Castration in Dogs: The Pros, Cons and Best Timing

Castration is one of the most common procedures performed on dogs, but growing research suggests that the timing of castration may have important implications for health, behaviour and development. While castration can provide benefits, it is increasingly recognised that reproductive hormones play a much larger role than simply enabling reproduction.

The Benefits of Castration

The primary benefit of castration is preventing unwanted litters. This remains one of the strongest arguments in favour of neutering, particularly in areas where accidental breeding and dog overpopulation are concerns.

Castration also eliminates the risk of testicular cancer and can reduce the likelihood of benign prostatic enlargement and certain prostate-related conditions later in life.

Behaviourally, some dogs may show reductions in roaming, urine marking and sexually motivated behaviours after castration. The study by McGreevy et al. (2018) found that earlier castration was associated with lower rates of indoor urine marking and howling when left alone.

The Potential Drawbacks of Early Castration

Sex hormones such as testosterone and oestrogen do far more than influence reproduction. During puberty and adolescence they act as developmental hormones, helping shape the brain, skeleton, muscles, joints and emotional responses.

Testosterone contributes to muscle development, bone density, confidence, resilience and social behaviour. Oestrogen plays an important role in skeletal maturation, ligament health, cognition and growth plate closure.

Researchers Sisk and Zehr (2005) concluded that:

"Pubertal hormones organize the adolescent brain and behavior."

In practical terms, hormones help guide the development of neural pathways involved in learning, emotional regulation, stress responses and social interactions. Studies have found that removing these hormones before physical maturity may increase the risk of certain orthopaedic conditions. Research by Torres de la Riva et al. (2013) found significantly increased rates of joint disorders in Golden Retrievers neutered before one year of age. Other studies have linked early neutering with increased risks of cruciate ligament injury, hip dysplasia and altered skeletal development due to delayed growth plate closure.

The National Animal Interest Alliance review of long-term health effects also identified evidence linking early neutering with increased risks of certain cancers, endocrine disorders and immune-related diseases in some breeds.

Behaviour and Brain Development

One of the most common reasons owners consider castration is behaviour. However, modern research suggests the relationship between hormones and behaviour is more complex than previously thought.

McGreevy et al. (2018) analysed behavioural data from more than 6,000 male dogs and found that dogs who retained their gonads for longer periods were less likely to display many fear related, anxiety related and aggressive behaviours. The researchers reported that longer exposure to gonadal hormones was associated with lower odds of 26 undesirable behaviours, including several forms of aggression and reactivity.

Adolescence is a pivotal phase in human development, marked by significant changes not only in behavior and social dynamics but also in the intricate architecture of the brain. According to McCormick and Mathews (2010), adolescence is a transformative stage during which various hormonal changes play a crucial role in shaping cognitive functions such as learning, memory, and emotional regulation. These hormonal fluctuations are largely driven by the onset of puberty, leading to increased levels of sex hormones like estrogen and testosterone. These hormones do not merely influence physical growth; they also have profound effects on neural pathways and synaptic connections, which are essential for cognitive processes.

During this period, the brain is undergoing extensive remodeling. One of the key features of this developmental phase is the maturation of the prefrontal cortex, the area of the brain responsible for higher-order functions such as decision-making, impulse control, and emotional regulation. Spear (2009) emphasizes that adolescence is characterized by heightened emotional sensitivity. This increased sensitivity can often lead to intense emotional experiences, which may seem overwhelming and can affect an adolescent's ability to respond to situations with the level of self-control typically expected in adulthood.

Moreover, the limbic system, which is involved in emotional responses, undergoes significant changes during adolescence. This part of the brain matures more rapidly than the prefrontal cortex, leading to a period where emotional reactions can often override rational thinking. This imbalance may explain some of the risk-taking behaviors commonly associated with adolescence, as individuals may prioritize immediate emotional gratification over long-term consequences.

In addition to these structural changes, adolescence is also a time when individuals are forming their identities and establishing social connections. The development of social cognition and the ability to understand and navigate complex social dynamics are critical during this stage. As adolescents seek

social interactions, the brain's reward systems become increasingly activated, reinforcing behaviors that are socially rewarding but sometimes risky.

In summary, adolescence is not merely a transitional phase; it is a crucial period for brain development where hormonal changes significantly impact cognitive functions and emotional responses. The interplay between the developing prefrontal cortex and the limbic system creates a unique landscape for learning and personal growth, influencing how adolescents navigate their world, manage their emotions, and develop their identities. Understanding these changes can provide valuable insights into the challenges and opportunities that arise during this complex stage of life.

Although much of this research comes from human and animal neuroscience rather than canine-specific studies, the biological principle remains consistent across mammals: puberty is a developmental process, not simply a reproductive one.

This may help explain why many behaviourists now view adolescence not as a problem to be eliminated, but as an important developmental stage that dogs need to progress through.

When Is a Dog Finished Adolescence?

There is no single age at which all dogs become adults.

Small breeds such as Jack Russell Terriers, Cavalier King Charles Spaniels and Miniature Schnauzers often mature between 12 and 18 months of age.

Medium breeds such as Border Collies, English Springer Spaniels and Staffordshire Bull Terriers commonly mature between 18 and 24 months.

Large breeds such as Labrador Retrievers, Golden Retrievers, German Shepherds and Boxers often continue developing until around 24 months.

Giant breeds such as Great Danes, Mastiffs, Newfoundlands and Saint Bernards may continue developing physically and mentally until 30 to 36 months of age.

Signs a Dog Is Reaching Maturity

Age alone should not determine whether a dog is ready for castration.

Many dogs show clear signs that adolescence is ending. These include improved impulse control, greater consistency in training, reduced emotional overreactions, an increased ability to settle and relax, and improved recovery from stressful situations.

Socially mature dogs are often less frantic around other dogs, better able to disengage from distractions and more confident when encountering new environments.

Physically, growth slows or stops, musculature develops, the chest broadens and adult body proportions become established.

So When Is the Best Age to Castrate?

Current evidence suggests there is no universal age that suits every dog.

For many small breeds, waiting until at least 12 months allows most developmental processes to occur before castration.

For medium-sized breeds, waiting until around 18 months may be beneficial.

For large and giant breeds, many veterinarians and behaviour professionals now support waiting until 18 to 24 months or longer, allowing growth plates to close and musculoskeletal development to complete.

This does not mean every dog should remain intact indefinitely. Preventing unwanted breeding remains essential. However, where responsible management can prevent accidental mating, allowing a dog to complete puberty and much of adolescence may provide benefits for skeletal development, behavioural resilience and overall health.

Conclusion

The current evidence suggests that castration offers clear benefits for population

control and prevention of certain reproductive diseases. However, hormones play an important role in skeletal growth, brain development

behavioural maturation. For many dogs, particularly medium, large and giant breeds, allowing puberty and adolescence to progress naturally before castration may support healthier physical and behavioural development.

Ultimately, the decision should be based on the individual dog, taking into account breed, size, lifestyle, health considerations and the owner's ability to prevent unwanted breeding.

References

Asher, L., Friel, M., Griffin, K., Collins, L. M., Millman, S. T., & McGreevy, P. D. (2020). Adolescent behaviour in domestic dogs and its relationship with attachment and puberty. Biology Letters, 16(9).

Dishion, T. J., Nelson, S. E., & Bullock, B. M. (2004). Premature adolescent autonomy: Parent disengagement and deviant peer process in the amplification of problem behaviour. Journal of Adolescence, 27, 515–530.

McCormick, C. M., & Mathews, I. Z. (2010). Adolescent development, hypothalamic-pituitary-adrenal function, and programming of adult learning and memory. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 34(5), 756–765.

McGreevy, P. D., Wilson, B., Starling, M. J., & Serpell, J. A. (2018). Behavioural risks in male dogs with minimal lifetime exposure to gonadal hormones may complicate population-control benefits of desexing. PLoS ONE, 13(5), e0196284.

Mongillo, P., Scandurra, A., D'Aniello, B., & Marinelli, L. (2017). Effect of sex and gonadectomy on dogs' spatial performance. Applied Animal Behaviour Science.

National Animal Interest Alliance (NAIA). (2007). Long-Term Health Effects of Spay/Neuter in Dogs.

Sisk, C. L., & Zehr, J. L. (2005). Pubertal hormones organize the adolescent brain and behavior. Frontiers in Neuroendocrinology, 26, 163–174.

Smetana, J. G., Campione-Barr, N., & Metzger, A. (2006). Adolescent development in interpersonal and societal contexts. Annual Review of Psychology, 57, 255–284.

Spear, L. P. (2009). Heightened stress responsivity and emotional reactivity during pubertal maturation: Implications for psychopathology. Development and Psychopathology, 21(1), 87–97.

Steinberg, L. (1988). Reciprocal relation between parent-child distance and pubertal maturation. Developmental Psychology, 24, 122–128.

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.

Weiss, E., Slater, M., Garrison, L., Drain, N., Dolan, E., Scarlett, J. M., & Zawistowski, S. L. (2014). Large dog relinquishment to two municipal facilities in New York City and Washington, D.C.: Identifying targets for intervention. Animals, 4, 409–433.