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The aim of this study summarizes the experimental knowledge on efficacy, possible modes of activity and aspects of application of phytogenic products as feed additives for poultry. Feed additives are a group of feed ingredients that can cause a desired animal response in a non-nutrient role such as pH shift, growth or metabolic modifier. Many substances found in nature have a wide range of growth promoting, immunostimulatory or antimicrobial activity. Common feed additives used in poultry diets include antimicrobials, antioxidants, pH control agents and exzymes. Phytogenic are a relatively young class of feed additives and in recent years this feed additives have gained considerable attention in the feed industry. They are a wide variety of herbs, spices and products derived thereof and are mainly essential oils. Although, numerous reports have demonstrated antioxidative and antimicrobial and immune stimulation efficacy in vitro, respective experimental in vivo evidences is still quite limited. A limited number of experimental comparisons of phytogenic feed additives with antibiotics and acidifiers have suggested similar effects on the gut. Gut microflora has significant effects on host nutrition, health and growth performance by interacting with nutrient utilization and the development of gut system of the host. In addition, some phytogenic compounds seem to promote intestinal mucus production. However, a systematic approach toward the efficacy and safety of phytogenic compounds used as feed additives for poultry is still lacking.
Hashemi et al. (2010) studied this question.