balancing a diet for animals. Notwithstanding these lim-itations, the study suggests that OA can be fed to sheepafter deactivation of tannins especially during the shortageof high nutritive value concentrates. As the price of PEGis quite expensive, further research is needed to evaluateother methods of tannins deactivation. In addition, fur-ther research regarding the assessment of other secondarymetabolites and the effect of oak acorn with differentnitrogen sources on productive ruminants (i.e., lactating orgrowing ruminants) would be worthwhile.