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Many producers tend to focus most of their heat abatement efforts on their lactating cows due to the immediate decline in milk production. Often the calves are forgotten about because the production responses are less apparent. However, as previously heat-stressed calves continue through
life, growth and production will be depressed when compared to nonheat-stressed calves.
Nutrition
During heat stress, calves must use more energy to regulate their core body temperature, which requires them to consume more nutrients to meet this need. Research conducted by Provimi North America has indicated that as calves become heat-stressed, intakes decline, therefore reducing average daily gain (ADG). During the winter months calves will make up for the additional energy requirement to thermoregulate by consuming more starter, but in the summer months calves won’t consume more starter,
even though their maintenance energy requirements have increased due to heat stress. One way to increase energy intake of the calf is to increase energy density of the diet so the calf can get more
energy but eat the same amount. This is often achieved by adding fat because of its high energy density. Fat has also been shown to reduce metabolic heat production per unit of energy fed according to a study conducted at Louisiana State University, but careful consideration needs to be taken into
account to not add too much fat as it may impair ruminal fermentation.
Another strategy to increase the amount of energy consumed by calves during heat stress is to feed more milk replacer. Studies at Provimi North America have found increases in ADG and hip width when calves were fed more milk replacer under heat stress. Providing fresh starter and water is
also extremely important during the summer months and should be offered ad libitum. Even though most calves will not increase their starter intake during heat stress, it is important to provide fresh starter to encourage them to eat, so that they can better meet their increased energy needs due to heat stress. Water is important to avoid dehydrated calves and during heat stress, water intakes will increase, which may require filling water buckets multiple times per day or adding an additional or larger bucket of water during heat events.
Management
As temperatures rise, finding ways to cool the calf’s environment is important to reducing heat stress on
the calf. This can be accomplished by opening doors and vents on calf hutches or propping up the back of
the hutch with a block to provide more airflow. If calves are housed in a barn make sure side walls and doors are open. Fans can also be added to provide more airflow. Shade is another important factor to help cool the calf’s environment. Studies conducted at the University of Missouri and Auburn University in Alabama found that placing a shade cloth above hutches was found to reduce temperatures inside the
hutches by 3-4 °F. Adding a reflective surface to the hutches can also reduce temperatures inside of hutches. Another study found that the inside temperature of a calf greenhouse covered with either a clear plastic film overlaid with shade cloth or a white plastic film without shade cloth was cooler than the outside ambient temperature.
Material used may have an impact on the calf’s environmental temperature
as well. For example, plywood hutches have been shown to have a lower inside temperature than
polyethylene plastic hutches and inorganic bedding such as sand has been shown to cool calves by
absorbing and dissipating body heat compared to organic bedding such as straw or sawdust.
Another strategy to reduce heat stress in calves is to work with calves during the cooler times of the day. This includes feeding, pen movements, vaccinations, and dehorning. All of these things can increase core body temperature and respiration, so doing any of these tasks during the hottest part of the day will further exacerbate the effect of heat stress on calves. Reducing heat stress in calves through nutrition and management is important to the economic status of a dairy farm as well as the welfare of the calf. By implementing heat abatement strategies, ADG can be increased, while mortality and morbidity can be
decreased, making your farm’s calf program more successful.