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.

The Animal

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 Conditions

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.

Factors that increase risk of a heat event

Factors that decrease risk of a heat event

Bos Taurus genotypes
Dark coat colours and winter coats
Animals with high fat scores ready for market
High energy diets
Sick and recovering, particularly with BRD, ergot and other mycotoxins
Cattle induction and new arrivals (first 20 days)
Unacclimatised to local weather conditions (hotter)
Movement of cattle
Pens in a wind shadow or in a valley
West and north facing slopes
Unclean pens
High humidity and light winds
Multiple days with high heat load
Limited nighttime recovery

Heat tolerant breeds such as Bos Indicus and Wagyu
Light coat colours
Access to sufficient shade to limit bunching
Access to multiple water points
Low energy rations or reduced rations
Water sprays (in some conditions)
Acclimatised animals
Well-managed manure
Well exposed pens such as on a ridge top
Low humidity and a good breeze

The HLI threshold is then used to calculate the Accumulated Heat Load (AHLU). The AHLU value 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.

AHLU	Cattle indications	Heat load indicator
0	No load	Negligible
1-20	No load or panting score 1	Low risk
21-50	Panting score 1-2	Moderate risk
51-100	Panting score 2-4	High risk
Over 100	Panting score 4	Extreme risk