Tom O’Connor, aged 32, of Clonfert, Newmarket, Co Cork, was jailed for 18 months for the crimes.
Detective Sergeant Hugh Twomey testified at Cork Circuit Criminal Court that, on September 9, 2017, gardaí were approached in the early hours of the morning about the discharge of a firearm in a farmyard.
Denis McCarthy told gardaí his dog had been shot dead and that shots were also discharged into his 4x4 and car, which were parked outside the house.
Mr McCarthy told gardaí he came out and confronted the man, whom he recognised as his wife’s nephew, Tom O’Connor, who left the scene.
Armed gardaí were dispatched to the area and a search was undertaken.
As well as the shooting in his farmyard, Mr McCarthy later found that one of his horses had been shot dead at the back of the house.
Early in the morning, Mr McCarthy’s son, Denis Gerard McCarthy, found six of his horses had been shot on his property.
There was a report of O’Connor trying to drive his vehicle through the gates of a property. O’Connor was eventually located at a house in Newmarket. His car was found crashed a short distance from the house.
The shotgun used for shooting the farm dog and the vehicles was located in O’Connor’s own car.
When O’Connor was arrested and questioned, he told gardaí where he had discarded a rifle and where this firearm was located.
The main charges to which O’Connor pleaded guilty were of discharging the weapons.
Alice Fawsitt said O’Connor was diagnosed with a mental condition known as mixed affective disorder.
She said that he was found to have the capacity to instruct his legal representatives and was fit to plead to the offences.
She said: “Nothing like this every happened in the past. A large number of his family members are here in court to support him. He was out of work at the time.”
Judge Seán Ó Donnabháin said: “This matter comes before me for carrying a firearm on September 9, 2017, in a reckless manner.
“He used that firearm to kill a number of horses and a dog. He said he had some gripe or other.
“Then he went along and shot the animals. To shoot six horses with a single-bore rifle is an act of unspeakable cruelty, not in any way explained by the real or imagined gripe he had against the person.
“There is no explanation for what this man did on the night in question.
“It was a deliberate act of destruction without mercy and without any justification whatsoever.”
The judge said O’Connor had been on a proper regime of medication under the direction of a competent doctor, but that he had decided to go online and top up his medication with other tablets sourced on the internet.
The judge imposed a total sentence of three years, with half of it suspended.