Fire destroyed barns, an office and at least 78 dairy cattle at Walker Farms near Aylmer.
Firefighters worked for seven hours to control the fire that caused about $3 million damage.
Firefighters were able to save some of the operation, but not the offices, milk house and several buildings. They and farm staff were able to save most of the farm's 850 cows.
“We know the ones that were lost in the fire we could not get out, but certainly there are others that … may succumb to the smoke from the fire. So (the number of dead cattle) is highly likely to climb,” said fire chief Brant Smith.
Electrical failure in the milk house is believed to be the cause of the fire.