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Here’s a question I recently received from a reader:

How old should my dog be when he gets neutered? The recommended age for spaying/neutering seems to keep changing.

As a young boy growing up on a family farm in southern Idaho, the answer as to when to spay or neuter was simple: never. Our male dogs had the run of the 160-acre ranch and visited neighboring spreads when they sniffed a bitch in heat. Yes, there were unwanted pups and serious injuries.

As a young practicing veterinarian in the early 1980s, I was able to deliver a new and definitive answer as to when it’s best to spay/neuter dogs: Ideally, when they were in for their rabies vaccination at 16 weeks (4 months), but definitely before 6 months of age.

Now, as an older practitioner with 35 years of practice and thousands of exam room consultations about spaying/neutering under my belt, the questions I’m asked and the options I explain about sterilization are quite complex.

Dr. Nancy Kay is an author and specialist in small animal internal medicine who has written and lectured extensively on changing perspectives about canine spay- ing/neutering. “Recent compelling research has shed new light on some drawbacks of neutering dogs, particularly at a young age,” she has stated. “Based on what we’re learning, I suspect that veterinarians’ recommendations pertaining to neutering dogs will change significantly over the next decade.”

Here are some of the research studies Dr. Kay referenced:

• A study on Rottweilers demonstrated that dogs neutered before 1 year of age had a three- to four-times-higher risk of developing a particular type of bone cancer called osteosarcoma.
• Another Rottweiler study showed that females spayed before 4 years of age had shorter life expectancies compared to those who were either not spayed or were spayed at an older age.

• A Golden Retriever study demonstrated that a dog’s age at the time of neutering influenced the incidence of two orthopedic issues — hip dysplasia and cruciate ligament disease — and three forms of cancer: lymphosarcoma, hemangiosarcoma, and mast cell tumors.
• A Labrador Retriever study determined that neutering before 6 months of age increased the incidence of hip dysplasia, elbow dysplasia, and cruciate ligament disease.
• A study of Vizslas documented an increased incidence of some cancers in neutered dogs. A variety of behavioral disorders were also more common in dogs neutered before 6 months of age.

These studies suggest that elimination of reproductive hormones can influence disease occurrence and longevity.

“The results of these studies may be breed-specific, but I believe it makes sense to share this information with my clients when they are deciding if and when to neuter their dogs,” Dr. Kay acknowledged. “Whether or not to neuter a responsibly cared for dog who will not be used for breeding purposes is no longer a simple decision.”

Along with newer neutering research, we have newer spaying/neutering techniques. Some newer techniques are catching on in the United States, and Dr. Kay is a vocal advocate of two of them:

• Ovariectomy: Traditional spay surgery (ovariohysterectomy) involves removal of the uterus and both ovaries. Just the ovaries are removed in an ovariectomy. Research has suggested that there’s simply no good reason to routinely remove the uterus. Removal of just the ovaries induces sterility and is a simpler surgery.
• Zeuterin: The use of Zeuterin to induce sterility in male dogs is also referred to as zinc neutering because a small volume of a zinc arginine solution is injected into each testicle. This procedure is quick, less expensive than surgical neutering, and there is no need for general anesthesia. Additionally, Zeuterin leaves the dog with the ability to continue to produce some testosterone; surgical neutering leaves him with none. This may prove to be protective against some of the orthopedic diseases, cancers, and behavioral issues documented in the studies cited above.

Just as with any medical or surgical procedure, think about the pros and cons when contemplating spaying or neutering your dog. If your dog was not already neutered when you adopted him, Dr. Kay strongly encourages an informed discussion with your veterinarian before making a decision.

In the range of my own 60-year lifetime and 35-year career, I’ve seen the arc of spay/neuter recommendations go from “seldom/never” to “always” to “maybe.” The question of if to spay or neuter — and if the answer is yes, when to do the procedures — is best handled with an in-depth discussion with your local veterinarian.

Read more about spay/neuter:

• When Can I Have My Dog Safely Spayed or Neutered?
• A Checklist for Getting Your Puppy Spayed or Neutered
• Is It Always the Right Thing to Spay or Neuter a Dog?

About the author: Dr. Marty Becker, “America’s Veterinarian,” has spent his life working toward better health for pets and the people who love them. The author of 24 books, Dr. Becker was the resident veterinary contributor on Good Morning America for 17 years. He is currently a member of the board of directors of the American Humane Association, as well as its chief veterinary correspondent; a founding member of Core Team Oz for The Dr. Oz Show; and a member of the Dr. Oz Medical Advisory Board. When his schedule allows, he practices at North Idaho Animal Hospital. Connect with him on Facebook, YouTube, Pinterest, Twitter, and Google Plus.