Despite my very best efforts, one of my beautiful Cochin roosters has frostbite on his comb. 
Last week it was unusually cold in Maryland and dipped well below zero several nights.
Our coop is not heated, but well ventilated, very dry (low to no humidity) and I added extra bedding and put vasoline on everyone each night before going up to roost. I also gave them corn before bed to help warm them up.
I guess I am just feeling a bit guilty! Was there anything else I could’ve done?
I’m also a little bit nervous because we are going out of town next week. We have someone house sitting and watching them while we are gone but of course they were calling for sub zero temps again.
Is frostbite just unavoidable sometimes? I feel like such a bad chicken mama!
Any help would be much appreciated!

Last week it was unusually cold in Maryland and dipped well below zero several nights.
Our coop is not heated, but well ventilated, very dry (low to no humidity) and I added extra bedding and put vasoline on everyone each night before going up to roost. I also gave them corn before bed to help warm them up.
I guess I am just feeling a bit guilty! Was there anything else I could’ve done?
I’m also a little bit nervous because we are going out of town next week. We have someone house sitting and watching them while we are gone but of course they were calling for sub zero temps again.
Is frostbite just unavoidable sometimes? I feel like such a bad chicken mama!
Any help would be much appreciated!