, too, occurs virtually always in large-breed dogs, such as Dobermans, Great Danes, Irish Wolfhounds, and Rottweilers. Research on one set of Rottweilers showed that those castrated before one year of age had a significantly greater risk for eventually getting osteosarcoma than those castrated later than the age of one (although the overall incidence of osteosarcoma in that particular Rottweiler population was much higher than in the general population, which suggests a hereditary component). Thus, if your male dog is a Toy Poodle, deciding against castrating him for the sake of avoiding hemangiosarcoma or osteosarcoma is misguided. For large breed dogs, waiting until the dog reaches maturity may be a reasonable approach.

Of course, if you have small children in the house and a male dog whose breed is known for an aggressive temperament, you may want to have the pet neutered as a young pup no matter what his predilection for various cancers.

“It’s a case by case basis that requires discussion with the dog’s veterinarian,” says Dr. Berg. “There’s no one clear rule that’s right for all male dogs.”

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