It still feels like winter in many parts of the country, but if the temperature swings of this season and the trend of last summer are any indication, it may not be long before we need to consider how heat is stressing our dairy animals — and that means every animal on the farm.

“Heat stress does not discriminate,” stated Jimena LaPorta during an Iowa State University Extension webinar. The assistant professor at the University of Wisconsin-Madison recognized that there is often a perception that calves are less vulnerable to heat stress or more able to cope with heat. That’s not exactly true, though.

Calves are, of course, not milking, so they are producing less metabolic heat, and they do have a wider thermoneutral zone, LaPorta noted. But they still experience stress from high temperatures that can have significant impacts on health and, consequently, growth and production.

Just like cows, heat-stressed calves are going to eat less and can become dehydrated. And when calves have an elevated body temperature, their energy is going to go to cooling off instead of growing and fighting off potential disease.

The specific ideal thermoneutral zone that a calf will be comfortable in will fluctuate depending on the age of the calf, wind speed, and humidity, LaPorta said. Her research in both the tropical climate of Florida and the temperate climate of Wisconsin has found general guidelines for when calf rectal temperature and respiration rate start to change, thus indicating the beginning of heat stress.

LaPorta described that in their Florida experiments, respiration rate started to rise at a temperature-humidity index (THI) of 65°F, while rectal temperature rose quickly when the THI reached 67°F. These numbers correlate to ambient temperatures of about 68°F and 72°F, respectively.

In the more moderate climate of Wisconsin, respiration rate and rectal temperature both began to climb at a THI of 69°F, which relates to an ambient temperature of about 70°F.

Though a calf won’t necessarily be heat stressed at these temperatures, they will start to feel differently, LaPorta said. She highlighted that these numbers are a bit lower than where we see heat stress in milking cows and are generally comfortable temperatures for humans, so we might not think about calves being uncomfortable in this environment, but they likely are.

Reduce the stress

Relieving some of that heat pressure largely depends on how our calves are housed. With hutches, LaPorta said to consider adding extra shade, shifting the orientation or elevation, adding more passive ventilation with a fan or vent, and looking into what options are available for hutch material.

She noted that in group housing, we often discuss airflow for ventilation but don’t focus as heavily on cooling. There has not been much research into if mechanical ventilation helps with animal cooling.

LaPorta’s group has studied adding fans above group pens and at the calf level and found that raising air speed this way does help calves thermoregulate, which led to them eating and drinking more. The study was with group-housed calves on autofeeders, and the cooled animals drank more per visit than the calves with no fans that drank more, smaller meals throughout the day.

Heat abatement may not be as heavily considered when designing calf facilities as it is with the milking herd, so it is not always as easy to cool calves. But any efforts you can take to improve airflow and speed will pay off by reducing stress and allowing these young animals to meet more of their potential.