Predicting the standardized ileal digestibility of crude protein in feather meal fed to broiler chickens using a pH-stat and a FT-Raman method

•The digestibility of crude protein in feather meal can be predicted by means of FT-Raman spectroscopy.•Disulphide conformers are predictors of digestibility of crude protein in feather meal.•A pH-Stat method does not predict accurately the digestibility of crude protein in feather meal.•A novel enzymatic pre-treatment improved the digestibility of crude protein in feather meal.