CHAMBERSBURG, Pa. — Hot, humid weather can cause heat stress in dairy cows, but it can also be stressful for pre-weaned calves. During the hot summer months, it’s important to know the signs of heat stress in calves and to take action promptly if it is detected.
The ideal temperature for calves, the temperature where they do not have to expend any additional energy to maintain normal body temperature, is known as the thermoneutral zone. When a calf’s body must work to maintain its core temperature, that energy is diverted away from the calf’s other systems responsible for growth and development. According to the University of Wisconsin, a newborn calf’s thermoneutral zone is 50˚ F to 77˚ F. And 32˚ F to 73˚ F is the thermoneutral zone for a one-month-old calf (Van Os and Kohlman, 2020).
At temperatures above 78˚ F and with elevated humidity, a calf’s normal vital signs, including body temperature and respiration rate may increase as the animal attempts to cool itself (Bohlen, 2018). A heat-stressed calf may have a respiration rate above 60 breaths per minute and body temperature can range from 102˚ F to 108˚ F. A high body temperature of 108˚ F can be fatal to calves (Jones and Heinrichs, 2023).
Below is a chart showing the normal vital signs of dairy calves.
Normal Vital Signs for Calves
Vital sign
Normal
Temperature
100.0–102.5 °F
Heart (pulse rate)
100–140 beats per minute
Respiratory rate
30–60 breaths per minute
Source: Bohlen, 2018
Signs of heat stress in calves include:
Increased respiration rate
Decreased activity
Decreased feed and milk intake
Increased water intake
Panting
Decreased lying time
Higher body temperature above 103˚ F (Johnson and Wright, 2022)
Ensure employees or family members who work with calves know how to recognize the signs of heat stress, including signals like elevated respiration rates.
Tips to Prevent Heat Stress
Ensure all calves have free-choice access to fresh, clean water. During hot weather, calves can double their water intake as they may lose fluids due to increased respiration and sweating (Van Os and Kohlman, 2020).
Provide shade and good ventilation in calf housing. Research has shown that calves will have lower body temperatures and respiration rates in calf hutches that are shaded (Coleman and Heinrichs, 2023). Calf barns should be oriented east to west to avoid exposure to the afternoon sun. For calf hutches, ensure all vents are open and consider propping up the back of the hutch about six inches to allow for airflow. For indoor housing, solid paneling is recommended between calves for biosecurity. Open paneling on the front and back of the pen can allow for more airflow. Fans can also be beneficial to minimize flies and to keep calves cool. Studies have found that fans can help increase starter intake and weight gain during the summer months (Van Os and Kohlman, 2020).
Provide fresh clean bedding. Sand bedding can help dissipate heat compared to straw bedding, but regardless of the type of bedding used, offering clean, dry bedding is key to keeping calves healthy, minimizing flies, and limiting bacteria growth in the bedding.
When it comes to feeding, a calf’s energy requirements can increase by 20 to 30 % when heat-stressed (Van Os and Kohlman, 2020). Feeding additional milk or milk replacer can help meet the calf’s added energy needs. Ensure fresh grain is offered at each feeding to encourage consumption.
Because added hydration may be needed, electrolytes can be offered in addition to milk. Follow label recommendations for how to mix and when to feed the electrolytes as some electrolytes must be fed separately from milk. If a calf appears severely dehydrated, consult with your veterinarian as additional intravenous fluids may be needed.
And lastly, avoid added stressors during peak temperatures such as transporting calves, disbudding, and vaccinations. On a hot day, a calf may need four to six hours to cool its body temperature back to a normal range (Van Os and Kohlman, 2020).
If you would like to learn more about calf care, Penn State Extension is hosting the Calf Care: Training for Calf Raisers and Youth Employees Workshop on July 31, 2024. The in-person workshop is tailored for calf raisers, including youth employees ages 13 and up working on dairy farms and college students interested in calf care. Workshop topics include:
Colostrum management strategies
Feeding strategies to promote calf growth and rumen development
Weaning strategies to avoid post-weaning growth slumps, with emphasis on calf starter composition
Key biosecurity protocols required to ensure thrifty calves
Common calf scoring systems used to identify sick vs. healthy calves
How to develop and implement calf care protocols
The workshop will be at Hollow Acres Farm at 6969 Upper Strasburg Road, Pleasant Hall, PA 17246 from 10:00 a.m. – 2:00 p.m. Pre-registration is required. Registration is $15 ($10 for each registrant from the same family or farm) and lunch will be provided. For more information and to register, go to https://bit.ly/PSUcalfworkshop.
If you have questions about calf care or the Workshop, contact Daniela Roland at 717-809-2194 or [email protected].
Resources
Bohlen, J., Rollin, E. 2018. Calf Health Basics. University of Georgia Extension.
Jones, C., Heinrichs, J. 2023. Heat Stress in Dairy Calves. Penn State University Extension.
Van Os, J., Kohlman, T. 2020. Managing the Heat in Pre-weaned Calves. University of Wisconsin-Madison Extension.
Johnson, K., Wright, A. 2022. Managing Heat Stress in Young Calves. University of Minnesota Extension.
–Daniela Roland, Penn State Extension
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