My local feed mill offers dried distillers grains with solubles (DDGS) made from non-GMO corn, and a byproduct of the bourbon industry (not ethanol). The DDGS runs about 24% protein, I believe. I picked up a bag to supplement my chicken and duck feed and have initially only been adding a small amount. My animals free range, and protein will be hard to come by in the winter, so this seems like a viable supplemental source. I've read studies that found that 3% seems to be the optimal proportion of DDGS to add to chicken feed. Is anyone else using it or have experience/tips to share (or want to know more)? There are some threads on it here, but they're several years old.