Calves attempt to maintain a constant body temperature regardless of the outside temperature, and within a certain temperature range—called the thermoneutral zone—calves can accomplish this without expending extra energy.
The boundaries of the thermoneutral zone are affected greatly by the effective ambient temperature experienced by the calf, which depends on air movement, moisture, hair coat, sunlight, bedding, and rumination. Many of these factors can be influenced by the housing and environment in which the calf is placed. Each of these factors affects temperature regulation, and the impact may differ in summer and winter.
How Hot is Too Hot?
In comparison to adult animals, calves may be better able to cope with warmer temperatures due to their large surface area relative to their body weight and also due to the much smaller amount of heat generated by calves compared to cows.
Observations of calf performance in summer months show that average daily gain declined as average nursery temperature over the calf’s first 2 months of life increased from 20 to 80°F and suggest that calves may not be able to dissipate accumulated heat from their bodies when daily low temperatures (in calf housing, not the outside temperature) exceed 77°F (Bateman et al., 2012).
It seems that calves, like cows, experience less stress when temperatures drop overnight; periods with no night cooling provide no opportunity for accumulated body heat to dissipate. Grain intake is reduced and the energy required to regulate body temperature increases (a maintenance cost), so feed efficiency decreases and weight gain may suffer during heat stress. Rumen development may be slowed by reduced grain intake, leading to a more difficult transition and a growth slump after weaning.
In addition immunity can be compromised if energy is redirected to cooling functions. Body temperature rises as calves experience heat stress, and if it reaches approximately 108°F calves are very likely to die from heat stroke.
Here are a few strategies to help calves beat the heat:
Studies have shown that providing shade reduces the temperature inside hutches and lowers calf body temperature and respiration rate. Shade may be from solid roofing, 80 percent shade cloth, or by moving hutches to an area shaded by trees. Calves confined to hutches may be at greater risk of heat stress than calves that are able to choose where they lie.
Providing a pen in front of the hutch or using a tether allows calves more freedom to select a comfortable spot. Calves housed in barns with solid roofs have built-in shade, but depending on the layout, some pens may experience more direct sunlight than others. If calves do not have the ability to move out of direct sunlight, shade curtains may provide some relief. In greenhouse-style barns, clear plastic covered with shade cloth or white plastic have been found to be equally effective in blocking solar radiation.