The horses were huddled under a tree on a property near Dewdney Trunk Road and 246th Street.
Stephanie Jeanneret, a veterinarian in Maple Ridge who was called to the farm on Thursday night, said neighbours told her they saw a huge flash of lightning.
When she examined the scene, Jeanneret said it appeared lightning struck the tree, but there was little evidence showing how the horses died.
"There were pieces of wood scattered on the field, the ground didn't look burnt, the field didn't look burnt, the horses didn't look burnt, nothing," she said.
"Like they dropped, dropped dead literally. They were laying there right where they were standing."
A fourth horse, that was being boarded at the same barn as the others, was not killed.