It’s possible that the dogs leave the property, but responsible dog owners train their dogs to remain on their own property.
The possible scenarios could just as easily involve a person who intruded onto her property and tried to shoot one or more of the dogs.
The type of fencing that would kept an animal like a dog would be prohibitively expensive as any suburbanite with an enclosed backyard dogpen can atypest.
Even something as simple as “pig wire” fencing would be hard on the wallet for “hobby farmers” to enclose fifty acres. Unless the the dogs owners are retired millionaires with lots of spare change to spend, the fields were "easy access" for dogs to enter and leave.
The dog as big as an Golden retriever could easily be shot off their property and bled out once it retuns to it's home turf, depending on the wounds severity.
Of course there could be a dog hating sadist lurking around their farm. If more pets, especially animals that are leashed turn up dead nearby we may have our answer.