How is heat risk calculated?

The overall risk of a heat event occurring is a combination of many factors. These can be broken down into three categories: the animal, the feedlot conditions and the weather.

There are various attributes of an animal that can increase or decrease the risk of a heat event, such as breed, the colour and type of coat, the acclimatisation of the animal to the feedlot conditions, the type of ration being fed and the fat score of the animal. Other factors such as sickness or handling of the animals can also impact the risk of a heat event.

The feedlot characteristics can also increase or decrease the risk of a heat event. Some pens in the feedlot will be at higher risk due to aspect (e.g. western facing/south facing) or reduced airflow due to structures or natural flow of the land. Shade, access to water and the condition of the pen floor are all critical to determining the heat risk.

The Risk Assessment Program (RAP) is designed to take you through a series of steps to help you identify the factors that impact the risk of a heat event. The RAP calculates an HLI threshold based on animal characteristics, feedlot environment and other factors that can change the risk. This is the HLI value at which the animals will start to accumulate heat. The HLI Threshold Calculator can also be used to determine the risk level.

The HLI threshold is then used to calculate the Accumulated Heat Load (AHLU). The AHLU value then determines the risk of cattle heat stress.

The table below summarises the levels of heat stress, the associated AHLU values and the physical indicators. You can use the Panting Score chart to understand the animal indicators.