The bottom line, (which I am putting at the top for those of you who like to scan articles) is that spayed and neutered dogs statistically live longer than un-spayed and un-neutered dogs. In a 2014 study involving 40,000 dogs, it was shown that sterilization increased the life expectancy of male dogs by 13.8% and female dogs by 26.3%. In your average mid-sized dog with a life expectancy of around 10 years, the spayed female lives 2.6 years longer than the un-spayed female, and the neutered male lives 1.4 years longer than the un-neutered male. That is a significant length of extra time to share with our treasured pets!
Studies have shown an increased incidence of some immune mediated diseases (such as hypothyroidism) and cancers (such as lymphoma and osteosarcoma) and a decreased incidence of other cancers (such as prostate and mammary cancer) in sterilized dogs. The Hoffman study theorized that as the sterilized pets live longer, they are more likely to get old age type diseases, such as cancer. If the male or female hormone levels are reduced by sterilization, dogs are less likely to get cancers of the reproductive organs. Other studies in golden retrievers have shown a higher incidence of anterior cruciate ligament tears and hip dysplasia in dogs sterilized at a young age, possibly due to the different growth rate between the tibia and fibula and the increased length of the long bones. Fun fact: spayed and neutered dogs grow taller than unsterilized dogs! A 2011 study in Vislas has shown that there is a higher incidence of behavioral problems in dogs sterilized before 6 months of age. The younger the dog at sterilization, the higher the likelihood of behavioral problems such as separation anxiety, timidity, and aggression.
These studies show that although neutered and spayed dogs do live longer, there are other things to consider. So, when is the best time to sterilize your dog? Rescue organizations sterilize their critters at a very early age, often as young as 2-3 months of age. This is in an attempt to deal with the serious pet overpopulation problem; 1.5 million pets at US Humane Societies and 18,000 pets at Canadian Humane Societies are euthanized every year. So, if you are adopting a rescue the decision has already been made. For those who still have to make the decision, it has been the norm to sterilize pets at 6 months of age. With the advantage of hindsight, we are now questioning that standard.
We want our dogs to live longer, healthier lives. We want them to have strong joints, no cancer, and have good dispositions. We don’t want to have to deal with roaming and fighting intact male dogs. We don’t want to have to deal with messy heat cycles in female dogs. So, what to do?
In small dogs and medium dogs that mature under 10 kg, spaying and neutering at 6 months still makes good sense. They are very close to being physically and sexually mature at that age, so are less likely to experience any of the deleterious effects of sterilization. They are also less prone to orthopedic diseases.
In female dogs that mature at over 25-30 kg, waiting until they are reproductively and skeletally mature is a good idea. This occurs between 12 and 18 months of age. Many female dogs will have gone through one or two heat cycles by this time. Some families are not able to care for females in heat. In this case spaying at around 8-9 months will ensure that they are mostly mature and are unlikely to have gone into their first heat.
In male dogs that mature over 10 kg, waiting to neuter them until they are over a year of age is ideal. The exception would be dogs showing aggressive tendencies or roaming behavior. Neutering these dudes will remove unwanted testosterone-driven behaviors.
In female dogs that mature between 10 and 25 kg, spaying around 8-9 months of age will reduce the chance of them going into heat. Waiting until they are a year of age may reduce their chances of health problems.
There is no perfect answer to the question of when to spay or neuter your pet. Now that you are informed, you get to make your own decision! Your veterinarian can help you. It is a lot of work keeping current with updates in the veterinary world, but it is part of our commitment to caring for you and your pets.