In the past, the use of plants in monogastric diets was restricted because of some negative aspects on feed intake and nutrient utilization attributed to phytochemical composition that varies greatly due to variety, location and climate (Steiner and Wegleitner, 2007 and Xiao et al., 2012). As with AGPs the exact mode of action by which plant bioactive substances exert their positive effects on bird performance is not well understood. Nevertheless, it is speculated that the main site of activity is within the gastro-intestinal tract is by modification of gut micro-flora, maximizing both feed digestibility and growth rate. As reported by Jamroz et al. (2005), stimulation of appetite and feed intake and the improvement of endogenous digestive enzyme secretion are among the beneficial effects of active plant substances in animal nutrition.