Spaying/Neutering, what is the right choice?
Summary of this page as a whole:
The research on canine spay and neuter suggests that gonadal hormones play important roles beyond reproduction. They are involved in skeletal development, growth-plate closure, metabolism, behavior, and brain development. Because of this, the age at which a dog is gonadectomized may have consequences that extend beyond reproductive health.
One of the more consistent findings is the effect of early gonadectomy on physical development. Research has shown that removing the gonads before puberty delays growth-plate closure, with earlier gonadectomy producing a greater delay (Salmeri et al., 1991). Larger studies have also found associations between early neutering and increased orthopedic disorders, particularly in larger dogs and certain breeds (Torres de la Riva et al., 2013; Hart et al., 2020; Hart et al., 2024). These findings suggest that allowing gonadal hormones to remain present during skeletal maturation may be beneficial for some dogs.
There are also associations between gonadectomy and certain cancers, urinary incontinence, and other health conditions. These relationships are not consistent across every breed or sex, and gonadectomy can reduce the risk of some reproductive diseases. However, the variation between breeds and individuals makes it difficult to support a single ideal age for every dog. The research instead suggests that the potential effects of gonadectomy should be considered alongside the individual dog's characteristics and circumstances.
Behavioral effects are less predictable. Gonadectomy can reduce reproductive behaviors such as roaming and mounting, but studies have not consistently demonstrated improvements in aggression, fear, anxiety, or other behavioral concerns. Some research has found associations between gonadectomy and certain undesirable behaviors, while other studies have found little difference between dogs neutered before or after puberty (Farhoody et al., 2018; McKenzie et al., 2022). Therefore, early gonadectomy should not automatically be viewed as a behavioral treatment.
Research outside of dogs also provides evidence that gonadal hormones participate in brain development. Studies in adolescent rhesus macaques found that prepubertal gonadectomy altered normal patterns of brain maturation and neural development (Knickmeyer et al., 2021; Morris et al., 2010). These findings cannot be directly applied to dogs, but they provide biological evidence that puberty-related hormones contribute to developmental processes beyond reproduction. Current research is still insufficient to determine exactly how these changes translate into long-term behavioral development in dogs.
An important distinction in the newer research is that sterilization and gonadectomy are not necessarily the same thing. Vasectomy and ovary-sparing spay can prevent reproduction while retaining the gonads and their hormones. In a 2023 study of more than 6,000 dogs, longer exposure to gonadal hormones was associated with lower odds of general health problems as well as problematic and nuisance behaviors (Zink et al., 2023). Because this was an observational owner-survey study, it cannot establish causation, but it provides evidence worth considering when comparing hormone-preserving sterilization with traditional gonadectomy.
The 2024 WSAVA guidelines similarly recognize that the effects of gonadectomy depend on factors such as breed, sex, age, and individual circumstances. They acknowledge potential developmental effects of early gonadectomy while also recognizing that evidence for many long-term behavioral outcomes remains complicated (Romagnoli et al., 2024).
What the Research Suggests
Taken together, the research provides several reasons to consider allowing dogs to experience normal puberty and, when practical, delaying gonadectomy:
Gonadal hormones contribute to normal physical development and growth-plate closure.
Early gonadectomy is associated with increased orthopedic risk in some dogs, particularly certain larger breeds.
Health effects vary considerably by breed, sex, and age rather than affecting all dogs equally.
Gonadectomy does not consistently improve behavioral problems such as aggression, fear, or anxiety.
Gonadal hormones participate in adolescent brain development in mammals.
Reproductive sterilization can be achieved without necessarily removing the gonads.
Longer exposure to gonadal hormones has been associated with fewer health and behavioral problems in at least one large canine study.
Current veterinary guidelines support considering the individual dog rather than applying one universal age for gonadectomy.
This does not establish that every dog should remain intact permanently. Spay and neuter can provide important benefits, particularly by preventing unwanted reproduction and eliminating the risk of certain reproductive diseases. However, the available evidence provides a reasonable basis for considering delayed gonadectomy or hormone-preserving sterilization when reproduction can be responsibly prevented, especially during periods of ongoing physical development.
Professional Observations
Separate from the published research, there are also observations from clinical behavior work. In my experience, I have encountered more dogs with behavioral concerns involving social understanding, communication, and appropriate dog-to-dog interaction among dogs that were altered prematurely compared with dogs altered after approximately two years of age or dogs that remain intact.
These observations are anecdotal and cannot establish causation. Individual temperament, genetics, socialization, environment, and other factors can contribute to these behavioral differences. They are therefore best considered alongside, rather than as evidence equivalent to, the published research.
Studies on Dogs Specifically:
Zink, M. C., Farhoody, P., Elser, S. E., Ruffini, L. D., Gibbons, T. A., & Rieger, R.
H. (2014). Evaluation of the risk and age of onset of cancer and behavioral disorders in gonadectomized Vizslas. Journal of the American Veterinary Medical Association, 244(3), 309–319. https://doi.org/10.2460/javma.244.3.309
Zink, C., Delgado, M. M., & Stella, J. L. (2023). Vasectomy and ovary-sparing spay in dogs: Comparison of health and behavior outcomes with gonadectomized and sexually intact dogs. Journal of the American Veterinary Medical Association, 261(3), 366–374. https://doi.org/10.2460/javma.22.08.0382
Torres de la Riva, G., Hart, B. L., Farver, T. B., Oberbauer, A. M., Messam, L. L. M., Willits, N., & Hart, L. A. (2013). Neutering dogs: Effects on joint disorders and cancers in Golden Retrievers. PLOS ONE, 8(2), e55937. https://doi.org/10.1371/journal.pone.0055937
Farhoody, P., Mallawaarachchi, I., Tarwater, P. M., Serpell, J. A., Duffy, D. L., & Zink, C. (2018). Aggression toward familiar people, strangers, and conspecifics in gonadectomized and intact dogs. Frontiers in Veterinary Science, 5, 18. https://doi.org/10.3389/fvets.2018.00018
McKenzie, E. C., et al. (2022). A prospective cohort study investigating the behavioural development of bitches in a guide dog training programme neutered prepubertally or post-pubertally. Animals, 12(14). https://pubmed.ncbi.nlm.nih.gov/35873697/
Salmeri, K. R., Bloomberg, M. S., Scruggs, S. L., & Shille, V. (1991). Gonadectomy in immature dogs: Effects on skeletal, physical, and behavioral development. Journal of the American Veterinary Medical Association, 198(7), 1193–1203.
The researchers found:
Both neutered groups had delayed growth-plate closure compared with intact dogs.
The 7-week group had a longer delay in growth-plate closure than the 7-month group.
Some physical sexual characteristics remained less developed in the early-neutered dogs.
Behaviorally, neutered dogs were rated as more active, and males neutered at 7 weeks were rated as more excitable than intact males.
Romagnoli, S., Krekeler, N., de Cramer, K. G. M., Kutzler, M. A., McCarthy, R. J., & others. (2024). WSAVA guidelines for the control of reproduction in dogs and cats. Journal of Small Animal Practice, 65(7), 424–559. https://doi.org/10.1111/jsap.13724
Romagnoli, S., Krekeler, N., de Cramer, K. G. M., Kutzler, M. A., McCarthy, R. J., & others. (2024). WSAVA guidelines for the control of reproduction in dogs and cats. Journal of Small Animal Practice, 65(7), 424–559. https://doi.org/10.1111/jsap.13724
Hart, B. L., Hart, L. A., Thigpen, A. P., & Willits, N. H. (2020). Assisting decision-making on age of neutering for mixed breed dogs of five weight categories: Associated joint disorders and cancers. Frontiers in Veterinary Science, 7, 472. https://doi.org/10.3389/fvets.2020.00472
Hart, L. A., Thigpen, A. P., Hart, B. L., Willits, N. H., Lee, M., Babchuk, M. M., Lee, J., Ho, M., Clarkson, S. T., & Chou, J. W. (2024). Assisting decision-making on age of neutering for German Short/Wirehaired Pointer, Mastiff, Newfoundland, Rhodesian Ridgeback, Siberian Husky: Associated joint disorders, cancers, and urinary incontinence. Frontiers in Veterinary Science, 11, 1322276. https://doi.org/10.3389/fvets.2024.1322276
Hormone studies impacting brain development:
Knickmeyer, R. C., Nguyen, C. T., Young, J. T., Haunton, A., Kosorok, M. R., Gilmore, J. H., Styner, M., Rothmond, D. A., Noble, P. L., Lenroot, R., & Weickert, C. S. (2021). Impact of gonadectomy on maturational changes in brain volume in adolescent macaques. Psychoneuroendocrinology, 124, 105068. https://doi.org/10.1016/j.psyneuen.2020.105068
Morris, R. W., Kincaid, A. E., Hester, R., & Weickert, C. S. (2010). The effect of gonadectomy on prepulse inhibition and fear-potentiated startle in adolescent rhesus macaques. Psychoneuroendocrinology, 35(5), 896–905. https://doi.org/10.1016/j.psyneuen.2009.12.002
Baxendale, S. (2024). The impact of suppressing puberty on neuropsychological function: A review. Acta Paediatrica, 113(6), 1156–1167. https://doi.org/10.1111/apa.17150
Baxendale reviewed studies investigating puberty suppression and neuropsychological development in both humans and animals. The review identified 16 studies, including 11 animal studies.
The review found that suppression of puberty can affect brain structure and cognitive/behavioral development in mammals, although effects were complex and often sex-specific. Importantly, the author concluded that there aren't currently adequate human studies with proper baseline and follow-up testing to determine the long-term neuropsychological consequences of suppressing puberty.
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