23rd July 2025
How monitoring THI can reduce the risk of heat stress and maintain productivity during extreme heat
The Met Office reports that extreme heat events are rapidly becoming the norm in the UK. These events are expected to become more frequent, with the chance of temperatures hitting 40°C now over 20 times more likely than in the 1960s.
As the climate changes, farmers face increasingly urgent herd management challenges around protecting animal health and welfare and productivity against extreme heats.
In this blog, we explore how farmers can take a proactive approach against heat stress in cows.
What does increased heat mean for cattle?
Higher average temperatures and humidity during warmer months can significantly increase a cows’ susceptibility to heat stress.
Hot cows can demonstrate several signs of heat stress which can all impact milk yield, cow fertility and wellbeing.
Examples include:
- Increased water intake
- Reduced feed intake
- Panting
- Sweating
- Shorter lying down periods
- Bunching in darker and cooler areas
Prolonged periods of heat stress can also weaken the cow’s immune system, making them more susceptible to disease and lameness.
Read more about the signs of heat stress in cattle.
What is THI and why does it matter?
The temperature in cattle sheds is typically 2-6 degrees warmer than outside – largely due to increased humidity.
To understand the risk of heat stress in their herd, farmers can use the Temperature-Humidity Index (THI) metric which considers humidity levels as well as temperature.
A THI level of 68 is when a cow might start to enter a state of heat stress and can start at just 22°C when partnered with the average high humidity in the UK.
By identifying and understanding THI, farmers are at an advantage to implement the necessary preventative measures against heat stress.
Measuring THI
To help farmers understand the heat stress risk in dairy herds, Galebreaker and Philbro Health have developed a free online THI Live tool. This showcases real-time THI data from numerous dairy buildings, providing insights into the comfort and wellbeing of dairy cows.
The platform details and captures data from a range of building types in the UK and Europe. This helps farmers understand how different cattle shed designs and building features can influence the risk of heat stress.
Producers can also sign up for a weekly THI update email which summarises the latest THI data.
This snapshot is accompanied by possible implications for cow wellbeing and health, with insights into the week ahead reminding farmers of what to consider going forward.
To calculate THI levels at your farm or sign up to receive weekly THI snapshots of the latest average THI levels across regions
The importance of data
The real value of knowing THI values lies in responding in real-time.
With easy access to data, farmers can take timely action to minimise the risks of heat stress in their herd, such as:
- Implementing livestock ventilation systems, such as Galebreaker’s VentTube Cool, to introduce fresh air into the building – reducing humidity levels and enhancing the cooling effect over pens and cubicles to reduce cow temperature
- Open up buildings using doors and inlets, such as side curtains
- Adjust feeding times to cooler times of day
- Check water flow into troughs
For more information on preventative measures, read or watch the Galebreaker webinar here.
Having access to historical THI data allows farmers to identify trends and plan ahead to increase herd resilience against the expected increasing temperatures.
This can help when considering cattle shed design for new, or current buildings, by addressing features such as lighting, shed orientation and building exhausts, which all play a role in preventing heat stress.
By acting early farmers can prevent drops in milk yield, avoid growth setbacks, and protect reproductive performance, whilst safeguarding long-term herd health and productivity.
Further support
The Galebreaker animal health and welfare team are available to support with further services such as farm building ventilation assessments, and on-site housing assessments to understand how effective a building is in mitigating and managing cow susceptibility to heat stress, with expert recommendations on how to make potential improvements.
Farmers who are concerned about heat stress in their herds, could also benefit from a THI monitoring service which provides humidity and temperature sensors.
The data collected via the sensors for THI Live can accumulate into a heat map report which compares THI data and overlaid milk production analysis, to support farmers’ understanding of how THI is influencing milk yields.
Galebreaker’s advisory service can also incorporate fertility and lameness data to highlight the impact.
Become part of the THI-Live network here.
For more details on THI monitoring services and how to manage and minimise the risk of heat stress, contact our team or watch the webinar in full on our YouTube channel.
