As climate change leads to more extreme weather events and long-term increases in temperature, milk yields, and milk properties can be affected.

The dataset - What is it?

Heat and humidity are combined into an index called the Thermal Heat index (THI). THI gives a value of how hot we (or cattle) feel. The dataset shows the number of days THI is over 72 throughout New Zealand. A THI of 72 is approximately 25.5 degrees and 50 % humidity and is the value at which milk yield has been shown to drop.

The map above shows the predicted number of days over 72 for the year 2040 in the highest emissions scenario. The dataset includes further scenarios.

Why it's important

Cattle heat stress = hot environment + humidity + metabolic process. As humidity increases animals reduce their ability to cool by transpiring. Cattle also produce heat in metabolism and lactating cows in milk production. To reduce their temperature cattle, reduce feed uptake and in cows, also reduce milk production. Feed growth may also be reduced due to the heat stress.

Knowing the effect of heat stress, operational changes can be made to minimize the effects on cattle. Site selection can be made to reduce the chance of critical THI being met often. Different breeds respond differently at different THI, making breed selection important, and coat colour within breeds. Other operation decisions include altering feed times to reduce metabolic heat and water spray.