The breaks were high up in the tails, close to the hips which suggested there was a significant amount of force required.
Judge Krebs said cows would often use their tails to flick at flies and in the case of where those breaks were, that could cause them ongoing pain, or restrict their movements.
He said none of the cows had been treated or provided with pain relief.
Many of the incidents had been the result of Dunlop losing his temper.
Two cows had also been ill-treated by being dehorned without anaesthetic.
Judge Krebs said the incidents indicated an abuse of a position of trust.
Dunlop's lawyer Darren Foster told the court there were a number of personal factors.
He said his client had left farming and was now working in a factory, with no intentions to return to farming.
However, Dunlop had undergone a psychological assessment which put things in a different perspective.
"You've had a number of stressors in your life."
Judge Krebs said he was not going to send Dunlop to prison, but he did need to impose a sentence to hold him accountable.
Due to the fact Dunlop was now in a job that required shift work, home detention was the appropriate sentence.
He was given four months and two weeks' home detention and would have to undergo counselling.
Dunlop was also disqualified from owning or having control over farm animals indefinitely, although he could apply to have that lifted after two years.
Joanna Tuckwell, MPI Regional Manager Animal Welfare and NAIT Compliance said the investigation was launched following a routine inspection of the Dannevirke farm by animal welfare inspectors.
She said a further investigation was underway, but no charges had been filed at this stage.
