The Balanced Guide to Neutering Dogs - Part 2: Behavioural Effects

Part 2 or 3

Welcome to the second of three guides from Hindes Hounds. This guide focuses on the behavioural effects of neutering, particularly in male dogs. If you haven’t read the first guide on health considerations, we strongly recommend doing so. The third guide will explore social pressures and decision-making around neutering. 

 Across all three guides, our message is clear: 

"One size does not fit all"

 Our goal is to empower you to make informed decisions with the support of your vet and, where appropriate, a certified behaviourist. 

What is dog Neutering? A guide.

Neutering refers to the surgical removal of a dog’s reproductive organs.

Males: Castration (removal of the testes)

Females: Spaying (removal of the ovaries and often the uterus)

While commonly recommended, neutering is not a universal solution, especially when it comes to behaviour. 

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Fearfulness, Aggression, and Excitability

A landmark study by McGreevy et al. (2018) examined over 6,000 male dogs and found that early neutering, particularly before puberty, was linked to increased: 

• Fearfulness (e.g., loud noises, strangers, unfamiliar dogs 

• Aggression in everyday situations 

• Excitability and excessive barking  

Dogs neutered after puberty were: 

• More confident and less fearful 

• Less aggressive 

• More responsive to training 

Only two behaviours-indoor urine marking and howling when left alone—were less common in dogs neutered early. 

Read the study: McGreevy et al. (2018) 

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Mounting, Urine Marking, and Roaming 

A 2023 study by Roulaux, van Herwijnen, and Beerda surveyed nearly 1,000 dogs to explore hormone-driven behaviours. 

Key findings: 

• Mounting and urine marking were more common in intact males, but neutering only reduced—not eliminated—these behaviours. 

• Roaming was not significantly affected by neutering. 

• Age mattered more than neuter status: Younger dogs (under 2 years) showed more mounting and roaming regardless of neuter status. 

Read the study: Roulaux et al. (2023) 

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Aggression and Unwanted Reactions to Other Dogs: Why Neutering Isn’t Always the Answer 

Neutering is often suggested to reduce aggression, especially male–male competition. But when it comes to fear-based or learned aggression, the evidence tells a different story.  McGreevy et al. (2018) found that dogs with longer exposure to natural hormones before neutering were less likely to show fear and aggression. Hormones like testosterone help dogs develop emotional resilience and social confidence.

Early removal may: 

• Disrupt emotional development 

• Increase fearfulness and reactivity 

• Lead to impulsive or defensive aggression 

Behaviourist’s Perspective

As a canine behaviourist, I often see aggression that was originally rooted in fear (but evolves into aggression). Neutering won’t fix these issues—and may worsen them if done too early. 

Tips for Managing Aggression Thoughtfully:

1. Assess the root cause of the aggressive behaviour—was it fear, is it frustration, or a lack of training/behaviour modification?

2. Don’t rush to neuter—especially if your dog is still maturing.

3. Focus on behaviour modification—motivational training and socialisation are key.

4. Work with professionals—a vet and behaviourist can help tailor the best plan for your dog. 

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Dog Neutering and Anxiety: What the Science Says 

Emerging research shows that early neutering (before emotional maturity) may increase: 

• Anxiety and nervousness 

• Noise sensitivity and separation anxiety 

• Fear-based aggression 

• Emotional reactivity 

Supporting Research: 

- Zink et al. (2014) 

- McGreevy et al. (2018) 

- Arroub & Pereira (2025) 

Social Behaviours and Cognitive Impact – males and females 

Read the study: Farhoody et al. (2018) 

Read the study: Scandurra et al. (2018) 

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Behavioural Effects of Spaying Female Dogs 

Spaying is commonly recommended to prevent unwanted litters and reduce hormonally driven behaviours such as attracting males, mounting, and escaping to mate. While it does eliminate the heat cycle and associated reproductive behaviours, its impact on overall behaviour is more complex—especially when performed early. 

What the Research Shows 

A large-scale study by Starling et al. (2019), involving over 8,981 female dogs, found that the timing of spaying significantly influences behavioural outcomes. Using C-BARQ data, the researchers identified: 

• 23 behaviours that differed between spayed and intact females 

• 12 behaviours linked to percentage lifetime exposure to gonadal hormones (PLG) 

• 5 behaviours associated with age-at-spay  

Read the study: Behavioural risks in female dogs with minimal lifetime exposure to gonadal hormones | PLOS One 

Key Findings: 

• Later spaying (after puberty) was associated with: 

• Reduced fearfulness 

• Lower aggression 

• Improved trainability (e.g., recall and retrieval) 

• Early spaying (before emotional maturity) was linked to: 

• Increased chewing and howling 

• Reduced boldness and social confidence 

These behavioural differences, though modest (5–7%), are clinically relevant—especially for dogs predisposed to anxiety or reactivity. 

Hormones and Emotional Development 

Estrogen and progesterone play a role in emotional regulation and brain development. Removing these hormones too early may: 

• Disrupt emotional maturity 

• Increase sensitivity to stress and noise 

• Reduce social engagement and confidence 

This aligns with findings from Scandurra et al. (2018), which showed that ovariectomized females had impaired responsiveness to human social cues—suggesting a decline in socio-cognitive function. 

Read the study: Scandurra, A., Alterisio, A., Di Cosmo, A., D’Ambrosio, A., & D’Aniello, B. (2019). Ovariectomy Impairs Socio-Cognitive Functions in Dogs. Animals, 9(2), 58. https://doi.org/10.3390/ani9020058 

Behaviourist’s Perspective 

As a canine behaviourist, I often see behavioural issues in spayed females that stem not from hormones alone, but from: 

- Poor early socialisation 

- Lack of environmental enrichment 

- Fear-based learning 

Spaying may reduce some hormonally driven behaviours, but it is not a behavioural fix. In fact, early spaying may exacerbate anxiety and reactivity in sensitive dogs. 

Tips for Owners 

1. Consider emotional maturity—waiting until 18–24 months (for most dogs, this can be longer for some breeds) may reduce behavioural risks. 

2. Assess your dog’s temperament—is she bold, anxious, or reactive? 

3. Focus on training and socialisation—these shape behaviour more than hormones alone. 

4. Consult your vet and a behaviourist—especially if your dog shows signs of fear or anxiety. 

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Alternatives to Traditional Neutering/Spaying 

• Chemical Neutering: Reversible implants (e.g., deslorelin) allow behavioural observation before committing. 

•  Vasectomy / Ovary-Sparing Spay: Prevent reproduction while preserving hormones.

Final Thoughts: Rethinking Routine Neutering 

Neutering should be a case-by-case decision, not a default. Dogs are individuals, and their behavioural development is shaped by genetics, environment, training, and hormones. 

Tips for Thoughtful Decision-Making:

1. Consult a vet and behaviourist before deciding to neuter.

2. Consider your dog’s breed and maturity.

3. Focus on training and socialisation.

4. Don’t rush—waiting until after puberty may support healthier development. You may even decide neutering isn’t needed at all. 

What out for blog 3 on the pressures we are often under to spay/neuter.

Best Regards,

Pamela Hindes

Hindes Hounds – https://hindeshounds.co.uk

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