When should a dog be spayed? What are the pros and cons?

Original Question: Hello Doctor we have a Welsh Springer that is 4 months of age. The breeder suggested we don't spay her until 15 months. The breeder advised that new research has somewhat shown the incidence of breast cancer is very low compared to the benefit of not being spayed which is proper growth. - Daryl

When should a dog be spayed? What are the pros and cons? Jul 25, 2017

Hi Daryl,

Thanks for your question.

I am always fascinated by this type of question. Not that you ask it, but that you have not been presented with more information by your breeder. I find this is a common occurrence.

As a rule, I do not tell people what to do. In short, I do not extend my bias when I’m giving a recommendation. All of my answers are supported by evidence-based research and I simply inform a client of options and the pros and cons of them. Breeders will tend to give you their bias in most cases and not back it up with research or encourage you to make your own decision. The good ones will give you options and explain the benefits and complications with each.

So let’s start with this. There is a famous research trial that any veterinarian in the world should be able to quote and I wish most breeders knew about. It has to do with age of the spaying a female dog and the incidence of mammary cancer later in life. The results showed that female dogs have a 0.05% incidence of mammary cancer. If the dog is allowed to have a heat cycle, which typically occurs between 7-8 months of age, that risk jumps to 8%. If they have 2 heat cycles, it jumps to 26%. This is a dramatic risk of later disease that causes many people to decide to spay before the dog’s first heat, performing it at 6 months of age.

On the negative side, simple spaying of a dog at any time in its life will increase the risk of hypothyroidism, which can easily be treated. It increases the risk of obesity which can be reduced through proper diet control. It increases the risk of urinary incontinence which can easily be treated. It will reduce maximum growth if done at 6 months because the dog will not have the advantage of hormones that allow them to reach their maximum size. Spaying has been known to increase the risk of bone cancer in large breed dogs but certainly not to the same degree as that of mammary cancer. I encourage you to check out our video Should I Spay or Neuter My Dog or Cat? for more information on this topic.

So there are always pros and cons. It’s important to share the information and let an owner decide what pieces of information are most important to them.

I have never heard a consistent answer to this question from breeders. Some of them will say to spay at 6 months, 8 months, 10 months, 12 months, 14 months, in your case 15 months and then incredibly, there are many breeders who spay at 8-10 weeks of age so that their customers cannot breed their dogs when they sell them. Furthermore, they spay them this early so they can still sell them as puppies even though there is a greater risk of anaesthetic complications at that young of an age. So my question back to your breeder is why 15 months? What is so special about 15 months? What research or evidence is this particular time based on? Many veterinarians will recommend 6 months because of the study performed that I outlined above and that at 6 months you guarantee that a heat cycle will not have happened and you’re waiting as long as possible to lessen anaesthetic complications. It’s a recommendation that is well supported by research. That is not to say that your breeder doesn’t have something they can use to support the exact age of 15 months. If they do, I would be really interested in seeing it.

I would greatly appreciate hearing about any evidence your breeder has to support their recommendation. If you ask them and they provide detail, please be sure to forward it to me.

I hope this was helpful,

Dr. Clayton Greenway

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