10/31/2026
Just another reason to spay your dog. It doesn’t need to have a litter first.
Saturday
TL:DR Spaying a dog before her first heat cycle can eliminate the risk of mammary cancer almost completely. Each successive heat cycle increases the chance of your dog developing mammary cancer, which is the single most common tumor found in dogs.
Now for the details behind the statistics:
As Breast Cancer Awareness Month comes to a close, I wanted to make one final reminder of the dangers of mammary cancer, and the relationship between spay and mammary cancer (canine breast cancer).
If a female dog is spayed before she has her first estrus (regardless of the dog's age), the chance of the dog developing mammary cancer is barely more than zero. After the first heat, that chance goes up to 8%, and after the second heat cycle, a female dog has a 26% chance of developing mammary cancer. According to the Veterinary Society of Surgical Oncology, mammary tumors in female dogs account for 42% of all diagnosed tumors in all dogs regardless of s*x.
About 50% of all mammary tumors are malignant, and of those that are malignant, about half are likely to metastasize (spread to other parts of the body). Large breed dogs appear to be more predisposed to MALIGNANT tumors.
The dog in this photo is not a Bluebonnet dog, but we've had dogs who had the same surgery which results in an incision like this one. We just didn't get a photo. Large breed dogs such as those we rescue typically have 10 mammary glands -- 5 pairs arranged in parallel chains on each side of the undercarriage. We've had at least one dog who had to have one full chain removed, plus one or more tumors from the other chain. This is a MAJOR surgery, but it can be both life-saving and life-extending.
Sadly, many veterinarians never talk to their clients about the risks of mammary cancer (or of pyometra, but that's a subject for a different post). Vets are quick to talk about the benefits of delaying spay/neuter until a dog is older, so they have the benefit of their s*x hormones for the development of strong bones and connective tissue. But they rarely tell their clients that this delay brings additional risks. And please, don't argue with me about this. We know this is true based on our personal experience and our adopters' experience, and Dr. Marty Greer DVM has said the same thing. In an article for the AKC, Dr. Greer writes "In contrast to humans, mammary tumors in dogs are nearly 100% preventable if owners would take one simple step – to spay female dogs prior to age 2 or younger....[V]eterinarians have not always done as well to educate clients that spaying under the age of 2 prevents most mammary tumors, and that spaying before the first heat cycle protects nearly all dogs."
Yes, there are other factors to consider when choosing the appropriate age for spay/neuter of any dog. But given the very sobering statistics for mammary cancer, this merits serious consideration as a reason for spaying sooner rather than later.
Pay attention to your dog's "undercarriage" -- look for lumps or bumps or redness and make an appointment with your vet if you see anything worrisome.
