When we think of temperature stress on calves, the common concern is cold, but as temperatures are moving to the 900F mark this week, producers need to remember soaring summer temperatures, hot sun, and high humidity can cause heat stress in calves and heifers just as in the milking herd. Reduced feed intake and increased maintenance energy needs coupled with lowered immunity can lead to poor growth, higher susceptibility to disease, and in extreme cases death.
Calves attempt to maintain a constant body temperature regardless of the outside temperature, and within a certain temperature range called the thermoneutral zone. The boundaries of the thermoneutral zone are not constant and are not determined by the outside temperature alone. They 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 comparison to the milking herd, 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 due to fiber digestion.
Observations of calf performance in summer months show average daily gain declined as average nursery temperature over the calf’s first two months of life increased from 20 to 80°F and suggest calves may not be able to dissipate accumulated heat when daily low temperatures in calf housing exceed 77°F. 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. Most likely the nutrients consumed during this time will go more towards trying to drive off heat from the calf’s body rather than growth. Short term, this could have effects on average daily gain, disease incidence, and morbidity. Long term, this could have effects on breeding size and age at first calving.
Northeast Iowa Dairy Specialist Jennifer Bentley notes important visible signs of heat stress include:
- Reduced movement
- Faster breathing rate
- Open-mouthed panting
- Decreased feed intake
- Increased water consumption
Here are practical strategies to help calves beat the heat.
Studies have shown providing shade reduces the temperature inside hutches and lowers calf body temperature and respiration rate. In an Alabama study (Coleman et al., 1996), 80 percent shade cloth positioned about 4 feet above plastic hutches reduced the temperature inside the hutch by 3°F (92 and 89°F measured at 3 p.m.) and reduced calf body temperature by about 0.5°F compared to hutches with no shade.
Move More Air
Calf housing should be positioned to utilize prevailing winds and should incorporate as many openings as possible to take advantage of natural air movement. Typically, open-faced buildings should face southeast. Hutches may be turned to face east in summer to maximize air movement and minimize solar heating.
If calves are housed in hutches outside, open up as many vents as possible to allow airflow through the pen. To allow air to circulate through the hutches, space them 4 feet apart and 10 feet between rows. A common practice is to prop the back edge of the calf hutch up 6-8 inches to allow air flow. Plastic hutches can retain heat and actually make the temperature inside the hutch greater than the outside temperature.
If calves are housed in a naturally ventilated barn, consider using additional fans or a positive pressure tube system designed for summer ventilation rates. Once temperatures reach75 F, curtain sidewalls on calf barns should be completely open.
Offer Plenty of Water
As calves attempt to maintain their body temperature, water is lost through increased respiration and evaporative cooling (sweating). Healthy calves under heat stress will drink between 6 and 12 quarts of water daily just to maintain normal hydration. Severely sick calves under heat stress sometimes require up to 20 quarts replacing what has been lost.
Although it is recommended water be provided to calves beginning in the first day or two of life, the USDA Dairy 2007 survey reported the average age calves were first offered water was 15.3 days. Calves less than two weeks of age are the most vulnerable to diarrhea, which can lead to rapid dehydration. If calves are scouring and no water is available, they are extremely vulnerable to heat stress.
In addition, when the temperature exceeded 77°F calves increased water consumption independent of their grain intake (Quigley, 2011). Whether calves are eating grain or not, they need to have access to water in hot weather. In addition, it may be critical to introduce each calf to water to insure they understand water is available.
Keep Grain Fresh
During times of heat stress, we notice a drop in feed intake while energy requirements for maintenance increase 20-30 percent, leaving the calf with a depressed immune system and a higher susceptibility to disease and dehydration. This means efforts to encourage starter intake take on added importance. Offer only small handfuls at each feeding until calves begin to eat starter. Remove uneaten starter and clean out wet or moldy feed daily to maintain freshness. A divider between the grain bucket and water bucket can help keep starter fresh longer by limiting the amount of transfer between the two buckets. This may be a good time to visit with your nutritionist and re-evaluate your milk replacer program and make sure it allows for maintenance and desired growth to be achieved. Increasing feeding frequency from two times per day to three times per day may also aid in achieving energy requirements.
Consider Inorganic Bedding
While straw is a gold standard for bedding in winter time for its nesting ability, sand or sawdust will not retain as much heat, making them suitable options for summer. Regardless of the material used for bedding, the priority should be to provide a clean, dry area for calves to rest.
Work Calves in the Morning
As always, when handling animals, but especially during times of heat stress, they should be handled properly and gently. It is recommended to 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.
Sanitation and Fly Control
Select options to control flies during the hot summer months that break the life cycle and prevent build-up. In addition, keeping the area around the calves clean and dry and free of weeds will also aid in fly control.
Because of the immune system depression caused by heat stress it is even more important to maintain environmental cleanliness during this time. Warm, damp, soiled areas are the perfect environment for the growth of bacteria and parasites.
Be mindful about keeping all feeding equipment (water and feed buckets, milk mixing equipment, bottles, and nipples) disinfected by using current recommended protocols for cleaning feeding equipment and housing.
When disinfecting housing, make sure all areas have adequate time to dry before re-bedding or putting a new calf into that area.
More information on calf health and housing are available at the dairy team website: http://www.extension.iastate.edu/dairyteam