In the midst of a particularly hot Summer you may have noticed that your working day has gotten particularly sweaty over the past few months. Now if you add a black leather jacket and pants to your attire as well as a many-fold increase in water requirement you may have some idea of how a dairy cow in a Waikato Summer feels.

Heat stress occurs when a cow’s body is unable to regulate its temperature effectively due to hot weather and/or high humidity, leading to discomfort and physiological strain. Heat stress is generally due to high air temperatures, especially those above 25°C though other factors like humidity, direct exposure to sunlight and lack of ventilation can amplify the effects. Below is the Temperature Humidity Index (THI) which you can use to assess your herd’s risk of heat stress on a given day.

Heat stress may manifest in your herd as shade seeking, gathering at water sources, panting and drop in milk yield through to collapse and death in extreme cases. It is also a common cause of early abortion which explains some of the empty cows that never cycled again after mating that we find during summer scans.

So what can you do?

• Providing Shade: Shade from trees, shelters, or shade cloths helps cows avoid direct sunlight and stay cooler.
• Cooling Systems: Fans, sprinklers, and misters in barns or feed areas can help cool cows by increasing air circulation and moisture evaporation.
• Water Availability: Access to clean, cool water is critical in hot weather. Cows will drink more to stay hydrated, and farmers should ensure that water troughs are plentiful and easily accessible.
• Deferring Milking: Move milking times so that the hottest part of the day is avoided.

In this particularly hot Summer you will never fully combat the effects of heat stress but there is plenty you can do to help. Remember that if it’s hot for you, it’s hot for them!