The unemployed Raffael V. was arguing with his girlfriend Petra G. about money when "Pebbles" stepped in to protect his mistress.
According to a report in Friday's Bild newspaper, the dog's noisy intervention sent the 21-year-old into a rage and he fetched a meat cleaver from the kitchen and attacked the animal.
"He was hacking at Pebbles for 15 minutes, until he stopped moving," the 28-year-old woman told the paper. "I was scared he was going to do something to me."
The terrified woman called the police, and six officers promptly arrested the man.
State prosecutor Claudia Krauth said, "We have not seen such a gruesome case in years."
Raffael V. - who was 20 at the time of the crime - was sentenced to three weeks juvenile detention, 120 hours community service, and a five-year ban on keeping an animal.
He told Bild, "I've received my sentence and I just want to forget the whole business."
Petra G. has since separated from the man. "I have had Pebbles cremated," she said. "I will never get rid of those horrible images."