Police are appealing for information about the death of a racehorse on the Mornington Peninsula, south of Melbourne.

The thoroughbred, named Arrier, was shot in the head at close range on a property near Myers Road in Balnarring on Saturday morning.

The owners had filled the horse's feed trough at 8:00pm the night before.

Police said the eight-year-old was found lying in the paddock close to the trough, with a bullet wound to the head.

"Sadly she was found near the unfinished feed which leads detectives to believe she may have been killed not long after she was fed," Victoria Police said.

The horse was valued in excess of $100,000.

Anyone with information has been urged to contact Crime Stoppers.