Silkie with a dirty behind

[Bushastead]

I have a 7 month old Silkie that has had matted poop on her behind for the past two weeks. And up until then I have never seen that before on her. I cleaned it all off a week ago and checked on her again and its back.
I switched their feed from the Purina organic chicken feed to a sprouting mixture i got from a chicken farm. I add some egg shells, sea kelp and herbs to it every morning.
My first question is, would a change in food create diarrhea? My other Silkie is not having this problem.
Second, should i be trimming her back freathers so there is not so much fluff for things to get stuck to?
Thank you of your input!

 

[oldhenlikesdogs]

You could trim but that would expose the skin. Does she roost? Some silkies don't, that would cause poop to get matted to their bottoms.