Current Progressive Dairy digital edition

Managing heat stress in preweaned calves

Ana Paula A. Monteiro and Sha Tao Published on 17 July 2015

dairy calf

During a busy routine schedule at a dairy farm, calves can be easily overlooked, and that is the biggest mistake a farmer can make. The future performance of a heifer is well-linked with her performance during the preweaning period, and being negligent during this period will translate into a less productive and profitable cow.



During summertime, one of the major factors that can impair calf performance is heat stress. Calves are more resistant to high ambient temperatures than adult and lactating cows, but they can be dramatically affected by heat stress as well. A recent study suggests that calves are not able to dissipate heat when the daily minimum air temperatures are above 77ºF.

The behavior changes one may notice in a heat-stressed calf are an increase in respiration rate, open-mouthed breathing and decrease in appetite. These factors, combined with impaired immunity, can result in poor growth of calves and make them more susceptible to diseases.

Heat stress on calf growth

Calf growth is negatively affected by the hot weather if no management interventions are taken to minimize heat stress. Indeed, for every 10ºF increase in air temperature in the calf nursery, there was a 5 percent decrease in average daily gain and 1 percent decrease in starter intake.

Even though the decrease in starter intake was not too high, the growth was significantly impacted, suggesting that during periods of heat stress, calves direct more energy toward heat loss rather than growth.

Heat stress on calf immune system

Heat stress negatively alters different arms of a calf’s immune system. A study conducted in Florida evaluated the concentration of serum protein in calves born in the course of a year and found that calves born during the summer had the lowest concentration.


Serum protein and blood immunoglobulin concentrations are highly correlated; thus, these data indicate that calves born during hot months have impaired passive immune transfer.

The impact of heat stress on cellular immunity of calves was also evaluated by a Mycobacterium tuberculosis challenge, and calves exposed to heat stress had a lower response compared with calves under the thermoneutral environment.

From these studies, we can conclude that calves exposed to heat stress at an early age have a compromised immune system and, hence, are more susceptible to diseases. However, good management strategies can be adopted during summer months in order to minimize the negative impacts of heat stress on calves.

  • Provide shade: Reducing sun exposure is a key strategy when managing calves during summer. Placing a shadecloth over hutches can significantly improve calves’ performance.

    A study showed that providing shade to calves increased serum immunoglobulin concentration at 2 and 10 days old and also decreased mortality rate from 25 to 2.8 percent during the first 20 days. And it is preferred to use the opaque hutches over the translucent hutches.

    calf hutch

  • Keep calves dry and clean: Assuring good drainage is a key factor to keep beds clean and dry. Use of inorganic bedding is preferable because it retains less heat compared with organic bedding, and it may assist in reducing fly population as well.
  • Improve air flow: Keeping a good air flow inside the hutches and within the calf barn helps to decrease the air temperature and pathogen load in the air. During hot months, buildings should have all vents and doors open as well as sidewall curtains.

    Also, it has been demonstrated that elevation of the back end of the hutches by just 1.6 inches using concrete or wood blocks significantly improves the air quality as the concentration of airborne bacteria is reduced inside the hutch.

    Additionally, air temperature is lower inside the hutches than outside at the hottest time of the day, while the opposite happens when hutches are not elevated. When possible, the use of fans to improve air flow should be considered. A recent study conducted in Ohio compared the use of fans from 8 a.m. to 5 p.m. daily with natural ventilation on preweaned calves housed under a barn.


    Although no differences were observed in milk and starter intake, preweaned calves cooled with fans had an increase in average daily gain of 23 percent and in feed efficiency of 20 percent, which indicates that the maintenance energy requirements was lowered when fans were used. However, it is important to ensure there are no air drafts on calves, which also negatively impacts performance.

    dairy calf feeding

  • Provide fresh water 24-7: Providing constant access to free-choice fresh water during the day is essential during the summertime as heat-stressed calves can drink up to 6 gallons of water per day. Water buckets may need to be filled more frequently or switched to a bigger size. It is also important to keep water buckets clean. It was demonstrated that rinsing water buckets daily versus weekly can improve average daily gain.
  • Increase liquid feed offered: The energy required for maintenance is elevated during hot months as calves need to spend more energy to dissipate heat and keep themselves cool. Although calves usually have a decrease in starter intake during summer, healthy calves don’t refuse milk or milk replacer if an extra amount is offered.

    Thus, feeding more liquid feed will provide calves with extra energy toward growth. A study compared the amount of milk replacer (containing 20 percent protein and 20 percent fat) fed during summer and observed that calves fed 1.5 pounds of solids daily had a greater average daily gain compared with calves fed 1 pound, and it did not affect starter intake.

  • Keep calf starter fresh: Starter intake will likely drop during periods of heat stress, so it is very important to keep grain fresh. Otherwise, it can become spoiled and result in further decrease in grain intake and average daily gain. One way to keep grain fresh longer is placing a divider between the water and grain buckets, or placing them far away from each other, which will prevent carryover of water to the grain bucket.
  • Stressors: Stressful events, such as grouping, vaccinating, castrating and dehorning, are preferred to be performed during the early hours of the day instead of in the afternoon or evening, when the environmental temperature is at its peak and so are calves’ body temperatures.

    Dairy calf

  • Electrolyte therapy: The crewworking with calves needs to be trained to recognize clinical signs of dehydration. Calves’ eyes should be bright and fully placed in the head and not sunken into their sockets. Sunken eyes indicate that the calf is already 4 percent dehydrated and will need electrolyte therapy.

    Another way to identify a dehydrated calf is the skin test. To perform the test, one should grab a fold of skin on the calf’s neck and squeeze it together; after this pinch is released, the skin should go back to its normal position within two seconds. If the skin remains in a pinched or tented position for more than two seconds, the calf is most likely at least 4 percent dehydrated and electrolyte therapy is needed.

    These two signs, combined with the calf’s behavior, should be utilized to evaluate the dehydration status of a calf and make treatment decisions. Calves with diarrhea require extra attention. It is recommended to feed electrolytes as soon as the scouring starts to prevent further dehydration. The administration of IV fluids may be necessary if the calf gets to a higher level of dehydration. PD

Sha Tao is an assistant professor, Department of Animal and Dairy Science, University of Georgia – Tifton.

References omitted due to spacebut are available upon request. Click here to email an editor.

PHOTO: Good management strategies can be adopted during summer months in order to minimize the negative impacts of heat stress on the calves. Photo byPDstaff.

  • Ana Paula A. Monteiro

  • Research Scientist
  • University of Georgia – Tifton
  • Email Ana Paula A. Monteiro