Heat Stress in Dairy Cattle: Prevention and Management

Heat Stress in Dairy Cattle: A Growing Welfare Challenge

Heat stress is a major welfare and productivity concern in dairy cattle, and with climate change producing more frequent and intense heat events, its importance is increasing. Dairy cattle — particularly high-producing Holsteins — generate enormous metabolic heat that is difficult to dissipate in warm, humid conditions. Understanding, recognising, and mitigating heat stress is a critical welfare priority for dairy farms.

Physiology of Heat Stress

Dairy cows produce substantial metabolic heat — a high-producing Holstein generating 30+ litres/day produces approximately 6,000-8,000 kcal of heat energy daily. Unlike humans, cattle lack effective sweat gland cooling and rely primarily on respiratory evaporative cooling (panting). As environmental temperature and humidity rise, this cooling capacity is overwhelmed.

The Temperature Humidity Index (THI) combines temperature and relative humidity to predict heat stress risk. THI above 68 begins to impair welfare and production; THI above 72 causes significant stress; above 80 represents severe welfare compromise with mortality risk in severe cases.

Welfare Impacts

Heat stress causes a cascade of welfare-compromising effects:

• Reduced dry matter intake (cows eat less in heat) — increasing negative energy balance and nutritional welfare compromise
• Reduced lying time — cows stand to increase convective heat loss, causing leg and hoof stress and reduced rumen function from decreased lying/rumination time
• Elevated respiratory rate and hyperthermia (rectal temperature above 39.5°C)
• Reduced milk production (5-10% for mild stress; up to 30% for severe stress)
• Impaired reproduction — embryo death from elevated uterine temperature reduces conception rates dramatically
• Increased disease susceptibility — ketosis, displaced abomasum, and mastitis all increase under heat stress
• Severe acute stress can cause death — primarily in confined, ventilated housing during power failures

Mitigation Strategies

Shade provision: Essential for outdoor cattle — minimum 4m² per cow in purpose-built structures or natural shade.

Ventilation: High-volume fans (target minimum 2.5 m/s air velocity over cows) significantly reduce effective THI in housed cattle. Natural ventilation through ridge and side openings supplemented with mechanical fans in extreme heat.

Sprinklers: Soaking cows with sprinklers (wet hair to skin, not just surface wetting) combined with fans provides powerful evaporative cooling — reducing body temperature by 1-2°C.

Water availability: Multiple, clean, large-capacity water troughs ensure adequate drinking water — cows drink 50-80% more water in heat stress conditions.

Feeding management: Feeding during cooler periods (early morning, late evening), increasing dietary energy density to compensate for reduced intake, and providing buffer feeding prevents nutritional welfare compromise.

This page is part of the Animal Welfare Hub — providing evidence-based information to improve the lives of animals. Return to home.