Many operations, even those in Northern climates, have adopted heat stress abatement measures for their milking herds. A recent “Dairyland Initiative Podcast” explored the importance of mechanisms available for cooling young stock herds. “Calves transition from an in utero environment where they’re protected by the cow and then come into this world where they are trying to figure out thermoregulation,” explained University of Wisconsin-Madison’s associate professor Jimena Laporta. “One of the main misconceptions is that calves don’t need cooling because they don’t generate heat, but they’re still vulnerable, even if they aren’t making milk.”
Just how vulnerable?
Laporta cited research conducted on preweaned calves that showed heat stress begins around 65 to 69 temperature-humidity index (THI). The most common signs of heat stress exhibited by calves were elevated respiration rates and rectal temperatures.
“Calves can accumulate heat throughout the day,” Laporta detailed. “They can increase their respiratory rate by 25 breaths per minute and can increase rectal temperature by up to 2°F across the day.”
All of this heat can impact calf growth, feed intake, and raise the risk of disease and welfare concerns.
“The goal is to bring calves back to thermoneutrality, so they don’t have to destine those resources to thermoregulation and can apply them to growth and development of the immune system,” Laporta shared.
Addressing the heat
In group-housed calves, heat stress can be somewhat easier to manage because of the common open-air system. Positive pressure tubes or mechanical cooling by fans can be applied across a group of calves.
Laporta shared that the variety of housing situations for calves across the country can complicate cooling strategies. For example, fan systems in hutches can be difficult to implement and noisy to boot. However, her group is evaluating positive pressure cooling options and fans for hutch and individual settings. Through their studies, her research group has found that calf cooling can improve air quality, reduce respiration rates, and lower rectal temperature change throughout the day. “There are many ways to assess if a heat abatement system is working for calves,” she said. “It’s important to look at their micro-environment, which is the environment the calf is actually experiencing.”
Laporta recommends walking the calf housing area and counting breaths per minute on 10% of the group. Depending on the region of the country, she shared that 30 to 40 breaths per minute is when calves begin to experience the negative consequences of heat stress. “Determine if your calves are heat stressed or not, and then make a plan to address it,” she concluded.
