HLI - Heat Load Index. This is a heat stress index (i.e. it has no units and has a minimum value of 50). The HLI brings together all the weather parameters that impact the environmental load on an animal. It takes into consideration, temperature, radiation, humidity and wind speed.
For the most part, the HLI on its own does not indicate the likelihood of heat stress in feedlot cattle. This is done by calculation of the Accumulated Heat Load Unit (or AHLU). The only time when heat stress may be indicated by the HLI alone is when there is a rapid change in the HLI over a short period of time.