SPARTANBURG, S.C. -- Five of six horses seriously injured or killed in northern South Carolina this fall were attacked by wild boars and had not been shot or stabbed, as initially feared, state police said.

State Law Enforcement Division agents checked animal tracks found near the horses and examined evidence from video cameras and from several veterinarians' reports, agency spokesman Tommy Crosby said in a statement Wednesday.

A sixth case involved a horse who did turn out to be shot and that remains under investigation, Crosby said.

The attacks happened in Spartanburg and Greenville counties in late October and November. The horses had wounds so deep that intestines or bones were exposed. Three of the horses were killed or had to be euthanized, authorities said.

Horse owners were so frightened that some of them started working with neighbours to sleep in shifts to make sure their animals were protected.

To help control the rapidly growing wild boar population in northern South Carolina, the Department of Natural Resources is allowing both day and night hunting of the animals with a special permit.