Right - was it the explosion, or the resulting smoke from a fire? If this is "as reported", then it has to be death by smoke inhalation. If an explosion took out the electric (fans/ventilation) and then a grain storage was nearby, I could see a slow burning fire and pinned livestock. Odds are, one human was near the explosion, but the other humans were able to walk/run out of the building. But, no chance to release the cows.