Why Do Dogs Attack An Injured Dog



Because it is inherent in most people to feel compassion, we are perplexed when our dogs do things that seem to indicate a "killer" instinct. Attacking and destroying toys is a harmless outworking of an innate prey drive instilled in animals to help preserve the species. We understand that there was a time when animals had to source and kill their own food to survive.  That makes sense to us. What is more puzzling, and even frightening, is when we witness a dog attacking an animal that is old, injured, or sick. Our nature tells us to protect those who are weak and vulnerable, but human nature varies dramatically from that of what is instinctual in a dog. It is troubling behavior for an owner to witness, but for your dog, it is quite normal and even appropriate. It helps to understand that there are viable reasons why dogs choose to engage in this action though witnessing it does cause us great concern. Why do dogs attack other dogs that are old, sick, or injured?

The Root of the Behavior

If you have ever witnessed a dog attacking another member of its canine family, it is frightening indeed. It's even more frightening when the dog that was attacked seemed to do nothing to deserve it. As an owner, it causes you to jump to conclusions. Did I miss something? Is my dog actually an aggressive dog? Will these two dogs ever be able to live in the same household peaceably again? These are all normal questions to ask yourself after witnessing a dog attack. 

Charles Darwin wrote about survival of the fittest, and this theory certainly finds evidence in canine behavior. Dogs are descended from the wolf family and much of their innate makeup can be traced back to this heritage. Though today, we live with dogs that are far removed from the original wolf and his place in society, many of those instincts designed to ensure canine survival remain present in our dogs. Instinct cannot be denied. A dog selectively bred over years to assist his owner on a hunt will still exhibit these traits even if his purpose in his new home has changed. A leopard cannot change its spots, and a dog cannot deny thousands of years of genetics who have made him who and what he is. So though some of our furry friends' behaviors can give us cause for concern in terms of living in domesticity, it does not mean that those actions are wrong or even abnormal from the perspective of the canine.

Often this behavior rears its ugly head when two dogs who have lived in harmony for many years suddenly have a spat. Most often it is a younger dog attacking an older one or one who is physically compromised in some way. Why does this happen? The answers aren't clearcut, for sure. Many assume that since wolves traveled and hunted in packs that a sick, injured, or old family member merely slowed down and drew unwanted attention to the group as a whole. Since canine survival was dependent on remaining safe from predators and ensuring a plentiful food supply, dogs that could not contribute to protecting and hunting for the pack were eliminated so as not to drain or require additional resources. Though this is certainly possible, it is far more likely that there is some sort of physiological change in the vulnerable dog that sets off this ancient reaction in its housemate.

Encouraging the Behavior

We cannot change the fact that our dogs will age and suffer from illnesses and life-changing ailments throughout their lives. This means that at some point your dog could become the target of an attack within your own household if you have more than one dog in your home. Things like seizures or even a change in body or brain chemistry can elicit a strong attack response from dogs in your home that are normally very placid and who get along well with all of their canine brothers and sisters. Dogs react strongly to changes in smell, appearance, and behavior of other dogs. Things like kidney disease or diabetes can cause a vulnerable dog and his urine to smell differently. Witnessing a seizure is frightening to a human, but to a dog, it is unidentifiable, odd behavior and is a reason for an attack. Even the simple act of falling down a set of stairs can lead to a dogfight. 

While we do not want to encourage this behavior in our dogs in any way, there is little we can do to change instinct. What we can do is understand the "whys" behind it and take every precaution to protect our old, sick, or injured dog. The best thing we can do to prevent these things from happening is to stay aware of the potential problems and to supervise all dog interactions. If you cannot be there to actively watch your vulnerable dog when he is with other dogs, it is best to crate him in a comfortable location where he can rest without fear of conflict. To allow him sufficient time with you, you can also rotate crate time so that the younger dog also has some quiet time in his crate to allow your older dog the comfort laying on the sofa with you for awhile while you watch TV.  

Other Solutions and Considerations

Some behaviors are innate and cannot be eliminated entirely. The best we can do is manage them and try to prevent them. It is possible to have great success doing these things. As an entirely different species with origins in the wild, dogs do sometimes have behaviors that perplex and upset us. This is one that we can make our peace with and learn to manage well for the safety of all of the pets in our care. The unfortunate fact is dogs can and do attack their own canine family members at times. In some cases, an old, sick, or vulnerable dog has been killed through an unfortunate attack by a dog it formerly slept in the same bed with and ate from the same food bowl. It does not happen in every home, but the potential is there, and the wise owner is aware and prepared.


Canine behavior is fascinating. Because it can be so foreign to our own instincts, it can also be frightening. If normally friendly Fido suddenly attacks elderly Fifi, it is upsetting and scary, for sure. As much as we dislike it, Fido is only doing what comes naturally to him to do. As loving owners, the best we can do for our pets is try to understand what makes them tick and to set them up for success by ensuring that all canine interactions are supervised. As the old adage goes, "An ounce of prevention is worth a pound of cure!"