ISPCA Inspector Kevin McGinley made the grim discovery near Pettigo earlier this month.
He found the two-year-old bay trotter with a massive injury to its neck involving considerable muscle and tissue loss.
McGinley called a vet and began local inquiries.
He found was no link between the animal and the owner of the land where it was found. It appears that it was abandoned, most likely due to its injury.
Despite the extent of the wound, the vet was confident it could be treated and arrangements were made to take the pony to the National Animal Centre in Longford.
Further assessment showed there was no major damage to arteries, tendons, ligaments or vertebrae.
The horse has now been named Sunny by staff due to his sunny disposition.
Equine supervisor Cathy Griffin said: “He is so kind and gentle with everyone he meets and very happy in himself considering what he suffered.
Efforts are continuing to trace the person responsible for abandoning Sunny, who is expected to make a full recovery and will eventually be offered for adoption.
McGinley said: “We believe that this poor animal was dumped because its owners would not seek the veterinary attention that it needed.
“There is no excuse for this and we are very keen to trace those responsible.”