Why is my sweet chihuahua suddenly attacking and biting another dog?

Oh dear! That is a worry for sure! It's really important that you don't get hurt, because dog bites can be pretty serious. I would suggest making an appointment with your vet to talk about possibilities. They might be able to link you up with a behaviorist, or dog trainer that could help a lot. There also could be medications that might help. Or, like you said, there could be a medical problem that is upsetting him.

It sounds like she is having some anxiety and/or dominance issues with Bella. Try to take note if she is always doing this or if there is a specific cause or causes like food nesrby, treats, bones, you nearby (they can be protective over their "humans"), etc. If so, try to find a way to keep them separate when one of those things are involved. I would start with trying a calming collar on her like adaptil. If this doesn't work, talk to your vet about a low dose of an anti-anxiety medicine like fluoxetine. Also make sure guera is getting plenty of alone time with you as they can get jealous and protective over you. I hope this helps!

There are many possible reasons for this, I'm afraid - aggression is a complex behavior issue, so it can be hard to provide a succinct answer in this format. Many dogs develop aggression issues related to fear or anxiety around the age of 2-3 when they reach social maturity, so it's possible that this may be the issue. Or, since I see that Chucky is a bit older than that, he may have a medical problem causing him to be painful or uncomfortable - this is a common reason for "new" aggression in a previously friendly dog. I would recommend having Chucky examined by a vet as a good first step - he/she can check for anything that may be causing him pain or making him not feel well, and get him started on treatment if needed. If everything is normal medically, then it would be best to make an appointment with a veterinary behaviorist to help you determine what is causing the aggression - he/she can observe your dogs in person and also give you a step-by-step treatment plan to work on the issue.

Anxiety can lead to aggression, and it may be Skye's anxiety has gotten so great that she is now acting aggressive. I'd have her seen by a vet for this to discuss putting her on anti-anxiety medication.

Any continued abnormal symptoms (longer than 24 hours) warrants a vet exam. I cannot tell you what is wrong with him just by your description. I can tell you that you need to be diligent about getting weird behavior changes checked out . Behavior changes could be due to an underlying medical issue (pain somewhere in his body, vision problem, etc) or a behavioral issue. It is always best to rule out an underlying medical issue first before just assuming it is behavioral. I suggest you get him to a vet for an exam.

This is quite strange behavior. It sounds like it is mostly anxiety and stress related due to the change in environment and care givers. I would have your girlfriend try to give him some treats and feed him to help "win him over" again as long as he isn't being too aggressive. I do not want her to get bit again. If this behavior continues on and off, I would consider putting a calming collar on her like adaptil and giving him a calming chew like vetriscience composure. Finally, if that doesn't help, I would talk to your vet about starting him on an anti-anxiety medicine like fluoxetine. I hope this helps and he starts to get back to normal soon!

Abrupt changes in behavior like this in dogs is very concerning to me. I would be worried about some underlying neurologic disorder that could be going on. If nothing has changed at home, her routine, or the environment in general, then I would suspect an underlying medical issue. I would recommend taking her to be examined by your veterinarian and possibly having some lab work performed so they can try and determine what is going on. Your vet may recommend further work up by veterinary neurologist or may recommend a behavior modification drugs like Xanax or Prozac. I hope this helps. Thanks for using Petco Pet Education Center, formerly Petcoach. Best of luck.