I snap when I am stepped on. I was once part of a tree. I'm not a branch. What am I?

Loose and not baled, my shape is quite grand, a mountain of food on a green plot of land. Left out in the pastures, I stand through the storm. Then pitched to the livestock to keep them fed and warm.

A man with a twang to his voice was asked what he’d call a blind doe. He wasn’t too sure, so he said:

I whisper in ears and vanish from sight. Then leave behind reasons to scratch all night.

I fall from the sky when it is cold. I am white and soft, and children use me to build a man.