It is widely accepted that diets containing large amounts of forage affect animal performance due to low digestibility of structural carbohydrates. This limitation is mainly attributed to lignification and to covalently bound hydroxycinnamic acids. Most of the work related to the effect of hydroxycinnamic acids on cell wall digestibility has been conducted towards specific plant species and distinct plant parts. However, the results regarding the influence of hydroxycinnamic acids on the digestibility of roughages such as hays and straws are rather scarce. The objective of the present study was to investigate several methodologies in order to evaluate the influence of phenolic compounds on the digestibility of northern Portugal meadow hays.