Purina chicken feed.

[texsuze]

I also make a "plate" of flock raiser crumbles mixed with water, each morning. I let it set up several minutes until the water is fully absorbed, adding more water if needed, so it becomes a mash. I tell my girls it is "Chook Mash" and they think it is a special treat

 

[ChickenCanoe]

I have some guaranteed analysis tags from Purina Start & Grow. The primary listed ingredients are grain products, processed grain by-products and plant protein products.
There are several possibilities in there that could be those dark specks.