Why heat stress matters

Heat stress in livestock, particularly in dairy cows, is a major concern during warm weather. Rising ambient temperatures, high humidity, and poor airflow can push cattle beyond their thermoneutral zone, affecting health, productivity, and welfare.

Understanding the risks, recognising symptoms early, and taking practical steps to reduce heat load can make a big difference to herd performance and farm profitability.

Why is heat stress dangerous?

Cattle are homoeothermic animals, meaning they maintain a relatively stable core body temperature, typically around 38.8°C ± 0.5°C.

When environmental conditions reduce the animal’s ability to regulate body temperature, heat stress can develop. One of the key measures used to assess this risk is the Temperature-Humidity Index (THI), which combines both temperature and humidity to reflect the thermal pressure cattle are under.

Cattle generally begin to experience heat stress when THI rises above 68. Without enough shade, water, airflow, or cooling, short-term stress can quickly become a more serious issue, affecting both animal welfare and farm performance.

Heat stroke symptoms in cattle

Recognising the early signs of heat stress is important, as prompt action can help prevent more serious health problems or death.

• Increased respiration rate or laboured breathing
• Open-mouth panting
• Lethargy or reluctance to move
• Reduced feed and water intake
• Standing with heads lowered or grouped tightly together
• Elevated body temperature
• Drop in milk production and fertility
• Poor rumination or higher somatic cell counts in dairy herds
• In severe cases, collapse or death

Monitoring respiration rates and body temperature can provide an early warning that cattle are struggling to cope with heat load.

How to prevent heat stress in cattle

Ensure constant water access

Provide easy access to clean, cool water at all times. Water troughs should be positioned conveniently, ideally within 250 metres of grazing areas. During hot weather, water demand can rise sharply, so supply needs to be checked regularly.

Provide shade and shelter

Grazing cattle should have access to natural shade, such as trees, or artificial shelter where possible. In some cases, housing cattle during the hottest part of the day can help reduce overheating, particularly where ventilation is good.

Improve air movement

Good airflow plays an important role in helping cattle lose excess heat. Fans, tunnel ventilation, sprinklers, or misters can all help improve cooling and support better temperature regulation.

Adjust feeding and milking times

Feeding during cooler parts of the day, such as early morning or late evening, can reduce the heat generated through digestion. Moving milking times outside peak heat hours may also help reduce pressure on dairy cows.

Reduce stocking density

Lower stocking density can improve airflow and reduce heat build-up, especially in housed systems. Good shed design also helps limit radiant heat and create a more manageable environment for cattle.

How heat stress impacts your farm

Heat stress can significantly affect the performance of dairy cows and other livestock. It reduces feed efficiency, increases respiration rate, and disrupts normal hormonal balance.

Over time, this can lead to a range of production and health issues:

• Reduced milk yield and butterfat content
• Increased risk of mastitis and high somatic cell counts
• Lower reproductive efficiency
• Greater risk of metabolic disorders

Understanding the relationship between temperature, humidity, and cattle performance can help farmers spot risks early and protect profitability during warm weather.

Monitor cattle health with Herdwatch

Herdwatch helps farmers track the effects of heat stress and respond with better data. The Milk Performance Module makes it easier to monitor changes in dairy cow performance that may be linked to environmental conditions.

How to access the Milk Performance Module

• Go to Dairy
• Click Milk Recordings
• Select Per Cow
• Filter by SCC, milk solids, fat, protein, calving date, and more

How Herdwatch can help

• Track daily health and performance metrics
• Spot heat-related drops in milk performance earlier
• Set alerts for water checks, feeding changes, and heat stress action plans
• Use historical records alongside weather trends to plan ahead

Protect herd performance during hot weather

Heat stress is more than just a seasonal inconvenience. It can be a serious barrier to milk production, fertility, and overall herd health.

With practical prevention strategies, good ventilation, and strong monitoring through Herdwatch, farmers can reduce risk and help keep cattle cool, healthy, and productive throughout the summer.