essential oils (eo) from aromatic plants (ap) are used in ruminants' diets due to several biological activities. the inclusion of ap in ruminants' diets can be done as dried material, as they are harvested once a year. however, storage is one of the main factors that affect the eo content and chemical composition. thus, the objective of this study was to determine the effect of storage, in the shade under ambient conditions, on the eo content and chemical composition (a) of origanum vulgare spp. hirtum as a whole plant (op) and/or (b) as the powdered form after mixing with the concentrate diet. the results showed that storage of the whole op in the shade for six months has a very low eo loss (5.8%), while grinding and mixing op with concentrates causes different losses, which depend on the op/concentrate ratio and the storage period.