Recognizing Heat Stress in Cattle

As summertime approaches, temperatures begin to rise, and the concern for heat stress in cattle grows. The U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA) reported that 2021 was among the top six warmest years on record. It is suggested that 2022 will follow this trend. If that’s the case, it is strongly recommended to study and understand the signs of heat stress in cattle, to maintain a healthy herd throughout the summer season.

What is Heat Stress?

Heat stress, in cattle, occurs when a cow must alter its natural behavior to cope with the environmental changes around it. When a cow’s body cannot cool itself or get rid of excess heat, a biological strategy comes into play to attempt to lower its core temperature. Increased heart rate, elevated breathing, and restlessness are common results of this strategy. Heat stress can reduce dry matter intake in lactating cows, affect milk production, alter pregnancy rates, and lower the semen count of bulls.

When Do Cows Become Heat-Stressed?

Cows can experience heat-related stress at a much lower temperature than humans. At 50% humidity, mild heat stress can start at approximately 70°F.

Please note: Cattle rely heavily on respiration to cool themselves. Although they have sweat glands, they are generally not as effective for cooling during the summer months. Take note of respiration breaths per minute as a gauge for heat stress levels. Mild heat stress is in effect at 60-75 breaths per minute (bpm). 75-85 bpm is considered mild to moderate, 85-100 is moderate to severe, and 100+ is severe.

Stages of Heat Stress

USA Agricultural Research Service

• Stage 1: elevated breathing rate, restless, increased standing time.
• Stage 2: elevated breathing rate, slight drooling, most animals standing in pen and restless, animals may group together.
• Stage 3: elevated breathing rate, excessive drooling or foaming, most animals standing in pen and restless, animals may group together.
• Stage 4: elevated breathing rate, open mouth breathing, possible drooling, most animals standing in pen and restless, animals may group together.
• Stage 5: elevated breathing rate with pushing from flanks, open mouth breathing with tongue protruding, possible drooling, most animals standing in pen and restless.
• Stage 6: open mouth breathing with tongue protruding, breathing is labored, and respiration rate may decrease, cattle push from flanks while breathing, head down, not necessarily drooling, individual animals may be isolated from the herd.

Reduce the Risk of Heat Stress

Keep a consistent eye on cattle during periods of elevated temperature. Address behavioral abnormalities promptly and provide solutions to heat stress with urgency to avoid injury or death.

Avoid transporting, processing, or moving cattle when possible. Consider cool, early morning hours and low-stress handling techniques when necessary. Always provide additional water for cattle on pasture or in the paddock. The water source must remain clean and free of defecation; otherwise, the cattle may refuse to drink. If cattle are contained in a paddock or barn, consider using fans to allow for adequate ventilation through openings in the structure. For cattle in the field, access to shelters or lean-to’s can provide sufficient shade when trees are not in abundance.

With planning and preparation for the hot summer season, you can significantly reduce the risk of livestock injury and increase the comfort and health of your animals. When questions or concerns arise, always reach out to a veterinarian to support and care for your herd.