Younger Boxer Attacks the Older Dog During Excitement

Boris, Betsy and Buster
Why would a younger dog suddenly attack an older dog in the same home?
All three Boxers have a wonderful life, with lots of freedom and lots of love. They have old boy Buster, 11 and entire. There is Boris aged 2 and they have six-year-old Betsy – in the middle. They had Boris castrated a month ago. (I didn’t take the photo as Boris never sat still enough while I was there).
The problems between the two boys have been growing over the past two years. Boris goes for Buster. Nearly always this is in times of arousal or excitement.
The most recent attack seemed to come out of nowhere. (more…)