Veterinarians have long advocated for early spay/neuter in small animal patients. Not only does this reduce pet overpopulation, it can also offer behavioral and medical benefits.
In recent years, however, many have begun to question whether universal early spay/neuter is truly the best approach. Yes, there are clearly benefits… but are there hidden costs?
The Benefits of Pet Sterilization
Addressing pet overpopulation is certainly a primary driver of spay/neuter. However, there are also medical benefits for spayed and neutered pets.
A 2013 study at the University of Georgia examined the records of 40,139 dogs in the Veterinary Medical Data Base with a listed age at death and cause of death.1 The authors of this study found:
- Spayed female dogs live 26.3% longer than intact females.
- Neutered male dogs live 13.5% longer than intact males.
- Intact dogs are more likely than spayed or neutered dogs to die of trauma, infection, degenerative disease, or vascular disease.
- Spayed/neutered dogs are more likely than intact dogs to die of neoplasia (lymphoma, osteosarcoma, mast cell tumors, transitional cell carcinoma) or autoimmune disease.
Lifespan variability likely explains some of these differences. An intact dog’s increased risk of trauma or infection likely contributes to a decreased lifespan, while spayed or neutered dogs are more likely develop neoplasia due to their longer lives. Differences in degenerative disease, vascular disease, and autoimmune disease are less easily explained and may warrant further study.
Spaying females at an early age is known to reduce the risk of mammary cancer. Dogs spayed before their first heat cycle have only a 0.05% risk of mammary neoplasia; this risk increases to 26% after their second heat.2
Finally, spaying a female eliminates the risk of pyometra while neutering a male dog eliminates the risk of testicular neoplasia and benign prostatic hypertrophy.
Clearly, there are significant benefits associated with spaying and neutering our patients.
Studies on Spay/Neuter Timing: The Evidence
Between 2013 and 2016, researches at the University of California – Davis conducted several studies to assess the potential health impacts of early spay/neuter.
- A study of 759 client-owned Golden Retrievers found an increased risk of cruciate ligament tears in dogs spayed or neutered at an early age and an increased risk of hip dysplasia and lymphoma in males that were neutered at an early age.3
- A study of over 1,000 client-owned Golden Retrievers and Labrador Retrievers found that orthopedic risks associated with early spay/neuter are relatively similar in Golden Retrievers and Labrador Retrievers.4 This study also looked at cancer risks associated with spay/neuter status; the results of this analysis varied between sex and breed.4
- A study of 1,170 client-owned German Shepherds found that dogs spayed or neutered before one year of age were approximately three times as likely to develop joint disorders as intact dogs.5
- A study of 90,090 client-owned dogs found an increased risk of immune-mediated diseases in spayed and neutered dogs, including atopic dermatitis, autoimmune hemolytic anemia, immune-mediated thrombocytopenia, inflammatory bowel disease, hypothyroidism, and hypoadrenocorticism.6
In 2020, UC Davis published an additional, larger study, in which 35 different dog breeds were examined.7 The study findings can be summarized as follows:
- Many large breed dogs show an increased risk of orthopedic disease and cancer when spayed/neutered at an early age. However, there are exceptions. In Great Danes and Irish Wolfhounds, for example, early spay/neuter is not correlated with an increased risk of joint disease.
- Early spay/neuter typically does not increase the risk of orthopedic disease or cancer in small-breed dogs. However, there are exceptions. In Shih Tzus and Boston Terriers, for example, early spay/neuter is correlated with an increased risk of cancer.
The study goes on to make breed-specific recommendations for all breeds included in the study, which may be beneficial for some patients.7
The Evidence: A Summary
In general, we can conclude that spayed and neutered pets live longer lives and are less likely to die of infection or trauma. Spaying or neutering pets also reduces the risk of mammary cancer, pyometra, testicular neoplasia, and benign prostatic hypertrophy.
However, early spay/neuter has been associated with an increased risk of orthopedic disease in many large-breed dogs. Early spay/neuter may also increase the risk of certain cancers (lymphoma, osteosarcoma, mast cell tumors, and transitional cell carcinoma) in large-breed dogs. Finally, early spay/neuter may increase a patient’s risk of autoimmune disease.
Making a Recommendation
At this time, there is no evidence to suggest that early spay/neuter is risky for small-breed dogs. Therefore, continuing to spay/neuter small breed dogs prior to sexual maturity is likely best for these patients.
But what about large-breed dogs?
Large-breed dogs are at higher risk of orthopedic disease, and it appears that we can decrease this risk by allowing them to reach skeletal maturity before spay or neuter. However, there are other factors to consider.
In a female dog, postponing their spay surgery until after one or more heat cycles increases the risk of mammary cancer. This risk must be balanced against the benefits of delaying their spay surgery. According to the 2013 UC Davis study, a Golden Retriever spayed before one year old has an 8% likelihood of cruciate rupture.3 However, a dog spayed after her second heat cycle has a 26% risk of mammary cancer and 13% risk of malignant mammary cancer.2 The risk of malignant mammary cancer in a late-spayed female is higher than the risk of a cruciate rupture in an early-spayed female. Malignant mammary cancer is arguably a more problematic condition, but both diagnoses can be life-changing. Ultimately, the client must determine which risk they would prefer to minimize; there is no single “right” answer to this dilemma.
In large-breed males, neuter timing decisions are a bit more straightforward. Delayed neutering reduces the risk of orthopedic disease. Yes, delaying a dog’s neuter requires an owner who is willing to contain and closely supervise their dog, to prevent roaming, fighting, and pet overpopulation, but the associated orthopedic benefits may outweigh these headaches for many owners.
What Does Organized Veterinary Medicine Recommend?
In 2019, the American Animal Hospital Association issued the following guidelines on spay/neuter timing.8
Males & females with expected adult weight <45 lbs.: spay/neuter at 5-6 months old
Males with adult weight 45+ lbs.: neuter when full-grown (9-15 months old)
Female with adult weight 45+ lbs.: use clinical discretion to balance risks and benefits
The American Veterinary Medical Association (AVMA) has also looked into this issue. While they did not take a specific stand, they emphasized the need for dialogue and shared decision-making between pet owners and their veterinarians.9
Conclusion: What Should You Recommend?
In small-breed dogs, there are few drawbacks associated with early spay/neuter. These pets should be spayed or neutered before sexual maturity.
Large-breed males should be neutered after reaching skeletal maturity, in most cases. However, it is important to assess your client carefully to determine whether they are willing and able to confine and supervise an intact male until the dog is neutered.
In large-breed females, this decision is complicated and must ultimately be made by the dog’s owner. Delaying the dog’s surgery until skeletal maturity will reduce the risk of orthopedic disease while increasing the risk of mammary cancer. Begin discussing the trade-offs associated with spay timing during puppy visits, providing ample opportunity for owners to ask questions and make an informed decision.
Hoffman JM, Creevy KE, Promislow DE. Reproductive capability is associated with lifespan and cause of death in companion dogs. PLoS One. 2013;8(4). Retrieved from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0061082
ACVS. Mammary Tumors. Retrieved from: https://www.acvs.org/small-animal/mammary-tumors
Torres de la Riva G, Hart BL, Farver TB, et al. Neutering dogs: effects on joint disorders and cancers in golden retrievers. PLoS One. 2013;8(2). Retrieved from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055937
Hart BL, Hart LA, Thigpen AP, et al. Long-Term Health Effects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers. PLOS ONE 2014; 8:e102241. Retrieved from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102241
Hart BL, Hart LA, Thigpen AP, Willits NH. Neutering of German Shepherd Dogs: associated joint disorders, cancers and urinary incontinence. Vet Med Sci. 2016:1-9. Retrieved from: https://onlinelibrary.wiley.com/doi/full/10.1002/vms3.34
Sundburg CR, Belanger JM, Bannasch DL, et al. Gonadectomy effects on the risk of immune disorders in the dog: a retrospective study. BMC Vet Res. 2016;12(1):278. doi:10.1186/ s12917-016-0911-5. Retrieved from: https://bmcvetres.biomedcentral.com/articles/10.1186/s12917-016-0911-5
Hart B, Hart L, Thigpen A, Willits N. Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence. Front. Vet. Sci. 2020; 7. Retrieved from: https://www.frontiersin.org/articles/10.3389/fvets.2020.00388/full
AAHA. Proposed ages for sterilization. 2019. Retrieved from: https://www.aaha.org/aaha-guidelines/life-stage-canine-2019/spay-and-neuter-timing/
Nolen S. When should we neuter dogs? It depends. JAVMAnews. 2021. Retrieved from: https://www.avma.org/javma-news/2021-03-01/when-should-we-neuter-dogs