Can you over ferment feed?

[Vian]

So I tried out fermented feed on my 3 week old chicks. I put some feed in a mason jar with some water and a little home-made yogurt as a starter culture. I let it sit in a warm spot in my house for a couple days until it looked like it was fermented, then fed them some. They loved it and gobbled it up. But I still have some of the feed in the jar, but now it smells really strongly fermented and there's a film on top that's got a purple tint to it. Can the feed turn alcoholic? Can it be over fermented to the point where it's not safe for the chicks?

By the way, I'm not new to fermentation. I brew my own kombucha and make my own yogurt, and ferment pickles and vegetables.