The best age to spay or neuter cats and dogs is a very controversial subject in veterinary medicine. Many studies published in the last ten years have revealed significant risks to the health of dogs that are spayed and neutered. (Cats seem to be less affected and I will cover this in detail later.)
With the current overpopulation of pets in the United States, the veterinary and rescue communities are reluctant to integrate this information into their protocols and recommendations. I would like to emphasize my neutrality on this subject. The veterinarians that perform spays and neuters on young animals should not be villainized. However, it is important that you, as a pet parent, make informed medical decisions.
Current Spay & Neuter Age Recommendations
Most small animal veterinarians recommend spaying or neutering dogs and cats around 6 months of age. This generally prevents female cats and dogs from experience a heat cycle and prevents male cats and dogs from becoming fertile. Shelters and rescue organizations will perform spay and neuter procedures as early as 6 weeks.
The current body of research has conflicting evidence of the long term effects of removing sex hormones at 6 months and younger. In this article, I will outline the current evidence that has found significant impacts on spaying/neutering animals early and at anytime during life. I will then outline practical considerations for deciding if and when you should spay or neuter your pet. Click here to skip to information about cats.
Orthopedic disease is very common, especially in big dogs. Growth plates in large dogs close at around 12-14 months. When sex hormones are removed by spaying and neutering, the growth plates are delayed in their closure. This causes the bones to become longer and the biomechanics of joints are altered. A common orthopedic injury in dogs is a cranial cruciate ligament injury. This is a ligament in the knee and it’s injury often requires invasive surgery to repair. A study done in 2007 showed that neutering dogs caused a three fold increase in a biomechanical risk factor for cranial cruciate ligament injuries (1). Another study done in 2008 showed that dogs that had been neutered or spayed were 2-3 times more likely to suffer from cranial cruciate ligament injury compared with unaltered dogs (2).
Other studies have shown increased incidence of joint disorders including hip dysplasia, elbow dysplasia and cranial cruciate ligament disease in spayed and neutered dogs. The breeds studied were Golden Retrievers, Labrador Retrievers and German Shepherds (3-5).
Spaying and neutering dogs are not the only risk factors predisposing dogs to orthopedic disease. Genetics, lifestyle and obesity can also play an important role.
The increased risk of developing common cancers is the most alarming finding of studies investigating the effects of spaying and neutering dogs. Several studies have found an increased risk of cancers including osteosarcoma, lymphoma, mast cell tumors and hemangiosarcoma in spayed and neutered dogs (6-11).
As mentioned previously, there are other risk factors to consider in developing cancer such as genetics and lifestyle.
For decades many veterinarians recommended that dogs be neutered or spayed to prevent or treat behavioral disorders such as aggression. Many studies have shown that neutering or spaying dogs does not decrease aggressive behaviors towards people. However, some studies are revealing that neutering and spaying before 6 months may contribute to an increased risk of behavioral disorders including aggression and storm phobias later in life (11). More research is needed to investigate the relationship between behavioral problems and the age of sterilization.
Female dogs that have been spayed can show symptoms of urinary incontinence in middle or older age. This is due to the lack of estrogen in controlling the sphincters of the urinary tract. Female dogs that are left intact generally do not experience this disease.
As usual, there are more studies done on dogs when it comes to the long term health effects of spaying and neutering. The studies that have involved cats have been focused on the effects of early spay and neuter (less than 16 weeks of age) procedures in relationship to urethral diameter. Urethral obstruction (blocked cats) is a life threatening condition that seems unrelated to age of spay or neuter. Other studies have looked at the long term health effects of spaying and neutering but were only conducted for 2 years past surgery date. Many more retrospective studies are needed. It is known that removing sex hormones in cats makes them prone to obesity. Being overweight increases risk for inflammatory disease such as diabetes and arthritis.
More studies are warranted to investigate long term outcomes of early spay and neuter programs in relationship to common diseases such as inflammatory bowel disease, cystitis, pancreatitis and lymphoma.
The practical considerations of living with an intact female or male cat may prohibit delayed spay or neuter much past 6 months of age. Cats can have many litters each year, and the urgency to sterilize cats before adoption in the shelter should be considered.
There are many factors to consider when deciding if and when you should spay or neuter your pet. Here are a few points of consideration for dogs and cats.
Breed. Many breeds are genetically more predisposed to cancer such as Golden Retrievers and Boxers. Labrador Retrievers and German Shepherds are genetically predisposed to orthopedic disease. Simply waiting to spay or neuter until 12-15 months may decrease the chances of orthopedic disease significantly. Delaying spay or neuter several years or keeping your dog intact may decrease the likelihood of developing cancer.
Purpose. If you plan on involving your dog in athletic activities such as agility or other sports, you may consider delaying spaying or neutering until the growth plates are closed. Other activities such as participating in a service program may require that your dog be spayed or neutered.
Lifestyle. Having an intact dog requires a bit of extra work and planning. Female dogs, depending on size, will experience an estrus cycle approximately once every 6 months. During this time female dogs bleed from their vulva and have behavioral changes. Intact male dogs will also be more attracted to them. Intact male dogs may be more prone to having negative interactions with other dogs. To avoid unwanted pregnancy intact males should be housed in environment that prevents their escape.
In my practice I recommend that clients that feel comfortable and confident with having an intact animal wait until 12-14 months to have their dog spayed or neutered. If this seems like too big of a risk or burden, I recommend spaying or neutering at 6 months. If my client would like to keep their female dog intact for life, it is important to understand the risk and symptoms of pyometra, a life threatening infection of the uterus. Male dogs that are kept intact may have an increased risk of prostate cancer and perianal cancers.
If possible, I recommend waiting until 6 months of age before spaying or neutering cats. It is possible for female cats to become fertile around 4-5 months. This is an important consideration when housing unaltered males and females together.
What are your spaying or neutering questions? Ask them below and I’ll do my best to respond as soon as possible.
- Duerr F.M., Duncan C.G., Savicky R.S., Park R.D., Egger E.L. & Palmer R.H. (2007) Risk factors for excessive tibial plateau angle in large-breed dogs with cranial cruciate disease. Journal of the American Veterinary Medical Association 231, 1688-1691.
- Witsberger T.H., Villamil J.A., Schultz L.G., Hahn A.W. & Cook J.L. (2008) Prevalence of and risk factors for hip dysplasia and cranial cruciate ligament deficiency in dogs. Journal of the American Veterinary Medical Association 232, 1818-1824.
- Hart B.L., Hart L.A., Thigpen A.P. & Willits N.H. (2014) Long-term health effects of neutering dogs: comparison of Labrador Retrievers with Golden Retrievers. PLoS One 9, 7.
- Torres de la Riva G., Hart B.L., Farver T.B., Oberbauer A.M., McV Messam L.L., Willits N. & Hart L.A. (2013) Neutering dogs: effects on joint disorders and cancers in golden retrievers. PLoS One 8. 2.
- Hart B.L., Hart L.A., Thigpen A.P. & Willits N.H. (2016) Neutering of German Shepherd Dogs: associated joint disorders, cancers and urinary incontinence. Veterinary Medicine and Science, 2, pp. 191-199.
- Ru G., Terracini B. & Glickman L.T. (1998) Host relationed risk factors for canine osteosarcoma. The Veterinary Journal 156, 31-39.
- Ware W.A. & Hopper D. L. (1999) Cardiac tumors in dogs: 1982-1995. Journal of Veterinary Internal Medicine 13, 95-103.
- Prymak C, McKee L.J., Goldschmidt M.H., Glickman L.T. (1988) Epidemiologic, clinical, pathologic, and prognostic characteristics of splenic hemangiosarcoma and splenic hematoma in dogs: 217 cases (1985). J Am Vet Med Assoc 193: 706– 712.
- Villamil J.A., Henry C.J., Hahn C.J., Hahn A.W., Bryan J.N., Tyler J.W. & Caldwell C.W. (200() Hormonal and sex impact on the epidemiology of canine lymphoma. Journal of Cancer Epidemiology 2009. 1-7.
- White C.R., Hohenhaus A.E., Kelsey J. & Procter-Grey E. (2011) Cutaneous MCTs: associations with spay/neuter status, breed, body size, and phylogenetic cluster. Journal of the American Animal Hospital Association 47, 210-216.
- Zinc M.C., Farhoody P., Elser S.E., Ruffini L.D., Gibbons T.A. & Rieger R.H. (2013) Evaluation of the risk and age of onset of cancer and behavioral disorder in gonadectomized Vizslas. Journal of the American Veterinary Medical Association 244, 309-319