As many as 9,000 turkeys have died and damage is estimated at $500,000 after a large fire north of Aylmer.
The blaze broke out around 9:30 p.m. on College Line, just west of Imperial Road (Hwy 73).
Malahide Fire Chief Jeff Spoor told CTV News London flames covered the steel structure as his crews arrived.
Immediately he radioed for two other stations to attend and later requested fire trucks from Yarmouth Centre and Belmont.
At peak, nearly 50 firefighters were on scene and immediately worked to contain the blaze in one barn.
Efforts were largely successful, though a neighbouring structure was slightly damaged.
The fire was under control around 1 a.m. and by Tuesday morning, little of the main barn remained. The cause has been listed as undetermined.