Cattle Heat Load Toolbox

Helping you proactively manage summer heat.

The main observational factors of the Cattle Heat Load Toolbox

During the heat of summer there are a number of tasks that need to be undertaken on a daily basis to protect your herd from heat load.
Do your RAP here: Set your alerts here: See the latest tools here: chlt-toolbox-button


We hope that you had a lovely Christmas break and you are enjoying the summer holiday for the lucky ones!

Some parts of Australia have experienced extremely high temperatures for many days in a row. Thankfully, the humidity has been low and in most parts there has also been enough wind to keep the heat load down. Unfortunately, the seasonal forecast for the next three months (Feb-Apr) is worrying: warmer than average conditions are likely for almost all of Australia. You can find more details here.

Based on your feedback during the last few weeks, we want to share with you some of the comments that we have received with a brief explanation:

  • “The HLI is forecast to be higher than 87 for today, I set up my alerts for AHLU83 and I didn’t get an alert”
    Although AHLU is based on HLI, they are different indexes! The AHLU is calculated every hour using the HLI for that hour and the HLI threshold. The HLI threshold is the level at which cattle will begin to accumulate heat. Then, for every hour that the HLI is above the HLI threshold, heat load increases at a rate that is equal to the difference between HLI and the HLI threshold.

    Let us suppose that we have the forecast HLI values shown in the top panel. Up until 9am the HLI is lower than 80, so both AHLU80 and AHLU86 will remain at 0. At 10am the HLI is up to 85, therefore AHLU80 will be (85-80=) 5 whereas AHLU86 will still be 0. At 11am, HLI=87 and therefore AHLU80 (87-80+5)=12 and AHLU86 (87-86)=1, and so on. More information can be found on the website on the FAQs page under Science “What is an Accumulated Heat Load Unit (AHLU) and how is it calculated?”). You can see the types of alerts available in this link once logged in.

  • “One of my colleagues is getting alerts for the same feedlot as I have, but I’m not receiving any alert!”
    Most likely this is because you have set up the alerts with different AHLU. Going back to the above example, if someone has set up the alerts to AHLU80 would receive an alert for that day because AHLU80>50 units, whereas another person with their alert set for AHLU86 would not. (Note that you can change your alerts here after logging in.)
  • “The temperature forecast from Katestone differs from other sources”
    The weather forecast is nowadays based on numerical weather prediction models, there are many models run by various agencies and private companies, which will result in different predictions for a specific location. Also, bear in mind that numerical models are not perfect due to inherent flaws that limit the accuracy and skill of forecasts. Therefore, it is common to see some discrepancies among different models, especially under certain weather conditions such as an abrupt weather change.
    It is important to remember that the daily maximum temperature alone will not determine the heat load at your site. The combination of temperature, humidity, radiation and wind speed are all important (this is the HLI), as well as the duration of the event (this is the AHLU).
    Having said that, we have analysed the performance of our model for previous seasons and its skill is generally high, at least up to 6 days.

  • “Where does the weather forecast come from?”
    Katestone runs the Weather Research and Forecasting (K-WRF) model, which is one of the world’s most widely used numerical weather prediction model. The model is initialised daily producing a 7-day forecast at an hourly time step. The modelling domain encompasses the Australia’s land area and a significant portion of the oceans around the country to better resolve the generation of tropical weather systems. The horizontal resolution of the model is 12 km.
    As a backup system, Katestone also provides the Australian Digital Forecast Database (ADFD), which contains the official Bureau of Meteorology weather forecast. Therefore, in the event of a K-WRF failure, ADFD forecast is utilised and the website is updated with the related forecast data.
    The forecast you receive in any of the two models used is site-specific, i.e, for the location where your feedlot is. Therefore, it might be different compared to your closest town if the feedlot is far away.

  • “How do I set Heat Load alerts?”
    Alerts can be configured for any user who is associated with a site. Users can be associated with multiple sites and can set separate alerts for each site. To set your alert for a site go to Account -> Manage Alerts. The alerts are based on the AHLU and the HLI threshold that is representative of your site. Use the HLI Threshold Calculator to determine the risk threshold you want to manage your cattle to. Then, use the calculated HLI Threshold to set your AHLU alert level rounding it down to the closest AHLU alert level. For instance, if the HLI Threshold is equal to 88, choose AHLU86. Finally, select the delivery method: Email, SMS or Both and click Submit.

As always, if you have any more questions or need further explanation on how to best use the system you can contact us via email ( or give the team a call during office hours on 07 3369 3699.

Finally, you can still download here the notes about the maintenance of your weather station.

From your CHLT team,

Christine, Esteban, Frank, Dush and Trent