Similarly, a clear correlation between in vitro and animal trial results is needed with special focus on standardizing the in vivo studies where efficacy of EOs is evaluated [3]. Investing in the determination of PFA mode of action could lead to their increased price in the end market and cost efficacy of their application in the animal industry. Therefore, application and further development of techniques, such as microencapsulation of EOs, is essential to standardize safety and efficacy and to provide reliable and cost effective natural feed additives.