What age to spay or neuter my dog?
Sometimes I yearn for the ‘good ol’ days’. Back then, if a client wanted to know when or at what age to spay or neuter their dog, the dialogue went like this:
Client: “What age should I spay (or neuter) my dog?”
Me: “At six to seven months.”
… and then we would talk about something else. It was a quick and easy conversation that required very little thought.
Now when a client poses that same question, my answer starts with “Well, that depends…”, and then devolves into a ten minute lecture full of conflicting information. It is no longer a simple question with a simple answer*, and my advice differs depending on who I’m talking to.
Orthopedic conditions such as cruciate ligament rupture or hip dysplasia are affected by the age that the dog has been spayed or neutered
*Ironically, I had first started writing this blog on the flight back from the WAO worlds in Spain just a few months ago, and since that time more information has come forward that complicates the issue even further. Now the question isn’t just “At what age should I spay or neuter my dog?” but also “Instead of a spay or neuter, should I consider a vasectomy or tubal ligation for my dog?”
I was originally going to incorporate both questions into the same blog, but that just made my long rambling explanation even longer, so I decided to tackle the vasectomy/tubal ligation question in part #2. So for now, let’s just address the question of what age to spay or neuter your dog.
So, where was I? Oh ya….
The reason why this question is so much more complicated to answer these days is because now we know a lot more than we used to about the effects of spaying or neutering at an early age. There are benefits and there are drawbacks. We’ve known about the benefits for some time but have only learned about the drawbacks more recently. Here is an overview of the many factors to be considered:
Exiting the tunnel at the BC/Yukon regional agility championships
Mammary tumours are the single most common type of tumour found in in-tact female dogs. Although most dog mammary tumours are benign, as many as 1 in 5 in-tact female dogs will develop malignant breast cancer in their lifetime.1,2 Other research has shown that the risk of breast cancer is almost non-existent in dogs that have never gone through heat. By spaying your dog before the 1st heat, you reduce the chance of breast cancer by 99.5% compared to intact dogs. By spaying after the 1st heat but before the second heat, you reduce the chance of breast cancer by 92%. If you fail to spay your dog before 2.5 years of age, or before they have gone through 2 heats, your dog is just as likely to develop malignant breast cancer as a dog that has not been spayed at all3. However, spaying after the 2nd heat may still reduce the chance of benign mammary tumours from forming4.
Bottom Line: Spaying before your dog’s 1st heat, and especially before the 2nd heat greatly reduces the chance of developing malignant mammary tumours during their lifetime. Spaying after the second heat won’t reduce the incidence of malignant cancer but may reduce the chance of benign cancer (and the surgery that goes with it).
Urinary incontinence is uncommon in intact female dogs, but relatively common in spayed females. The incidence of urinary incontinence due to spaying is estimated to range from 3 to 21%, depending on the researcher5-18.
Other factors are at play as well, including breed genetics and size of the dog. One study of boxers found that 71% were likely to develop urinary incontinence if they were spayed after their 1st heat, but if they were spayed shortly before their 1st heat, that risk could be cut in half19-21.
Another study found that dogs spayed before 3 months of age were more likely to develop urinary incontinence22.
Bottom Line: Spaying your dog increases the chance of urinary incontinence. It would appear that to minimize this risk (in boxers anyway), the best time to spay your dog is shortly before her 1st heat.
This patient received a TPLO to repair a ruptured cruciate some time ago
It has been demonstrated that spaying or neutering before your pet is fully grown won’t change the rate of growth, but it will delay the closure of growth plates23,24. This results in a longer leg length when compared to intact dogs.
It is also believed that this may contribute to a steeper slope of the tibial plateau, which has been identified as a cause of cruciate ligament rupture. Spayed or neutered dogs are two to three times as likely to rupture their cruciate ligaments as intact dogs are25,26. Spaying females before six months of age makes them 1.6 times as likely to rupture their cruciate ligaments26. At this time, there is no reason to believe that spaying or neutering a dog after it is fully grown predisposes it to cruciate disease. One school of thought is that the later you delay the age of spaying/neutering, the less the chance of developing cruciate disease, up to 17 months of age. This theory is supported by the data that will be discussed in part 2 of this blog.
One study found that 6.7% of dogs neutered before 5.5 months of age developed hip dysplasia, whereas dogs neutered between 5.5 and 12 months of age only had a 4.7% incidence27.
Bottom Line: Delaying spay and neutering until after your dog is fully grown will reduce the chance of rupturing the cruciate ligament down the road. Waiting until your dog is at least 6 months of age will reduce the chance of developing hip dysplasia.
The increased incidence of aggression and other undesirable behaviours in intact males is well documented28-32. Neutering before the onset of puberty is one way to decrease the chance of these behaviours from manifesting. Researchers concluded that neutering decreases inter-dog aggression by 62%, and roaming by 75%. Dogs neutered earlier in life tend to be less reactionary33,34.
Bottom Line: To avoid aggression and other undesirable behaviours, neuter male dogs before puberty.
So what do you recommend?
Again, the bottom line answer is “Depends”. It depends on who the client is, and who the dog is.
If the client represents an animal shelter, whose primary concern is to not contribute to the pet overpopulation problem, I recommend spaying or neutering all dogs before they get adopted out, from 7 weeks of age upward.
For the owners of female dogs, one has to weigh the risks of malignant mammary cancer against those of potential cruciate ligament rupture or hip dysplasia. If I had to choose between the two, I would rather have a ruptured cruciate ligament than malignant cancer. For that reason I generally recommend spaying as late as possible before the first heat – 7 months of age in smaller dogs, but closer to 10 months in very large dogs. That is what I would do if it were my dog, except of course this issue gets more complicated with part 2 of this blog.
However, for working, or competition, or otherwise very athletic dogs, cruciate ligament rupture is not something to be taken lightly. For that reason, some owners take the opposite approach and make it a priority to minimize cruciate disease by not spaying their dog before 17 months of age, and cross their fingers that she doesn’t go through a second heat before then. Others choose to split the difference and spay their dog at 17 months of age, or 5 months after her first heat, whichever comes 1st. In doing so, they still maintain a 92% reduction in the likelihood of breast cancer, and minimize the risk of cruciate ligament rupture at the same time.
Other factors can also play a role in the decision of when to spay or neuter – these two testicles came from the same patient, but one was cryptorchid or “retained” inside the body wall, so never grew to a normal size. Retained testicles are 13 times more likely to develop testicular cancer.
Male dogs don’t face the same risk for malignant breast cancer as a result of not being neutered before puberty. However, the onset of puberty can lead to undesirable behavioural issues.
For routine family situations, I recommend neutering male dogs before puberty.
For working, or competition, or otherwise very athletic dogs, many owners elect to delay neutering until 17 months of age. They monitor their dog for behaviour changes, and respond by neutering earlier if they see unwanted changes following the onset of puberty.
All owners who delay spaying or neutering until after puberty need to remain hyper diligent about preventing unwanted puppies. The only way to guarantee that a sexually mature dog cannot reproduce is to have a vasectomy or tubal ligation performed.
I hope this helps… It’s a complex issue with no clear best answer for all situations. Hopefully though, by learning about the major pro’s and con’s, you are in a better position to decide what is best for your individual situation and for your pet.
As promised, part #2 of this blog will be posted soon. It will discuss the concerns with spaying or neutering your dog vs. electing for a vasectomy or tubal ligation instead.
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