In beef cattle production systems world wide, the majority if not all of the energy requirement of the cow herd comes from forages, either native or tame. Thus grazing management decisions greatly impact beef cattle production by altering the available energy supply for grazing cattle by influencing such variables as forage availability, sward botanical composition, and nutritive value. A better understanding of the effect of grazing management on grazing behavior as it relates to energy expenditure (EE) of beef cattle should provide more precise and timely information for both production systems researchers and grazing system and animal modelers. Newly developed remote sensing devices now offer the opportunity for the near continuous study of grazing behavior under free-range conditions. The present research proposal utilizes a comprehensive monitoring system, integrating five independent measurements which can relate to animal performance: 1) heart rate (HR) for estimation of EE, 2) activity determined by pedometers; 3) grazing time based on vibracorders; 4) body temperature to monitor environmental effects, and 5) animal position based on GPS. The first objective will be to measure the grazing activity of lactating beef cows under Mediterranean and subtropical environments.