Technical Abstract: Summer heat can result in stressful conditions for Bos taurus feeder cattle, and in extreme instances these conditions can be fatal. A study was conducted during the summer of 2001 at RLHUSMARC to determine physiological responses of cattle under shade or no shade conditions. The study involved eight steers assigned to individual pens, with four pens fitted with shade structures and the remainder had no shade available. Respiration rate (RR), feed intake, and body temperature were measured as response variables to the shade treatments. Environmental conditions were monitored for the experimental period. The resulting RR data demonstrated a 25C threshold for the treatment of shade/no shade. A linear regression was developed for RR that included effects of temperature, humidity, air speed, and solar radiation. Thresholds were developed from that linear relationship to relate RR to THI (Temperature-Humidity Index) to estimate thermal status of livestock. The equations and the corresponding thresholds have been implemented in a monitoring device for use at livestock production facilities. The monitoring device, referred to as a Livestock Safety Monitor (LSM), consists of a commercial weather station (Vantage PRO by Davis Instruments, Hayward, CA) coupled to a microcomputer (TFX-11, by Onset Computer, Pocasset, MA). The weather station collects current weather data including temperature, humidity, wind speed, and solar radiation. The weather information is transferred to the micro-computer where values alert the operator of current conditions that include: (1) normal, (2) alert, (3) danger, and (4) emergency. This report will summarize operating experience using the LSM.