Find out how the A-SHED project is using data to raise awareness of heat stress and drive practical decisions on farms

Most dairy farmers understand that heat stress can affect cow health and performance.

By measuring conditions within individual livestock buildings farmers can identify the risk earlier and choose the most appropriate response.

As part of A-SHED, Galebreaker is working with Scotland’s Rural College, and project partner, Smartbell, on a two-year research project into heat stress, with Temperature Humidity Index (THI) monitors installed across 23 farms across Cumbria and Scotland.

In this blog, animal welfare specialist Chloe Rodriguez shares what the results mean for future heat stress management.

THI monitors  

Chloe says THI monitoring helps farmers understand how temperature and humidity combine to affect a cow’s ability to lose heat.

“Humidity reduces a cow’s ability to release heat through evaporation. This means moderate temperatures can still create heat-stress conditions, particularly in enclosed or poorly ventilated buildings,” she adds.

Shed-level monitoring also reveals conditions that cannot always be identified from a regional weather forecast.

“Internal THI may be influenced by roof materials, restricted air inlets, stocking density, moisture produced by the cows and limited airflow through the building,” she says.

While a THI of 68 is commonly used as a reference point, A-SHED data suggests that some herds may begin to experience production effects at lower values, with the extended impact of prolonged heat stress seen 2-3 months later in reduced fertility.

“Project data indicates that the point at which milk yield begins to fall varies between herds,” says Chloe.

On another farm involved in the project, Chloe says milk yield began to decline at a THI of approximately 61.

“When mechanical ventilation was activated at around THI 66, yield recovered despite conditions remaining challenging, highlighting why farm-specific monitoring is important,” she adds.

Using THI data

Chloe says using THI data is key to making changes that will work for your farm.

“Monitoring the three-day rolling average THI values can be used as a strong indicator of how heat stress may affect milk yield,” she explains.

“Some herds began losing yield at a THI of just 53. On average, every five-point rise in THI reduced milk yield by 0.31kg per cow, costing a typical herd around £25 per day.

“During extreme heat events, losses could reach £150 per day.”

She says without humidity data, the temperature alone may not prompt action.

“This means two farms in the same region, or even two buildings on the same farm, may experience very different levels of heat-stress risk,” she adds.

Chloe says there are five steps to using THI data on your farm:

1. Monitor temperature and humidity within the livestock building
2. Compare THI patterns with milk yield, behaviour and feed intake
3. Identify the level at which the herd begins to respond
4. Introduce ventilation or management changes before performance falls
5. Review whether the intervention improved conditions

Removing heat effectively

Monitoring can also help farmers understand whether a livestock building is removing heat effectively.

“Natural ventilation might not be enough in older buildings or sheds that are no longer being used for their original purpose,” says Chloe.

“Farmers often describe older, low-roofed, small and multi-pitched sheds as difficult environments to manage effectively,

“However, mechanical ventilation systems may provide an option for older buildings where natural airflow is inadequate.”

She says mechanical ventilation is useful in:

• Retrofitted buildings
• Older sheds
• Buildings converted from another use
• Housing with limited natural air movement
• High-stock-density environments

What the A-SHED project has revealed

1. Overnight temperatures

Alongside understanding THI data and interpreting values, Chloe says other factors from the project were found to influence heat stress.

She explains: “Some monitored sheds remained hotter overnight than during the day, limiting cows’ opportunity to release accumulated body heat, highlighting the importance of night-time recovery.

“Early findings suggest that when cows experience cooler night-time conditions, they may recover some of the milk yield lost during hotter periods. This means ventilation decisions should not be based solely on daytime temperatures and may need to continue into the evening or overnight.”

2. Different groups of cows  

Although milkers are often prioritised because production changes are easier to measure, Chloe says another element of the A-SHED project is also to encourage farmers to consider monitoring dry cows and youngstock.

“Where these groups are housed separately, their buildings may require their own monitoring,” she adds.

“Heat stress during pregnancy may have consequences for the developing calf, meaning the effects can extend beyond the immediate production period.”

Key takeaway

Overall, A-SHED’s farm-specific approach can help farmers move from reacting to visible signs of heat stress to managing the risk before cow welfare and performance are affected.

“By combining THI monitoring with building assessments and herd data, farmers can make earlier, more informed decisions and identify which changes are most likely to benefit their farm,” says Chloe.

“This can also provide clearer evidence of the potential return on investment from ventilation and housing improvements, which was identified as a key priority in the project survey.”

By understanding when, where and why heat stress develops, farmers can invest with greater confidence and make improvements based on evidence from their own herd and buildings.

Get in touch

Contact to find out more about Galebreaker’s THI Monitoring here: marketsupport@galebreaker.com