As a result of various human activities, such as increase inhuman population, decrease in arable land due to soil degradation, urbanization, industrialization and associated increase in the demand for livesk products, dramatic changes are occurring in the global ruminant livesk sector. These changes includeshift inthesize of regional livesk populations and in the types of management and feeding systems under which ruminant livesk are held, and increased demand of a wider range of quality attributes from animal agriculture, not just of the products themselves but also of the methods used in their production. The livesk sector will need to respond to new challenges of increasing lives productivity while protecting environment and human health and conservingbiodiversity and natural resources. The micro-organisms in the digestive tracts of ruminant livesk have a profound influence on the conversion offeedinto end products, which can impact on the- imal and theenvironment. As the livesk sector grows particularly in developing countries, there will be an increasing need to understand these processes for b- ter management and use ofbothfeed and other natural resources that underpinthe development of sustainable feeding systems.