It is huge. 20 million birds.
The good news is by the pic it looks like fires could be contained to a single building.
I count 8 buildings... so maybe 2.5 million birds in each?
Everybody names their chickens. These guys would need, maybe, the New York City phone book for this bunch.
Hillandale has a number of farms. Each barn has on the order of 100,000 hens, probably less for this place in CT. They have farms in PA and OH as well.
Not nearly the 20 million are at just that one location.