June 2026 THI Summary

Summer arrived with force in June, delivering one of the most significant heat stress periods recorded since Galebreaker monitoring began. While the month started with conditions cows can withstand, temperatures escalated rapidly through the second half of June, culminating in an exceptional heat event during the final week that affected farms across the whole of Great Britain.

Key Observations from THI-Live

A Comfortable Start

The first two weeks of June were manageable for dairy cows, with many sheds remaining below 20°C and average THI levels sitting between 57 and 64. Conditions allowed cows to recover from the late-May heat event, with normal feeding, lying and standing behaviours observed across most regions.

Heat Builds Rapidly

By mid-June, temperatures began climbing across England and Wales, with southern sheds regularly reaching THI levels above 68. Peak temperatures reached 33.7°C in Somerset, generating a THI of 84 and triggering significant behavioural responses associated with heat stress.

Record-Breaking End to the Month

The final week of June produced one of the most severe heat stress events experienced in UK dairy housing in recent years. Daily average THI values exceeded 70 across multiple regions, while the South of England recorded a 24-hour average THI of 79 during the hottest period. A Somerset shed reached 39.4°C with a THI of 91, the highest THI recorded within the monitoring network to date and firmly within the emergency stress category.

High Humidity Intensified Conditions

Unlike previous heatwaves characterised by dry heat, June’s extreme temperatures were accompanied by persistent humidity. Relative humidity remained above 50% during the day and frequently rose into the 70-80% range overnight, severely limiting cows’ ability to cool and recover between heat events.

Regional Heat Stress Trends

South of England

Recorded the most severe conditions throughout June, including the month’s highest temperature of 39.4°C and a THI peak of 91. THI levels above 68 were recorded daily during the latter half of the month, with prolonged overnight heat stress preventing adequate recovery.

Midlands and Wales

Experienced sustained periods of severe heat stress during the final two weeks of June. Temperatures regularly exceeded 30°C, with extended periods above THI 67 and limited overnight cooling.

Northern England

Conditions remained relatively comfortable early in the month but deteriorated rapidly during the final fortnight. Farms experienced widespread heat stress, with temperatures and THI values reaching levels more commonly associated with southern regions.

Scotland

Scotland largely avoided significant stress during the first half of June but was not immune to the late-month heat event. By the third week of the month, heat stress conditions had spread into the south of Scotland, affecting behaviour and subsequent performance.

On-Farm Effects

June highlighted how quickly heat stress can develop and the lasting impact it can have on dairy performance.

During the latter half of the month, farms would have observed:

• Increased respiration rates.
• Higher water consumption.
• Reduced feed intake during warmer periods.
• Increased standing times.
• Shifts in feeding and activity towards cooler overnight hours.

The final week’s sustained temperatures and humidity will likely have consequences extending well beyond the heat event itself, including:

• Reduced milk yield & quality.
• Lower conception rates.
• Increased risk of claw horn lesions and lameness.
• Longer-term fertility impacts resulting from prolonged elevated THI exposure.

Where heat stress persisted through both day and night, cows had limited opportunity to dissipate accumulated body heat, increasing the severity of these impacts.

Also, worth thinking about In Utero Heat Stress effects on calves:

• Heat stress doesn’t only affect the dam it also affects her in utero calf.
• Calves are born small and gain less weight during growth
• They produce less milk in their 1^st, 2^nd, and 3^rd lactation
• Have poorer antibody absorption at birth
• Shorter productive lifespan
• Decreases mammary development

Have you downloaded our Heat Stress Supplement written for Cow Management?

Looking Ahead

June demonstrated the importance of preparing for heat stress before temperatures rise. What began as an exceptionally comfortable month rapidly developed into one of the most challenging heat events observed in recent years.

As we move further into summer, key signs to watch for include:

• Increased standing behaviour.
• Elevated respiration rates.
• Reduced feed intake.
• Clustering around water troughs and fans.
• Reduced night-time lying behaviour.

What should you do?

• Increase access to water
• Open the shed up – get fresh air in
• Think about mechanical ventilation – make sure it is advised correctly
• Look at feeding times during a heat wave
• Make sure lighting in shed is uniform – helps avoid bunching
• Cover roof lights – these will massively increase solar gain
• Monitor your shed temperature and humidity levels

Following the extreme conditions experienced during June, now is the ideal time to review how your buildings performed and identify opportunities to better protect cows during future heat events. Get in touch with Galebreaker if you want specific advice. 

You might be interested in our blog giving Practical Tips on Managing Heat Stress.