Kite Feedlot Team
December 1, 2023
Tips for Summer
The HLI is called a heat stress index and does not have any units. It is derived from several different weather variables, namely humidity, wind speed and black globe temperature (which is a measure of temperature and radiation). The HLI reacts to changes in these underlying variables in different ways.
Let’s look at wind speed first. Across a yard, there will be many areas that are more exposed, or sheltered than others. The chart below may look complicated but when you know how to read them they can give a large amount of information about how the HLI changes.
Let’s look at the 1 m/s chart first (the middle one). Select the temperature you are interested in from the button axis (for example select 30°C) then select the humidity you are interested in from the vertical axis (for example select 50%). Now follow along the lines until they intersect (in the example it shows the HLI will decrease from 98 to 90 and then 85 as the wind speed increases from calm to 1 m/s and then 5 m/s.
Remember if your weather station is located in a sheltered proposition (or the bearings have not been replaced recently in your anemometer and it is stalling at low wind speeds, which means it will be recording zero and the winds are maybe 2 m/s) then the HLI recorded on your weather station may be significantly higher than what the animals are experiencing.
Now let’s look at humidity. As you all know humidity in the pens can be significantly higher than outside the pens if you have received recent rain. If your pens are also carrying a deep manure pack, the humidity in the pens will be even greater.
In the example below for a wind speed of 2 m/s and temperature of 26°C, the HLI will increase by 4 HLI units every 10% the humidity is increased.
Some sites use 15 mm of rain as a trigger to drop the HLI threshold to account for the difference in humidity in the pens and their weather station (or forecast). Therefore if you normally assess your risk by looking at the AHLU86 you may want to assess AHLU83 or even AHLU80 to account for the different conditions.
Have You Been Paying Attention To What Your Animals Are Telling You? The importance of cattle observations.
As the riskier month of the warm season approaches, another important factor to consider when managing your cattle heat load is cattle observations. Read more.
The team at Katestone is very happy to announce that we reached another milestone today: the release of the Kite Feedlot Mobile App! Find out how you can access it.
The weather forecast is used in the calculation of both the HLI and AHLU for every site. But how important is it that the calculations use an hourly forecast in comparison to a daily forecast?