How cold can chicks tolerate?

[montanachicky]

I have 9 chicks...2-6 week old, 4-5 week old, and 3-4 week old. I have them in an outside coop and turn on their heat lamp at night (it is still getting around 30 degrees at night in Montana)...my question is how much longer should I be plugging in the lamp? I see posts all of the time to follow the rule of thumb 95 for the first week, 90 for the second week, ect...but at what point are they okay to regulate their body heat? I also worry because there are a few weeks between the oldest and youngest.

 

[donrae]

I'd give them supplemental heat at night until the youngest are fully feathered. You might go a week or so past that depending on how cold it is at the time, but after the youngest is say 7 weeks you should be good to go.