Forty-four cows are dead after a powerful blaze tore through a southern Ontario dairy barn Saturday night, killing all but one of the animals inside.

The fire broke out at the Maryhill, Ont. farm, about 100 kilometres west of Toronto, after a piece of hot metal or stone blew into a pile of dry straw the farm owners had been chopping, fire officials said.

“It went up very quickly,” district fire chief Kevin Karley told CTV Kitchener.

The blaze erupted around 9 p.m. Saturday night and raged for more than 12 hours, with about 50 firefighters called to the scene. The heat was so strong that it melted a nearby tractor.

“It was one of the old style barns with beams and barn boards, so they’re not air-tight,” Karley said.

The cows killed in the blaze included calves and the farm’s breeding stock. Of the 45 animals inside the barn, only a single cow survived.

“Their animals are like their family,” Karley said of the farm owners. “They’re with them every day and taking care of them, so they’re quite upset at the loss.”

Karley added that fire crews were able to save the milking parlour and approximately 200 cows in an adjacent barn.

Neighbour Jennifer Wraight was alerted to the blaze after the electricity in her home suddenly cut out.

“It was a big fireball,” she said. “There was a couple, probably two times, when we saw other explosions.”

The total loss is estimated to be at least $500,000

With files from CTV Kitchener