Understanding acts of aggression between two dogs who previously got along well requires us to identify a trigger point that leads to a sudden change in behavior.
A dog suddenly aggressive toward an existing dog with whom they previously had a harmonious relationship is stressful for all concerned and must be addressed without delay.
Dog bite injuries resulting from such aggression can lead to significant physical harm and emotional distress for both the animals and their owners.
Immediate veterinary attention is crucial to prevent infections and ensure proper wound care. Additionally, addressing the underlying cause of aggression can help minimize the risk of future incidents.
Sudden aggression in dogs can be concerning. Consulting with experts at the Chestnut Hill Animal Hospital can help identify underlying causes and develop a management plan to ensure the safety and well-being of all pets involved.
Our guide will help you.
Why is my dog suddenly attacking my other dog?
The most common reason why a dog is suddenly aggressive toward another dog from the same household is a dispute over one of three things:
- Possessions
- Food
- Space / Territory
All three can be managed provided the problem is addressed promptly.
Aggression between two dogs from the same home is unpleasant and often shocking if it appears to come from nowhere. A dog being suddenly aggressive toward a dog who they are normally friends with can be jarring.
What are the reasons for sudden dog-on-dog aggression:
Key questions we need to establish the answers to when establishing the cause of sudden aggression between two dogs are:
- Was this a one-off incident?
- Did you witness the event that led up to the aggression?
- How did the aggression manifest (i.e. snarling, lip curling, low growling, or a full-on bite)?
- Did the aggression persist?
- What was the other dog's response to the aggression?
- Has it happened more repeatedly since and what were the triggers?
Intact male dogs tend to have more innate aggression than either female dogs or neutered males. However, this is certainly no guarantee.
Aggression - including sudden aggression - can come from old dogs, young dogs, female to male, and male to female.
Dogs are pack animals and the dynamic of the pack is established between dogs over a period of time.
"I once had a client who came to me and asked this very question "why is my dog suddenly aggressive to our other dog?" when there had been absolutely no disruption to their previously harmonious relationship."
Upon further investigation the answer revealed itself. The aggressive dog, in this case, a female, was spayed. The victim of her aggression - a young, intact male dog.
Another female dog in a yard nearby had come in to heat and the intact male dog had started showing sexual behavior toward the female in his own household. The owner, unaware that this had happened, only caught the act of aggression but not the preceding behavior.
The answer as to why this dog had suddenly become aggressive toward the other dog was discovered when we set up a secret camera.
As the amorous male started to bother his female housemate, she lashed out at him. This prompted further defensive aggression every time he came near her for a short time afterward.
The problem eventually corrected itself with time, as is often the case, dogs can deal with other dogs quite well. Particularly dogs they know and have lived with for a long time.
Aggression toward existing dogs: trigger point identification
So to summarise, if you have a dog that is suddenly aggressive to another dog in your own home you need to establish the exact trigger point. Look for the following:
- Aggression related to food or toys
- Aggression related to jealousy (one dog wants more attention from you)
- Aggression related to fear
- Aggression related to space/territory (as in the example provided above)
If aggression persists and you are unable to identify the trigger yourself, you should certainly seek the assistance of an experienced dog behavior expert. Injuries between two dogs in the same home are more expensive and upsetting to deal with than fixing the problem before it gets that far.
In addition to seeking expert advice, many pet services, such as behavioral consultations and professional training, can provide invaluable support in managing and resolving sudden aggression between dogs in the same household.
Important: aggression toward existing dogs!
When it comes to matters of sudden aggression (or any aggression) always seek the opinion of a vet. Underlying health concerns can often manifest as sudden changes in behavior, including aggression.
Once any medical issues have been ruled out, get the view of a dog training expert who can help you deal with this stressful event.
This article touched the surface of the issues I’m having between my two dogs, though I am still a bit at a loss. I have a 3 year old, 20 pound female Chihuahua mix who has been with me since she was 10 weeks old. She had been a fostered bottle baby from birth, and so still can be somewhat needy. She is very attached to me. My 16 and a half year old 12-1/2 pound female Boston Terrier passed in January. The two used to interact to an extent, up until about a year prior to her passing. The interaction dwindled to being very little once the older pup developed CCD. The two really had never shared a bond. Two months ago, I brought a 3 year old, 16 pound female Boston Terrier into our family “mix.” It’s just myself and the pups plus a 9 year old female cat. No other household members. The two pups have been doing very well together over all, though there have been 6 instances of an attack. Before having gotten the new pup, I created a safe, gated off space for her within my living room. Her crate is also in that space. Also, I kept the pup I’d already had on a leash when in the house for about the first eeek or so. This was so that I could quickly resolve any scuffles, should one occur. The Chi x pup was not at home when I brought the new pup in. She spent a good part of the day with just me there with her, so that she could investigate her new home. After I’d gone to pick the other pup and we arrived at home, I stepped into the gated off area, let the new pup out of her crate, and left her in that enclosed area for some time. When I felt it was ok (there had not bern any alarming body language that I witnessed), I opened the gate. The new pup stepped outside her sheltered area and immediately positioned herself on her back, showing she was not a threat. I had been told by the breeders I got her from, that she was an alpha. She doesn’t really demonstrate that at all here. I honestly don’t think either of the girls has taken on the role of being an alpha. The two are very good at sharing the same space, though there have been a few attacks on the BT by the Chi. One of the attacks happened when the BT was up close to my face. The Chi x went right at her. I believe this was jealousy and/or resource guarding me. I was, as with each time since, able separate the two as quickly as it had come on. The BT did not get aggressive toward the Chi x. She more so just stayed in place. Another attack happened when the BT started to lick the Chi x’s ear. A couple days prior, the Chi x had been licking the BT’s ears and face, and they both had been very relaxed. Again, I got the Chi x away from the BT immediately. The most recent attack happened due to something I did. I had saved a little bit of the muffin I was eating, to give some small nibbles to the Chi x after I was done eating it. We were sitting together on the couch as I fed the bites to her. She is always very gentle when taking food from my hand. The BT had been asleep behind me between my back and the back of the couch. I suddenly had the thought that maybe she’d like a coupe nibbles of the muffin too. Hindsight bring 20/20, I realized very quickly, the huge mistake I had made. It was too late however. When I put the BT on the couch next to the other pup and went to give her a little nibble, the Chi x lunged right at her. I broke them up, though not before getting bitten on my arm by the Chi x. I didn’t sustain any puncture wounds, just some superficial tiny bites on my arm. I did get a big, horrible looking bruise on my upper arm, which I was surprised at how very quickly it appeared. The BT never fights back. She just stays in place. Immediately after this happened and I cleaned up my arm, I went and sat back in the living room, mainly to give myself some space to decompress a bit. During this time, the Chi x was looking at me, though without direct eye contact, trying to get my attention. She kept pawing at my leg, though I just kept ignoring her. I could tell my not acknowledging her was really bothering her. I didn’t know what else to do though. She did what she did, because she was just being a dog who was guarding what she perceived to be a very high value treat. It was in essence, my fault that the attack happened. What she did by attacking my other pup however, I feel she needed to know and learn that it was wrong. I didn’t yell at her nor put her in her crate. I didn’t know what to do, other than to continue to ignore her for a bit. There’s been once more attack since. It was over a toy. They share all the many toys great. The Chi x does however, have 3 “guys” that are her lifeline. The BT was licking one of the special stuffies, and when the Chi x saw it happening, she lunged right at the BT. I pulled them apart immediately, then they were fine. I put all 3 of the “special guys” in my dresser drawer. That’s where they are kept now, and only taken out for her to have at bedtime when the two girls are separated. My biggest question through all of this, is what do I do with the Chi x after she’s attacked the BT and I’ve gotten them apart? I don’t ever yell at nor do I ever hit my pups. How do I teach her that what she did was wrong, and a very bad thing to do? I read someplace else, to give her treats for calm behavior. This doesn’t seem right to me at all. It’s like rewarding poor behavior, in my opinion. I’ve learned a lot about how to remain mindful and proactively ward off the attacks, by the environment I create and maintain for the girls. It’s not 100% fail proof though, and so I’m sure I won’t be able to catch any/all future attacks. The two girls are beginning to play a little bit together now finally. The Chi x actually has been encouraging and enticing the BT to come play with her. The BT will interact sometimes, though not to much extent when she is approached by the Chi x. They really are becoming more friendly toward one another. They snuggle together wherever there’s a blanket to lay with. I know my BT is still somewhat adapting to her new environment, home, other animals, and having a new pet parent, all the while, probably being confused as to where her entire previous life just vanished away to. As an additional note, the Chi x does also aggressively chase the cat if she enters a space where the pup is watching me eat a snack for instance, like she’s afraid the cat might try to get something she anticipates she may be getting. She can’t catch the cat, and the cat really couldn’t care less about the dog OR my snack. I do appreciate any guidance you can provide me with. Thank you!
When my female Golden Retriever was four, I adopted a 10 week old male Labrador mix. From day one the two of them played together and we had no problems at all. Sadie, my Golden is now 6 and Riley the Lab mix will be 2 in April. All of a sudden Riley is beginning to become aggressive towards Sadie and I can’t understand it at all. Sadie went to get a toy this evening and Riley jumped up and started growling and attempting to bite her. He has NEVER done this before. I’m at a loss and don’t know what to do. Both of my dogs have had professional training and have been socialized with other dogs outside the home. Please advise on what could possibly be wrong and how I can quickly correct this problem. Also, it has gotten very hot where I live, so could the extreme heat be an underlining factor for Riley’s behavior, despite both dogs being mostly indoor dogs and only go out for potty breaks and exercise. Any information you can provide with regard to this urgent matter will be greatly appreciated.
Unaltered 9 mo old male over 100# began showing aggression toward my 12 yr old altered female about 6 weeks ago. Trigger was rawhide chews, male in his playpen, girls (2) at large. Pup literally exploded in his pen, I thought he was coming out. They’ve always been separated at mealtime, no issues. Pup has developed what appears to be separation anxiety. The combatants excessively greet me which I dont reciprocate, so I’m a high value trigger. Food is a trigger. Carpet fuzz, hairball, interesting smells on the floor, they’re all triggers. Pup is now trying to follow her around in a too interested manner which I step into and block. I’ll add that for months, I’ve had to check the pup for following the old girl around and pulling hair off her. Not shed hair, hair that’s still attached. I’ve never before seen or heard of that behavior. He’s like the bratty little brother from, well, you know where.