Los Angeles County, California, fire authorities believe burning manure could have caused a barn blaze that claimed the lives of four Friesian horses.

Los Angeles County Fire Department spokesman Rick Flores said fire department personnel responded to an emergency call about a barn fire in rural Palmdale in the early hours of July 27. Upon arrival, firefighters found the barn fully involved in fire, Flores said. Four Friesian horses, including a pregnant mare and a 4-month-old foal, and a herd of goats were in the barn at the time of the fire, he said.

“All four horses and seven goats were killed,” Flores said.

Fire inspectors said the blaze was likely caused by accidental spontaneous combustion