Fourteen horses were found shot to death in rural eastern Kentucky, leading to an investigation of who was responsible for what a sheriff called a "heartbreaking" slaying.

A horse owner contacted authorities in Floyd County on Monday after finding one of his animals had been killed, before investigators found more slain colts, fillies, mares and stallions the next day, Sheriff John Hunt told NBC News.

In total, 14 dead horses — three of them were pregnant — were found shot to death, within the length about "two or three football fields," according to Hunt.

"It's heartbreaking," Hunt said. "We're in a region where horses are still part of our daily life. We show them, race them, ride them back and forth every day."

The area of Floyd County where the slain horses were found, about 200 miles east of America's most famous racetrack, Churchill Downs in Louisville, is difficult to reach and can only accessed by all-terrain vehicles, the sheriff said.

Vehicles near the scene where dead horses were discovered in Floyd County, Kentucky. via Floyd County Sheriff's Office

It had been a site for strip-mining of coal, but there's been no mining there for years, according to Hunt. And in that time, vegetation that has taken hold there has made it a popular place for wild horses, elk and other wildlife.

It's illegal to hunt horses in Kentucky, and Hunt said he doesn't believe the killer or killers are trained hunters.

"To kill 14 of these beautiful horses, just out there grazing, is not hunting." said Hunt, adding that he's hopeful a reward of $20,000 might help in turning up witnesses and clues.

The Dumas Rescue group, which is working with Floyd County sheriff's deputies, called the horse killings "horrific."

"The response across the country to this horrific situation has restored our faith in humanity and given Dumas volunteers the strength to keeping fighting to find the perpetrators," according to a statement by the group.