By BILL MILLER Six horses died Monday in an early-morning barn fire near the southwest shore of Lake Arlington in east Fort Worth, a Fire Department spokesman said.The blaze was reported at about 6 a.m. in the 6000 block of Wilbarger Street, said Lt. Kent Worley, the spokesman.The barn was "fully involved" with flames when firefighters arrived, Worley said.Firefighters opened the door but they had a hard time doing it, he added."When they did, some horses came out," Worley said.