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What is Heat Load?
If heat into the system is greater than heat out of the system then heat will be stored. This is called a heat load.
All animals have a need to maintain core body temperature within a small range, so that body cells and tissues can function optimally.
For humans, the range is 36.5 to 37.5°C, for cattle its in the range of 37.9 to 40.2°C depending on the cattle breed/genotype.
Cattle Heat Energy Balance
For feedlot cattle, the major source of heat into the system is from the conversion of food into energy (Internal Metabolic Heat). This source of heat is generated in the core of the body and therefore any excess energy needs to be dissipated to the surrounding environment. Problems can occur when the environment’s ability to cool the animal is not enough to keep up with the internal heat generation. In this situation, an animal will start to store heat.
How are the Heat Load Alerts defined?
The ALERT issued for your AHLU alert level is defines as follows:
AHLU event today: AHLU >50 units for today
AHLU event tomorrow: AHLU >50 for tomorrow and AHLU = 0 for less than 6 hours
Extended AHLU event: AHLU >50 units for more than 3 consecutive days
Incomplete nighttime recovery: AHLU = 0 for less than 6 hours for more than 3 consecutive days in 7 day forecast period
Rapid HLI change*: change in HLI >40 units over 4 hours. (Please Note: This alert is likely to change when more research becomes available)
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There is a push notification service that will allow us to send notifications. These are different to alerts, which are e-mail or sms messages. The notifications will include any technical issues experienced by the site, important notification or newsletter. These are per device, so you will need to allow on all devices you login to if you wish to receive these. You can opt out of the notifications at anytime, as well as opting back in.
How is my cattle’s heat risk calculated?
The overall risk of a heat event occurring at your site is calculated using a combination of three factors; animal, environment, and weather. The interaction and change of these three factors (some on an hourly basis) is crucial to an accurate heat event forecast.
To quantify your cattle’s heat load risk you need to find out which HLI threshold applies to your feedlot site’s location and each type of cattle. Use the HLI Threshold calculator to enter all the animal and environment factors for your cattle.
How do I use the HLI Threshold Calculator?
Select the characteristics and conditions of your highest risk cattle via the dropdowns. Once complete the HLI Threshold Calculator will generate the HLI Threshold for your operation, which provides you with the reference point for interpreting AHLU forecasts relevant to your site.
For example, the AHLU80 forecast refers to the AHLU where the HLI threshold = 80.
CHLT forecasts are provided for AHLU80, AHLU83, AHLU86, AHLU89, AHLU92 and AHLU95.
Where your HLI threshold falls between two AHLU reference points, you need to either estimate the AHLU, or, for a conservative approach, refer to the AHLU for the HLI threshold that is closest to, but less than, the calculated HLI threshold.
How do I reduce my site’s risk of a heat event?
There are many things you can do to reduce your risk of a heat event occurring.
Understanding your risk from the Risk Analysis Program (RAP) is a good start. The RAP provides a method to determine what measures need to be in place for your site. For example, if the RAP indicates a risk of more than 2 extreme events per year you may decide to reduce your risk by installing shade or alternatively not run high-risk cattle genotypes at your feedlot during the summer months. You can find the Risk Analysis Program (RAP) by clicking here.
Monitoring the weather via your weather station and/or your forecast on your Site Summary page, and using the Daily Monitoring tool (coming soon) to keep track of conditions during the summer will also reduce your risk.
All these tools and more are available to CHLT account holders on the Toolbox page.
Where does the weather forecast come from?
The two weather forecasting models utilised by Weather Intelligence are an implementation of the Weather Research and Forecasting – Advanced Research and Weather (WRF-ARW) model (WICAST), as a primary forecast, and the Australian Digital Forecast Database (ADFD), as a backup system.
WICAST is initialised daily producing a 7-day forecast at an hourly time step. The modelling domain extends from 105°E to 160°E and 8°S to 45°S encompassing a significant portion of the oceans to better resolve the generation of tropical weather systems. The resolution of the model is 12 km. WICAST receives its initial and boundary conditions (IBCs) from the Global Forecast System (GFS) model, which already contains data assimilated from the Australian WMO monitoring sites, as well as satellite and upper air soundings.
The ADFD operates continuously as an alternative weather forecasting product. It contains the official BOM weather forecast elements produced from multiple models and they are controlled by the BOM’s operational meteorologists. Unlike WICAST, ADFD does not make solar radiation data available to the public, therefore a clear-day assumption is considered to estimate solar radiation.
What is the Heat Load Data Network?
The Heat Load Data Network (HLDN) is an initiative of Katestone-Weather Intelligence and MLA that allows feedlots to send in your weather station data our servers and include these data in your site-specific forecast for the AHLU. The integration step involves re-calculating the forecast AHLU for the next time steps and for all thresholds based on the most recent observed HLI.
Let’s see the value of having a weather station on site. For instance, the forecast HLI might be 79 but the observed HLI (from the weather station) might be 82. In this example, the initial forecast of AHLU80 at that time would be 0 but after measuring HLI=82 (and not HLI=79) we know that now the AHLU80 would be 2, not 0. Then, the forecast of AHLUs for the next 7 days would be updated accordingly. Following the same example, if HLI=81 was forecast for the next hour, initially at that time AHLU80=1 but, as the AHLUs forecast has been updated, the new AHLU80=3.
By registering on this site and requesting to be part of the Heat Load Data Network here, you will receive all the assistance you need to get your weather station data uploaded and displayed as observations alongside your site-specific forecast.
I can’t login because I forgot my password. What do I do?
If you are having difficulty logging in, please double check you are using the correct user name and password.
PLEASE NOTE: If you enter your user name and password incorrectly more than 5 times you will be locked out for 60 minutes.
Otherwise, you will get an error message like the ones below:
To regain access, please do the following:
STEP 1: Click ‘Lost Your Password’
The next screen will ask for your username OR email address (see below).
1) Enter your email or username (whichever one you can recall).
2) Click the ‘Get New Password’ button.
Once you enter the correct email or username, you will see the Confirmation Message (below);
STEP 3: Go to your email program and look for an email with the subject ‘[Cattle Heat Load Toolbox] Password Reset’ from firstname.lastname@example.org
The email will contain both your username and a link.
Click the ‘reset your password’ link at the bottom of the email (or copy and paste the URL into a new browser window).
STEP 4: In the new browser window, set your new password to whatever you like.
Please do try to make it memorable AND strong. Click “Reset Password” button.
You will be prompted to ‘Log in’. Enter your retrieved username (as per the reset password email) and your new password.
If you still aren’t able to login after following all of the steps above, please contact your Site Supervisor to make sure you are registered for CHLT.
If you are the Site Administrator and you still can’t login, please contact the CHLT Team via our contact form here.
How can I add Town Forecast Locations to My Site Summary page?
You can add any of the Town Forecast locations to your My Site Summary page by going to Manage -> Manage Sites and selecting a location from the State drop-down lists.
You can also review the sites that you are associated with and remove yourself from those sites that you no longer wish to be associated with. Remember that any site you are associated with you can also set alerts for.
How do I change my details?
You can change your username, email, phone number and password by clicking on the “settings” button as indicated in the below image. You can update the fields you wish to change and click the “Update Account” button.
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 set your AHLU alert level, round it down to the closest AHLU alert level. Select the delivery method: Email, SMS or Both and click Submit.
Note:Consider changing your alert threshold throughout the summer to reflect cattle condition.
What’s the difference between a site user and a site administrator?
The first person to register their feedlot with CHLT is the default nominated Site Administrator. Site Administrators are able to view, add, update, and delete contact details and alert preferences of all users registered to their site on CHLT.
Site Users are added to existing CHLT sites by their Site Administrator. Site users are able to view and update their contact details and alert preferences.
What are the equations for calculating HLIs and AHLUs?
Heat Load Index Calculation
Calculation of the Heat Load Index (HLI) requires Temperature (T) in °C, Relative Humidity (RH) expressed as a percentage, Wind Speed (WS) in m/s and Black Globe Temperature (BGT) in °C. Of these, T, RH and WS are routinely measured by the great majority of weather stations. Although sensors for measuring BGT exist, these are not normally included as part of the standard weather station and must be ordered from a suitable supplier. In the absence of a BGT sensor, the BGT can be inferred from measurements of T and Solar Radiation (SR).
The equation for calculating BGT from T and SR is:
where log is the logarithm (base 10) function.
In the past, the HLI was calculated using one of two equations, depending on whether the BGT is above or below 25°C as follows:
If BGT is < 25°C:
If BGT is ≥ 25°C:
The HLI value was taken as either HLIHIGH or HLILOW depending on the BGT value.
One issue that has been identified is that large jumps in HLI occur under some circumstances when the BGT passes through 25°C; for example, from 24.9°C to 25.1°C. To overcome this, a blending function, S(BGT), is used to produce a smooth transition in HLI values calculated using the two different equations. The blending function is:
Using this blending function, a value of the HLI is calculated as follows:
>where HLIHIGH and HLILOW are defined above. Finally, the HLI value is not allowed to decrease below 50. HLI values smaller than 50 are set to 50.
Download the HLI Calculator spreadsheet to try it out for yourself.
Accumulated Heat Load Unit Calculation
The Accumulated Heat Load Unit (AHLU) represents the amount of heat accumulated in cattle over a period of time. The rate of accumulation depends on the current HLI value. Large HLI values result in a more rapid increase in AHLU, conversely, low HLI values result in a decrease of the AHLU (ie the cattle cool down and recover). Whether cattle recover or become stressed depends on the value of certain thresholds. The first threshold occurs at a HLI value of 77. For HLI values below 77, the cattle cool down and recover. The second or UPPER_THRESHOLD depends on the type and condition of the cattle and their pen environment. Its value ranges from about 80 for unacclimatised (and possibly compromised) black angus cattle to about 95 for acclimatised Brahman cattle. The range of HLI values between 77 and the upper threshold is called the thermo-neutral zone. For this zone, cattle neither recover nor become stressed.
It is important that the correct UPPER_THRESHOLD is used otherwise the AHLU values will erroneously indicate the state of the cattle. The UPPER_THRESHOLD can be calculated using the CHLT on-line calculator at: http://chlt.com.au/toolbox/rap-calculator/
The equation for calculating AHLU is as follows:
For example, the AHLU at 2pm is calculated by adding an INCREMENT to the AHLU at 1pm. The INCREMENT is calculated as follows:
If 77 < HLI < UPPER_THRESHOLD, then
If HLI ≤ 77, then
If HLI ≥ UPPER_THRESHOLD, then
where Delta t is the time interval between successive HLI measurements. Its value is 1.0 for an interval of one hour, 0.5 for an interval of 30 minutes, 0.25 for an interval of 15 minutes and so on.
Some points worth noting:
The INCREMENT can be positive or negative.
If HLI is below 77, then INCREMENT is halved (ie the rate of recovery or heat loss is half of the rate of heat accumulation.
AHLU values do not go below zero. If any calculation results in an AHLU value below zero, it is set to zero.
The following table contains sample data that you can use to test your implementation of the HLI equations above:
Relative Humidity = 33%
Black Globe Temperature
Relative Humidity = 66%
Black Globe Temperature
Relative Humidity = 99%
Black Globe Temperature
The following table contains data that you can use to test your implementation of the AHLU equations:
What is the Heat Load Index (HLI) and how is it calculated?
The Heat Load Index, referred to as the ‘HLI’, is an index that brings together all the weather factors into one number to allow easy interpretation of the cooling capacity of the environment. The Heat Load Index has been developed in Australia from over 10 years worth of research into assessing heat events in Australian feedlot conditions for Australian cattle.
The basic weather information required to determine the capacity of the environment to cool a body consists of:
radiative temperature – a combination of temperature and radiation called Black Globe Temperature (BGT)
air movement (Wind Speed)
a measure of the moisture in the air (Relative Humidity)
As you can see above, the HLI is calculated from measurements of BGT (°C), relative humidity (%) and wind speed (m/s) using a simple relationship. A tool is available on CHLT to calculate HLI from the available input parameters.
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.
What is an Accumulated Heat Load Unit (AHLU) and how is it calculated?
1 – 20
21 – 50
51 – 100
The Accumulated Heat Load Unit (or AHLU) is a measure of the amount of heat that may be stored in a body. An animal’s “heat energy balance” is determined by the duration of exposure above the Heat Load Index (HLI) Threshold. Cattle may accumulate heat during the day (the body temperature rises) and dissipate this heat during the night. If there is insufficient night cooling, cattle may enter the following day with an accumulated heat load.
On CHLT, Accumulated Heat Load Units are calculated every hour, using the HLI for that hour, and the HLI Threshold.
For every hour that the HLI is above the HLI Threshold, heat will be stored in lot cattle and will progressively increase without intervention if the conditions remain the same.
Figure 1: Relationship between HLI and HLI Threshold
As illustrated by Figure 1, for every 1 hour period that the HLI (green contour lines) is greater than HLI Threshold (orange line), heat load increases (red areas) at a rate equal to the difference between HLI and the HLI Threshold. (Note: The HLI Threshold can move up and down).
For example, around 10 am on Day 1, the HLI Threshold = 86 and the HLI = 98. Therefore the heat load is accumulating at a rate of 12 AHLU/h.
Figure 2: Relationship between HLI and heat dissipation
The heat will only begin to dissipate when the HLI decreases to below the lower threshold (shown by blue areas in Figure 2). Current research indicates that this threshold is 77 for most breeds, but may be higher for BosIndicus.
The HLI Threshold is important to understand as it tells you at what point your cattle may start accumulating heat. The HLI threshold will change for even one beast as they go through the feedlot process.
Undertaking activities when the environment is cooler may not necessarily mean the cattle have a lower heat load (see Figure 3).
Figure 3: AHLU over 3 consecutive days
Figure 3 shows the HLI (green contour line) and the AHLU (red vertical lines) over a three day period. The high HLI on Day 1 and minimal recovery time overnight means that the heat load on Day 2 is actually higher than on Day 1, even though the HLI is lower.
Note: AHLU86 means an AHLU with an HLI Threshold of 86.
“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 Manage -> Manage Alerts 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 Weather Intelligence-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.
“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 Manage -> 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.
Note: Consider changing your alert threshold throughout the summer to reflect cattle condition.
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