When we hear the term heat stress, it is often associated with extreme sunshine and high summer temperatures. However, the reality is that dairy cows are highly sensitive to the combined effects of air temperature, humidity, and fluctuating weather conditions. These factors can increase a cow’s core body temperature beyond its natural ability to dissipate heat, resulting in heat stress.
Heat Stress in the UK – More Common Than You Think
In the UK, fluctuating temperatures are common throughout the warmer months. For example, between May and August, temperatures can vary significantly from one day to the next. Even during these changes, humidity levels often remain above 60%, which is widely recognised as the trigger point on the Temperature Humidity Index (THI) scale.
This means that despite our moderate climate, UK dairy herds can be exposed to heat stress conditions regularly from May through to August, and in some years even earlier.
The Impact on Fertility and Performance
Research shows that fertility and production can be negatively affected at surprisingly modest THI levels. In fact, reproductive performance can begin to decline at lower thresholds than many producers expect.
When the daily average THI over a 24-hour period reaches these levels:
- THI 70 (23.5°C) – Milk urea nitrogen (MUN) increases
- THI 68 (22°C) – Milk protein yield declines
- THI 65 (20°C) – Conception rate declines
- THI 57 (14°C) – Oestrus activity reduces
This helps explain the seasonal dips in fertility and milk performance often experienced during the summer months.
Signs Your Cows May Be Heat Stressed
Fluctuating temperatures can alter a cow’s normal daily routine and behaviour, affecting both welfare and productivity. Common signs include:
- Altered feeding patterns
- Lower feed intake
- Panting and drooling
- Standing rather than lying down
- Gathering around fans or breezy areas
- Choosing cubicles at the ends of sheds
- Drinking or feeding only in shaded areas
- Increased restlessness or lethargy
Heat-stressed cows naturally reduce feed intake as a survival response, since digestion generates additional heat. Unfortunately, this reduction in intake often leads directly to lower milk yield and poorer fertility.
Strategies for Mitigation
Practical management steps can help reduce the impact of heat stress:
- Ensure constant access to clean, fresh water
- Keep feed fresh and regularly pushed up, feed in an evening if once a day feeding, or two thirds of the feed in an evening if twice a day feeding
- Improve ventilation and install fans where possible
- Provide adequate shade for grazing cows
- Monitor cow behaviour closely during warm spells
- Use nutritional support designed specifically for heat stress periods
Support Your Herd with Equaliser® CoolCow
Equaliser® CoolCow is a specialised feed additive developed by Cargill to support dairy cows during periods of heat stress and temperature fluctuation.
It contains a unique blend of:
- Internal cooling elements
- Buffering agents
- Flavouring components
Together, these help cows maintain hydration, sustain feed intake, and support production performance and fertility throughout warmer periods.
Key Benefits of Equaliser® CoolCow
- Helps maintain feed intake during heat stress
- Supports milk production performance
- Aids fertility during challenging conditions
- Encourages quicker recovery following heat stress
- Helps improve overall cow comfort
Recommended Application
Equaliser® CoolCow is recommended for lactating cows from May through to the end of September, ensuring cover throughout the key risk period.
Feeding Instructions
- Mix into the basal ration or concentrate meal
- Do not top-dress
- Replaces any existing buffer in the ration
Prepare Before Heat Stress Hits
Heat stress can affect herds long before temperatures feel extreme to us. Taking early action can help protect performance, fertility, and cow welfare throughout the summer months.
For more information about Equaliser® CoolCow, contact your local DN Sales Specialist or call the team on 01200 420201.
