Heat Stress in Dairy Cattle: A Growing Welfare Crisis

Heat stress in dairy cattle causes significant suffering, reduced production, and reproductive failure. As global temperatures rise, managing thermal comfort in dairy herds is an increasingly urgent welfare and economic challenge.

Key Facts

Dairy cattle experience heat stress when the Temperature-Humidity Index (THI) exceeds 68 — roughly 24C at 50% humidity
Heat stress causes reduced feed intake, increased water consumption, altered rumen function, and elevated body temperature
Milk production drops by 10-25% during heat stress events in unmanaged herds
Reproductive performance is severely affected — conception rates can fall below 10% during prolonged heat stress
Cows with higher milk production are MORE susceptible to heat stress due to greater metabolic heat generation
Effective mitigation includes shading, forced ventilation, evaporative cooling (fans plus sprinklers), and modified feeding times
Climate change is extending both the duration and intensity of heat stress periods across major dairy-producing regions

Welfare Considerations

Heat-stressed dairy cows experience physiological distress that is measurable at a THI that many producers historically considered mild. They stand for longer periods (reducing lying time, a key welfare indicator), pant heavily, crowd around water troughs, reduce feed intake, and show impaired immune function. Core body temperature above 39.5°C causes systemic physiological stress. Severe heat stress can cause heat stroke and death. The welfare impact is compounded by the high milk production of modern dairy breeds — metabolic heat generated by intensive milk synthesis amplifies thermal load. Transition cows (around calving) experiencing heat stress have substantially higher rates of ketosis, displaced abomasum, retained placenta, and metritis — each of which causes additional suffering.

What You Can Do

Support dairy farms that have invested in comprehensive heat abatement systems (shade, ventilation, evaporative cooling)
Choose dairy products from farms with documented heat stress management protocols
Advocate for welfare standards that require minimum heat abatement provisions for dairy cattle
Reduce dairy consumption during hot periods when farms without cooling systems are most likely to be sourcing milk under stress
Support climate action to limit the temperature rises driving increasingly severe heat stress events
Donate to agricultural research organisations developing affordable heat abatement solutions for smaller dairy farms