1. Cooling Strategies During Heat Stress
Pete Hansen, Serdal Dikmen, Miki Sakatani, and Geoff Dahl

2. Take Home Message #1
Cooling cows
When air temperature is high, the best
method to reduce heat stress is to:
1) reduce solar radiation
2) increase evaporative heat loss
in conjunction with fans

3. Heat Gain
Heat Loss
Heat Production
metabolites
Feed
Heat Production + Heat Gain = Heat Loss

4. TYPES OF HEAT EXCHANGE
Radiation – heat transmitted by light
Sunlight but also from other objects
Conduction – heat transmitted by physical contact between
two stationery substances
--still air
--the ground Heat is lost 22.4 times faster
into water than air
--surface water
Convection – heat transmitted by physical contact of two
substances moving past each other
wind
Evaporation – heat required to evaporate water
It takes over 500 times as much heat to evaporate water as to raise its temperature by 1oF

5. TYPES OF HEAT EXCHANGE
Radiation
Rate depends on difference between
Conduction body temperature and environment
Convection
Evaporation Rate depends on humidity of the air
It is easier for cattle to regulate body temperature when:
--heat production is not high (non-lactating vs lactating)
--air temperature is lower than body temperature (101.3oF)
--solar radiation is not high
--loss of radiation to night sky is high (no roof or clouds)
--humidity is not high

6. Air temperature = 85oF Relative humidity=50%
Cow is under shade
evaporation conduction radiation
by sweating convection
101.3oF
Heat Production = Net Heat Loss
Body temperature remains normal
evaporation
by respiration

7. Air temperature = 94oF Relative humidity=90%
Cow is not under shade
conduction &
radiation
convection reduced
evaporation gain from sun
by sweating
reduced
102.4oF
evaporation
by respiration
reduced
Heat Production > Net Heat Loss
Body temperature rises

8. Increase evaporation
and convection
Increase conduction Reduce radiant heat load
& convection
Increase evaporative
heat loss
102.4oF
101..7oF

11. Take Home Message #2
Evaporative cooling
Not clear whether sprinklers or foggers work
best
probably sprinklers, esp. when humidity
is high
Tunnel ventilation doesn’t necessarily work
better than freestall barns
Cross ventilation may be very effective
high investment costs

12. Designed to wet
the cow
Increase loss of heat
--conduction
-convection
--evaporation

13. Designed to cool the air by evaporation
--increased conduction and convection
Some water reaches cow but the small drop size limits
water that penetrates hair coat

16. Average afternoon rectal temperatures of cows
in Florida during the summer
Rectal temperature (oF)
103.1
102.2
101.3
100.4
Farm 1 Farm 2 Farm 3 Farm 4 Farm 4 Farm 4 Farm 5 Farm 5 Farm 5 Farm 5
Barn 1 Barn 2 Barn 3 Barn 1 Barn 2 Barn 3 Barn 4
Freestalls with fans and sprinklers Tunnel ventilation

19. Take Home Message #3
Which Animals Should be Cooled
Don’t forget the dry cows
Cool calves and growing heifers too

20. Effect of cooling dry cows with fans and sprinklers from
46 days before expected calving
on subsequent milk yield (Florida)
cooled
16.5 lb diff
Not cooled
Do Amaral et al., J Dairy Sci. 92:5988-5999 (2009)

21. Body temperature – Wisconsin
(Sartori et al., 2002)
104.0
103.6
103.3
102.9
102.6
102.2 Infertility
101.8
101.5
101.1

22. Vaginal temperatures in two non-lactating
cows during one summer day
105
Vaginal temperature ( F)
Shade cloth
o
104
103
Infertility
102 Foggers and fans
101
100
8 10 12 14 16 18
Hour of the day

23. Growth rate from birth to weaning of dairy calves
reared in hutches as affected by month of birth
(Slovak Republic)
Rectal temperature Maximum THI ADG (lb/d)
April 4-June 11 65.2 1.0 + 0.04
June 12 – Sept 14 74.8 0.9 + 0.04*
Sept 15-Nov 24 59.7 1.1 + 0.04
*P<0.05
Broucek et al., Int J Biometeorol. 59:201 (2009)

24. Take Home Message #4
Assessing the degree of heat stress
Measure body temperatures!!!
Measure differences in performance between
summer and winter

25. Body Temperatures at Which Cows
Experience Declines in Production
And Reproduction
Milk yields and conception rates decline at afternoon
rectal temperatures > 102.2oF
The critical vaginal temperatures are ~ 102.2 to 102.5oF
in the PM

26. DS1921H-F5#
iButton Maxim Integrated Products, 120 San
Gabriel Drive, Sunnyvale, CA 94086
High-Resolution Thermochron®
iButton® model DS1921H, Range H:
+15°C to +46°C
CIDR
1 inch

27. Average vaginal temperatures for lactating Holsteins on
a grazing dairy in Florida during the summer
102.6
39.4 Infertility
Temperature,(oC) oF
39.2
102.2
Vaginal temperature
39.0
101.8
38.8
101.5
101.1
38.6 Irrigation pivot
100.8
38.4 milking
38.2
0 400 800 1200 1600 2000 2400
Hour of the Day
Vaginal temperatures are about 0.2-0.4oF higher than rectal
temperatures

29. Summer to winter ratios for conception rate in Israeli
herds as affected by production level and intensity of
cooling (Flamenbaum and Galon, 2010)
High production Low production
Intensive Moderate Intensive Moderate
Conception
cooling cooling cooling cooling
rate (%)
Winter 39 39 40 39
Summer 19 12 25 3
Summer:winter 0.49 0.31 0.62 0.08
ratio
Intensive – wetting/fans 10X/d Moderate wetting/fans 3X/d
Values for milk yield are 0.96-1.03 for intensive cooling and 0.84-0.90 for moderate cooling

30. Take Home Messages
Cool cows by providing good shade and
a combination of evaporative cooling and fans
 More water the better if available and waste
not a problem
 Tunnel ventilation may not be best
 Cross ventilation may be worthwhile
Don’t just cool lactating cows
heifers and dry cows as well
Measure how effective cooling is
 Body temperatures
 Summer: winter ratios

31. Supported by Agriculture and Food Research Initiative Competitive Grant
no. 2010-85122-20623 from the USDA National Institute of Food and
Agriculture