Let’s stop dancing around the truth. In the dog training industry, we are facing a self-inflicted epidemic. For decades, the "standard of care" dictated by veterinary boards and animal welfare organizations has been the mass gonadectomy—the surgical removal of the primary sex organs—of almost every dog in the country. We were told this was the responsible thing to do. We were told it would "calm them down." We were told it would eliminate aggression.
It was a lie. And not just a small lie—it was a biological catastrophe.
If you are dealing with a dog that is reactive, fearful, or displaying "out of nowhere" aggression, and that dog has been neutered or spayed, you aren't looking at a "bad" dog. You are looking at a biologically compromised animal. You are looking at a system that has had its primary internal stabilization mechanism ripped out, leaving the brain to navigate a world of stress without the necessary chemical armor.
The latest research is finally catching up to what I have been seeing on the training field for years: Neutering and spaying is not a cure for aggression; it is frequently its primary driver.
The "I’ll Fix Him First" Trap: A Race Against the Clock
I see it in my inbox every single week. A prospective client reaches out because their dog is lunging at neighbors or snapping at other dogs at the park. They are stressed, they are embarrassed, and they want a solution. Then comes the sentence that makes my heart sink: "We want to start training with you, but we’ve scheduled his neuter for next Tuesday so we can get the 'hormone stuff' out of the way first."
Stop. Right. There.
If you are reading this because you think you are doing me—or your dog—a favor by "fixing" them before we start training, you are actually doing the exact opposite. You aren't clearing the slate; you are pouring gasoline on a behavioral fire. You are walking into a catastrophe that will likely double the time and effort required to rehabilitate your dog.
When you tell me you’re going to neuter a reactive dog to "calm him down," you are operating on a myth. We are in a race against the clock to keep those organs in your dog’s body—at least until the training is done. Think of your dog’s reactivity as a car speeding down a hill. The aggression is the speed. The hormones—testosterone in males, estrogen and progesterone in females—are the brakes.
When you surgically remove the gonads of a reactive dog, you aren't slowing the car down. You are cutting the brake lines.
The Myth of the "Testosterone Demon"
The traditional argument for neutering male dogs is based on a prehistoric understanding of behavior. The logic goes like this: Testosterone causes aggression; remove the testicles, remove the testosterone, remove the aggression.
This is biologically illiterate.
Aggression is rarely driven by "too much confidence." In the vast majority of cases—upwards of 90% of the dogs that come through my doors for rehabilitation—aggression is driven by fear, anxiety, and environmental insecurity. Testosterone is not just a "sex hormone." It is a foundational health hormone. It provides emotional stability, cognitive focus, and, most importantly, confidence.
When you castrate a male dog, you aren't just taking away his ability to reproduce; you are lowering his threshold for fear. You are taking a dog that might have been slightly unsure and turning him into a dog that feels vulnerable. And what does a vulnerable predator do? He strikes first. He becomes "reactive" because he no longer has the hormonal buffering to ignore perceived threats.
The Endocrine Feedback Loop: A System in Chaos
To understand why this happens, we have to look at the endocrine system as a whole, not just the gonads. The body is a feedback loop. The hypothalamus, the pituitary gland, and the gonads (the HPG axis) work in a delicate dance with the adrenal glands (the HPA axis).
When you surgically remove the gonads, the brain doesn't just "turn off" the signal for those hormones. Instead, the pituitary gland goes into overdrive. It begins screaming at the body to produce sex hormones that are no longer there. This results in a massive, chronic spike in Luteinizing Hormone (LH).
Recent research has shown that neutered dogs have LH levels up to 30 times higher than intact dogs. Why does this matter for behavior? Because we have discovered LH receptors throughout the body—including in the brain, specifically the areas responsible for emotional regulation. We are effectively flooding the dog’s brain with a "demand" signal that can never be satisfied, creating a state of chronic biological unrest. This isn't "behavioral"; it’s neurological.
The 2023 Research: Data Doesn’t Lie
We no longer have to rely on "anecdotal evidence." Recent large-scale studies have decimated the pro-neutering argument for behavior.
A massive study utilizing C-BARQ data (the gold standard for behavioral assessment) involving over 15,000 dogs found that neutered dogs were significantly more likely to show aggression toward strangers, more likely to be fearful, and more likely to exhibit "touch sensitivity" than their intact counterparts. Specifically:
Increased Stranger Aggression: Neutering was associated with a 30% increase in stranger-directed aggression.
The Fear Factor: Neutered dogs are 70% more likely to show increased barking at strangers and general fearfulness compared to intact dogs.
Research published in Frontiers in Veterinary Science also highlighted the "Age of Neutering" factor. We are seeing that the earlier the surgery is performed, the more profound the damage to the dog's amygdala and hippocampus—the parts of the brain that process fear and memory. By removing these hormones during critical developmental windows, we are essentially "freezing" the dog in a state of permanent juvenile insecurity. They never grow the "thick skin" that adult hormones provide.
The Spay Myth: Female Aggression
For a long time, the focus was on males. But the data on females is even more damning. We have seen a terrifying trend: spaying a female dog, especially one that already shows a hint of "sharpness" or reactivity, often leads to a massive escalation in aggressive behavior.
Why? Because when you remove the ovaries, you remove estrogen and progesterone. In the female brain, these hormones have a calming, anti-anxiety effect. Progesterone, in particular, is a precursor to allopregnanolone, which acts on the GABA receptors in the brain—the same receptors targeted by anti-anxiety medications like Xanax.
When you spay a female, you are effectively performing a "chemical withdrawal" of her natural stabilizers. If she was already a bit insecure, you have now removed her ability to self-soothe. Furthermore, without estrogen to balance the system, the adrenal glands may compensate by producing more androgens (male-type hormones), which can lead to "persistent" or "proactive" aggression in females. They become irritable, snappy, and lose their social flexibility.
We must also talk about the adrenal glands. When the gonads are gone, the adrenal glands try to pick up the slack. They become overworked and often enlarged. This puts the dog in a state of Hyperadrenocorticism-lite. The dog is constantly "on." Their baseline cortisol (the stress hormone) level is elevated. Imagine living your life after drinking ten cups of coffee and not sleeping for two days. That is the internal state of many neutered dogs. They are hyper-vigilant. They cannot settle. They overreact to the mailman, the squirrel, or the dog across the street because their nervous system is "stuck" in a sympathetic (fight or flight) state.
You cannot "train" your way out of a biological cortisol spike. You can manage it, you can counter-condition it, but you are fighting an uphill battle against the dog’s own internal chemistry.
Why Training MUST Come First
I am not just being difficult when I tell you to cancel that surgery. There is a physiological reason why we need those hormones present during the rehabilitation process.
Learning Requires Stability: A dog in a state of hormonal withdrawal cannot learn effectively. Their "learning threshold" drops through the floor.
Confidence is Chemically Driven: To fix reactivity, we need to build confidence. Testosterone and Estrogen are "confidence chemicals." If we remove them, we are trying to build a skyscraper on a foundation of wet sand.
The Window of Maturity: Many of the dogs I see are "adolescent" reactives (12-24 months). This is the worst possible time to neuter. You are essentially freezing them in their most insecure developmental stage. We need them to reach social maturity with their hormones intact so they can realize the world isn't out to get them
What can we do?
If you have an intact dog, keep them intact. If you are worried about reproduction, look into a vasectomy or a tubal ligation—surgeries that prevent pregnancy while preserving the endocrine system. These are common in Europe but ignored in the US because they require more surgical skill than a standard "hack and slash" neuter.
If your dog is already neutered and is struggling with aggression, you need to change your perspective. Stop looking at your dog as "dominant" or "mean." Understand that your dog is fragile. Their "aggression" is a desperate attempt to create space because they feel biologically incapable of handling a confrontation.
Rehabilitation for these dogs must focus on:
Lowering Arousal: Minimizing unnecessary stress to manage the cortisol ceiling.
Building Cognitive Confidence: Building the confidence that their hormones are no longer providing.
Endocrine Support: In some cases, exploring LH blockers or hormone replacement therapy to restore homeostasis.
Final Thoughts and My Directive to You
We have to stop treating the dog’s body like a collection of disposable parts. Every organ has a purpose. The sex hormones are not just for making puppies; they are for making a whole, stable, confident animal. When we remove them, we break the dog.
If you are considering Canine Evolutions because your dog is reactive, hear me clearly: Cancel the surgery. Do not "fix" the dog until we have fixed the behavior. Give me six months of solid training with an intact animal. Let’s build the neurological pathways for calm, confident behavior while the dog still has the biological tools to support that growth. Once the dog is stable, once the dog is regulated, and once the dog has reached full social maturity—then we can have a rational conversation about the pros and cons of surgery.
Doing it the other way around isn't "responsible ownership." It is biological sabotage. Don't make your dog's struggle harder than it already is. Let’s keep them whole, let’s get them trained, and let’s avoid the catastrophe of a "fixed" dog with a broken mind.
Bart de Gols