We already had two dogs -15 year old female dachshund (Esper) and 6 year old male scottie (Izak) when we decided to adopt a puppy about 2 months ago. We adopted a 8 week old Australian Shepherd / Labrador mix male who we named Bo to be a companion for Izak when Esper passes away - she is not in the best of health.
Esper is the dominate dog and Izak and Bo respect her. Izak and Bo wrestle inside and outside, play with toys together, chase each other and we have had no problems until one week ago. I must mention that when they are playing, Izak appears to be the dominate one, making noises, chasing Bo, throwing him down and putting his head on Bo's neck. Bo is happy to run around with Izak, falls down when Izak catches him, and shows no resistance to Izak "pinning" him down, shows his stomach, etc.
A few days ago, the dogs were inside the house with me when Bo and Izak started fighting over nothing, as far as I could tell. I quickly separated them by pulling Bo off of Izak however, Izak came after Bo when I was holding him. I put them in separate rooms and when they met again, they were fine. There was no bloodshed with this fight.
On Saturday, I was 1 1/2 hours late feeding the dogs. While I was getting the bowls ready (which I have done the same way for the past 2 months), Bo attacked Izak by standing on top of his back, grabbed him by the back of the shoulders and was shaking his head back and forth. Izak did not fight back, just was screaming. Esper was not involved. My husband and I separated them and after they cooled off, they were the best of friends once again. Izak hasn't had a haircut in a while so there was only a minor scratch on him. Later that night, Bo attacked Izak again - I believe it was over a dog bone crumb that Bo thought was in the carpet. Before this, they all ate in the same area with no problems. Izak did not fight back this time either. I believe he was afraid of being scolded by my husband and me.
My theory is that Bo was overexcited with being fed late and attacked Izak because he was closest to him. The second time I believe was over a crumb.
Since these last 2 fights, the dogs do not get treats and Bo is fed in a different room. When he is done, he rejoins the other two in the back yard.
Bo is no longer sleeping on the bed with us, he is on the floor with the other two. I am working on the Alpha dog techniques and have had success with going out the door first, etc.
What I'm not sure of is if the fights were food related or if it is a dominance thing between them. Is there anything else I can do to try to keep everyone safe and happy?
Bo was the biggest of his litter and I don't believe he had to defend himself. There is no growling, no warning at all to indicate Bo's aggression. When we adopted him, he was diagnosed with Parvo but luckily, he recovered quickly and appears to be a happy, healthy puppy. Because of what we have already been through, giving Bo up is the last thing we want to do.
Also, will there be a possible problem when Esper, the dominate dog, passes away? All the dogs are spayed/neutured.
Thank you for any advice you can give me.