الفهرس 
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Abstract
INTRODUCTION
The animal production sector is under intense political and social pressure around the world to produce safe food products with minimal use of antibiotics or synthetic origin substances. Essential oils (EOs) extracted from medicinal and aromatic plants have been used as feed additives in recent years to improve the performance of productive animals. These natural materials may have a variety of effects, such as improved feed consumption and flavor, increased gastric and intestinal motility, stimulation of digestive enzymes secretion (Giannenas et al., 2013), along with properties of antimicrobial, antifungal, antiviral, antiparasitic, immuno-modulating, antioxidant, and anti-inflammatory (Arjmand and Dastan., 2020). Furthermore, evidence suggests that there is a chance to find EOs or their active components that selectively inhibit ruminal methanogenesis (Benchaar et al., 2008), but the biggest challenge is to find EOs that lead to reduce methane production without reducing feed digestion at the same time. As a result, animal biologists and nutritionists are looking into EOs and their ability to suppress ruminal methanogenesis (Benchaar et al., 2008 and McIntosh et al., 2003).