The present application provides systems and methods for analyzing animal feeds and for adjusting animal feeds to improve the digestibility of animal feed components. Digestibility of animal feed can be determined by performing in vitro digestion of the feed and analyzing concentrations of residual components in the digested feed by NIR spectroscopy. Animal feed compositions can be adjusted to improve digestibility of components in the feed. The systems and methods of the present application can be used to determine the effect of an additive on the digestibility of feed.