If you think that spaying and neutering is the right thing to do, well, I would never argue. On the other hand, if you did not subject your dog to surgical removal of the testicles, ovaries, and uterus, procedures I have done thousands of times in my career, I wouldn’t challenge you to a duel. Either decision can constitute responsible pet ownership.

I believe that taking the time to read this blog qualifies you as a committed dog parent. You’re not going to allow unrestricted, willy nilly, gratuitous, canine promiscuity. The hugely important priority of controlling runaway growth in the population of unwanted dogs isn’t a problem that you are going to worsen. You just want your dog to be as healthy as possible because you love that little creature. I get it. I’m that way with this man’s best friend, a Border collie named Miss America.

Why Miss America, you ask? Well, gee, she’s cute and perky and she wants to cure world hunger – all by herself, I might add. What other name could she have? She is delightful. When MA, as she is known to her family, was adopted as a baby 10 years ago there was a lot we didn’t know about the effect of age at the time of surgery.

Knowing that I would never allow my little girl to consort with suitors of questionable character, her reproductive and moral issues were never a factor in deciding when or if I would spay her. I did it for sound medical reasons but, had I known then what I know now, I might have timed it differently.

I have also had male dogs of major importance in my life. I’ve neutered them too. A big, wonderful Airedale named Juan Gomez, UD may have had his procedure at a later age had the research been available when he was a kid. (The UD stands for Utility Dog. Juan and his daddy were serious, in fact nationally ranked one year, obedience competitors.)

We’re lucky to live in the information age. Modern medicine provides many tools for the repair and management of physical and behavioral disorders of pets. Here, I’m going to share the results of research that can reduce some risks. This may help guide your decision on when or even if to spay or neuter your next dog.

Most veterinarians recommend spaying a female dog before her first heat cycle or neutering a male before he starts to get too studly, you know, brawling and staying out all night skirt chasing. What follows are a few considerations that might influence your decision.

First, what won’t happen: Spay/neuter status or timing has nothing to do with trainability. But (there are always buts, aren’t there?) dogs who have been surgically sterilized prior to age 5 months may be more prone to noise phobia, separation anxiety, and submissive urination. These are not training issues, rather they are behavior disorders. But (there’s that word again) it is harder to obedience train a dog who freaks out and wets himself when someone approaches to say hello.

On a more sobering note, spayed female dogs can be more prone to reactive behavior toward unfamiliar people and even aggression toward family members regardless of their age at the time of the procedure. Don’t fret; these are statistical findings. I certainly treat aggression toward pet parents in my behavior practice but the overwhelming majority of spayed dogs are gentle and sweet. Genetic factors play a part in many of these cases.

A commonly cited reason for spaying is to reduce the risk of mammary (breast) cancer. These are the most common tumors, benign or malignant (~50% in each category), in female dogs. The average age is 10 years with some breeds (boxer, Brittany, cocker spaniel, dachshund, English setter, English springer spaniel, German shepherd, Maltese, miniature poodle, pointer, toy poodle, and Yorkshire terrier) at higher risk. Being unspayed raises a dog’s chances of mammary cancer 7 fold. Age of spaying matters. A female dog spayed before her first cycle (under age 6 months) faces a 0.5% mammary cancer risk through her life. This rises to an 8% possibility if she’s spayed between her first and second cycles (usually between ages of 6-12 months). Those having the procedure after their second heat cycle face a 26% risk of mammary cancer. Age 5-6 months is a good time but other considerations intrude on the discussion for large breed dogs.

The boys have their own challenges. If you have your male dog neutered he is at a 2-8 times higher risk of prostate cancer than intact (unneutered) dogs. Does this matter? Prostate cancer occurs in fewer than 1% of male dogs. But a swollen prostate (benign prostatic hypertrophy-BPH) is an advancing problem with age. Unneutered male dogs who reach age 9 years have a BPH risk of about 100%. Inflammatory prostatic disease can follow BPH but neutering – even in the later years – treats both problems.

Another turn in the discussion comes with malignant bladder cancer, with spayed and neutered dogs having a 2-4 times higher risk than those who kept their reproductive organs. Unspayed females have a somewhat higher risk than their unneutered male counterparts.

Bone cancer (osteosarcoma) and cancers of the blood vessels (hemangiosarcoma) are common malignancies in middle aged to older dogs, especially the big breeds. These are aggressive, often fatal, and occur more commonly in spayed and neutered dogs. Spaying a female Golden retriever after age one year raises her risk of blood vessel cancer 4 fold when compared with girls who were spayed under age one year. A large study showed that the blood cancer lymphoma also affected spayed Golden females at a higher rate than those who were not spayed. The same is true of mast cell tumors, another malignant cancer.

The truth is that we are all intended to function with all of our parts. The gonads (ovaries in females, testicles on males) secrete sex hormones that have far-reaching influences. When we spay or neuter a dog before they have finished growing their bones actually get longer. This can affect not just the length but the shapes of the bones. Spaying and neutering a less than fully mature dog raises the risk of hip dysplasia and cruciate ligament rupture in the knees. For small dogs these may not be significant risks; for their bigger brethren it may be safer to wait until natural bone growth has topped-out or at least until they are 6 months or older. Of course, there are other factors including heredity, whether the dog carries excess weight, and the type of food. (Too much nutrition too early raises the risk. Feed large breed puppy food to large breed puppies.)

Obesity is a disease that’s more prone to occur in spayed and neutered dogs. This problem, a common contributor to hip dysplasia and cruciate ligament ruptures, is less prone to occur if the procedure is done young – less than age 5 months. But – and this is a very important but – a committed pet parent can carefully feed and consistently exercise their dog and control his or her weight just fine.

There are other connections. Spayed females are more prone to low thyroid hormone levels and possibly urinary infections. And they can dribble urine while asleep because of their low estrogen levels. This side effect of spaying, more prone to occur if the surgery is done under age 3 months, sounds like a messy problem but it’s easy to control with safe medication. My girl dog, Miss America, was a somnolent dribbler but not since I’ve medicated her for it. So it’s not a real problem.

Horrible pus-filled infections of the uterus, called pyometra, occur only in dogs who have a uterus. Spaying includes removal of the uterus. In the early years of my career there were a lot of unsprayed middle-aged and older dogs with pyometra. I did many surgeries to cure these dangerous infections. Today’s young veterinary graduates rarely see these because few dogs still have a uterus. Interestingly, breeding females who’ve carried litters to full term are at low risk of uterine infections. Reproductive tracts have a purpose. They are actually meant to be used.

Here’s one correlation we can all relate to: Spayed and neutered dogs are likely to live longer.

Can we make sense of all of these conflicting correlations and apparent contradictions? Should your dog be spayed or neutered? If you have it done, what age is best? Well, I won’t tell you those things but I will nudge you in one direction or another. If you want puppies don’t sterilize. Want more?

If you run a shelter you are dealing with large numbers of creatures. The broad rule in population control is to spay and neuter early, like around 8 weeks of age. Studies have shown that relatively few adopters return for the procedure later even to retrieve a significant cash deposit.

But if you are a pet person, like me, the size and activity of your dog are significant factors. Large breed dogs should be allowed to keep their gonads until their bones have reached full growth, around 18 months. Smaller dogs are best surgically sterilized at about age 5-6 months.

What if you and your dog prefer to go au naturale? Hey, I get that. Beyond a delightful spayed dog and two sweet neutered cats the Nichol family includes 4 humans. The members of Homo sapiens still have all of our anatomy, and we intend to keep it that way, darn it.

Miss America the Border collie? She is a medium sized dog. I spayed her at age 6 months, before her first heat cycle and before her bones finished growing. We didn’t have all of the above research then. MA later had a bone growth problem in each of her shoulders that did fine following surgical repair. Was it related to being spayed before her bones finished growling? We’ll never really know. But she hasn’t had mammary cancer. I’m paying attention. I’ll always do whatever it takes for her to enjoy a great long life in our family.

So if you are responsible and can reliably prevent canine hanky panky I am fine with getting out of your way and letting you make the call. You’ve read this diatribe. I encourage you to make your decision based on scientific evidence instead of emotion. I will urge you, like any good pet parent, to get to know your veterinarian. Follow our advice. We are almost all pretty darn good at what we do. Trust modern medicine. Spaying and neutering can be essential to saving a well-loved life.

I hope you find this information useful. You’re welcome to share this blog with any of your pet-loving friends. If they are considering having their dog spayed or neutered, well, they’ll be glad for the advice.

Each week I share a short video, a podcast, or a blog to help bring out the best in pets. You can sign up at no charge on my website, drjeffnichol.com. And when you do, I’ll send you my free at-home pet first aid and CPR guide.

Thanks for your dedication to your pets. I’m Dr. Jeff Nichol.