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At what age do dogs become aggressive?

Aggression Toward Owners is Always Problematic, but When is it Pathologic?

If you have a behavioral concern regarding your pet, do not email Dr. Hopfensperger directly. Please visit the American College of Veterinary Behaviorists to locate a behaviorist in your area or call the MSU Small Animal Clinic.



Regardless of Diagnosis

  • Avoid punishment. Confrontational training techniques, including verbal scolding and physical corrections, will likely escalate aggression in the moment and worsen long-term outcomes.
  • Consider an SSRI. Serotonin levels are abnormally low in cases with pathologic aggression, and boosting serotonin is beneficial for cases involving underlying fear, anxiety, and/or impulse control issues.
  • Avoid triggers for aggression. Without behavior modification, response to triggers will be unchanged. Avoidance of triggers enhances safety and gives the dog’s brain a break from previous response pathways. Triggers may be avoided long-term if necessary and feasible or reintroduced in the context of behavior modification.
  • Find a force-free behavior modification professional in your area. These are dog trainers with additional expertise in helping change how the dog feels about challenging situations; they are not focused on obedience training. Look for the following credentials: CAAB (Certified Applied Animal Behaviorists), CDBC (Certified Dog Behavior Consultant), CBCC-KA (Certified Behavior Consultant Canine-Knowledge Assessed), CPDT-KA (Certified Professional Dog Trainer-Knowledge Assessed), and/or KPA (Karen Pryor Academy).

Owner-directed aggression is problematic for any dog and owner; it most commonly comes in two forms: a genetic disorder referred to as Rage Syndrome, and a more typical diagnosis called Conflict Aggression.

The behavior associated with Rage Syndrome includes outbursts of aggression that are intense and at times unpredictable. These episodes also tend to be large dramatic responses relative to a seemingly benign situation. Affected dogs often freeze, stare, and may rapidly escalate to biting. This intense aggression contrasts with the dog’s otherwise pleasant personality. After episodes of aggression, dogs seem to not be fully aware of what just happened. Many dogs do not have dominant behavior, but likely have moments of mental “misfiring” due to underlying neurochemical abnormalities in their brains.

In comparison, Conflict Aggression is the diagnosis of the more typical variant of owner directed aggression. Dogs with Conflict Aggression tend to exhibit somewhat ambivalent body postures (e.g., tail tucked while lunging forward) and tend to display warning signs (e.g., growling) prior to a bite incident. Episodes of aggression tend to be related to predictable triggers over resources, invasion of the dog’s personal space, and grooming or handling. Dogs with this diagnosis often learn that aggression is an effective tool for ceasing uncomfortable interactions. These dogs are not dominant but are emotionally torn during moments of confrontation or discomfort.


Meet Ruby. Ruby was brought to the Michigan State University Veterinary Medical Center’s Behavior Service for complaints from her owners regarding her aggression.

Ruby was adopted from a local humane society three months prior to her visit to the Hospital. Her early life history was unknown. In addition, her two owners (both retired adults) Ruby also lives with an eight-year-old neutered male Jack Russell Terrier. Aggression toward the owners was noted within the first few days of adoption; however, aggression toward the female owner subsided over the two months prior to coming to the MSU Behavior Service. Unfortunately, aggression toward the male owner remained consistent.

Persistent triggers of growling, lunging, and snapping at either owner included petting of her back and physical contact with her while she was at rest. Growling, lunging, and snapping directed only toward the male owner included being approached while at rest on an elevated resting place, while on the female owner’s lap, or when in the kitchen during meal preparation. Ruby also was reported to bite when either owner attempted to place the harness on her. In all incidents of aggression, Ruby was reported to first bare her teeth, lay her ears back and tail down, and then lunge toward the victim. She also cowered after episodes of aggression.

When the Behavior Service team met Ruby, she was anxious, alert, and responsive. She was appropriate but not overtly social with Dr. Marie Hopfensperger, veterinarian for the Hospital’s Behavior Services. She solicited attention from both owners but spent most of the time on the female owner’s lap. After Dr. Hopefensperger evaluated Ruby, interacted with her, and ran a series of tests, it was confirmed that she was diagnosed with Conflict Aggression.

Ruby’s Behavior Modification Plan

To manage and treat Ruby’s aggression, her owners were advised of the need for lifelong management. As such, they were instructed to refrain from punishment, as any form of confrontation tends to escalate aggression in the moment and worsen aggression for the long-term as well. It also was recommended that they avoid all situations that had resulted in aggression in the past, except when engaged in prescribed behavior modification exercises.

Ruby’s day-to-day behavior was to be managed with cues and rewards for compliance for all interactions and as needed to redirect her at the first sign of tension. Dogs with Conflict Aggression do best when we have their buy-in for compliance; they especially struggle and may become aggressive if physically forced or scolded into listening. Desensitization and counter-conditioning (DS/CC) exercises were implemented for Ruby’s specific triggers. The owners were instructed to gently touch Ruby on parts of her body that elicited no reaction and follow each contact with a palatable treat. These instructions included gradually working up to touching the parts of Ruby that did cause an aggressive reaction, like her back or touching her while at rest.

In a similar manner, the owners were coached to practice DS/ CC to the process of getting Ruby’s harness on and off. They were told to show Ruby the harness and then offer a palatable treat. Then they worked on clasping and unclasping the harness while near Rudy, offering her a treat with each clasp sound. The owners then worked on placing the harness around Rudy’s chest and eventually placing it on her and clasping it prior to offering the treat. The male owner was instructed to practice short sessions of DS/CC during which he would approach Ruby while at rest on the floor and couch, but not so close that a reaction was elicited, and toss her a treat. In a similar manner, DS/CC was implemented when Ruby was on the female owner’s lap. The variation, however, was that treats were offered by the female owner contingent on the male owner’s gradually nearer approaches.

Ruby’s Follow-Up

After six months of at-home management and a low dose of medication (paroxetine 10 mg. per day without any adverse effects reported), Ruby was no longer exhibiting signs of aggression when touched on her back and when at rest, and the owners were able to get the harness on and off her without incident. A baby gate remained in place to keep both dogs out of the kitchen. Ruby no longer exhibited aggression when approached by the male owner whether she was at rest on the ottoman or the female owner’s lap.

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Rage Syndrome in Dogs: A Mysterious & Rare Genetic Disorder

In practically the dark ages of 1982 when I was a young girl, I remember one particularly snowy night when I went out with a friend. It was bitterly cold — like 20 degrees below zero cold — and when we got back to her house, my car wouldn’t start.

I spent the night with my friend who happened to have a Borzoi or Russian wolfhound. These are the dogs that have a steep arch in their back and a very narrow face. They’re actually bred to jump up in the air and come down on top of wolves to kill them.

Anyway, I remember this night because my friend’s electricity went out, and I woke up on the couch in the morning with this dog on top of me. I mean it was cold. He seemed like a nice dog to me, and so, I cuddled with him to stay warm.

Later that morning, I witnessed that same sweet dog erupt with extremely aggressive behavior at my friend (the dog’s owner) and her brother (also an owner) in two separate, unprovoked rage incidents.

The term rage syndrome was relatively new at that time, and many experts disputed its existence. It’s still not clear exactly what causes this type of dog aggression. It can certainly be problematic, and it can even result in euthanasia.

Let’s look at rage syndrome, what it is, how it manifests, and what to do if your dog has it.

What is Rage Syndrome in Dogs?

To put it simply, rage syndrome is a sudden, intense, and unpredictable form of dog aggression. Other forms of aggressive dog behavior typically result from some kind of trigger, such as fear aggression, anxiety, or when they’re protecting their territory.

With rage syndrome, however, there is no clear reason for the aggressive behavior. It is classified, therefore, as idiopathic aggression.

While it is seen in many different dog breeds, it is seen most frequently in English Springer Spaniels. For that reason, it is also referred to as “Springer Rage.”

What distinguishes rage syndrome from other types of aggressive behavior includes several common characteristics:

  • There is no identifiable stimulus/stimuli that trigger the incidents
  • The dog erupts in intense, explosive, and extremely aggressive behavior
  • The sudden onset of the rage episodes occurs between 1 – 3 years old
  • The dog may demonstrate a glazed or possessed look in its eyes just prior to the episode. They may also seem confused
  • It is more common in certain breeds including Cocker Spaniels (where it’s known as ‘Cocker Rage’), English Springer Spaniels, Doberman Pinschers, German Shepherds, Bernese Mountain Dogs, St. Bernards, and Lhasa Apsos. This points to a possible genetic disorder or at least a genetic component as part of the cause.

What Causes Rage Syndrome?

rage syndrome in dogs

Back in those dark ages when rage syndrome was new, there were a number of theories regarding the cause. One that my friend and I learned in vet tech school was that it might be related to certain traits breeders were selecting for in some breeds of dogs.

More specifically, the theory was that many breeders were breeding for increasingly narrow heads in breeds like Collies, the Borzoi, and Doberman Pinschers. Some experts posited that the narrow bone structure was putting pressure on and physically damaging the brain of these dogs. That, they suggested, was causing unpredictable behavior or perhaps symptoms similar to epilepsy.

Dominance aggression, brain damage, or genetics?

Unfortunately, with over 30 years of research, we still don’t have a clear cause for idiopathic aggression. Some experts believe that seizures are part of the problem. This does fit with confusion following or prior to an episode. Dogs who have had a seizure will commonly exhibit aggression and confusion.

Some of the other aspects of idiopathic aggression suggest the possibility that it’s simply a case of misunderstood status-related aggression. Status-related aggression or dominance aggression typically appears around 1 – 3 years of age. That’s also, however, a common age for idiopathic epilepsy to develop.

Some researchers have found that dogs exhibiting idiopathic aggression have abnormal electroencephalogram, or EEG, readings. The problem is that not all dogs exhibiting this aggressive behavior had those abnormal EEGs.

Another theory related to the narrow head hypothesis is that there has been damage to the area of the brain responsible for controlling aggressive behavior. This allows for other types of brain damage than just breeding for a narrow head, although it would include that reason for the brain damage.

Still, others have suggested that this is nothing more than dominance aggression or status-related aggression that is being triggered by some kind of very subtle stimuli. The fact is that we just don’t know for sure.

Part of the problem is that researchers have been unable to induce idiopathic aggression, which makes it very difficult to study. It’s possible to induce something like aggressive behavior associated with resource guarding or possessive aggression in a research setting, but so far, nothing seems to trigger the sudden, violent, but short-lived rage we see with this syndrome.

What are the Warning Signs of Dog Aggression?

While many owners only describe a glazed look in their dog’s eyes before an aggressive outburst, there are other warning signs of dog aggression that might indicate another type of aggression.

The glazed look that owners report might be what animal behaviorists describe as a ‘hard stare’ or ‘freeze’ that many dogs exhibit before an attack. According to the ASPCA, other warning signs include certain types of body language like a still, rigid body, certain movements like lunging forward or charging at the object of their aggression, and certain sounds like guttural barks, snarls, or growling. Your dog might also show his teeth.

Dog owners also sometimes receive what is known as a ‘muzzle punch’ where your dog punches you with his nose. Your best friend might also mouth you to try to control you without really biting you.

Of course, hard nipping and biting are clear signs of aggression. These range from nips with significant pressure, to repeated bites and biting and shaking.

It will be important to take note of any of these warning signs to accurately identify the specific form of aggression you’re really dealing with. That also affects how to treat the problem.

How Do You Treat Idiopathic Aggression?

dog at the vet

Of course, the first step in any kind of treatment plan is to make sure there isn’t a medical problem. That’s why it’s helpful to get a full medical examination by your DVM. If something like a tumor is pressing on your dog’s brain, that’s a much different treatment for that behavioral problem than if it is rage syndrome.

Once you’re certain there is no physical ailment behind your dog’s behavior, the next step is to get in touch with an animal behavior consultant. Rage syndrome is very rare, and a behavior consultant can help you determine if that is really what your dog has or if it is some other type of behavior problem.

If it is determined that your dog does have a rare case of idiopathic aggression, consult with a veterinary behaviorist. There are some drugs, like phenobarbital, that can help, although experts aren’t sure if these are truly helping or just sedating your dog.

Management & Worst-Case Scenario

If such drugs don’t help, it will be time for some hard decisions. Rage syndrome can be managed, but not cured, so that means that all of your family members have to be aware that episodes of rage can happen again.

You want to make sure everyone knows what warning signs to look for that might signal an aggressive episode. It may also be important to determine how you will handle your dog if an episode of rage occurs.

Basically, it means constantly monitoring your dog’s behavior to determine if you need to do anything differently. If you’re finding that the problem cannot be managed, then it might be time to consider euthanasia. That’s a very difficult decision to make, but it might be the only choice you have.

Because of the nature of these aggressive, unpredictable episodes, it is not safe or fair to expose family members, friends, and yourself to the possibility of an attack. While most episodes of aggression are brief, they can be very harmful, maybe even deadly if a child is involved.

While euthanasia is not the optimal solution, and it’s one that I am loath to recommend, it may be the only thing you can do to keep everyone safe. If that is what you have to do, give your dog a loving goodbye, and then be sure to take care of yourself as well. You did everything you could, and hopefully, you can take some comfort in that.

Final Thoughts

Rage syndrome can be the result of a genetic disorder or something like epilepsy that causes unpredictable outbursts of dog aggression. It is likely confused with other forms of aggressive behavior; and so, before a diagnosis is made, it’s important to watch for the warning signs.

If your dog does have a rare case of rage syndrome, some medications may help, but you may also have to make some tough decisions.

As for my friend, they simply lived with the occasional outbursts of rage from their Borzoi. They didn’t have any children around the dog, and they made sure everyone was aware of the situation. I’m just glad I’ve never had to make that tough decision, and hopefully, neither will you.

The Easy Guide to Training an Aggressive Puppy

aggressive puppy

Here at Zigzag HQ, we really love all puppies, but we also know how troublesome they can be and that things don’t always run smoothly. We know this isn’t an article you want to read, no one wants to learn about puppy aggression do they? It’s everyone’s worst nightmare to think their puppy might be aggressive.

So… whether you think your puppy is displaying aggressive puppy signs, or you’ve been doing some reading up on puppy dominance aggression, we’re here to separate the fact from the fiction when it comes to puppy aggression, and also help puppy owners work out what to do.

In this article we’ll be going over

puppy chewing toy

  • Signs: What aggressive puppy signs to look out for
  • Is it play?: Figuring out if your puppy is really being aggressive or if they’re just playing
  • Why are they doing that? Reasons why your puppy might be displaying aggressive puppy signs
  • Nipping it in the bud: How to stop puppy aggression quickly

What aggressive puppy signs should you look out for?

So what should you look out for? Here’s a list of the most common signs of aggression in puppies.

  • Freezing
  • Growling or snarling
  • Lip curling
  • Whale eye (where you can see the whites of their eyes more than when they are relaxed)
  • Hard stare
  • Ears flat back
  • Body stance forward
  • Body hunched, tail tucked under
  • Snapping and biting (not to be confused with normal puppy biting though)

We have an article on how to quickly stop your puppy biting you that you might find useful to read through too.

Is your puppy aggressive or are they just playing?

So the reassuring news is that a lot of the time the untrained eye can interpret puppy play as aggressive behaviour. We know it looks rough, really rough but they are actually just practicing skills which lead to a greater chance of survival in the wild, or they are doing very normal puppy play behaviours.

Puppies play rough – no really. Especially when they are playing with each other, it sounds like they are trying to kill each other in that wrestling match! All the snarls and growls!

Sometimes they play like that with us too, and it can feel a bit scary, especially for children.

We’ve put a little table together that gives you an idea if it’s play or aggressive puppy signs you’re seeing.

A low growl – accompanied with a freezeA high growl with lots of movement
Snapping and grabbingTugging
A forward body stance – often frozenA backward stance with bum in the air – often called a play bow
Stiff body posture – looks tightLoose body posture – looks wiggly
Tight furrowed brow – hard stare – closed mouthSoft face – open mouthed, lips covering teeth

By the way, is your puppy nipping you? Read our article on puppy nipping here.

Why is your puppy aggressive? Top reasons explained

Perhaps you’ve been told that your puppy displaying aggressive signs is them having dominance aggression. We want to reassure you that this label is old fashioned and really so called puppy dominance aggression and actually most forms of aggression are about your puppy being in conflict over something.

There are other reasons you might feel that your puppy is being aggressive, and we’ve tried to give you some good explanations below to help you understand, and hopefully think about how you might tackle puppy aggression.

  1. Overstimulation and not sleeping enough

This is soooo common! Here at Zigzag we feel like we bang on about sleep all the time. Well you get fractious and irritable too when you don’t have enough sleep, don’t you? No surprise your puppy gets a bit snappy when they’re tired. This is often misinterpreted as aggression when really it isn’t, it’s quite normal.

  1. Resource Guarding

They’ve learnt to be protective over resources – this often occurs when the over zealous puppy owner repeatedly takes ‘unsafe’ things off of the puppy without doing swaps. We want our puppy to think that swapping items is fun and taking things away from them should be no big deal, but we need to be careful we don’t end up with resource guarding related issues.

  1. We’ve told them off for growling

When a puppy’s earlier signs of discomfort were ignored or even punished such as when they growl, they learn that that early warning sign didn’t work. Puppies and dogs generally give us lots of warning signs before they get to the biting stage.

There is a saying ‘never punish a growl’ and it’s true because that growl was communicating something, and by punishing it we remove that early warning system and so they feel like they have to escalate to a snap, or a bite.

  1. Dog-dog aggression – fear based

Maybe your puppy is scared of other dogs – dogs have a fight or flight system just like humans, If they can’t get away (flight) then they’ll typically have to use aggression to tell the other dog ‘I don’t like that’ this can then become learnt behaviour. It can be a result of inappropriate play at a puppy class or dog park, where you don’t get the switching of roles (i.e chaser becomes the chased, or puppy who was on top then becomes the one on the bottom when wrestling).

yorkshire terrier puppy sat on colourful rug

  1. The frustrated greeter – dog/dog reactivity

They’re overstimulated and frustrated about getting to other dogs – you know, that dog you see on their two back legs, snarling and lunging down the road. Well, some of those dogs started out as puppies who were allowed to go and say hello to whoever they pleased! Until they were told they couldn’t, making them hugely frustrated and turn into a snarling, hot mess.

When puppies have missed out on early socialisation they can become fearful of many things, and react in an aggressive way towards them, sometimes for the rest of their lives. Puppies reared in poor conditions such as puppy farms with not enough stimulation or exposure to novelty, can become shut down or react aggressively when they experience something new.

  1. Territorial aggression

Similar to resource guarding, though this time it’s not over a thing or object, it’s over a location or space. It might be a dog who guards their bed area from you or another dog, or it might be a dog who guards their house from that terrifying delivery man that’s come to murder everyone – just kidding, but that’s what puppies can sometimes think.

  1. Dominance aggression

You may have heard of this label, that your puppy is being dominant or that they’re displaying puppy dominance aggression, but the honest truth is it’s not really a thing. It’s generally when there’s conflict between dogs, they’re not vying for any kind of hierarchical positioning or top dog; it actually tends to be more attached to resource guarding, and wanting the same thing.

Dominance in the dog-human world isn’t really a thing either and has been disproved many many, times over. Dogs do what works for them that’s all, they’re not being dominant over you, we promise.

  1. Predatory aggression

Another kind of aggression that gets talked about but is actually quite rare. All dogs have an Eye-Stalk-Chase motor sequence. This is how they learn to hunt and take down prey. For most breeds of dog, pieces of this sequence have been removed, it’s no good having a gundog who dissects the bird they are meant to bring back, but in a terrier it’s very useful to have that part of the sequence to ‘dispatch’ the rat! In some breeds of dog this sequence gets switched on to other animals at times, particularly larger dogs playing with small dogs. We call this predatory aggression or predatory drift. And yes thankfully it’s not too common, but just something to be mindful of if you have a little squeaky dog who plays with very big dogs.

How to stop puppy aggressiveness in its tracks

We’re here to help you overcome your puppy’s aggression, so have provided you with some info below as a starting point. Emotions have a huge effect on how a puppy behaves, so we will need to change how they feel in order to influence how they behave.

We hope by reading this far down that you know it’s unlikely to be puppy dominance aggression, and that you’ve managed to spot the puppy aggression signs vs what puppies do when they’re playing. Here’s our top tips for stopping puppy aggression in its tracks.

  1. Identify – is it actually aggression or is it just your puppy playing?

A lot of puppy play can look aggressive, but it often isn’t, so the first thing to do is find out if your puppy is actually being aggressive or are they just getting a little over enthusiastic during play?

Filming your puppy playing and when you think they’re being aggressive can be useful as you can watch it back later and see what was really happening. Turn the sound down and watch it in slo-mo – it’s fascinating!

  1. Find out what the triggers for your puppy’s aggressive behaviour are

Is your puppy guarding something they don’t want you to have or take away from them?

Have they learnt that biting/mouthing/growling stops you from ‘doing that thing’? Are they terrified of the courier, who knocks dramatically on the front door?

  1. Develop a structured plan to desensitize your puppy to the triggers, and work on changing their emotional response

I know, it’s a lot of words, but it’s important if we want to change behaviour to get a plan together.

For instance, if your puppy is guarding objects you’ll need to teach them that us coming towards them and taking things off them is a nice thing, and that they’ll get something better in return.

Similarly if your puppy is fearful of people and has learnt there are things they can do to make scary people move away (let’s be honest who wants a dog growling at them?) then you’ll need to teach them that nice things happen when strangers are around.

  1. Understand that your puppy isn’t GIVING you a hard time, they’re HAVING a hard time, help them learn to cope with things better and behave more appropriately.

Really get inside your puppy’s head and try to understand and have some empathy for the reasons why they behave in a certain way. Once you teach them there are other ways of behaving and those ways will be rewarding to them, they’ll start changing the way they think about things.

  1. Seek professional help

Particularly if there are biting incidents, you have children in the home, or there has been a sudden onset of puppy aggression, then seeking a professional dog behaviourist or dog trainer is something we strongly suggest you consider. They’ll be able to support you in training your puppy and give you advice on how to proceed.

With any behaviour problem it’s also an idea to get a vet check too, just to make sure your puppy is all ok health wise.

small puppy looking at older dog

We hope you found this guide on puppy aggression useful, as always if you need help with your puppy, you can reach out to our Zigzag experts for help, via the Zigzag puppy training app. They’ll be able to give you strategies if it’s your puppy just playing a bit rough, or help you locate a professional trainer or behaviourist in your area if there might be more to it than just play.

We also have articles on puppy growling if you want to learn more.

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