Dog bites our other dog unexpectedly

4. Have a Blue Heeler mix (20 months old) and a Aussie Shepherd (15 weeks old. They have been together for a while now and there were no problems. But a few days ago I was brushing the Heeler in the back yard and the Aussie came up to him and he bit her in the face and drew blood. I never heard him growl. (Took her to the vet she is ok) I have been working with the heeler to be my service dog. for a few weeks and this was unexpected. Should I be worried about leaving these dogs alone. They seem to be getting along again. What should I do or am I worrying too much?

Instances of biting can be worrying, especially when it is completely unexpected and without warning. It is especially concerning in a pet that is intended to be a service dog.  You are right to be worried, as this type of behavior is not desired in a service dog or even as a member of the household.  However, there are a few things to consider in this scenario.

Biting can happen due to a variety of stimuli or situations.  A few things could have happened in your case.  The Aussie could have surprised the Heeler, resulting in a quick bite without any warning. However, this is not desirable behavior in any pet. The Heeler could have also given some warning signs, such as a change in posture or body language, that you missed and the Aussie missed. Dog body language can be subtle, quick and very difficult to read. Another possibility is that your Heeler has become territorial and is “guarding” you from the Aussie. Guarding behavior happens when the dog sees you as a “resource”. It can also morph into guarding of other “resources” such as food and toys. A good article about Resource Guarding behaviors can be found here through the Veterinary Partner education website.

Hormones can also influence levels of aggression between dogs.  If your dogs are not sterilized yet (spayed and neutered), I recommend having this done soon. After this event, I strongly recommend talking to a trusted dog trainer or veterinary behaviorist who is experienced in training/raising service dogs. If a problem is just starting, it can be addressed quickly.  An experienced expert can also give customized, specific instructions on how to correct the bad behavior. They can also help to evaluate if the Heeler is “cut out” to be a service dog. Some individuals, even with careful training, are not suited for this job. This may be a one-time occurrence (especially if the Heeler was surprised by the Aussie), but it is best to get help now before further problems arise.