increasing production efficiency. Because of the complexity and high degree of specificity ofionophore resistance, it appears that ionophores do not contribute to the development of antibiotic resistance to importanthuman drugs. Therefore it appears that ionophores will continue to play a significant role in improving the efficiency of ani-mal production in the future (Callaway et al., 2003) The gastrointestinal tract of animals harbors many complex microbialcommunities including bacteria, especially, anaerobic bacteria, protozoa, fungus and bacteriophages which interact with theanimal host, forming a complex ecosystem. These microbial interactions within themselves and the host ensure the stabilityof the ecosystem and the health of the host by enhancing vitamin synthesis, digestion, absorption of nutrients, resistance toinfection and antagonism towards harmful micro-organisms. Maintenance of the normal balance of intestinal flora is thusessential for the health of domestic animals and fowls and also for the promotion and improvement of livestock productivity,such as growth and feed efficiency