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Canine Behavior/Sudden Aggression


I adopted a 2 year old American Bulldog from a young couple with a 14 month old child.  In my home I have a 6 yr old blind Scottish Terrier that developed SARDS approximately 7 months ago.  The two dogs were introduced approximately 2 months ago.  The Scottish Terrier is spayed, the American bulldog is not. I was planning on spaying,but I have not made appointment with vet.  

Yesterday morning, the Scottish Terrier was attacked with minor wound and bleeding on neck by the American bulldog which was initially unwitnessed.  No toys or food involved.

Separated dogs, and placed American bulldog in her kennel to calm down.  Later same evening I reintroduced dogs.  Everything seemed fine for approximately 10 minutes or so.  The Scottish terrier was simply walking at foot of bed to come into room where I was,  the American bulldog leapt off of bed on top of Scottish terrier while growling, barkin, and snapping.  No aggression on behalf of Scottish terrier.  I was able to separate dogs before either one was injured.  Have separated dogs now.  Scottish terrier is terrified.  She was shaking, trembling, and would not come out of bathroom where she hid after second attack.  

Is there any hope to curtail this behavior? Not sure what training, environment, etc prior to my adoption.

Thank you for your question. This is a new relationship so they may still be finding their footing with each other. There's a large size difference between an American Bull Dog (ABD) and a Scottie, so safety is a real concern if we can't get to the bottom of issue and address it.

Without a much more detailed discussion about the environment, activity of each dog, body language of each dog, who/what else was present, etc. it's not really possible for me in this forum to determine with any certainty the cause of the new dog's sudden aggression toward the Scottie.

I highly recommend an in-person behavior consultation with a professional who is well versed in canine body language, learning theory and who subscribes to force free, nonaversive training methods.

There are a number of potential reasons for her sudden behavior change and without a proper consult, it would not be possible to offer a ranking order of those possibilities.

One possibility is resource guarding - the ABD is feeling possessive of something in the space and feels threatened by the Scottie and so is becoming defensive. Resource guarding, in the end, is a fear-based behavior and not terribly difficult to work through. Though it's a bit more complicated when it's between dogs rather than from dog to human, and I expect slightly more complicated still when one of those dogs is blind as it may appear that she's staring at the ABD (which would be considered a challenge) even though the Scottie can't actually see.... Dogs can resource guard absolutely anything they feel is a prized possession. it can be food or toys or water or sleeping/resting areas. But it can also be people, doorways, entire rooms... I've seen dogs resource guard leaves as they fell off a tree during autumn! This is best determined by a professional who knows what behaviors signs they're looking for.

Another possibility is that the ABD is coming into heat. When a female is in her heat cycle, her mood and behavior can change pretty dramatically. She can be irritable, show significantly lowered tolerance for others, be off her food or overly hungry, have a heightened sensitivity to touch or sound, etc. Very much like human women during their cycle.

I would encourage getting her spayed sooner rather than later no matter what the core reason for her behavior in an effort to try to prevent any more escalation of the situation.

Note: of all the combinations of dogs we can have (male/female, male/male or female/female), a female/female combination is statistically more likely to have aggression between the two and the level of aggression is statistically likely to be significantly greater than than in either other combination. So we definitely want to nip this in the bud quickly or make the determination that your home home is not the right fit for the ABD.

That's always a difficult thing to hear and even contemplate. But the reality is that not every dog will get along with every dog. Not every house is right for every dog, nor every dog right for every house/family. It is not a failure to recognize that your home and your Scottie's special needs may mean that your home is not suitable for a high energy dog 3 times her size. That's being responsible. And the Scottie's needs and safety must be the top priority as she is the resident dog.

I am not saying it can't work. I am saying that you need an in-person evaluation to determine if it can work. And I'm suggesting that you keep an open mind to the option that the right answer for everyone may be to find the ABD a home where she can thrive and where she doesn't feel defensive on a regular basis. Sometimes re-homing is the greatest gift you can give a dog.

If that was already your inclination, then I would trust your gut and go with that.

If you're hoping to work this out and help them learn to live comfortably. Then I encourage you to seek out local professional help.

A vet behaviorist would be my first choice. They are the psychiatrist of the veterinary world. They are veterinarians, but have gone on to do a Masters in behavior. They will work with your current vet to get needed blood tests to make sure there are no medical conditions manifesting with aggressive behavior (there are several such medical conditions). They can oversee any medication if they deem medication a necessary part of the behavior modification process. And they will create and help you implement a behavior plan (management through retraining) to improve the situation if they feel it's something that can be improved.
You can search for a vet behaviorist here:

If there is no vet behaviorist in your region, your vet may have a relationship with one who will work remotely by phone, email, skype, etc. Or you can reach out to the behavior clinic at Cummings School of Veterinary Medicine (Tufts university):

Another option is a Certified Applied Animal Behaviorist (CAAB). This person has a PhD in an animal related field and years of experience. An associate (ACAAB) has a MA or MS, but is also a certified applied animal behaviorist. You can search for one here:
Again, if there isn't one right in your area, they may be willing to consult remotely.

Finally, you can search for a certified professional dog trainer at

Or a professional dog trainer who is committed to continuing education, but may not be certified at the Association for Professional Dog Trainers:

In all of this, be sure to consult with your veterinarian. Not only should they be in the loop, but they may have local professionals to whom they refer regularly. Just be sure that they are choosing science-based learning theory methods that do not use aversive tools such as prong collars, shock collars or infinite slip (choke chain) collars. Make sure they use positive reinforcement and set the dog up to succeed so they can say 'Yes! do that some more!!!' rather than setting the dog up to fail so they can tell the dog "No! Don't do that!"

Especially in this case, since practicing that undesired behavior puts the Scottie at direct risk of injury.

Good luck to you. Please let me know if I can be of any further assistance.

Los Angeles Behavior Specialist

Canine Behavior

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Jody Epstein, CPDT- KA, APDT


IF YOU BELIEVE YOUR DOG IS ILL OR INJURED, PLEASE CONTACT YOUR LOCAL VETERINARIAN IMMEDIATELY. THIS IS NOT THE FORUM TO ADDRESS URGENT MEDICAL ISSUES. I AM NOT A LICENSED VET AND HAVE NO DIAGNOSTIC SKILLS. ***I have been answering questions on All Experts for over 5 years now. I enjoy being able to offer assistance in this forum. I do need to be clear, though. If you’re looking for free advice about a specific behavior question, you MUST submit your question to me via All Experts. If you bypass All Experts and write to me directly through my website, I will ask you to submit via All Experts. On the flip side, if you’re local to Los Angeles and you wish to speak to me privately about an in person consultation, please go through my website. I appreciate your assistance in keeping my volunteer work on the volunteer site.*** I can answer questions about the following canine behavior issues: obedience, timid/fearful & fear-based aggression, nuisance behaviors, families that are expanding with either new human or new animal members. If you have potty training questions please first read my trio of blogs at If you still have questions after reading the blogs you can post your specific questions here. PLEASE be as specific as possible when asking a question. Give me a detailed example of the situation - dog's behavior, body language, circumstances surrounding the issue, what the consequences are (another dog's response, your response), etc. I can only provide insight if I can get a picture of the whole scenario. If I ask for further details, please provide them. In person I would normally observe for at least 90 minutes to assess the situation and the dynamics before offering tools and suggestions to modify it. In writing it is ever so much more difficult. Thank you for your participation in the process.


I have been professionally modifying behavior and training obedience for 7 years. I have owned dogs my entire life. I have just changed the name of my business. It is no longer Good Dog! Dog Training. The new name is Nutz About Mutz!. If you see previous questions with the Good Dog! website information, that is my response.

I am a Certified Profession Dog Trainer - Knowledge Assessed (CPDT-KA), #2133301 ; I am a member in good standing with the Association of Professional Dog Trainers (APDT), #77763 ; I am an AKC certified Canine Good Citizen evaluator (CGC), #71253

Publications ; ; Multiple articles in the local pet magazine Pet Press (found across Southern California)

I have a graduate education in animal behavior and learning. (While I completed my coursework and did the requisite research, I did not defend a dissertation. I am qualified, but not certified and so technically not a doctor. This is commonly referred to as Ph.D.-ABD which means All But Dissertation.) My educational focus was with non-human primates, but my personal interest is with domestic dogs and their relationships with humans and other animals. I continue to educate myself to canine-specific behavior through extensive reading, online interactive workshops, vidoes and attending canine behavior conferences.

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