Why Would a Loving Dog Suddenly Become Aggressive?


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You’ve probably heard stories about random aggression in dogs that go something like “I don’t understand it; my dog was just sitting quietly on the sofa between me and my girlfriend, and all of a sudden, he turned around and latched onto her.” Or you hear, “He was playing with the kids, and everything seemed to be going fine, and then suddenly he snapped at Kayla.” Another common tale is “I was just petting him, and he grabbed my hand, and I ended up needing stitches.” Still another is “He was such a sweet boy, until he ate the neighbor’s cat.”

A lot of the time, these stories end with “So I took him to the vet and had him put to sleep; after all, I can’t take that kind of chance again.”

That’s sad, because there is no such thing as “random aggression” in dogs. Loving dogs don’t just suddenly become aggressive – there’s always a reason, even if we don’t know what that reason might be.

Even the Best Dog Can Show Aggression

I recently had a phone call from a woman who had adopted a puppy out of the first litter from Janice and Leroy. She was in tears because the dog (now three years old) had snapped at a neighbor’s child who was visiting her home, and now the neighbor was demanding that she have the dog euthanized. “There was no reason!” she said. “This kid has been here a million times; she loves the dog and the dog loves her! I don’t know what to do.”

I asked if the dog had actually bitten, and the answer was “No.”

With a bit of questioning, I learned that the dog had been soundly asleep, and the child had approached from behind to pet the dog. The dog woke suddenly, and not being able to see immediately who had initiated the contact, turned around and delivered an “air snap.”

An air snap is just what it sounds like – the dog is frightened, and closes its jaws, not aiming at anything in particular and neither making, nor even intending to make, contact with anyone.

The child was terrified and ran home crying, and then the neighbor marched over with the sobbing child in tow. Voices were raised, nothing was resolved, and then I got the phone call.

Dog Aggression

Was This an Example of Random Aggression in Dogs?

No, it wasn’t. In fact, it’s about as far from “random” as I can imagine. The dog had been approached in a manner that most humans don’t like, never mind dogs! And, lacking human self-control, the dog reacted in what I consider to be a perfectly normal, sensible fashion – albeit a possibly dangerous fashion. At least it was just an air snap, not a full-on bite.

I suggested that since the owner had been able to determine what had set the dog off, she might want to go over, apologize to the neighbor, explain, and try to make things right before matters got even worse.

The Outcome

When the owner went to the neighbor’s house, the neighbor still wasn’t in a good frame of mind, and reiterated that she wanted the dog put to sleep. The dog’s reprieve came from a surprising source – the child, who had been listening to the conversation. She immediately resumed sobbing, bordering on hysterical, and saying “Mommy, Gino didn’t mean to do it, you can’t mean for him to die, and if you do, then you’re just the most horrible, hatefulest, meanest mommy in the whole world! You want to kill Gino, and I hate you!”

Lee Bailey couldn’t have delivered a better defense, from where I’m sitting.

The dog’s owner seized the advantage, saying softly, “If I put Gino down, who’s she going to blame? Me or you?”

Finally, cooler heads prevailed. The neighbor relented, and the child now knows not to approach Gino from behind when he’s sleeping. Or for that matter, any sleeping dog.

The Moral of the Story

This long digression is simply by way of pointing out, again, the fact that a loving dog does not generally “turn,” and that there is no such thing as random aggression in dogs.

That’s not to say, though, that aggression in dogs should be taken lightly, and there can be other reasons why a normally loving dog might display aggressive behavior.

Knowing the reason is the first step toward addressing the aggression, which is most of the time, simply the first indication of an underlying problem. Sometimes, it’s a “one-off” like the scenario I’ve described above, but equally often, something else is at work, and if the dog is acting aggressive, and that aggression is not dealt with, it will usually escalate.

Related Content:

Top 3 Reasons for Aggressive Dog Behavior, and What to Do About It
Why Would a Loving Dog Suddenly Become Aggressive?
5 Ways of Dealing with Aggression When You Have More Than One Dog (Video)

Most Dogs Don’t Want to Be Aggressive

A loving dog will almost always, if given the choice of aggression or another response, choose the other. Dogs want to have their needs met, and if they can have those needs met without resorting to aggression, that’s the course of action they’ll pick. Just knowing this makes it a lot easier to deal with a dog that is acting aggressive.

That said, though, I want to reiterated that aggression is serious, and you should never put off dealing with it. Most dog owners are not usually well-equipped to solve this sort of problem on their own, so it’s generally best to consult a dog trainer or an animal behaviorist. Don’t waste time, either – do it right away. The longer you live with the problem of a dog that is acting aggressive, the more difficult it’s going to be to correct. I can tell you too, that the dog trainers I know want to see you right after the first incident, and they just hate it when people come to them saying “He’s bitten three people.”

What? He’s bitten three people, and you didn’t see a professional after the first bite? You didn’t think you had a problem on your hands? That’s just demented, irresponsible and wrong on just about every level!

An “air snap” is a warning, and not necessarily an indication that you have a dog that’s going to be acting aggressive habitually – it’s usually the result of some action on the part of a human, however innocent. A bite, however, is most definitely not a warning,and should never be ignored or considered to be a “one-off.”

What Is Aggression?

Aggression in dogs is the same that it is in humans – a deliberate attempt to injure someone, or to intimidate someone by threatening to cause an injury. But when you’re considering what aggression is, you also have to think about what it isn’t. Not every act on the part of a dog constitutes aggression.

As an example, some dogs “smile” differently than others. We usually think of a “dog smile” as the lips being pulled back, and the teeth visible but not bared. Some breeds, though (the Australian Shepherd is one example) tend to pull their lips back so that their gums are visible, and the teeth can look pretty scary. To know whether a dog is being aggressive, or simply smiling, you need to look at the rest of the body language. More on that in a bit.

Growling is another thing that doesn’t necessarily mean aggression. Sometimes growling is just growling, Many dogs growl when they’re playing, and some dogs even growl when they’re feeling particularly happy. Rottweilers are known for this – they might growl when having their tummies rubbed, for instance, as a way of saying “That feels good; do it some more!” Some breeds are simply more “talkative” than others, and growling doesn’t invariably mean that the dog is acting aggressive.

Of course, that said, it’s worth keeping in mind that growling can be the precursor to full-on aggression. When that happens, the growling dog is telling you, “I would prefer not to bite you, but I will if I absolutely have to. Just please, don’t make me have to.” Another thing that you should keep in mind is that a dog who is about to bite might not necessarily growl beforehand. Generally speaking, though, the time to worry is not so much when the dog is growling, as it is when a growling dog stops. That means that the dog has decided “All right, enough talking – now it’s time to get physical in a huge way!”

This is a good time to mention that it’s not a good idea to discourage growling in dogs. When a dog growls, he’s delivering a message. In many cases, dogs that don’t growl before biting have been corrected by well-meaning owners. They’ve been taught that growling is frowned on, so they dispense with it and go straight to the bite.

So, how do you identify a dog that is acting aggressive? Take a look at the dog’s body language. Is he standing stiffly, staring at you, throwing his weight forward and raising his hackles? These are all signs that you could be in trouble. Most of the time you won’t see these behaviors from your own dog, toward you. These are generally the things you need to worry about when encountering strange dogs. If you’re concerned about aggressive behavior on the part of your own, ordinarily loving dog, though, there are things to watch for.

Signs That Your Dog is Acting Aggressive

If you’re reading this article, I’m thinking that you may already be concerned that your beloved pet might be a threat to you at some point. Here are some warning signs:

  • You’re afraid to take things away from your dog
  • You’re unable to approach your dog when he’s eating
  • Your dog growls at you when you try to put him off the furniture
  • You’re afraid of your dog for any other reason

To take this further, if you’re afraid to take your dog for walks because you worry that he might bite someone or try to fight with another dog, or if you’re constantly telling people to keep their distance because you’re afraid they might end up being bitten, then you definitely have a dog that is acting aggressive. You have aggression issues that might not be directed at you, but if they’re not corrected, the outcome could be very bad indeed for someone else. If your dog bites someone, or harms another dog, you could end up being sued, and your dog could end up being put down

Reasons Why Your Dog is Acting Aggressive

Let me point out yet again that there is no such thing as random aggression in dogs. There is always a reason, and dogs can have any number of reasons for displaying aggression. Here are some of the most common causes of aggression in normally loving dogs.

1. Mental Illness

If your typically loving dog suddenly displays aggression, your first course of action should be to see your veterinarian, because the first thing you need to do is rule out mental illness.

We now know that in humans, clinical depression and bipolar disorder, to name just a couple of conditions that affect the brain, are not due to lack of character or a failure to “pull up our socks” – they’re the result of a chemical imbalance in the brain. In other words, it’s a physical problem that affects mental function, and requires medication to correct the imbalance. Dogs can also be mentally ill. Sometimes the cause is organic, and can be treated using medication. In the case of a rescue dog, though, the cause could be situational – it might be that the dog has been tormented to the point of being vicious, and in cases like that, behavioral intervention is required.

Your vet can do bloodwork and other tests to determine if your dog’s brain is functioning the way it should, and can prescribe medication to correct the imbalance that’s causing the aggression. If the aggression is the result of abuse, then a lot of love and gentle handling can go a long way, but the reality is that you may never have a dog that is one hundred per cent safe around people – in a case like that, all you can do is keep the dog away from other people. It’s not a cure, just a preventative measure that works for the dog and the humans he may encounter.

2. Thyroid Dysfunction

If the thyroid gland is not producing the right amount of thyroid hormone, this is another condition that can cause aggression. Usually, this condition can be corrected using medication.

3. Lyme Disease

This is another disorder that can affect both humans and dogs, and that in both species, can result in sudden aggression. Lyme disease is spread by ticks, so if your ordinarily loving dog has suddenly become aggressive, and you live in an area where ticks are known to be present, I would suggest that your vet have your dog tested for Lyme disease. Of course prevention is always better than a cure, so if ticks are a problem where you live, have your dog vaccinated against Lyme disease.

4. Rabies

Remember Cujo, the sweet-natured Saint Bernard in the Stephen King book (and later the movie of the same name)? He ended up being transformed into a slavering, homicidal hell-hound when he contracted rabies.

Fortunately, the chances of encountering “Cujo” today are low. Thanks to increased public knowledge about the importance of regular rabies vaccines, the disease is fairly uncommon in dogs today. If your dog has not been vaccinated, though, this could be a cause of his sudden aggression.

I can’t stress enough the importance of vaccinating. There could be several reasons for sudden aggression in your typically loving dog, but if you keep the vaccinations up to date, you can definitely rule out rabies as a potential cause. Also, if your dog is suspected of having come into contact with a rabid animal, he can be seized and euthanized, and you will have absolutely no recourse.

5. Brain Injury

A blow to the head can also be a cause of canine aggression, as can anything else that causes pressure on certain areas of the brain – tumors, or water on the brain, for instance.It’s the same with humans – brain injuries can result in uncontrolled aggression.

These conditions can also lead to random acts of aggression on the part of the dog, but again, there’s a reason for that aggression. It’s not that the dog has suddenly decided, “Hey, I think it would be cool to start biting people.” There is an organic cause for the aggression – a reason.

6. Reaction to Pain

If a dog is injured, and you’re trying to help him, he might lash out at you thinking that you’re the cause of the pain. Think of it this way – if you’ve sustained an injury, and someone reaches for the affected area, your reaction is likely going to be to try to push them away. Your dog is going to have the same sort of reflex. You will probably use your hands, but a dog will use his teeth to try to remove what he perceives as the cause of his pain.

This actually shouldn’t be considered as sudden, or random, aggression in dogs – it’s more like “situational aggression.” However, I’m including it here simply because it seems like a good opportunity to warn you against handling an injured dog without first muzzling him. Even the most loving dog in the world can bite if he’s in pain.

7. Fear

A frightened dog can also be prone to sudden aggression, or “fear biting.” If you’re dealing with a strange dog, then you don’t know how loving that dog might ordinarily be, and the best course of action is to keep your distance. If it’s your own dog, avoid putting him in situations where he feels threatened. I have known more than a few dogs who were perfectly kind and gentle with family members, but very afraid of strangers.

The potential for “fear biting” is much more easily prevented than cured. It’s very important to make sure that your dog is socialized in his early months – exposed to a variety of situations, environments, and people. A well-socialized dog is hardly ever a fear biter.

Puppies are often afraid of people that they don’t know, but if they’re taken out regularly and exposed to different people, they will learn that most people are friendly and that there is nothing to fear.

8. Predatory Instinct

All dogs are predators. It’s simply in their nature. A dog that kills the neighbor’s kitten, for instance, isn’t evil, or murderous, he’s simply dog-like. Also, prey drive can be considerably stronger in some breeds than it is in others.

Predatory instinct becomes a problem when you don’t control your dog, and when you can’t handle his aggression. This isn’t a situation where a normally loving dog loses it – it’s perfectly normal. Undesirable, but normal.

Predatory instinct can be controlled to some extent with vigorous training, and often channeled through finding the dog a job, like agility training. Prey drive is not “random aggression” in dogs, though – it’s hard-wired, and in some dogs, it needs to be channeled in a positive direction.

9. Territoriality

Having just said that dogs are natural predators, in the wild, they don’t survive mainly by predation. Mostly, they scavenge, looking for places where food is likely to be found. They find their territory, and they will protect it against other dogs.

In domestic dogs, this translates into guarding the food dish, and it’s why loving dogs will often react badly if you approach them while they’re eating. If you’re going to combat territorial aggression, or food guarding, you want to start when the dog is just a puppy. Make him wait for his food, put your hand in his food bowl while he’s eating, practice taking the bowl away, and so on. Do this before he’s big enough to fight you on the issue, and he’ll become very accepting of your occupation of his “territory.”

I’ve always done this early on with my dogs, and I’ve done the same with toys, offering them and then taking them away before the dog is big enough to think he can engage me in battle over something he wants. Because I do this, I’ve never had to worry about a loving dog suddenly showing aggression over food or property. In fact, people ae often amazed that I can reach into my dogs’ mouths, say “Give me that,” and have the dog immediately hand over the object or the food, no matter how desirable he considers it to be.

Snapping over an owner trying to take away food or a toy is not “random” aggression in dogs – it’s the dog trying to protect what he feels is his, and it’s up to you whether or not you want to allow that. I would submit, though, that if your dog is around other people, it would probably be a good idea to train him to the point where food and property are not issues. A territorial dog isn’t necessarily an unloving dog, but the result (a bite) is the same regardless of the emotional state or basic good nature of the dog.

10. Protectiveness

Protectiveness is not a bad thing in a dog, but if not properly channeled, it can be a problem. For instance, many breeds of dogs are very protective of their families, to the point where they can be dangerous.

In the introduction to this post, I offered a scenario where a dog was playing with children, and suddenly snapped at a child, Kayla. Although the reaction in this case would have been the same no matter who had approached the sleeping dog, it’s worth mentioning that there can be situations where a dog differentiates between “my kids” and “visiting kids.” A dog that is perfectly fine with his own family might perceive that his kids are being abused by kids that are not his, and react in a way that, to the dog, seems perfectly normal. Again, this isn’t “random aggression” on the part of a dog that is normally loving – it’s an example of a dog being very protective.

This seems like a good opportunity to point out, as I frequently do, that you should never leave children and dogs unattended.

Protective aggression can also manifest in other ways – for instance, if your dog won’t let your boyfriend or girlfriend near you, he’s displaying protective aggression. Again, it’s not “sudden aggression,” and it’s not random, so you don’t have to rush off to a trainer or animal behaviorist – you just have to work through the problem. See What to Do When Your Dog Hates Your Significant Other for more insight into this problem.

11. Frustration

If a dog becomes frustrated, and can’t take it out on whatever it is that’s frustrating him (that annoying German Shepherd next door, or letter carrier, or the UPS guy, or whatever), sometimes that normally loving dog will take out his frustration on his owner. In this case, you might not be able to do much about the source of the frustration. After all, the German Shepherd’s people aren’t going to move away just because your dog is troubled by the presence of their dog. You still have to have your mail and your packages delivered.

With this kind of situation, you might need professional assistance. If the aggression is being turned your way, this is not a case of random aggression in dogs – it’s a serious issue, and you could end up being hurt. Don’t try to handle this on your own – see a pro.

12. Dominance

With dominance aggression, your dog wants to be the alpha. He might see you as weak and think that he’d be a better “pack leader,” and he might display hostility when you try to control him. Again, this is probably a job for a pro.

Often, dominance issues appear in young dogs. If your puppy is suddenly acting aggressive, and you’ve ruled out territoriality, it may simply be that you have a naturally dominant dog that is “testing” you.

Dogs will do that.

I once experienced something like this with a young dog that I was training for a friend. At some point, Carla decided that she wanted to be the boss. Carla and I had always gotten along famously, but on this particular day, she decided that she wasn’t disposed to sit, stay, walk at heel, or do anything else that I was asking of her, and she made it very obvious. It took me 45 minutes of “leash wrangling” to bring her under control, and the whole time, she was trying to get a piece of me.

I was younger and stronger then. I don’t know if I’d try to handle a dog like Carla at this point in my life. As it worked out, I got her settled down, with one of those alpha rolls that some trainers hate but that Cesar Millan, the dog whisperer, says can be useful from time to time.

If you doubt your ability to do an alpha roll, don’t even attempt it. This is absolutely not a battle that you want to lose, and you can never back down, either – if a dog wins once, he’s probably always going to have it in his mind that he can win again. Take the dog to a pro.

13. Your Dog Isn’t Really a Dog

In Wolves and Wolf Hybrids as Pets, I talked about the inadvisability of selecting a wolf or wolf dog as a family pet. When it comes to wolves and hybrids, the aggression level is off the map. This is simply because wolves are not dogs, and the physical appearance notwithstanding, a wolf or wolf hybrid will never behave in the same way as a dog.

You could think of a domestic dog as a wolf puppy that never grew up – willing and eager to please his human, and perfectly happy to be number two when it comes to dominance.

An adult wolf, though, is going to challenge you every step of the way. And again, the aggression isn’t “random” or “sudden” – it’s just a wolf being a wolf. At some point, he’s going to decide that maybe he would be a better pack boss than you, and he’ll challenge you, aggressively, for the position. If you’re not both physically and mentally strong, there’s a good chance that the animal that was such a sweet, cooperative little boy when he was a puppy, will try to dominate you.

These are not animals that can be tamed or socialized to any real level, and if you’re going to own a wolf or a wolf hybrid, then you’re going to have to be very vigilant not just about your own safety, but about protecting your neighbors, and your neighbors’ animals. Ideally, you’ll create a very high fence around your property, and never for one minute leave your wolf or hybrid unattended.

Think long and hard before you consider a wolf or wolf dog as a pet. Many animal behaviorists will tell you that they’re not for everyone. Others will tell you that they’re not for anyone.

14. Maternal Instinct

I’ve had three litters out of Janice and Leroy, and I’ve never once experienced a situation that’s more common than you might think – where the mother is so protective of the litter that she won’t allow anyone near the puppies, not even her human.

On the contrary, Janice is quite happy to allow perfect strangers to pick up her puppies and handle them. Janice’s perspective is that everybody is a friend, and it would never occur to her that anyone might want to harm her babies.

Not all dogs are like Janice, though. Sometimes, a perfectly loving dog can turn into a holy terror if she thinks she has to protect her little ones.

The best advice I can offer here is, if your ordinarily loving dog doesn’t want you near her puppies, respect her wishes. Her maternal instinct could be even stronger than her love for you. And once the litter is weaned, have her spayed, because often maternal aggression can be translated into generalized aggression once the litter is gone.

15. Play

I touched on this briefly before. Often, when dogs are playing, they become very vocal, barky and growly. This is perfectly normal, and if you’ve ever seen a real fight between dogs, you’ll immediately know the difference between “play aggression” and “real aggression.”

Again, though, this differs from supposed random aggression in dogs, where a dog suddenly seems to “go off.”

Some people will suggest that you should curtail play aggression, on the theory that it will lead to “real aggression,” but that’s very unlikely to happen. In fact, play aggression actually helps dogs to learn when to pull back – a dog that is accidentally hurt during play will yelp, and the other dog will usually pull back. Your dog is far less likely to be aggressive if you allow him to play with other dogs.

As to the idea that playing “tug of war” with your dog causes aggression, I call bullshit. On the contrary, I think that tug of war allows dogs to display aggression in a happy, healthy way – playing with their human, or with another dog. I think that dogs know the difference between going into full-on “kill mode” and playing. If your dog likes tug of war games, there’s no reason why you shouldn’t play. Just make sure that the game is over when you decide it’s over – don’t let the dog decide. When it’s time to put the toy down, make sure that your dog cooperates. Be the boss!

So, we have lots of examples of aggression here. But random aggression in dogs? No. It simply doesn’t exist.

Related Content:

Top 3 Reasons for Aggressive Dog Behavior, and What to Do About It
Why Would a Loving Dog Suddenly Become Aggressive?
5 Ways of Dealing with Aggression When You Have More Than One Dog (Video)

The Final Word

Random aggression in dogs doesn’t happen, and when it appears to happen, it’s still not random. There is always a reason for aggression in dogs. Dogs don’t just suddenly “turn.” When aggression in dogs appears to be random, and mental illness has been ruled out, it’s generally the result of humans making mistakes, or misinterpreting the aggression as sudden or random.

If aggression is a problem in your dog, though, it really doesn’t much matter if it’s random or otherwise. It has to be dealt with, and if you can’t handle it on your own, you need the assistance of a professional trainer or animal behaviorist.

Look at the cause of the aggression. What happened before the aggression? Was the dog surprised, or tormented? Did somebody make a move that might have been misinterpreted by the dog?

If the aggression really does seem to have no reason, could the dog be ill? Has the dog been evaluated by a veterinarian to rule out brain tumors, Lyme disease or other conditions that could lead to aggression?

In the final analysis, I think that all I can say is that it’s reasonable to assume that your dog loves you and trusts you. And if it seems that he’s behaving out of character, it’s up to you to find out why. You may need the assistance of a veterinarian or an animal behaviorist, but the responsibility for the initial diagnosis is yours, and so is the follow-up treatment. You owe it to your dog, and to the people and other animals that he may come into contact with, to ensure that he is safe, stable, mentally healthy, and if aggressive, that he has non-destructive ways of channeling that aggression.

I don’t want you to end up in tears because things have gone horribly wrong, and your beloved companion has ended up on the receiving end of a needle loaded with euthanyl. Do everything you can to identify the cause of your dog’s aggression, and then deal with it, so that you can enjoy many happy, fulfilling years together.