As a vet student, you’re probably familiar with the discussion surrounding spay/neuter timing in canine patients. Every time a study is published, this issue seems to once again become a “hot topic.” A new study was released earlier this year, so it’s time for an update. 

The veterinary profession has historically recommended early spay/neuter, in order to prevent accidental matings and behavior issues that can arise in intact pets. In recent years, however, an increasing amount of attention has been given to potential medical risks that may accompany early spay/neuter.

Researchers are still working to understand the exact risks and benefits of early spay/neuter, in order to allow veterinarians to make the best possible recommendations for their patients.

What official recommendations exist regarding spay/neuter timing? 

The American Veterinary Medical Association (AVMA) has not released specific guidelines regarding the timing of spay/neuter surgery in dogs. In 2019, however, the American Animal Hospital Association (AAHA) did issue guidelines for dogs. Based on current evidence, they recommend the following: 

• Small breed dogs (45 lbs. or less): Spay females at 5-6 months of age, before the first heat cycle. Neuter males at 6 months of age.
• Large breed dogs (over 45 lbs.): Spay females or neuter males when growth is complete, at 5-15 months of age.¹

While these guidelines are helpful, it’s important to understand the science behind these recommendations. This understanding will help you perform an individual risk assessment with each pet and owner, arriving at the best decision for that particular family. 

What does the evidence say?

In the last ten years, a number of studies have examined the timing of spay/neuter surgery in dogs:

• In early 2013, a study of 759 Golden Retrievers found that individuals spayed or neutered prior to one year of age had an increased risk of hip dysplasia, cruciate ligament tears, and lymphoma.²
• In late 2013, a study of approximately 70,000 dogs found that sterilization is associated with increased longevity in both male and female dogs.³ Intact dogs within the study were more likely to die of trauma, infectious disease, vascular disease, or degenerative disease, while spayed/neutered dogs were more likely to die of neoplasia (lymphoma, osteosarcoma, mast cell tumors, transitional cell carcinoma) or autoimmune disease.³ 
• A 2014 study aimed to determine whether the early 2013 Golden Retriever study could also be generalized to Labrador Retrievers. This study examined over 1,000 Goldens and 1,500 Labs, finding that both breeds were more likely to develop orthopedic conditions if neutered early.⁴
• A 2016 study of 1,170 German Shepherds found that individuals spayed or neutered prior to one year of age were approximately three times more likely to develop an orthopedic disease than dogs spayed or neutered later in life.⁵ 
• A 2017 study of 90,000 dogs found an increased risk of immune-mediated diseases in neutered dogs.⁶

What about the effects of spay/neuter on cancer?

While a number of studies have looked at differences in cancer between spayed/neutered pets and intact pets, few of these studies have taken into account the age at which the pet was neutered. 

In general, however, these studies have found that intact females are at increased risk of mammary cancer, uterine cancer, ovarian cancer; however, they are less likely to develop transitional cell carcinoma, osteosarcoma, hemangiosarcoma, mast cell tumors, and lymphoma.⁷ Intact males are at increased risk of testicular cancer, but are less likely to develop transitional cell carcinoma, prostatic carcinoma, osteosarcoma, hemangiosarcoma, and lymphoma.⁷ 

What about the study published earlier this year?

A new study was released by the University of California - Davis in July 2020. This study attempted to expand the focus from earlier research on a limited number of large dog breeds, by including 35 different breeds.⁸

The study findings can be summarized as follows:

• Many large breed dogs show an increased risk of joint disease and cancer when spayed/neutered at an early age. Notable exceptions include Great Danes and Irish Wolfhounds, in which early spay/neuter is not correlated with joint disease.⁸ 
• Most small breed dogs do not have a higher risk of joint disease or cancer when spayed/neutered at an early age. Notable exceptions include Shih Tzus and Boston Terriers, in which early spay/neuter is correlated with an increased risk of cancer.⁸

The study goes on to make breed-specific recommendations for all 35 breeds that were included in the study, which may be helpful for clients who are seeking breed-specific recommendations. 

How can I use this information to help my clients and patients?

Ultimately, it’s up to you and the client to determine optimal spay/neuter timing for each individual pet. When making these decisions, consider questions such as: 

• Can the client prevent roaming and accidental breeding until the time of surgery?
• Are we trading a low-risk problem for a higher-risk problem?
• What outcomes will be easiest for the client to manage?

Our understanding is still not complete, which means there’s rarely an obvious right or wrong answer. Instead, your role is to provide the client with information and help guide them to the best decision for their individual pet. 

References

1. AAHA. Proposed ages for sterilization. 2019. Retrieved from: https://www.aaha.org/aaha-guidelines/life-stage-canine-2019/spay-and-neuter-timing/
2. 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
3. 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
4. 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
5. 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. doi:10.1002/vms3.34. 4. Retrieved from: https://onlinelibrary.wiley.com/doi/full/10.1002/vms3.34
6. 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/track/pdf/10.1186/s12917-016-0911-5
7. Bentley A, Thalheim L. Controversies in spaying and neutering: effects on cancer and other conditions. Retrieved from: https://www.cuvs.org/sites/default/files/inline-files/1-4%20Bentley%20Thalheim%20-%20SpayNeuter.pdf
8. 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