EUROPEAN POULTRY SCIENCE, vol.78, 2014 (SCI-Expanded)
Numerous in vitro studies have already confirmed the antibacterial actions of phytogenicfeed additives. Consequently, several in vivo studies were performed to confirm their beneficial effects. Effects on egg traits, such as egg composition, shell thickness or Haugh unit rating, were reported only rarely. Performance variables that were dominantly observed include feed intake, feed conversion ratio, egg production rate, and egg weight. Most studies concluded slight positive effects or trends, however significant results were rare. Since there are almost unlimited possibilities concerning dosage and combinations of herbs and EO, there is still more research needed. A lack of standardization of in vivo experiments leads to difficulties when it comes to comparing results. Generally, it can be stated that herbs and their respective EO have the potential to be considered as an alternative to antibiotic growth promoters in laying hen production. Nevertheless, further research in this area under more standardized condition is needed to determine the optimal dietary inclusion level, the exact mode of action of the examined active plant compounds as well as the optimal production performance and disease resistance in laying hens.