Sweating rates from heat-stressed dairy and feedlot cows were measured using a Portable Calorimeter and a Bovine Evaporation Meter. Measurements were taken when cows were in their natural habitat. The focus of the study was to compare sweating rates measured from different breeds of dairy and feedlot cows, and determine the level of influence of environmental factors (air temperature, relative humidity, solar load, air velocity), and hair-coat color on sweating rate. The cows were exposed to solar radiation greater than 500 W/m2 (average 833 ± 132 W/m2), average THI was 82.7 ± 1.64 for all studies except for the Nebraska data where the THI was 77.4 ± 4. Air velocity in the sample area was between 0.8 and 1.2 m/s, and body (rectal) temperature was greater than 38.8°C (threshold for heat stress). The range of sweating rates was between 189 ± 84.6 and 522 ± 127.7 g/m 2-h, and that of body temperature was between 39.3 ± 0.53 and 41.7 ± 0.19 °C. Breed difference, hair-coat color. Solar load, and air velocity are critical (statistically significant atP-values <0.05) on sweating rates.