Animal Skin and Allergy Clinic Blog

Traditionally, veterinarians in the United States have been fairly unified on if and when to spay or neuter pets. For most, the answer is yes and the typical recommendation is to perform the procedure at around six months of age.

In the last few years, though, some new research has come to light that makes the waters a bit murkier. Pet owners have begun to question whether that traditional spay and neuter timeline is the best path, and some veterinarians have begun to backpedal as well.

At this time, it does not appear that there is a conclusive answer as to if and when to spay or neuter your pets. The best thing to do at this point is put all the research on the table and work as a team to come up with the best answer for each individual pet, one case at a time.

What the Data Says About Spay and Neuter

As mentioned above, six months of age has historically been the magic number for when to spay or neuter a pet. This is when most pets are big and healthy enough to undergo anesthesia, but have not reached adolescence yet. The latter is important, as the hormonal changes that pets undergo can have an influence on behaviors such as roaming, urine marking, and mounting.

Also, a compelling reason for female dogs is the incidence of mammary cancer (which carries a 50% malignancy rate in dogs) increases from 0.5% in animals spayed before a heat cycle as compared to 26% in animals who have undergone two or more heat cycles.

This recommendation has served well for many years. Recently, though, studies have emerged calling this practice into question which has left the community to collectively scratch their heads about whether the current spay and neuter practice is really the right thing to do for the pet population. Take for instance:

• Several studies showing an increased risk of prostatic cancer in dogs castrated versus those who are left intact.
• A study demonstrating an increased incidence of splenic hemangiosarcoma, a devastating cancer, in females spayed over 12 months of age versus before or never.
• Another study showing an increased risk for splenic hemangiosarcoma in spayed female Vizslas versus those who were not spayed.
• A study that showed spayed or neutered dogs to be at twice the risk of developing osteosarcoma, an aggressive bone cancer.
• Several studies demonstrating an increased risk of mast cell tumors, another aggressive type of skin cancer, in dogs who were spayed or neutered at any age.
• Studies in Golden Retrievers and Vizslas showing increased incidence of lymphosarcoma, the most common type of cancer in dogs, in spayed and neutered animals.
• A possible link between separation anxiety and being spayed.
• A study that indicated decreases in cognitive function may be accelerated in neutered animals.
• Evidence that spaying a female dog may lead to an increased incidence of urinary incontinence.
• Demonstration of an increased finding of autoimmune diseases in pets who were spayed or neutered.
• Evidence that neutered male Golden Retrievers and Labrador Retrievers suffer higher incidences of orthopedic diseases such as cranial cruciate ligament rupture, hip dysplasia, and elbow dysplasia, especially when neutering was done prior to growth plate closure.

Who on Earth would still want to spay or neuter their pet after all that?

Interpreting the Data

While it is easy to jump to conclusions based on the above information, it is good to remember that just because a study shows something doesn’t make it a settled fact. There are several good reasons that we need to take these results with a grain of salt.

• Much of this data has not been repeated. In fact in some instances studies with the opposite findings have also published.
• All of these studies have relied on retrospective data and owner survey, meaning there are lots of variables that have not been controlled. For instance, could the propensity for neutered labs to be overweight increase the risk of orthopedic disease without the influence of hormones? Could the fact that spayed and neutered animals live longer put them at increased risk of some cancers?
• Many of these studies look at one specific breed, which may not translate to all breeds.
• Many studies look at a very small number of animals, making the data difficult to extrapolate.

It is known that, in general, pets have a longer lifespan when they are spayed or neutered. We also know that serious problems such as mammary cancer, pyometra, benign prostatic hyperplasia, unwanted sexual behaviors, and undesired breedings can occur in intact animals.

At this point in time, there is enough evidence to show that to spay or neuter a pet is not always benign, however, much research still needs to be done before there is a definitive answer.

Spay/neuter is not a one-size-fits all decision. It is best to take the individual pet’s health history, genetics, and purpose into account in order to arrive at the best decision for if or when to spay or neuter. It’s important to include trusted veterinarians, such as the experts at Animal Skin & Allergy Clinic as well as your regular veterinarian, in this important conversation since there is so much to consider.