The aim of this project was to test and validate the new Heat Load Index (HLI), Accumulated Heat Load Units (AHLU) and Risk Assessment Program (RAP) software for the beef feedlot industry. Targeted data collection was undertaken at 4 feedlots during the summer of 2005/06. The data collection was undertaken to isolate certain key factors in determining heat tolerance, such as: genotype, presence of shade, days on feed and nutritional status. The results confirmed previous assumptions regarding the difference in heat tolerance between genotypes. The results also suggest that the new HLI and AHLU do adequately reflect the heat load status of feedlot cattle. As a result of this project, it was recommended that both the HLI and AHLU remain unchanged and are further released to the industry. Some changes to existing thresholds, and addition of some new thresholds within the RAP software are also recommended.