The first half of June was a scorcher. Minnesota statistics put it as the hottest first half of June on record. In comparison to adult animals, calves may be better able to cope with warmer temperatures because they have a large surface area relative to bodyweight. Cows also generate much more heat due to the digestion of fibrous feedstuffs and the metabolic activity required to support high levels of milk production.
    Although it may not be to the same degree as adult cattle, youngstock do experience heat stress, potentially impacting their health and growth. It is critical to keep a good eye on calves in times of high temperatures and humidity.
    Calves attempt to maintain a constant body temperature regardless of the outside temperature. They can accomplish this without expending extra energy when the ambient temperature falls within their thermoneutral zone. University of Minnesota experts suggest a calf’s optimal thermal environment is between 55 to 78 degrees Fahrenheit. The boundaries of the thermoneutral zone are not constant or determined by the outside temperature alone. They are influenced 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.
    When we think of effects of the environment on calves, cold stress is often the more common concern, especially in our Midwest climate. But, similar to the milking herd, soaring summer temperatures, sunlight and high humidity can cause heat stress in calves. Signs of heat stress include reduced movement, increased respiration rate, open-mouth panting, decreased milk and starter intake, and increased water consumption.
    Studies have shown providing shade reduces the temperature inside hutches and lowers calf body temperature and respiration rate. Calves confined to hutches may be at greater risk of heat stress than calves that are able to choose where they lie. Hutches may be turned to face east in the summer to maximize air movement and minimize solar heating. Placing hutches 4 feet apart with 10 feet between rows allows air to circulate freely, eliminates calf-to-calf contact and provides easy access for feeding and cleaning. Air movement can be enhanced by opening vents on hutches and/or placing a block under the back wall (be sure to maintain this opening as bedding builds up inside the hutch). Washington State University researchers demonstrated that placing 7.9-inch concrete blocks under the back wall of hutches significantly reduced the temperature and carbon dioxide levels inside the hutch as well as calf respiratory rates.
    Calf housing should be positioned to use prevailing winds and incorporate as many openings as possible to take advantage of natural air movement. Typically, open-faced buildings should face southeast. Mechanical ventilation can effectively cool calves in closed barns. Focus on achieving 40 to 60 air exchanges per hour in the summertime.
    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 cannot move out of direct sunlight, shade curtains may provide some relief. Research has shown, in greenhouse-style barns, clear plastic covered with shade cloth or white plastic have been found to be equally effective in blocking solar radiation. Supplying calves with shade that doesn’t restrict airflow will be greatly beneficial in keeping calves cool.
    “Water, always an essential nutrient, is most important for calves living outside their critical temperature range,” said Dr. Sheila McGuirk with the University of Wisconsin. As calves attempt to maintain body temperature, water is lost through increased respiration and evaporative cooling (sweating). Calves must increase their water consumption to replenish the water lost to cooling functions. Water should be presented to calves at warm temperatures (60 to 65 degrees) for maximum consumption during the pre-weaned period. Buckets should be kept clean and rinsed daily.
    Calves will eat less grain during heat stress, so efforts to encourage starter intake take on added importance. Offer only small handfuls at each feeding until calves begin to eat starter. Remove uneaten, wet and moldy feed daily to maintain freshness. A divider between the grain and water buckets can help keep starter fresh longer by limiting the amount of transfer between the two.
    When starter intake stalls, calves have less energy to support their increased maintenance requirements. However, healthy calves are unlikely to refuse milk, so you may increase the energy provided to calves by increasing the amount of liquid feed offered.
    Inorganic bedding is preferred by some calf raisers as it helps keep calves cooler by absorbing and dissipating body heat rather than retaining it. Sand is cooler and can be an effective bedding source in calf hutches.
    As with all cattle, handle calves in the morning so that stressful activities, such as dehorning, vaccinations, pen moves or transportation, can be completed when both calf body temperatures and environmental temperatures are at their lowest point for the day.
    Minimizing heat stress in calves is important to the future performance and production of these animals. Reduced feed intake and increased maintenance energy needs in addition to lowered immunity can lead to poor growth, higher susceptibility to disease and, in extreme cases, death. Work with your nutritionist and calf advisors to determine what management and nutritional practices are right for your calves.  
    Barry Visser is a nutritionist for Vita Plus.