Dear Dr. Florez,

I have two dogs, a big one and a very little one. Both mixed breeds, both neutered females well over 5 years old, both healthy and good-natured most of the time, but the big dog has suddenly taken to attacking the little one. It has become a very stressful situation, as we now need to keep them separated at all times.

Dear Jay,

Obviously this is a very stressful situation for both you and your pets. The first thing you should do is rule out any medical condition that may be affecting you larger dog. It is unusual that a pet suddenly become aggressive without any reason. Closely examine your pet’s routine, and anything that may have changed, no matter how slight, before this behavior started. This could include the addition of a new roommate, the purchase of new furniture, remodeling the house, etc. Pets are very sensitive to any changes and they can react differently to a new environment.

Also be very cautious allowing your large pet to have any access at all to the smaller pet for the time being, since the larger one can seriously injure the little one. You should feed them at the same time, but in separate bowls and far apart from one another. Also, training is a must, regardless if they went to doggie school already. Refreshing your pet’s training on commands and reminding them of appropriate and inappropriate behavior should be done on a continual basis.

Plan on taking your pet to a veterinarian for a complete physical in order to rule out any medical conditions. Animals often lash out when they are in pain. Lastly, a behavior specialist can help you decide if more training exercises are enough, or medical treatment might be needed. With today’s medical advances, we can now treat animals for depression and other mental illnesses much in the same way that we treat humans.

Best of luck,

Diego Fernando Florez, DVM