This past weekend my 10 yr female Black Lab/German Sheperd (Midnight) and my 1 1/2 yr female German Sheperd (Misty) got into a fight. The result was Midnight receiving a puncture wound on her chest and Misty 3 bites to her left leg and part of her left ear was biten off. I have 4 dogs, Midnight, Misty, Black Lab-Cuddles (7 yr) and Dachshund-Otis (3 yr). Midnight is only showing aggression toward Misty.

Midnight is an outdoor dog and after some bad weather her coat was badly matted in places. I took her in to be groomed and she needed to be shaved, so since the weather was turning cold I left her inside. She started showing aggression when I would open the backdoor to let her out and Misty would be standing there. She would want to go after Misty. Misty still likes to play and will try to get the other dogs to play with her. I'm not sure if Midnight just had enough of the play or what happened for her behavior to change.

I currently have Midnight and Misty separated. While one is outside the other is inside. They are in to separate rooms while indoors. I know this is not a solution and could make things worse, but I am not sure how to handle Midnight's aggression. My brother suggested a muzzle for Midnight, but wouldn't both dogs need a muzzle since they engaged in a fight? I am truly afraid of another incident. Can anyone offer suggestions?

I have some questions.

I do agree that you should keep them separated for now.

With 4 dogs, you have a pack, and have multiple personalities to manage, which can be complicated and difficult.

Do you always supervise your dogs when they are free?

What is your level of control over each dog when they are out (i.e., voice control, lead, line, e-collar)?

Are you suggesting this is territorial aggression, over the backyard? Or just noting a change post-grooming/coming inside?

How much obedience training do your dogs have?

Do you work with your dogs regularly?

What sort of exercise do the dogs get?

Do you do groundwork/nothing is life is free (NILIF) with your dogs? I.e., what sort of pack structure is in place? How strictly do you follow this?

By changing the sleeping arrangements, albeit for a good reason; the dogs might well have interpreted it as a change in status. Especially Midnight might have felt smug in that your giving her special treatment meant she was being accepted by you as higher status than previous, so felt justified in throwing her weight around.

Also, at Misty's age, entering adolescence; she may have been giving signals of attempting dominance over Midnight.

Do you know what the status relationship was between Midnight and Misty before this?

In any case, until you have established that you are the only one who can mete out punishment to any pack member, better keep them separate. Bitch fights can be lethal.